Author Topic: M5 Stuart Light Tank  (Read 4355 times)

Online Vixen

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M5 Stuart Light Tank
« on: January 15, 2021, 07:03:23 PM »
The M3 Stuart and it's improved derivative, the M5 Stuart Light Tank were the first production-line tanks to be built in the US factories. The Stuart light tanks were made available to the British and Commonwealth forces under the Lease-Lend agreement. They were later used by the US Army and all the allied forces in all theaters, until the end of the war.

When the relatively thin armor and small 37mm gun became ineffective against more modern and more powerful opposition, the M5 Stuart was withdrawn from tank v tank operations and went on to serve as an excellent scout or reconnaissance vehicle. The Stuart tanks were well liked by their crews. It acquired the affectionate nickname 'Honey' because it was a joy to drive, a real 'Honey', due to light weight, powerful aircraft radial engine and good reliability.

Many Stuarts were modified, in the field, by removing the turret and the inadequate 37 mm gun. The reduction in weight improved both the speed and maneuverability of this remarkably reliable vehicle. The only down side of the M5 Stuart Recon conversion was when it rained.

Here is a full size M5 Stuart Recon giving joy rides at a military vehicle show.




Part 1  The Hull
My journey into the realm of 1/6 scale model tanks began when found a huge, 1/6 scale, radio controlled plastic model (made by 21st Century Toys) listed on E-bay at an affordable price, under 'for spares or repair'. It turned out that the battery charger had the wrong pins for British wall sockets and the model was sold, virtually unused, when the battery ran flat.

I planned to fit a 40cc 5 cylinder air-cooled Siedel ST540 radial engine, being as close as I could get to the original 7-cylinder Continental W-670 air-cooled aircraft radial engine. Close enough for me. I would also need to build some sort of transmission and steering gearbox. Fortunately, the tracks and running gear and most of the model parts could be reused with little modification.

My first task was to completely dismantle the vehicle in order to convert it to IC engine power. All the internal bulkhead and floor were removed from the hull so that a 3mm thick sheet metal inner hull could be fitted. As you can see, I recycled a No Entry sign, found in a waste skip (dumpster?) The inner hull would be screwed and riveted together.







The Siedel radial engine was suspended off the 8mm thick rear bulkead. The removable intermediate bulkhead, both stiffened the inner hull box, and provided a mounting point for the engine cooling fan. The exhaust gas collector ring is connected to the copper plumbing on the rear bulkhead. Later large cooling holes were machined into the rear bulkhead to aid engine cooling






Here you can see the remains of the plastic hull slipped back over the new metal inner hull. The plastic hull parts now only serve decorative purposes as the engine, gearbox and running gear are all to be bolted directly to the metal inner hull.




Air cooling for the 5 cylinder radial engine was achieved, like the full size engine, by a large diameter fan attached to the flywheel and prop-shaft. As you can see, I recycled a large industrial equipment cooling fan. The big brass flywheel was made the same size as the discarded electric motor.




Here you can see the running gear and tracks have been assembled back onto the tank. Some of the plastic suspension arms needed to be reinforced with 3mm metal inserts, but as much as possible was used with out further modification.




A small aluminium cooking pan donated it's body parts to make a cooling shroud to go around the cylinders and the enclosure underneath the hull. Lots more rivets.




This final image shows the internal layout of the M5 Stuart model rather well. The radial engine is in the rear, the engine pull starter is in the centre, beneath the turret ring and the transmission and steering gear box is in the front of the hull. The sponsons over the tracks, make convenient storage space for the new radio control equipment and batteries.

In the next installment I will describe the design and construction of the transmission and steering gearbox





Stay in and stay safe

Mike

« Last Edit: July 29, 2021, 07:50:09 PM by Vixen »
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Offline tghs

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Re: M5 Stuart Light Tank
« Reply #1 on: January 15, 2021, 08:10:41 PM »
what is path for the air cooling?
what the @#&% over

Offline propforward

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Re: M5 Stuart Light Tank
« Reply #2 on: January 15, 2021, 08:26:02 PM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp:  :praise2:

Excellent!
Stuart

Forging ahead regardless.

Online Vixen

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Re: M5 Stuart Light Tank
« Reply #3 on: January 15, 2021, 08:43:41 PM »
what is path for the air cooling?

Through the fan to the centre of the engine, than outward and rearward through and between the fins of the five cylinders. Through the cutouts in the rear bulkhead and eventually out through the vents at the rear and top deck of the tank. Much the same as the full size machine

Here is an additional photo showing the large airflow holes in the rear bulkhead which were added later.



Mike
« Last Edit: July 29, 2021, 07:50:52 PM by Vixen »
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Offline petertha

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Re: M5 Stuart Light Tank
« Reply #4 on: January 16, 2021, 02:47:38 AM »
Fascinating project. I've always been curious - why were radials considered a match for these tanks? Air cooled vs liquid?. Power/space footprint? Reliability? Or maybe 'inventory' from that particular wartime period? Seems like different flavors of tanks used different engines by different countries at +/- the same time.
https://www.wikiwand.com/en/M3_Stuart#/US_variants

Offline steamer

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Re: M5 Stuart Light Tank
« Reply #5 on: January 16, 2021, 03:45:56 AM »
That is a sweet looking installation buddy!    Loving this!   Following along!

Dave
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Damned ijjit!

Offline AVTUR

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Re: M5 Stuart Light Tank
« Reply #6 on: January 16, 2021, 12:45:28 PM »
Petertha

I am sure that Mike will answer your question better than me, but here goes.

Obviously a tank needs a light, powerful and reliable engine. I think most tanks designed before the war used engines designed for them, In most cases the tank was under powered and not too reliable. The Germans and, I think, the Japanese and Russians continued with this practice. The British and, initially, the Americans turned to the aero-engine. Most American aero-engines were air cooled (OK, the big Allison engines were not) which probably gave installation problems. This, the need for engines for aircraft and spare capacity in the car industry led to them using large multi-banked car engines as on the Sherman. The British used the RR Meteor engine, an un-supercharged version of the Merlin. In 1942 Rolls-Royce swapped their Meteor manufacturing plant near Nottingham for Rover's jet engine factories in Lancashire.

I may not have got everything correct since it is a quick reply.

AVTUR

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Offline tghs

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Re: M5 Stuart Light Tank
« Reply #7 on: January 16, 2021, 03:06:47 PM »
much better view of the air path.. that plate wasn't swiss cheesed in the early photos..
as for use of an radial air-cooled engine, the weight to HP ratio is great,, no need for a complex liquid filled cooling system,, Sherman tanks produced in great numbers operated in northern Russia to North Africa (from one extreme to another that would test a liquid cooled vehicle)  watch some of the hedgehog sherman vids,, they had great performance.. the main drawback was the high profile of the vehicle making it an larger target,  Gasoline was also a risk compared to diesel, but one good hit didn't really matter what kind of fuel was used..
what the @#&% over

Online Vixen

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Re: M5 Stuart Light Tank
« Reply #8 on: January 16, 2021, 03:08:43 PM »
The choice of engines powerful enough to propel a tank, at the required speed over a variety of terrain conditions, was limited by availability rather than an esoteric choice between radial or inline engine.

The power requirement for an effective armored tank is between 15 to 20 HP per ton. The choice of big powerful engines was limited. Suitable aircraft engine were available but even the biggest truck engine was nowhere near powerful enough. Big watercooled in-line engines were eventually developed, but it took time

A Light tank like the M3 or M5 Stuart needed a 220HP engine. Initialy a Continental W670 (220HP) radial was installed. Later, two Cadillac V8's (210hp) were needed to replace the the radial engines when supplies ran short.

A Medium Tank is much more heavily armored and needs a significantly more powerful engine. The M3 Lee/Grant and the M4 Sherman all started life fitted with the 400 to 450 HP Continental R975 radial engine. These big radials were eventually replaced with watercooled  in-line V engines, but only after engines of this enormous power had been designed and put into mass production.

By comparison the V12 RR Meteor tank engine was a  non supercharged derivative of the famous RR Merlin aircraft engine. It produced around 600HP from it's 27 litre engine and went on to power the more heavily armored and heavier tanks of later years.

Aircraft engines were therefore an obvious first choice. The US aviation industry in the 1930's favored the air cooled radial over the water cooled in line engine. In UK the industry were evenly split between the two. Bristol's lead the way with powerful air-cooled radials, while Rolls Royce produced equally good water cooled V12 in-lines.

The air cooled radial engine was light and compact but had the disadvantage of a larger diameter. The larger diameter engine forced their tanks to be much taller than desirable and therefore presented much bigger targets for the enemy to fire at.

Well that's my understanding

Mike
« Last Edit: January 16, 2021, 06:18:44 PM by Vixen »
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Online Vixen

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Re: M5 Stuart Light Tank
« Reply #9 on: January 16, 2021, 03:16:37 PM »
the main drawback was the high profile of the vehicle making it an larger target,  Gasoline was also a risk compared to diesel, but one good hit didn't really matter what kind of fuel was used..

Gasoline was always the fuel of choice, everything, including the cookhouse stoves ran on it. It was a question of logistics, one fuel ran all. Supplying more than one type of fuel to the forward troops was out of the question.

As to the vulnerability of gasoline v Diesel. It did not matter much. One good hit would usually set off a ton of high explosive ammunition first.

Mike
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Offline AVTUR

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Re: M5 Stuart Light Tank
« Reply #10 on: January 16, 2021, 03:34:12 PM »
the main drawback was the high profile of the vehicle making it an larger target,  Gasoline was also a risk compared to diesel, but one good hit didn't really matter what kind of fuel was used..

Gasoline was always the fuel of choice, everything, including the cookhouse stoves ran on it. It was a question of logistics, one fuel ran all. Supplying more than one type of fuel to the forward troops was out of the question.

As to the vulnerability of gasoline v Diesel. It did not matter much. One good hit would usually set off a ton of high explosive ammunition first.

Mike

The German army ran on hay all the way through the War. They had to. The only thing I do not understand is why they, the military, did not just give up.

There was a piece of amateur movie film shot by a Frenchman in the summer of 1944 near Falaise. The morning filming, done secretly, shows Germans retreating with big artillery pieces being drawn by horses. The afternoon filiming is of the arriving allies, completely mechanised.

On second thoughts, there is a lot I do not understand about WW2.
There is no such thing as a stupid question.

Offline petertha

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Re: M5 Stuart Light Tank
« Reply #11 on: January 16, 2021, 05:04:22 PM »
Sorry for some more tangent questions Mike. Pertains to a similar radial I'm building.
- I'm assuming the ignition module shown a Seidel original part? I cant seem to find much info on it, but maybe you know. After startup, does it continue to drive the glow plugs on high, or switch off, or revert to reduced current?
- was the ring exhaust assembly stock & modified or you made yourself?

If I have the story straight, Seidel's were actually pretty good RC engines. Eventually went out of production. Then my scent gets cold - picked up by a Swiss company & no more? I've also found links to HobbyKing (Chinese copy or maybe just distribution).

Interesting link of Seidel mods FWIW. I wish the web pics could expand, there are some good internal details throughout.
https://www.heilemann-sternmotoren.de/en/modification-seidel
https://www.heilemann-sternmotoren.de/en/ring-of-muffler

Online Vixen

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Re: M5 Stuart Light Tank
« Reply #12 on: January 16, 2021, 05:48:45 PM »
Hello Peter,

You are as impatient as ATUR, getting ahead and asking questions about things I have not yet come to.

But to answer your questions. The glow plug driver module provides full voltage during start up, it can be reduced or switched off, when the engine has warmed up. In the Stuart tank installation, the engine never reaches high revs (unlike in an aircraft) so I always ran at the reduced voltage setting. Five glow plugs consume something like 10 amps from the battery at the full setting, deducing to about half that at the reduced setting. It all meant the glow plug battery needed to be big and heavy and carried on-board the model tank.

The exhaust ring was home made from domestic 15mm copper tube bent into two half circles and joined. The five compression fittings, with fat rubber glands, were soldered to the exhaust ring. I used soft lead free solder, not silver solder. Methanol fuel burns at a much lower temperature than gasoline. The soft soldered joints lasted well, provided I ran a rich mixture; until one day when I had a very  'lean burn'. Silver solder or TIG would be much better....... If only.

The five compression glands were made from recycled BNC co-axial video signal connectors. I soft soldered a standard 15 mm copper compression gland (olive)  to join the two halves of the collector ring

Not realy sure what went wrong for Siedel, Last I heard, they were now being manufactured in India.

Thanks for the two links. I am going to enjoy studying them.

Go safe

Mike

To quote from one of your links "Why some parts have obvious hammer marks – probably only the Indian precision mechanic knows."  :hammerbash:
« Last Edit: January 27, 2021, 01:25:36 PM by Vixen »
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Offline petertha

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Re: M5 Stuart Light Tank
« Reply #13 on: January 16, 2021, 06:07:44 PM »
Thanks for the details. I'll throttle my enthusiasm & lay low now so you post without (too many  :D) distractions. You obviously did some detailed work on the powerplant side which I'm really looking forward to see as the story unfolds. Very interesting project!

Online Vixen

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Re: M5 Stuart Light Tank
« Reply #14 on: January 17, 2021, 02:33:36 PM »
Part 2   Steering systems

As we all know, a tracked vehicle is steered by reducing the speed of one track. When this happens, both tracks are forced to skid sideways over the ground. This action produces massive (sometimes destructive) forces on the track links, wheels and running gear and especially the transmission system. The steering loads require maximum power from the engine. The magnitude of the steering forces are very dependent on ground conditions. Smooth hard paved surfaces are much kinder than soft or rocky ground. For a model tank, even long grass can can provide difficult conditions.

Most model tanks have two powerful electric motors, their speed being varied independently by radio control. I did not want to follow this route. I wished my model Stuart tank is to be mechanically powered so I needed to devise a mechanical steering system. In full size tanks and tracked vehicles, there are a number of ways to do this, some are quite basic and some more sophisticated. Among the possibilities are:

1  Clutch/ Brake steering.  Here the drive is removed from one track and a powerful brake is applied. The disadvantage is a jerky uneven ride as the vehicles forward speed is suddenly reduced by half during the turn.

2 Braked Differential steering    A powerful brake is applied to one side of a differential to slow that track, the track on the opposite side increases speed and the vehicle turns very quickly. Such a high rate of turn is uncomfortable and undesirable, so this system is usually only used on very light tracked vehicles such as the Bren Carrier.

3 Controlled Differential steering    A more sophisticated system which produces fixed radius turns. It was widely used on the early US tanks.

4 Double Differential steering   A more complex system where an external, variable speed, steering shaft is applied to two differentials. One track speeds up and the other slows. This system can provide infinitely variable turn rates and steering not unlike a wheeled motor vehicle.


For my model Stuart tank I decided to build a CT1 steering gearbox based on a design by Iliya Cerjak, a brilliant young Dutch engineer who works in Amsterdam's University. The central drive shaft from the engine supplies power to two sets of multi-plate clutches, one for each set of tracks. The multi-plate clutches are operated by servos via a wishbone arm, fitted with roller bearings. The clutches engage the engine power and turn the intermediate shaft in either direction. The intermediate shaft turns the worm wheel in the final reduction dive in either direction. The worm and pinon arrangement was chosen for the final drive reduction (30:1) because a worm and pinion can effectively lock (brake) the tracks when neither clutch is engaged (centre position).

The CT1 gearbox allows each track to move forward , backwards or lock.






Here you can see the components of one set of multi-plate clutches. The friction plates were made from laminated printed circuit board (with the copper foil removed). Their serrated outer edge are a sliding fit in the aluminium clutch spider. The driven plates are made from steel sheet 




The centre of the clutch spider was broached with a hexagonal hole and is a sliding fit over a short length of hex bar attached to the input shaft. It's a poor mans splined shaft. The steel drive plates also have the broached hexagon hole and they fit over the hex extending from the output gears. The multi-plate clutches operate at engine speed and therfore see lower torque than if they were at the output shaft end, so can be comparatively small in diameter




The servo controlled wishbone arm fits between the two multi-plate clutch sections. The use of nylon for the gears was not a good choice and they were soon replaced with stronger steel gears.




Here you can see the CT1 steering gearbox installed in the front of the model Stuart tank. The linkage between the servos and the clutch control arms have not yet been fitted. The clear poly-carbonate top cover for the gearbox was useful for seeing what was happening inside. Gear lubrication was by grease (applied with a stiff paintbrush). Only a small amount of grease was applied, for fear of lubricating the friction plates of the clutches.




The movement of the two servos had to be carefully adjusted to ensure the clutches were fully engaged at the end of the servo's travel. There was always a risk of the servos stalling (and burning out) if they could not reach the end of their travel, so I fitted two adjustable coil springs in each control rod to prevent this overload situation from happening.

My Futaba radio control set allows electronic mixing of the control channels. I set the right hand joystick to control the steering gearbox. Stick forward; engaged both forward motion clutches, rearward stick motion would put the tank into reverse. Side motion of the joystick would disengage the appropriate clutch and the model tank would turn. I used the left hand joystick for the engine throttle servo




I was now in a position to fill the fuel tank, switch on and start the engine for the first time. Then began the fun time of seeing what worked, what  didn't, what needed modification. I always enjoy the development phase.

Did I ever tell you that I like engines and mechanisms? :noidea:

Mike


« Last Edit: January 17, 2021, 04:07:22 PM by Vixen »
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Offline crueby

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Re: M5 Stuart Light Tank
« Reply #15 on: January 17, 2021, 08:04:33 PM »
That steering box is very clever! Are there plans or a design document available for that?

Fascinating stuff!    :popcorn: :popcorn: :popcorn:

Offline tghs

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Re: M5 Stuart Light Tank
« Reply #16 on: January 17, 2021, 08:42:59 PM »
I stared at the photos a good while untill I noticed the idler gears on the back wall.. :facepalm:
« Last Edit: January 17, 2021, 10:46:14 PM by tghs »
what the @#&% over

Online Vixen

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Re: M5 Stuart Light Tank
« Reply #17 on: January 17, 2021, 08:48:25 PM »
Hello Chris

Iliya Cerjak had a website dedicated to tank transmission design. He produced a number of different designs, some good and some even better. The various designs were free to download, other than a voluntary contribution to any charity of your choice. Unfortunately, the website has been taken down and no longer exists. Websites cost money and Iliya's website was non money maker.

The CT1 design I used for the Stuart is only suitable for model tanks and tracked vehicles up to a weight of about 15Kg. Together, we developed other transmission designs for heavier and more powerful model tanks. An all metal 1/6 scale Tiger tank can weigh in at over 60 Kg.

Wait for a while, until I have discussed the CG2 DD transmission system used in my all metal StuG 111, which weighed in at around 45Kg.  If you are still interested, I will see what can be done to help you.

Stay safe

Mike
« Last Edit: January 27, 2021, 01:27:28 PM by Vixen »
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Online Vixen

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Re: M5 Stuart Light Tank
« Reply #18 on: January 17, 2021, 08:51:37 PM »
I stared at the photos a good while untill I noticed the idleler gears on the back wall.. :facepalm:

Well spotted.  :ThumbsUp: :ThumbsUp: Yes,  that little idler on the back wall is there to reverse the direction of rotation of the intermediate shaft when the reverse clutch is engaged.

I have just looked through my photo album to see if there is a better photo showing the reverse idler. The idler is always lost in the shadows, so the first photo is the best I can offer

Mike
« Last Edit: January 17, 2021, 08:59:06 PM by Vixen »
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Offline Roger B

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Re: M5 Stuart Light Tank
« Reply #19 on: January 18, 2021, 12:37:53 PM »
Lots of fascinating details :)  :)  :)  :wine1:

Thank you for deciding to post these model builds  :ThumbsUp:  :ThumbsUp: You had made a few tempting comments in the past and let a few secrets out like the epycyclic gearbox  :paranoia:
Best regards

Roger

Online Vixen

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Re: M5 Stuart Light Tank
« Reply #20 on: January 18, 2021, 05:03:48 PM »
Thank you Roger,   :ThumbsUp:

You know as well as anybody, just how much time and effort is involved in posting a log.   I am pleased to hear you are finding some interesting content.    Hopefully, there may be more to follow.

Mike   :atcomputer:
« Last Edit: January 18, 2021, 05:16:19 PM by Vixen »
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Offline nj111

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Re: M5 Stuart Light Tank
« Reply #21 on: January 18, 2021, 05:10:44 PM »
This is fascinating Mike.   I'm sure I saw this at the Bristol show maybe 15 or more years ago?   I also have the same Seidel 5 cyl Engine , of similar age and still with it's original maker's chipboard box. Not actually run it yet!
Nick

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Re: M5 Stuart Light Tank
« Reply #22 on: January 18, 2021, 06:20:33 PM »
Hello Nick,

The tanks were displayed at a number of shows about that time.

Best advice is to keep your Seidel in it's box. Once you run it, the caster oil gets everywhere and it's almost impossible the get it off.   :noidea:

Mike
« Last Edit: January 18, 2021, 10:33:55 PM by Vixen »
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Offline Laurentic

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Re: M5 Stuart Light Tank
« Reply #23 on: January 19, 2021, 12:31:22 PM »
Very interesting and intriguing - but I'm still trying to work out that gearbox/clutch arrangement in my head!

Chris


Online Vixen

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Re: M5 Stuart Light Tank
« Reply #24 on: January 19, 2021, 03:12:53 PM »
Part 3    Running and Testing

My Stuart tank was always intended to be a working tank, an engineers tank, to be driven hard, to be broken, fixed, modified and improved.  Not for me, a pristine show piece with authentically weathered paintwork and a crew of 1/6 scale dollies all in matching uniforms.

Engine. The Seidel ST540 is a 40cc five cylinder radial engine. It runs on a synthetic oil in methanol fuel mixture with glow plug ignition. The engine/ gearbox arrangement means the maximum engine speed was around 4000 rpm. The engine was supplied, from new, with a glow plug driver module, which could be switched between full voltage for starting, reduced voltage for running or switched off entirely (for flying?) At tick over and below 4000 rpm, the engine would not run cleanly without additional battery power to keep the glow plugs hot. This meant the tank had to carry the glow plug battery around all the time. Approximately 10 Amps were required during start-up, which could be reduced to about half that amount, when the engine had warmed up.

The fuel was 10% synthetic oil in straight methanol with no additional nitro methane.  The fuel mixture was drawn into the crankcase before being distributed to the five cylinders. The fuel oil mixture lubricated the crankshaft and con rod bearings and also the cam ring gears. !0% oil is a much lower percentage to that used by most single cylinder RC engines. It's what Seidel recommended and gave no trouble. I also meant that there were no visible smoke emissions, allowing me to operate the tank in indoor arenas without complaint.

The carburetor was a small 6 mm choke OS Max air bleed carb, typical of those fitted to RC engines of about 8 cc. The air bleed adjustment is used to set the air/ fuel mixture at tick over, the single needle valve is adjusted to set the air/ fuel mixture when the throttle is open. I found the engine would start easily and tick over smoothly with the throttle closed, The main needle jet could be adjusted to get the engine to run smoothly with the throttle 100% open and down to about 70% open. Below that, the mixture needle needed to be manually readjusted to match the reduced air flow. Adjusting the needle valve and air/fuel mixture was not possible via the radio control. I found the usable throttle range could be extended a little, by running the engine slightly on the rich side. This was possible because methanol has a wider burn range than gasoline. The richer mixture also provide extra engine cooling (through evaporation) and ensured adequate lubrication. This somewhat limited throttle range at the top end is of no real consequence when an air screw is fitted but is a limitation to the drive-ability of a wheeled or tracked vehicle.

A variable jet carburetor or a constant velocity (SU style) carburetor, similar to the ones Roger B is developing, could potentially prove useful to open up the throttle range over the simple OS Max style air bleed carbs. I do not have such a carburetor. Instead, I decided to operate the engine at a more or less constant speed, in the middle of the available throttle response range, and to design and fit an additional two speed gearbox to control the tanks actual speed. See below.

Transmission.  The nylon worm gears were damaged early on so they and some of the other spur gears were replace with steel gears and gave no more problem. Gear lubrication was by grease applied by brush to ensure an even distribution. The grease lubrication proved to be quite adequate, as shaft rotation speeds were low

The four multi plate clutches needed to be pressed hard to be fully engaged, all the time. This caused undue loading of the servos and the thrust bearings. The servo's force limits the amount of pressure that could be applied to the clutches, which would slip if overloaded. Any clutch slip tended to polish the friction plates and the clutch performance would suffer. The clutches would need to be removed and roughed up with sand paper to restore the friction. I considered replacing the fibre glass laminate clutch plate with plywood plates or some other material, but never actually got round to it. The risk of clutch slip meant I had to limit the tank driving to hard paved surfaced or very short grass. Long rough grass was always a problem.

Tracks and Running Gear The plastic tracks, wheels and suspension proved to be quite tough and able to withstand the abuse. The short outer connecting pieces between the track plates sometimes broke (just like the full size tank) I made a batch of replacement parts out of polycarbonate which worked well. The hull was made from a different type of plastic to the tracks. It was not as tough and cracked easily, cracks would grow from all the bolts holding the hull together, which had to be patched.

Two speed gearbox An additional two speed gearbox was added to provide better overall speed range to the tank. It was found that a top speed of little more than fast walking pace was adequate, otherwise you ended up running to keep up. The low gear ratio allowed a lower vehicle speed for maneuvering in tight places and for climbing hills. The engine was run at more or less constant speed, the gearbox changed the vehicles speed across the ground.

The two speed gearbox was a cut down version of the steering gearbox. The idler gear, necessary for the reverse operation, was not fitted. The gear ratios between the upper input shaft and the lower output shaft could be changed by altering the tooth count of the spur gears.








I hope you find this feedback both interesting and informative. The notes on the engine performance can be applied to other miniature four stroke engines, both single cylinder or multi cylinder. Some parts may also apply to two stroke engines.

Stay tuned, there is more to follow

Stay safe

Mike   :atcomputer:

« Last Edit: January 19, 2021, 05:45:53 PM by Vixen »
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Offline crueby

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Re: M5 Stuart Light Tank
« Reply #25 on: January 19, 2021, 06:19:05 PM »
Wonderful!  I find those gearboxes fascinating.

Offline tghs

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Re: M5 Stuart Light Tank
« Reply #26 on: January 19, 2021, 07:21:49 PM »
so are there 2 small bearings in the clutch yoke arms? I guess in this case they would be referred to as throw in bearings..
what the @#&% over

Online Vixen

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Re: M5 Stuart Light Tank
« Reply #27 on: January 19, 2021, 07:55:00 PM »
You all seem to be fascinated by the CT1 steering gearbox. There are some drawings for you to see how it all goes together. The two speed gearbox was also based on part of this design but without the reverse idler gear.



Hope this helps. You should be able to work out how it happens from these.

Mike :atcomputer:
« Last Edit: January 19, 2021, 08:04:22 PM by Vixen »
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Offline petertha

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Re: M5 Stuart Light Tank
« Reply #28 on: January 19, 2021, 08:05:08 PM »
Now that I see the layout, I'm even more impressed the servo can actuate engagement with normal arm rotation. I know nothing about clutch design. For example does adding more plates change the input force to engagement or just modify how the slip transitions? Do you recall nominal torque rating of the servo?

Online Vixen

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Re: M5 Stuart Light Tank
« Reply #29 on: January 19, 2021, 08:17:24 PM »
Peter,

Any clutch is all about coefficient of friction, surface area and contact pressure. the more you have of these, the greater the torque that can be transferred. Multi plate clutches get more surface area into a given space.

RC servos come in different sizes, chose one with an adequate thrust (force) rating to press the clutch plates together. I used a 'standard' servo, Typically 5 to 10 Kg thrust.

Mike  :atcomputer:
« Last Edit: January 19, 2021, 08:29:39 PM by Vixen »
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Offline sid pileski

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Re: M5 Stuart Light Tank
« Reply #30 on: January 19, 2021, 09:02:01 PM »
Is it just me?
I don't see any of the pictures.
I'm logged in.


Hmmmmmmm???

Sid

Offline crueby

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Re: M5 Stuart Light Tank
« Reply #31 on: January 19, 2021, 09:24:25 PM »
Is it just me?
I don't see any of the pictures.
I'm logged in.


Hmmmmmmm???

Sid
Showing for me here at the moment.

Offline Admiral_dk

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Re: M5 Stuart Light Tank
« Reply #32 on: January 19, 2021, 10:14:31 PM »
I really like the layout and construction Mike  :ThumbsUp:

You get a lot less torque load on the clutches if they work @ full engine RPM - but this means that you need four two speed boxes -> no go .... wonder if it's possible to scale the modern slipper clutches down  :thinking:
They use a ramp system -> when the torque is coming from the wheel it looses the spring pressure on the plates and when it's from the engine the ramp works the other way and grips even harder on the plates ....

Still following along  :popcorn:   :cheers:

Offline Laurentic

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Re: M5 Stuart Light Tank
« Reply #33 on: January 20, 2021, 10:52:12 AM »
Interesting stuff in your explanation notes Mike - and the exploded drawing of the gearbox made things much clearer, thanks for that.

Chris

Online Vixen

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Re: M5 Stuart Light Tank
« Reply #34 on: January 20, 2021, 12:25:45 PM »

You get a lot less torque load on the clutches if they work @ full engine RPM - but this means that you need four two speed boxes -> no go .... wonder if it's possible to scale the modern slipper clutches down  :thinking:
They use a ramp system -> when the torque is coming from the wheel it looses the spring pressure on the plates and when it's from the engine the ramp works the other way and grips even harder on the plates ....

Still following along  :popcorn:   :cheers:

Thanks for your input Per.

If you study the drawing you will see the four clutches are already spinning at full engine RPM.

I am not sure how your proposed slipper clutch works or how it would help with this steering system. Do you think they could be incorporated  by slightly modifying the existing design? If a complete re-design were necessary, I would abandon the four clutch steering system altogether.

The CT1 is an interesting and clever design, (that's why I built one). However, I have since discovered, that there are much better and more suitable steering systems available for tracked vehicles. Wait and see whats in store with the next tank.... the StuG  111

Just saying.

Mike   :atcomputer:
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Offline Admiral_dk

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Re: M5 Stuart Light Tank
« Reply #35 on: January 20, 2021, 01:00:49 PM »
You're right that I somehow missed the bit about them running at engine speed. On the other hand - if you got the two speed box installed too - you can't have all clutches running at the same speed ....

I did no suggest that you rebuild your tank (in my mind) but as you mention problems with clutch friction and that the servos have a problem with supplying a high enough pressure on the plates ...

As you clutches have a rather big similarity with motorcycle clutches - I just thought out loud ....  There is a difference though as on a motorcycle, it's springs that provide the pressure on the plates and you have a geared (lever or actual gear) action that releases them.

On the generation that is becoming the norm today, you got the slipper system. This uses the fact that for years the outside clutch-basket was made up off two parts spring loaded as a shock absorber (rotational direction). By putting a ramp on each part - you get the extra squeeze / loosening off the plates on the side that normally is 'fixed' in the previous generation. The two part described is the big gear in the primary gearing (driven directly by the gear on the crank) and the outside clutch-basket.

Online Vixen

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Re: M5 Stuart Light Tank
« Reply #36 on: January 20, 2021, 01:37:12 PM »
Hello Per

I found this illustration which shows how the slipper clutch works.



It works very much like a one way sprag clutch but with the addition of controllable manual engagement. The assist function would certainly help to lock the model tank's multi-plate clutch into full engagement.

I can see the advantage of such a clutch on a modern high power super bike. If the engine were to seize  :censored: , the back wheel 'pushes' the clutch out of engagement, so preventing the rear wheel from locking. It would disengage the clutch much faster than human reaction time. I could have done with one, years ago, when I went circuit racing. It would have saved me from the loss of a lot of skin.

Mike  :atcomputer:

Edit   During a turn the tracks of a tank can 'push' as strongly as the engine. Perhaps it would be necessary to keep the  'Assist' and eliminate the 'Slipper' function in a steering gearbox.
« Last Edit: January 20, 2021, 06:01:44 PM by Vixen »
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Offline Admiral_dk

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Re: M5 Stuart Light Tank
« Reply #37 on: January 20, 2021, 08:16:45 PM »
Oh they work fantastic without the infamous seizure .... you can see them banging down the box during heavy braking without any rear-wheel hopping or fear off other nasties - and by the way the Pro Offroaders use them too  :)    :cheers:

Offline Zephyrin

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Re: M5 Stuart Light Tank
« Reply #38 on: January 21, 2021, 07:48:09 AM »
this thread is really instructive, the model and the mechanics are awesome.
attention to mechanical solutions are impressive.
thanks to share all these knowledges.

Online Vixen

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Re: M5 Stuart Light Tank
« Reply #39 on: January 21, 2021, 03:01:17 PM »
I am pleased you like the content of this thread. Tracked vehicle design is a fascinating subject.

I too have enjoyed looking through my old photo albums, preparing this stuff and re-living an interesting journey of discovery.

Stay safe

Mike   :atcomputer:
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Online Vixen

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Re: M5 Stuart Light Tank
« Reply #40 on: January 21, 2021, 10:05:47 PM »
I've now got about as far as I can go with the development of my M5 Stuart. I have learned a great deal about the dynamics of tracked vehicle steering. Gained useful experience regarding the operation of clutch steering systems. Learned about the performance and limitations of model engine carburetors. I am now about ready for the next step, to embark on a slightly larger, all metal, model tank. Hopefully, with many improvements as a result of the lessons learnt from the Stuart

I also learned it was not necessary to use a model radial engine to replicate the full size original. Once the engine is covered up, in that big hump at the back of the tank, it is out of sight. Few casual observers can tell there is a radial engine installed, and even fewer know what a radial engine is.       They ask " Is it electric and has it got a sound system?" :facepalm: :facepalm:

The Start tank served me well, taught a lot and has given my immense pleasure and fun, but the cracks are beginning to show (literally). The plastic body shell has stress cracks radiating from all the attachment points, it's literally falling apart. (bit like me, in a way  :old: )







Before the Stuart goes into retirement, I have one more development task for it. I have heard many good reports about the 32 cc single cylinder Honda GX32 fourstroke industrial engine. It is said to be a highly reliable, well mannered little engine which should make an ideal power source for the next all-metal tank. The fuel tank hanging off the back was only a temporary arrangement






The Honda GX32 is a clean running, low revving fourstroke with pumped oil lubrication from a wet sump. It burns straight petrol (gasoline) with no added oil. It sounds sweet, not the high revving buzz of a two stroke chain saw engineand none of the evil smelling blue smoke. The engine comes equipped with a built in exhaust silencer (muffler?), a pull starter, self contained magneto ignition, Built in centrifugal clutch. perhaps the most important feature is the pumped, variable jet barrel carburetor, which gives an excellent throttle response, all the way from tick-over to full power, without the slightest hesitation.

The Honda engine is versatile, it can be installed in an upright position, as you can see here in the Stuart model, or it can be laid on side, horizontally, which will make for a much lower installed height.

This last photo shows the Stuart recon tank in it's final stage of development, running sweetly on Honda power. The Stuart served me well and paved the way towards the next tank, by demonstrating the suitability of the little Honda engine in a real tracked vehicle.





Stay Tuned, there's more to follow

Mike
« Last Edit: July 31, 2021, 12:17:49 PM by Vixen »
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Offline Admiral_dk

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Re: M5 Stuart Light Tank
« Reply #41 on: January 21, 2021, 10:50:47 PM »
I remember Honda claim that they really throw most of their immensely big (in MC Racing they are compared to NASA) R&D department into the development of this engine  :o  simply to ensure that it's virtually completely indestructible.
The reason - they use it in a huge amount of power tools they make and provide many years of warranty on + they knew that most of the customers would not treat these engines well ....

First time I see it use in a model, but it makes sense  :ThumbsUp:

Online Vixen

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Re: M5 Stuart Light Tank
« Reply #42 on: January 22, 2021, 08:57:06 PM »
The M5 Stuart light tank thread has reached the end. The petrol Powered Panzer saga now continues with the StuG 111 journey at

https://www.modelenginemaker.com/index.php/topic,10166.msg231371/topicseen.html#new

Stay safe and enjoy

Mike   :atcomputer:
« Last Edit: January 22, 2021, 09:30:53 PM by Vixen »
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Offline Dave Otto

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Re: M5 Stuart Light Tank
« Reply #43 on: January 23, 2021, 01:29:31 AM »
Thanks Mike, I have enjoyed this.  :ThumbsUp:

Dave