Author Topic: StuG 111 tank  (Read 1242 times)

Online Vixen

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StuG 111 tank
« on: January 22, 2021, 08:52:00 PM »
My journey of discovery with the M5 Stuart tank had shown the at fully controlled 1/6 scale i/c engined tank was feasible. Also the Honda GX32 was an ideal power source.

I felt ready to embark on the next stage, to move to a bigger and more robust all-metal tank with a more sophisticated steering and drive chain. The Panzer 111, or preferably the Sturmgescutz 111 (base on the Panzer 111 hull and running gear) appealed to me. A 1/6 scale Panzer 111 model was being offered by an unknown company, appropriately named Metal Box, in Beijing China and also by Armortek in the UK. At the time the StuG 111 was not available anywhere. Unfortunately, there would be a six to nine month waiting list for the Armortek model. Dealing with a company in China had the potential for all sorts of language and shipping and import problems.

I would therefore have plenty of time to prepare and make the transmission. I decided on a traditional clutch/ brake steering system. In the diagram below, the drive gearbox (shown in blue) is connected to the output shafts (red) by two constantly engaged clutches. To initiate a turn, one of the clutches is disengaged and a powerful brake applied to that output shaft. The two track drive sprockets being located on the outside of the output shafts (red)





I selected another of Iliya Cerjak's excellent designs. This time the CG-2, with combined steering and two speed plus reverse transmission. The central control arm, operated by a single servo controls both clutch/brake units. The first motion of the lever opens one of the clutches an further movement applies the steering brake. a second servo moves the gear selection fork in the two speed plus reverse gearbox




You can see I made some changes to the original CG-2 design.

I increased the size of the steering clutches and brakes

I added a lever to disengage the gearbox from both track. might be useful if I ever need to recover the tank from the field, in the event of a complete engine or transmission failure

I included  a centrifugal clutch bell

Added an alternative electric motor drive via a one way clutch. The electric motor (from a golf cart) would provide an alternative power source for indoor arena events that did not
permit i/c engine running, due to emission concerns, fire risk or whatever.





This is the gear cluster. The selector forks moves the gear cluster from side to side. The four pegs in the selector engage in corresponding holes in the gear wheel. The curved slot in the gear wheel makes engagement of the pegs in the holes easier.




Below is a sequence of photos showing the assembly of the CG-2 unit. It is a very neat and clean layout, all the shafts are conveniently at the same horizontal level. The poly-carbonate top cover allows inspection of the works while it is in operation. Lubrication is by grease as before. I tried oil but only once, but the box and the bearings were not oil tight. What a mess!










In addition to the CG-2 gearbox, further gear reduction stages are required. The overall reduction between the engine and the track drive sprocket is approx 30:1 There is a toothed belt drive between the CG-2 unit and two heavy duty epicyclic stages adjacent to  the track drive sprockets    I will deal with the rest of the gear train in the next installment.

Stay tuned

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

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

Offline Roger B

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Re: StuG 111 tank
« Reply #1 on: January 23, 2021, 07:19:48 AM »
That's a neat gearbox design  :ThumbsUp:  :ThumbsUp: I will be following along  :wine1:
Best regards

Roger

Online Vixen

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Re: StuG 111 tank
« Reply #2 on: January 23, 2021, 06:12:27 PM »
Thank you Roger.

Have I ever said I like mechanisms and engines  :facepalm: :facepalm:

The CG-2 box has two separate power sources. The Honda i/c engine and / or the electric motor. Does that make it the first ever plug-in hybrid tank?

An overall gear reduction of about 30:1 will be required between the engine and the track sprockets to give the model a speed of around 1 metre/sec (2.5 MPH), a comfortable walking pace. The CG-2 does not have that reduction capability, so additional reduction stages will be required. The CG-2 box will have a toothed belt drive to the final reduction gears.  A robust epicyclic final reduction stage will be required as the torque increases significantly towards the track sprockets. Epicyclic final reduction stages are common on full size tanks.

A bit more ingenuity is now called for. A suitable epicyclic gear set can be found inside a Sturmy Archer 3 speed bicycle hub. I am sure all of us will have ridden a bike with a Sturmy Archer gear hub when we were younger. They were robustly built and the gears inside could withstand any amount of abuse. I am sure all of you will recognise this.





These are the components needed to make the epicyclic final reduction stage. The Ring Gear has 45 internal teeth and would be difficult to make in the home shop. Beside it is the Planet Carrier in which the four 15 tooth Planet Gear wheels rotate. The Planet Gears fit inside the Ring Gear. The final component is the 15 tooth Sun Gear, which lives in the centre of the gear cluster. All components will need some modifications. The heat treatment of all the gears is first class, they are all strong and as hard as flint.





The Ring Gear requires the removal of some excess material, this is best done with a cut-off disc in the Dremel.





A new Planet Carrier must be made. The Planet Carrier will be attached to the Sprocket shaft. The Planet Gears and shafts are reused.





The Sun Gear only needs to be moved onto a new shaft





The ring gear is loctited inside a bored out toothed belt gear together with a new bearing housing





When all assembled, it makes a very neat final reduction stage which eventually hang off the track Sprocket shaft, one on either side. The central Sun Gear is held stationary, The outer Ring Gear is rotated by the CG-2 box. This causes the Planet Carrier and Sprocket shaft to rotate with a 3:1 reduction.





In addition to the Final reduction epicyclic stages, further speed reduction is required at the engine. The Honda GX-32 is delivered with only the centrifugal clutch shoes, so a clutch bell is required before the engine can be run. Fortunately, there is an industrial standard for this interface for different horticultural tools. Small dirt bikes also use this interface for chain drives. Suitable dirt bike clutch bell housing are readily available on e-bay.

Here you can see the components for the dirt bike centrifugal clutch bell and the epicyclic reduction gears.





The assembly sequence below, shows how the Sun Gear is fitted in place of the dirt bike chain sprocket. The Planet Carrier is made to bolt onto the Clutch bell housing cover. The Ring Gear also has a new housing and bearing and connected to a standard Jaw coupling and drive shaft









The final photo shows the epicyclic reduction stage on the front of the Honda GX32. This epicyclic configuration is different to the final reduction stages in that the Sun Gear is now rotating, while the Planet Carrier is fixed to the bell housing. This results in a 3:1 speed reduction but the output rotates in the opposite direction to the engine shaft.

Note to self. Make sure the output direction of rotation is taken into consideration while assembling the CG-2 box, otherwise you could end up with one forward and two reverse gears.





All I need now is the delivery of the Panzer 111 kit, then we can see how all these components fit together.

Mike   :atcomputer:
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: StuG 111 tank
« Reply #3 on: January 23, 2021, 06:14:53 PM »
Now THAT is clever use of components!!  I too remember riding a bike with that kind of geared hub, but never saw the insides.

Offline Art K

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Re: StuG 111 tank
« Reply #4 on: January 24, 2021, 03:01:38 AM »
Mike,
This is quite the project, very interesting. I have to say, my mom had that English 3 speed, I had a Raleigh 3+2 when I was a kid. That was a 3 speed with a hi low range.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline gerritv

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Re: StuG 111 tank
« Reply #5 on: January 24, 2021, 03:26:40 PM »
Memories of my first personal machine shop project in 1962, a new/longer shaft for my 3 speed Raleigh bicycle, so that I could add a derailleur style 5 speed hub. A 15 speed bike resulted in 5 years of riding pleasure.

This is a very creative design you are building.

Gerrit
Don't confuse activity with progress

Online Vixen

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Re: StuG 111 tank
« Reply #6 on: January 25, 2021, 01:57:55 PM »
A bike ride down memory lane for a lot of you. I did not realise Raleigh UK exported so many pushbikes.

Despite my worries, a deal was done with Metal Box in Beijing China. Five weeks later, a big wooden crate arrived on the doorstep from DHL. I had to pay some import duty there and then to take delivery. The customs label described the contents as being 'used model tank parts' with a lowish value.

Inside the crate I found a fully assembled 1/6 scale Panzer 111 lower hull and running gear, I had been expecting a kit of parts. Metal Box had sent me the bottom half of their prototype/ showroom model. The whole model was very well made and beautifully CNC machined, the track links were aluminium die-cast and very realistic. I was very impressed with the attention to scale detail. The Metal Box offering had much more accurate detailing than the Armortek version of the same Panzer 111 tank.

I was very pleased with what I had received and so was the Dog who moved in. Do you remember the Esso adverts from the 1960's "Put a Tiger in your Tank"?





Once I had evicted the Dog, it only took a few days to install the CG-2 gearbox, which had been built while waiting for the tank hardware.

You can clearly see the the CG-2 gearbox sits neatly inside the hull. The two wide toothed belts provide a useful speed reduction as they take the drive from the gearbox to the two epicyclic reduction stages mounted on the track link sprocket shafts. The cross shaft joining the two Sun Gears in the epicyclic reduction stages, is held stationary and the two epicyclic stages each give the final 3:1 speed reduction. The torque at the final stages is very high and everything needs to be very robustly built.

The central drive shaft is from the Honda GX32 engine which will be mounted in the rear of the tank. The electric motor on the side connects to the gearbox input via a one way clutch









In the next installment, I fit the engine and radio control gear and give my new toy it's first run in the garden.

Mike   :atcomputer:
« Last Edit: January 27, 2021, 01:34:32 PM by Vixen »
It is the journey that matters, not the destination

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

Offline cnr6400

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Re: StuG 111 tank
« Reply #7 on: January 25, 2021, 02:58:15 PM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:

Online Vixen

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Re: StuG 111 tank
« Reply #8 on: January 26, 2021, 02:41:44 PM »
To recap, the CG-2 gearbox is designed to give clutch/ brake steering. To do that, the drive is disconnected from one track and a powerful brake is applied. The tank skid turns around the stopped track. The tanks forward motion is also reduced by half during the turn.  In my installation, a toothed belt drive, followed by a 3:1 epicyclic reduction stage are used to reduce the speed the CG-2 gearbox shafts to that required by the track sprocket.

In a Eureka moment :noidea: I suddenly recognized my installation was remarkably similar to this diagram of the Wilson Double Differential steering system, shown below. Ignore for the moment, the blue steering input at the top of the diagram. The rest of the diagram was identical to my installation.

The blue components at the bottom and centre, diagrammatically represent the power input through the CG-2 box, with an epicyclic gear on either side. The diagram (blue lines) shows the drive being applied to the outer Ring Gear of the epicyclic stages. The pale blue Planet Gears drive the red Planet Carrier to which the Track Sprockets are attached. The central Sun Gear is shown in yellow. In my installation the yellow Sun Gears are held stationary.





 The Wilson steering system has an additional steering shaft input, diagramaticaly represented by the darker blue lines at the top of the diagram and the pale blue direction reversing gear. 

What if I were to devise a way to turn the two Sun Gears, in my installation, in opposite directions? One epicyclic would ADD the steering shaft speed to the drive shaft speed and that track would speed up. On the other side, that epicyclic would SUBTRACT the steering shaft speed and that track would slow down. The tanks speed would remain unchanged and the tank would perform a wide radius turn in a smooth controlled manner.

If I added the extra steering shaft input to my existing installation I would immediately transform the rather crude clutch/ brake steering system into a far more sophisticated Wilson Double Differential steering system, with the potential for precise, fully proportional steering.          Did I ever say I liked mechanisms? Here was yet another opportunity!!

The Wilson Double Differential tank steering system went on to form the basis of almost all modern day, tank steering systems, Lets call it the DD system. Major Wilson, who devised the DD tank steering system was the same person who devised the Wilson epicyclic pre-selector gearbox, which has been described on the forum before. Major Wilson certainly understood the secrets of the mysterious epicyclic and showed how to exploit it's huge potential.


I made so calculations and found I only needed to alter the relative speeds of both tracks by =/- 10 RPM for the tank to make a 2 metre radius turn. The turn could be widened or tightened by a greater or lesser speed differential between the two tracks. Also, if there were no forward motion, the same =/-10 RPM would allow the tank to perform a neutral turn about it's axis.

More calculations and design work followed. I found I could use a 2 speed cordless drill motor, in low gear, to drive the Steering shaft. The drill motor could be controlled by radio control, to give fully proportional speed control, turning in either direction. Some additional reduction gearing would be required to match the cordless drill speed to the final drive speed.

This is the steering drive I devised. The cordless drill turns two small, side by side, pinions, which give the required equal and opposite rotation. The speed of each pinion is reduced by the larger spur gear, which connects to the Sun Gears in the centre of the epicyclic final drives. The steering drive box is located adjacent to the left hand epicyclic, with a drive shaft reaching across to the other. You can see how it all went together from the following photos.








So, did it work? Was all the effort worthwhile?

The following  short clip of video shows one of the first runs of the Panzer tank with the Honda GX 32, the two speed plus reverse CG-2 gearbox and the DD steering system. You can see and hear the smooth throttle response of the engine and it's centrifugal clutch. You will see the forward and reverse gears being selected. You will also see the infinitely variable turn radius steering and even a neutral turn while stationary. Also evident is the ability of the tanks suspension to travel over obstacles.

https://www.youtube.com/watch

I was well pleased with the results but unfortunately one plant pot sacrificed itself during the making of the movie.

Do you want to see some more?

Mike
« Last Edit: January 29, 2021, 09:18:55 AM by Vixen »
It is the journey that matters, not the destination

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

Offline Roger B

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Re: StuG 111 tank
« Reply #9 on: January 26, 2021, 03:17:16 PM »
Excellent  :praise2:

With the DD system the brakes and clutches on the CG-2 are not used? It is just used for 2 speeds and reverse function?

More would be good :)  :wine1:
Best regards

Roger

Online Vixen

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Re: StuG 111 tank
« Reply #10 on: January 26, 2021, 03:35:19 PM »
Hello Roger

In the last of the photos above, you can still see the clutches and brakes on the CG-2 box and their steering servo. They were left in place at first, just in case the DD system did not turn out as planned. Later after my confidence grew, I locked the clutches and removed the steering servo.

Mike   :atcomputer:
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: StuG 111 tank
« Reply #11 on: January 26, 2021, 04:48:06 PM »
"Do we want to see more??"

Yes!
Following along.

Sid

Offline Laurentic

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Re: StuG 111 tank
« Reply #12 on: January 26, 2021, 05:45:55 PM »
Excellent Mike - and the Stuart tank before this, most enlightening, you do like your mechanisms, but you build them so well, the thinking behond them is so good.

Chris.   :ThumbsUp: