Supporting > Vehicles & Models
StuG 111 tank
Vixen:
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:
Roger B:
That's a neat gearbox design :ThumbsUp: :ThumbsUp: I will be following along :wine1:
Vixen:
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:
crueby:
Now THAT is clever use of components!! I too remember riding a bike with that kind of geared hub, but never saw the insides.
Art K:
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
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