Roy's StuG III (no. 2020/10)

[Roy Beukeveld]

Hi Simon, thank you very much

[florian rudolf]

Hello Roy,

nicely build of your StuG. Looking forward to see it running at militrcks 2021?!

[Tom OBrien]

Roy,

Your build looks great!

I just finished with the wheels and suspension on mine. I added springs inside the four shock absorbers with just enough tension so that if the torsion bar should come loose, the wheel won't stay suspended upward, as they have been known to do on other builds that rely on torsion bar suspension.

I primed the hull with Rustoleum self-etch primer in green (it's the only color they had available). Once the rest is together, I'll paint it with a sand colored matt finish. Maybe with a camouflage motif.

I'll put together the drive sprocket/final drive in the next day or two but then I'll wait for the motion and sound packs to arrive before going any further. I'm hoping Armortek will have those shipped before long.

Cheers... Tom

[yves mouton]

Hello Tom,

That's a good idea about use springs in the schock absorbers,
i gonna use also springs.

Best regards Yves

[Roy Beukeveld]

Hello Roy,

nicely build of your StuG. Looking forward to see it running at militrcks 2021?!

Hi Florian, about six months away from now... Hmmm who knows

[Roy Beukeveld]

Hi Tom, thanks!
The springs are a good idea, at first I thought they would be part of the kit but later i understood that some builders added them themselves.
If I remember correctly I read somewhere they were also used some times to restore the balance of the tank a bit if the centre of gravity was a bit off.
Anyway, when the wheel arms are on and the angle can be measured I can determine the free space in the damper, and doing some experiments with it will be a good idea
What angle did you set your wheelarms to?

[Tom OBrien]

Hi Tom, thanks!
The springs are a good idea, at first I thought they would be part of the kit but later i understood that some builders added them themselves.
If I remember correctly I read somewhere they were also used some times to restore the balance of the tank a bit if the centre of gravity was a bit off.
Anyway, when the wheel arms are on and the angle can be measured I can determine the free space in the damper, and doing some experiments with it will be a good idea
What angle did you set your wheelarms to?

Hello to Roy et al:

To set the wheel arm angle, I put the hull on several slabs of dimension lumber so that the wheels would sit at least several cm above the table top. At first, I merely estimated the correct angle, a violation of the engineer's first rule "measure everything, all the time". This resulted in too steep an angle, more like 35-40 degrees. So, I loosened all of the torsion bars and re-set the angle to something more like 25-30 degrees, which is a bit more than the recommended angle. However, the weight of the vehicle should reduce the angle by one or two degrees, plus, I prefer slightly more ground clearance because I plan to run it outdoors over rough terrain.

Someone once asked me why the original StuG or Panzer III designers didn't allow for greater ground clearance. I explained that they (the Germans) figured out that a lower profile meant a higher survivability rate, which is a lesson the Soviets also learned early. During my early days just out of graduate school working as a development engineer at Aberdeen Proving Ground in Maryland, I had asked the same question. One of the older mentors (who also worked at the Ballistics Research Lab there), without saying anything, pulled out some data sheets showing the probability of hits as a function of vehicle height (in this case the larger battle tanks). "Read this and get back to me", he said. It was the first of many practical lessons about armored vehicle design. Those were wonderful days as my first project assignment was the M1E1 Abrams Main Battle Tank. -- Sorry for the lengthy aside.

When installing the springs in the shock absorbers, I took an old light-tensile spring (about seven mm in dia), cut it to fit so that when fastening the top portion of the shock absorber frame, the spring would cause it to align just above where the holes are in the hull. This provides just slight tension downward against the wheel arm and should not distort how the wheel sits on the track. Yet, it should also provide enough enough tension so that if the torsion bar breaks or comes loose the wheel won't ride "tucked up" toward the hull. I experimented with the spring length before installing them, and found it very easy to adjust the length by simply stretching the spring using needle nosed pliers (It's also easy to over-stretch the spring, so take care not to do that).

Cheers... Tom

[Roy Beukeveld]

Hi Tom,

Very nice story about the lessons learned about ground clearance. Those Germans had their bright moments
Not lengthy at all by the way, nice to read!

The setting of the wheelarm angle is clear, what you describe seems like a good method. I had thought about it myself on how to do that and planned to put it on two blocks with an exact(calculated) height. That height being what I need to get the prescribed angle on the wheelarm. In that way I can lower all the arms to the workbench surface and tighten all the screws while all arms ar firmly held in the same place/angle.

Disadvantage may be that I cannot adjust an individual arm to a different angle if needed. Which brings me to that point, you say with the full weight on the angle might decrease a degree or two, how does that relate to centre of gravity? Will it be noticeable where I put the batteries? Or isn't it worth the effort, just set all arms in the same angle and it will be fine?

[Tom OBrien]

Roy,

My experience has taught me that it is more important to set the wheel arm angle the same for both sides of the track and don't worry much about getting the ground clearance exactly where you might want it once it is under the added load of the batteries, etc. Different wheel arm angles for one side of the vehicle might make it look like it's listing, as a ship might do when you have too much weight on the starboard as opposed to the port side, for example.

For myself, setting the torsion bars into their respective housings with grub screws that will not move over time, is the most challenging part. I used thread lock (BLUE or medium) and hope it will hold the grubs. I'm reluctant to use the high strength RED because it's very difficult working with it if you have to remove a fastener later.

The batteries, etc. should be distributed so that the weight is roughly equal along the floor of the hull. With the width of this vehicle and the relatively low wheel arm angles, center of gravity (CG) should not make much difference. As I'm sure you know, CG is a function of weight and height from the ground at points along a plane, and of all the armored vehicles, the StuG is probably one of the least affected by too much topside weight. Generally, I like to balance the weight of the motors with the weight of the batteries by placing the batteries toward the rear. Other components are light enough so that they should not affect the track's operation.

cheers... Tom

[Roy Beukeveld]

Regarding setting different angles on the wheelarms I actually meant different settings only length wise over the vehicle, not between left or right.
But I get your point. The StuG's profile is low and quite even, so if the components can balance out roughly well it will probably work out fine with all arms set equally. Because I don't have any batteries and motors yet I don't know exactly how the mass of the two relate. It will all fall into place when they arrive.

But then securing the bars in place once the angle is set. You mention the grub screws, the countersunk screw axially and the grub screw should hold it. But there will be quite a lot of torque on this connection. Perhaps it could be a solution to grind or drill a small depth in the fixed end (CL0222) so the grub screw can be screwed in a few millimeters so it is actually radially locked instead of relying on friction? But doing so requires an accurate drilling which is different for each part.

Let's first see how it works, if there is no problem then no need to fix it

[Tom OBrien]

Roy,

Yes, grubs can be problematic and if you have the tools to drill a slight depression in the torsion bar where you know the grub will set, it's better than a the grub sitting on a flat surface. But, the torsion bar is so narrow in diameter, it might be pretty difficult an undertaking even if you are able to mark the grub's exact location on the bar.

Another solution is to re-tap for a larger grub screw but that might weaken the assembly as you'll have to remove more metal from its base.

At the moment, I'm trying to solve the problem of one of the driven gears binding when mounted and secured to the hull. I think I might have put too much axle grease in the casement.

I'm also waiting on the sound and motion packs. I won't go any further without mounting the motors as it's already going to be difficult attaching the top screws. (I've attached the motor mounts and consider them more-or-less permanent now).

Tom

[florian rudolf]

On my first StuG I used the grub screws deeper.
After the pre-assembly I drilled with a 1.6mm drill, then drilled a recess with a 2m. grubs with a point were used. this could be screwed into the recess.
so i took little material, but the highest possible security.
I secured the grubs with loctite (blue).

[Steen Vøler]

Tom, check if the drive gear is slight oval on the end facing the hull

Both mine where a bit oval and was not able to turn when installed.

Grinded the surface 100% flat and even, installed again and its spins freely.

Just to add that everything is loctitet as per instructions

[Tom OBrien]

Tom, check if the drive gear is slight oval on the end facing the hull

Both mine where a bit oval and was not able to turn when installed.

Grinded the surface 100% flat and even, installed again and its spins freely.

Just to add that everything is loctitet as per instructions

Thank you Steen. I was wondering about exactly what you describe as a slight oval or bulge in the metal on the driven gear end.

I did notice a small protuberance, a piece of metal no more than a mm across and a mm in height, which I assumed was left from the machining process. I filed that off but there remains a slight bulge in the metal but I also wondered if that was not part of the design intent -- so that in the event the driven gear made contact with the hull (and possibly any uneven projections from CSK screws, etc), the slight cone-like bulge would keep the gear from full and potentially destructive contact from the hull. Although the driven gear is restricted in travel once the outer sprocket assembly is installed, the shaft with the gear should still turn freely after tightening down its housing.

Oddly enough, this problem occurs only on the right side while the left is fine.

There is always something about these kits that keeps it challenging, right?

Thanks again.

Tom

[Armortek]

Tom, if you are referring to this raised part on the driven gear, it is meant to be there. It is there so that the inner race of the bearing contacts the gear rather than both the inner and outer race.
If you have filed it away then add a shim - it will have the same effect.