Some SdKfz 222 Upgrades

[Liam Mahoney]

After talking with some fellow collectors on the weekend there seems to be the impression that the forum has lost a bit of its zip since Phil is no long entertaining use with his fabulous skill, not at all degrading the standard build from the plans in anyway, but it is that spark of imagination that can come from seeing someone else’s creativity that can really add to the enthusiasm and give you a little kick to keep the interest alive. So I thought that I might add some of the upgrades that I have done to my SdKfz222 over the past year or 2 (time is starting to go too fast) definitely not in the quality of some of the other posts but it might spark some imagination.

As our quality inspector at work would say these are not criticisms but improvement opportunities. I will try not to offend any initial design work done, but there is a lot of room for improvement that will make this an exception model. Bodo did a beautiful job with his adding and improving the overall look, far better than I could do, but I wanted to make it a more useable model something that I could drive anywhere.

Looking at the drive system it became obvious that the centres of the axle shaft joins where in the wrong positions the diff join too far away from the chassis rail and the wheel joint too close to the chassis. Also the hole through the chassis was a little too small. This caused the drive shaft to lock on full bump or droop, or prevented suspension movement when on full lock. To fix this issue I found some off the shelve drive shafts that would fit and machined some extensions for the diff housing so the inner join was closer to the chassis. I then increased the size of the hole in the chassis to the maximum. Then I machined up some new outer axle hub shafts to get the outer joint closer to the kingpin centre line. This then require a new wheel mounting hub and as I was making the new wheels this wasn’t an issue (the new wheels will fit the original hubs). Unfortunately I could not improve the scrub radius but on the real thing this was quite large anyway.

Drive Shaft Options

Drive Shafts

Diff Extension Housing

Diff Extension Shaft

Diff Extension and Shaft

Wheel Hub and Shaft

The new shafts now gave plenty of travel and the opportunity to improve the steering angles which I though where a little low. So after grinding the corners off the lower swing arm the steering arm could move further inward I then redesigned the steering arm with more of a curvature to reach around the lower control arm and full droop.

Full Shaft Travel

Full Shaft Travel -1

Lower control arms

Steering Arm and Top Mount support plate.

While I was working on the steering I thought that I might have a go at improving the linkages, with the hope to get the 2 wheel – 4 wheel steering to work. Based on as much information as I could find I estimated that the rear wheels did not turn as far as the front (I may be completely on the piss on this) so into the CAD for a day or 2 and I ended up with what I think is the right Achermann for the 4 wheel steering that still fits with the 2 wheel steering. Not that any of this really matters on this scale but nice to have it as right as I can.
During all of this I noticed that the diffs where only fitted with a single bearing on the pinion, being a rather heavy model I thought that this should be rectified. So a bit more laser cutting and machining and I ended up with a bracket that did both, fix the steering linkages and held in place a second pinion bearing.

Second Pinion Bearing

Diff Assembly

Pinion Support bearing

Steering Links

With the steering sorted I was back to the bump and droop, I was not a fan of the through bolt bump stops and hoped that I would eventually put Shock absorbers on that could do that job but until then I need something else. So a small laser cut plate bolted to the original bolts did the job. While I was here I looked at adding some camber adjustment on the upper control arm mount. After consideration of the effect the new bump stop will have (putting considerable bending load) on the chassis mount for the upper control arm and the fact that I have just made the mount weaker by the slots I put a 3mm support plate on top of the mount. (picture above) I also added smaller 3mm support plates to the bottom control arm lower mounts, at the area where that chassis rail acts as the bump stop for full bump.

Droop Bump Stop

Camber adjustment

So now with the control arms mounted to the chassis I looked at the kingpin and hub arrangements, my kit didn’t get the upgrade to the steel bearing housings so every thread in the aluminium housings was fitted with a recoil/helicoil to make sure that things stayed put. Which brings me to another issue and that is loctite which is good stuff in the right place but no substitute for the correct bolt tension on a good design. So back to the lathe to make some bushes for the pivot bolts that hold the kingpin housing. Using a simple tube bush so that the bolt can be tightened to a correct tension without loading/locking onto the arm worked a treat. Along time ago an old bloke said to me “if it needs to move to do its job than make sure it can move as free as you can make it move”, and I apply that to every moving part.

Bushes for steering

Then all I had to do was the steering from the servos, yes I chickened out on the mechanical change linkage as is on the real machine and went for the easy 2 servo option. It made for the 2-4 wheel change over easier in the program on the controller and is locked to the gear select.

Front Diff Mount

[Liam Mahoney]

But before I finished the servo mounts I had to deal with the drive motor, I didn’t want to use the original as I think it was a bit over the top, and I very much dislike the open gears, yes a fan of lubrication (let it move easily) so I looked at off the shelf gearboxes and found one that would do the job nicely (I have since found a better one) and it is 2 speed. Just had to try and fit it and hope that it would be strong enough to do the job. So I started with a plastic housing box mounted it up temporarily which then gave me the room to mount the servos and finish the main drive shafts. A small note to anyone wanting to have a go with their 222, the yoke on the diff coupling is 8.3mmID and the diff pinion is 8mm so it will always wobble once you lock the grub screw. This was exaggerated when I put the second bearing on the pinion, a thin sleeve will fix it.
Because the gearbox that I selected had different locations for the output shafts my main drive shafts ended up a bit on the chops, very bent but the uni-joints are well up to the job (the new gearbox has the shafts aligned). After a bit of cut and shut the drive shafts where fitted and it was ready to test. I programmed the controller so that the 4 wheel steering would only work in first gear and once second was selected 2 wheels steering. So off I went with my kick ass, so I was told, 540 motor and yes it moved quite nicely on the concrete... but with 18kg onboard the dirt was totally different, and second gear only on the concrete.

Main Drive Shafts

Rear Diff Drive Shaft

First Motor

So back to the evilbay for a bigger motor more torque but slow RPM, even comes with a cooling fan must have some mojo, perfect...

Motor Number 2

And yes it did go much better until the ESC overheated and it all stopped, which was only about 5-6 minutes, so maybe gear it down a bit to reduce the load? Of to my bucket of parts that I pulled out of an old printer that stopped working and giddy-up a drive reduction I did have.

Drive Reduction

And away we went... for about half an hour and again overheated the ESC, so no other option but to get some real kickass, Brushless it has to be and why stop there let’s go full tilt. Motor number 3 definitely fix all that, to the point that I had to re-programme the controller to 40% full throttle. While I was out doing the first test drive with the new motor I thought I might test the wheels and tyres to make sure that they will do their job, I have had the comment that they are only for mantle piece ponces, well with the new motor and running on an 11.2volt battery with 15kg ballast on a bitumen driveway it WILL spin all 4 wheels for the first 1-2m, yes I was very, very surprised and even more delighted that the wheels and tyres held up for the many times that I did this. But doing silly things like that, even in the name of testing eventually something will give. The gearbox comes fitted with a friction clutch a safety thing I imagine, well it didn’t like the bitumen and back to the work shop we went.

Final Motor and Drive

Burnt out Clutch

Now that the concept had been proven I ordered an aluminium housing gearbox just to make sure that everything was strong enough. This gearbox is so much better than the plastic box, it will spin so free, back to the old fella’s saying let it spin.

After a lot of driving testing it became quite obvious that the spring rate was way too high so many springs later I found a set the will do the job, one corner just reaching full bump as the opposite side wheel just starts to leave the ground. And while I was pulling the suspension apart why not add the shockies? Back to the laser cutter and a bit of drilling and fiddling and I think it works well.

Lower Arm Mount Support

Finished Suspension

New Gear Box

New Gear Box -1

And after all that it spent our drive day in the shed because I messed up the programme in the controller... very sad.
I hope my ravings weren’t too painful, enjoy the building.

Thanks
Liam

[David Brady]

Inrtesting Liam, must have taken some time to post

Cheers

[David Battson]

Hi Liam,
Excellent work and thank you for taking us through the development process, failures as well as successes. I find sorting out the mechanical details such as this easily as rewarding as adding the finer scale details, it's just a shame they are often less appreciated or at least less obvious when the finished kit is all put together. You have successfully nailed all the reasons why my 222 is still a non runner and sat on the shelf, is there any chance that you can offer some of your laser cut parts and springs etc as an upgrade kit ? I would be really interested to know how the universal joints you have used last, as I have thought about using them, but assumed they would be the weakest link on such a heavy model compared to the average RC rock crawler.
Best Regards
David

[yves mouton]

Hello Liam,

Awesome and a lot of work on the 222,
you got amazing engineering skills

Best regards Yves

[Phil Woollard]

I'm watching with great interest! Keep it coming

[Liam Mahoney]

Thanks all,

Hi Dave
Yes I did plan on sell all the upgrade parts as a kit but the more I got into it the more I realised that it would take a bit of lathe and mill work to modify the standard parts to mate up with the new parts.
The drive shafts are the most important upgrade but the most difficult to make as an upgrade unless you through all the standard parts out, which then makes the upgrade a lot more expensive.

Send me a PM with what you had in mind and I will look at my spares and what might work best for you.

Liam

[Christoffer Ahlfors]

Wonderful engineering, so much fun to read!
Thanks!