SDKFZ 7 steering

[Peter Wolfrom]

Hello model builders, I would like to convert the steering on my 7 Series to be functional for off-road or soft surfaces.
Driving on sandy ground in Overloon (Netherlands) it was impossible to steer. Does anyone of you have a good solution? Greetings from Germany.

[florian rudolf]

Well Peter,

you know about my solution on the Famo. A bit tuning on the Base brackets and it works.
Maybe if you take the same servo like the Famo have it will be work.
The wheels from the Sdkfz 7 are much smaler.

[simon_manning]

Hi Peter, Tonegawa seiko servo, PS 050, industrial strength, send a P.m. to Dave Brady he knows all about this conversion, that's where i found out, regards simon.

[Jerry Carducci]

You know I've seen those servos for years, back into the 90s listed at Tokyo Hobbies and always mused
what could I use a gigantic servo like that for.

http://www.tokyo-hobbies.com/tonegawa.html

Now I know!

[Peter Wolfrom]

Ok, thank you very much. With the servo that is clear so far.
But how did you improve the mechanics? Recently I broke off a rod on the thread.
The steering between the rods must be without play, without wobble. (don´t know if this translation is correct)
Pictures of your mechanical solution would help me.
Thank you very much.

[Jerry Carducci]

Peter you give voice to my concern: strengthening the servo will stress existing parts. As I've been revising elements of my own Sd Kfz 7
I've been looking over the steering parts overall. Uncertain how to make them stronger yet other than making them larger. That threaded part
you showed is most certainly going to be a weak(er) link when the greater power of a powerful servo is applied; also very likely metal fatigue is
playing a part here. Threaded parts have built-in failure points; because they're threaded.

Jerry

[Adrian Harris]

Vince Abbott had the part made from steel, with the arms brazed on.

i-HTkzP8z-M.jpg (24.46 KiB) Viewed 2191 times

Adrian.

[simon_manning]

The steering on the 7 was never that good, also not on the real vehicle, batteries placed under the bonnet will help to add some weight, that’s where a bigger servo comes in, as Adrian replied vince Abbott came up with the solution, and Dave Brady has tried and tested this vehicle and made it work. Having a mix on the tracks to aid steering aswell, it,s a combination of improvements to make it work better, regards Simon.

[Jerry Carducci]

The steering on the 7 was never that good, also not on the real vehicle, batteries placed under the bonnet will help to add some weight, that’s where a bigger servo comes in, as Adrian replied vince Abbott came up with the solution, and Dave Brady has tried and tested this vehicle and made it work. Having a mix on the tracks to aid steering aswell, it,s a combination of improvements to make it work better, regards Simon.

That would be my choice as well. Steel parts. I think I'll work on making those when I get to revising the assembly.

I have more powerful HiTec servos, at least more powerful than the stock examples. but I think I'll try to get the Tonegawa-Seiko type. The 24volt version isn't cheap. I have inquiries into Tokyo Hobbies and Tonegawa directly. As I have a Famo kit as well I'll likely want to do something similar there.

The experience I have with my 1/10 scale Kaelble trucks at 60+ pounds each was that the more powerful the servo the better when it comes to turning the wheels while stationary of operating at slow speeds in anything but paved surfaces.

Jerry

[Jerry Carducci]

After I read this I promptly trotted out to where my 7 is to examine these parts. Prior to this I hadn't looked that closely to the steering control
arms as I hadn't taken off the wheels and actually hadn't planned to.

Not that this would make a hill of beans difference but if I read the original instructions correctly( likely not) i the original intent was to
make the right hand wheel the 'steering ' wheel, that is connected to the servo. Here in the states I'd do left as old habits die hard and that in fact is the way this model was set up. Kudos there. So having disassembled this I have the left hand steering control in hand.

First thing I noticed is that these control arms are already steel, most definitely steel. The thing I saw that I didn't like was that the tie rod and steering arms were not screwed onto to the spindle all the way up to the shoulders that they were made with. I have to assume these two arms bottomed out in their respective holes before they could be cinched up? Or the thread timing didn't allow both fully tightening and proper orientation for the intended purpose? Either way with the machined shoulder unsupported it's a broken part walking.... I have to address that.

Second thing I noticed and at least have a question about. I see that the steering arm- that arm that was connected to the servo is already bent.
My question is was it for some reason made that way or was it bent in use? If it was bent in use that tells me two things. 1) the metal isn't up to task and
2) the supplied servo already has more than enough power but isn't being used properly. That arm, even of mild steel isn't a particularly weak part.

Steering or deflecting the wheels of a model that is stationary or at slow speeds in rough ground is going to put enormous stress on the front steering apparatus. Possibly more than it should have to deal with. Again with my experience in my heavy 1/10 trucks mentioned previously I used hugely powerful HiTec and Savox servos in them and they drew so much power doing what I asked them to do it caused my receiver to shut down as the voltage dropped so much - I had to use a separate dedicated BEC to power the servos. This the only reason I'd use a powerful servo here that gets its power independently.

I'm going to see about correcting what I've found in my own model, at least the way I believe it should be. I may consider a more powerful servo
but I think I'm going to build in a hard limit on what the servo can do . I'd rather have poor steering than broken steering.

[Jerry Carducci]

My apologies to the original poster, Peter Wolfrom. I don't normally hijack the threads of others. I should also thank you for
prompting me to look at this issue on my own model. Perhaps some of what I discovered could be of use to you. If you can remove the broken
part of your steering components and either purchase or make a replacement I feel my modification would help in the end.

Sometimes I'm a problem looking for a solution, or perhaps a solution looking for problems?

I try to only have to do a thing once and re-working the bits of this model, as enjoyable as it is, I only want to do once.

That said I expect and demand a high degree of mechanical reliability and predictability of my models from the smallest to the largest.
If I can't get that I'll have to change it. With these large models my nightmare is to be out somewhere and have a mechanical failure.
I'm an old guy, most of my friends are old guys. To have to call out the old codger brigade to come help me rescue a 100 kilo model
that's broken down in some far-flung marsh is the last thing I want to do...

So here's what I did to the steering in an attempt to help ward off this particular failure:

• discovered that on the stub axle frame (CG0304) the two 5mm threaded holes had no relief cut to receive the shoulders on the control arms

• I cut a relief on both holes.

• To improve the thread timing of the steering arm ( CG0306) on the lathe I trimmed off a few thousandths to allow correct orientation.

I'm still waiting to hear if I should straighten out ( CG0306) or if it was intended to be bent, Seems more pleasing to be straight but not an issue.

I could be way off base but I feel this is mechanically more sound. I feel that anyone who has a similar situation to take these steps to increase the mechanical reliability of the steering apparatus; the arms as I saw them were not properly supported and exposed to fatigue failure.

So below find what the assembly looks like:

[Derek Attree]

Hi All
When I made mine I silver soldered the arms into the block having counter sunk
the hole so the arms could sit in the correct position.

Hope that helps

Regards

Derek

[florian rudolf]

Its steel, so I would set in on place right. Than demount it and weld it, so it would'nt brake anymore.
The next woult be an Servobumper. If the Servo is too strong everythjin will going to brake down. You can make it by your own with a strong spring.
Otherwise use a smaler Servo. If this brake change it easyly

[Adrian Harris]

Do you have a copy of the manual ?

Page 31 shows the steering arrangement and the arm looks bent to me in the pictures.

Adrian.

[Peter Wolfrom]

Hello everyone,
these are the original parts from Armortek.
Welding or brazing is a good idea.
Peter