Halftrack steering questions

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sassgrunt
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Halftrack steering questions

Post by sassgrunt »

I would like to try and build a German sWs halftrack, and am having trouble trying to figure out how to make it steer. I can only think of a couple of ways to do it.

1) The easiest way is to use a gearbox that drives both tracks at the same time, and relies on the front tires for steering. This is how the Torro M16 US halftrack works, but the longer & heavier track runs of the sWs would tend to drive it in a straight line, no matter which way the front wheels point. (I have found this out from locking the differentials on multi-axle 1/14 scale trucks. Without a powered front axle to help pull it through a turn, it just wants to go in a straight line).

2) Although I can use a separate gearbox for each track and a simple Tamiya DMD control unit like the T-01 to control them; that doesn't allow for me to somehow synchronize the movement of a servo that controls the front axle steering. (Because the DMD unit plugs into the rudder and throttle channels of the receiver, and a steering servo would just be a third channel that doesn't relate to the DMD). I know that people have used a Y-harness to make two separate servos function together, but I don't know how a Y-harness would connect to both the DMD and the servo without screwing up the DMD.

3) The real things used a system whereby when the steering wheel was turned more than 15 degrees, it would interact with the braking system and cause that side's track to slow; allowing the non-retarded track to help steer the vehicle. So, the most prototypical thing would be to use one motor driving an axle with a differential, and using some kind of braking system that works in concert with the front axle. And, while that might be the coolest thing to have; trying to actually make something like this work would probably drive me to drink!

Any thoughts (or experience) you folks have will be greatly appreciated. (I went through all of the electronic threads and couldn't find anything similar). Thank you. -Mike
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Re: Halftrack steering questions

Post by Tiger6 »

All of the german halftracks I have seen (apart from the Asiatam Opel Blitz based one) have used independent drive for each track, and left the front axle unpowered.
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jarndice
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Re: Halftrack steering questions

Post by jarndice »

If you have seen any newsreel of German Halftracks you would have seen how ineffective the front wheels are,
The front axle is often in the air,
The vehicle gets along in a series of slews as the direction of travel is controlled by the amount of power being fed into the track opposite the desired turn.
I think I am about to upset someone :haha:
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43rdRecceReg
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Re: Halftrack steering questions

Post by 43rdRecceReg »

That's one fine conundrum, Mike! :D Clearly, on a left turn (for example) the front wheels should swivel to the left, while the right-hand track should run proportionately faster than the left.
Steering with the tracks alone, would leave the front wheels as a possible hindrance, if they're not pointing in the appropriate direction. In principle, a split signal via a y-piece would seem the best approach.
Whether the electronic division of labour, so to speak, would have an adverse effect on the DMD unit, or not, depends less on programming than the throughput (and respective needs) for power...and the threat of overheating. I'm guessing the DMD : could handle it, but maybe an inline fuse would help. :think:
"Get your facts first, and then you can distort them as much as you please"- Mark Twain.
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43rdRecceReg
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Re: Halftrack steering questions

Post by 43rdRecceReg »

The Kettenrad relied, mostly, on the front wheel for steering, but turning the handlebars could engage the braking system.
.The differential makes it possible for cars, and lorries, to be steered by the front wheels. Is there some sort of differential system from 1/16 truck that could be used on a half track? That's just a bit of speculation, as I'm a total half-track virgin. :D
"Get your facts first, and then you can distort them as much as you please"- Mark Twain.
sassgrunt
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Re: Halftrack steering questions

Post by sassgrunt »

Thank you all for your replies. I would MUCH rather go the simple route and just drive both tracks together and let the front wheels steer however well/unwell they are able to. But, I also like the idea of each track having a different speed as needed to turn. I think I will take your advice Roy, and see if using a Y-harness will work without burning out the DMD unit. And if worse comes to worse, I can always fall back on the more simple method.

I still have parts coming in for this build. Although Asiatam does make 1/16 sWS track, I'm going to use a set of Kenny Kong's transport tracks for the Tiger I, (I already had them in hand, but not earmarked for anything else). I just ordered a Tiger I lower hull from Taigen, which I will shorten as needed for the fewer amount of roadwheels of the sWS. And, it will give me a stable platform to build everything else around it.

Thank you all again. -Mike
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Re: Halftrack steering questions

Post by Tiger6 »

http://www.rcuniverse.com/forum/rc-tank ... track.html
http://www.rcuniverse.com/forum/rc-tank ... -18-a.html
http://www.rcuniverse.com/forum/rc-tank ... oject.html

You'll need channel mixing for the steering servo, either on a seperate board or within the radio if you have a more advanced one.
sassgrunt
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Re: Halftrack steering questions

Post by sassgrunt »

A lot of good info in those links. Thank you.
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jackalope
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Re: Halftrack steering questions

Post by jackalope »

When I built my 251 halftrack I solved that problem by using a split gearbox with 2 motors, 1 for each track. An IBU2 with the steering rate turned down to 10% which damn near stops the inner track during turns. I then used a servo Y plug to just straight off the IBU2 giving my steering servo full power. So when I would steer the truck to the right the front wheels would turn to the right AND simultaneously the right side track would slow down to a crawl while the left track continued at normal speed. This allowed the tracks to help steer the truck but retained the front wheels as doing the actual turning.
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jackalope
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Re: Halftrack steering questions

Post by jackalope »

You'll have to play with the steering rate % to get it dialed in LOTS of trial and error! Very slow going having to constantly pull the memory card, adjust it, put it back, nope not enough, then nope too much, damn not enough again, WTF too much again?, WHAT?! How is it not enough again?! F## THIS GOD DAMN TRUCK! Put in box for month to cool off. I think I wound up with my 251 set at 22% or something like that. It's been a while! I sold the truck to Dean along with my other 251's. At least I think it was Dean.
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