# Differential Steering to steer a tank

by voyager221
Tags: differential, steer, steering, tank
 P: 19 Why is it when a tread on one side of a tank stops the other side which is still moving will 'skid' in the direction of that tread? This is used to steer a tank but what is the physics behind this please
 Homework Sci Advisor HW Helper Thanks P: 9,929 Since one side is being propelled forwards but the other is being held back by the ground, there's a torque and the tank will tend to turn towards the halted side. Which point will be the centre of rotation depends on the distribution of weight. With an even distribution, I would expect it be somewhere within the halted track, but I'm not sure where.
 HW Helper P: 7,180 I'm guessing that voyager221 means that a tank tends to skid "outwards" while turning with the inner tread stopped. I don't know if this is true. If so, it could be related to the fact that the tread is a flat track like surface instead of a round wheel. It could be due to the fact that the inner tread is sliding as well as the outer tread. I don't know if the surface, such a pavement versus sand, makes a difference in the outcome.
 Sci Advisor Thanks PF Gold P: 12,266 Differential Steering to steer a tank If one track is not powered then I can't think of a situation where the tank would do other than steer in the direction of the stationary track. I know that the opposite can happen with a motor car when one wheel actually stops rotating (aquaplaning) but, with a tank??? Not likely to get a situation like that.
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 Quote by sophiecentaur If one track is not powered then I can't think of a situation where the tank would do other than steer in the direction of the stationary track.
The track is powered, but forced to not move. My guess is that the original post implies that the tank does not pivot about the stopped track, but turns and moves in a circle with a slightly greater radius, which would mean the inner track gets dragged forward a bit as the tank turns.
 Sci Advisor Thanks PF Gold P: 12,266 Do you mean 'powered' or 'braked'? But even if one track is powered (driven) a bit less than the other, you will still get some steering effect. This method of steerind is very messy and destroys the road because there is a lot of scuffing.
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 Quote by sophiecentaur Do you mean 'powered' or 'braked'?
In this cased "braked", but I'm not sure how braking is implemented for a tank.
 Sci Advisor Thanks PF Gold P: 12,266 The track system is very inefficient, I think. I bet they don't freewheel very well.
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 Quote by rcgldr My guess is that the original post implies that the tank does not pivot about the stopped track, but turns and moves in a circle with a slightly greater radius, which would mean the inner track gets dragged forward a bit as the tank turns.
The original post says "This is used to steer a tank", which suggests to me there's no subtle, unexpected effect being discussed.
From a quick web search, looks like, in the context of tracked vehicles, "steering", "skid steering" and "differential steering" are synonyms.
http://www.beam-wiki.org/wiki/Steering_Techniques uses "differential" for the independent wheel case (as a car) and "skid" for tracked vehicles.

That site also claims that with one track stopped the turning centre will be at the centre of the stopped track's footprint. That puzzles me. Linear forces from the dynamic friction on the stopped track would all cancel, leaving only the forward force supplied by the moving track. So I would have thought the turning centre would be displaced somewhat away from the centre of the vehicle.
 Sci Advisor Thanks PF Gold P: 12,266 I think that when they want to turn really tightly, they will reverse one track (like turning a rowing boat about the point where the rower is sitting) Some of those modern tracked vehicles can do 40mph+. God only knows what they steer like at those speeds. Ahead only, I should think, or you could tear the tracks off.