# How to create a LEGO Technic tank steering system

I found this video containing a steering system for tracked vehicles. Are there any steering system(s) that are more simple than the one shown in the video, and include a guide (in LDD or pictures format) to replicate for a tracked vehicle, such as a tank?

The simplest method would be to just have two motors, with one motor driving each side of track.

To go forward, both motors forward; backward both back; to turn set one motor to go faster than the other, only drive one side, or set one forward and the other backward. It is a fairly common treaded vehicle steering system.

The linked system with dual differentials, a drive motor, and a control motor, seems quite excessive to me.

However, it come with some cost as the system move without feedback, it's unlikely that both motors will be driven at the exact same speed. Variations in the build (e.g. how tight bushings are) and the motors (torque curves) means that it'll generally drive in a (large) circle unless you actively correct for it. To make it move relatively straight, it involves a lot of fiddling with loosening / tightening parts, and even then one may often find that it no longer drives straight on a different surface.

With a dual-differential drive, there's generally enough friction that it will indeed drive "exactly" straight when the drive motor is on - and if it doesn't, one can just add a bit of friction (e.g. clamped bushings around a stud) to the control motor to make it drive straight.

• Note that it can be a pain to ensure that the tank actually drives straight with the 2-motor system. – TLW Aug 24 '16 at 15:15
• @TLW, is it possible to let me know what type of pain you are referring to? – user275517 Aug 31 '16 at 1:31
• @user275517 - "pain" in the sense that, without feedback, it's unlikely that both motors will be driven at the exact same speed. Variations in the build (e.g. how tight bushings are) and the motors (torque curves) means that it'll generally drive in a (large) circle unless you actively correct for it. You can make it relatively straight, but it involves a lot of fiddling with loosening / tightening parts, and even then you'll often find that it no longer drives straight on a different surface. Hence, "pain". – TLW Aug 31 '16 at 19:29
• @user275517 - With a dual-differential drive, there's generally enough friction that it will indeed drive "exactly" straight when the drive motor is on - and if it doesn't you can just add a bit of friction (e.g. clamped bushings around a stud) to the control motor to make it drive straight. – TLW Aug 31 '16 at 19:30
• @user275517 - At one point I was part of an (informal) competition to see who could build a robot to drive in a (relatively large) pentagon and return to the start most precisely. 'Twas fun, but I ran into this problem at first. – TLW Aug 31 '16 at 19:33