Uses for VEX Differential Gear

I know there is a VEX Differential Gear Kit out there, and I know how, in general, differential gear sets work. So recently I was making a base/chassis design in which all of the wheels would be synced up. It’s pretty easy to sync up the sides. All you need to do is connect them with chains. Pretty simple, however that only synced up the sides and not the whole thing. So I looked at how this would be done. Most people would go to PID control, and I get it, it’s useful for programming because you have an estimation of the rotation of the wheels. Though I wanted this base to rely on at least programming as possible. Eventually I found the VEX Differential Gear Kit. I remember how differential gears worked and I thought this could be it. It would connect everything together and still allow it to go at different speeds. Is this a good idea? Will the plastic bevel gears strip because they aren’t metal? Will this actually be a hassle, and I should just stick with PID control? Thank you in advance to anyone who answer’s these questions.

~Inventor Inventor

Um… well… um…


Cars use a differential because they need to take a single power source (the engine) and drive at least two wheels. In Vex, however, we have multiple power sources (motors). If cars had two engines, there would be no need for a differential because one engine could power each side. In theory, you could make a drive train with every motor geared together on one axle powering a diff to split power between the two sides, but it would require a steering mechanism similar to a car, which would be very hard to implement. If this is for your own personal project to experiment with differentials, then go for it. Otherwise, I would recommend just direct drive on all four wheels for a competition bot, as it is more flexible and less prone to mechanical errors.

Also if you don’t know how/don’t want to program anything, I recommend learning.

Everything @evangs1 said, and…

An alternative to using encoders is to use a gyro, aiming for no rotation when you want to go in a straight line. Of course, gyros have their own problems, and you really can’t guarantee certain radius turns with them like you can with multiple encoders.

I understand about why differential gears are used in cars, because they only have one power source. But of course in Vex you can have multiple motors. But I was going for have 6 wheels, three on each side. Only four would be driven by motors. The ones that won’t are the middle wheels. I was thinking of connecting the two middle wheels with the differential. I still don’t understand why I would need a steering mechanism. I was hoping to use the differential to sync up the wheels so that the robot could go straight, not to actually drive them. Sorry if that wasn’t clear before.

@Inventor Inventor If you really wanted to use a differential in your drive, you probably could find a way to. However, it wouldn’t really provide much benefit compared to linking the middle wheels with gears or chain to your motors. Our school has found over and over that simpler solutions are generally easier to implement and better than overly complex ones. I also don’t see the need for linking the two sides together with a differential. A differential would allow the sides to spin at different speeds, no different from gears or chain. You probably don’t need a PID for your drive, as the two sides will move at the same speed (assuming you use the same gear ratios), and your robot will drive straight enough for the tiny area it has to drive straight in. During autonomous, you can use a quad encoder to keep the robot going where you want it to.

I thought that too. I don’t know, maybe when the season starts I can quickly install it. If it works great, but if it doesn’t I can always take it out. Also I’m thinking of taking out the middle wheels. I don’t know, I’ll have to experiment with this base.

Here’s one use: