Is it better to make a 3 motor gearbox with 1 sprocket coming out and then a chain connecting to sprockets on all of the wheels on each side. Or to independantly power each wheel?
I have seen more success with the gearbox method. I am not entirely sure why. The one wheel is driven by the shaft with the sprocket and a chain typically goes to the front wheel.
Two motors worth of torque together is powerful, but you divide the power across two wheels it should be even. But it does not seem to work that way. Maybe someone else can explain
Best I can imagine, one wheel may lose traction by being lifted occasionally while driving or pushing opponents. With a chained-together drive, all power would go to whatever wheel is on the ground.
I was mainly going to do this to save space. But now that i have heard its other pros, I will try it out.
@Matt4572 Just to clarify, you have 6 motors total, on your drive train?
We have 6 motors on our drivetrain and we use a 1:1 overall ratio (external) with all of the motors geared for speed. I believe that chaining the wheels together is a good decision because like @Team80_Giraffes said, the power is divided across all the wheels. (like they say, two brains are better than one) A few years ago, in 6th grade our team used four motors to direct drive each of our wheels. Since, they ran independent of each other, it caused our robot to turn in one direction, when we intended for it to go straight. Given, we are a field robot, we chose to have speed, so we could get the balls, and torque for intense pushing matches. We were able to achieve this with a 6 motor chained drivetrain. Just a pointer, make sure that the chain is tensioned correctly, too much and it will bend axels and cause friction, too little and power will be lost when the chain starts to skip. Also, if you only power, say, the back wheels with 4 or 6 motors, you will experience a lot of slippage between the wheel and the foam tiles since all the weight needs to be moved by the small points where the wheel and tile meet.
The issue with chained together drives is that it’s essentially treads. Your are putting a lot of extra friction on the drive, and affects turning, because the wheels need to slip independently and at different rates.
You can keep and independently driven drive straight through PID or other algorithms.
Imo, it’s better to chain the wheels together. The reason for this is that during any acceleration or deceleration, the wheel opposite to the direction of the acceleration takes a majority of the stress. If you power the wheels individually, one motor (per side) side be withstanding the strain. By chaining it, you ensure the power is distributed where it’s needed. The same concept will help if you are pushing or being pushed by another robot.
Nothing says you have to have four wheel drive. You can elect to drive just the back wheels. Your turning radius changes a bit but it works. You have all the pushing power just on two wheels with reduced friction of the chain missing.
But if you must do four wheel drive, a tensioned chin idler is another good thing to put in if you use a chain. Keeps it nice an taught.
We’ve had pretty good luck with gearing each motor to each wheel. We have three 2.75" wheels on each side, two omnis and a traction in the middle with a 3:1 external. It took up less space than the gearbox, and it even has a little bit to much power, we do a wheelie when we accelerate too quickly.
Ours does that too. That’s just from being top heavy.
What ever the normal gearing for motors is when you first get them. I haven’t tried high speed motors on it yet, we don’t have enough high speed kits for that.
Matt the wheel base you built last night will work fine its just a matter of finding the tension to make it so the sprockets cannot slip.
I know, I asked this before class.
If you have a choice, do not use chain, last year we had a chained together drive, and when the chain popped in finals we could not fix it fast enough. Having a chain run all the way up the drive will cause problems, try gears.