Currently, our bot has a 1/1.4 ratio. This is done with a 12 tooth pinion connecting to a 60 tooth gear. That torque ratio is then connected to a 1/7 ratio via axel connection to the 84 tooth gear. The final gear is another 12 tooth pinion. This all is driving a bot with a full dr4b, mobile goal lift, and cone gimbal/manipulator. The problem this ratio makes is just its sheer size. We have two of these compound ratios on either side of the inside faces of the bot. Making it impossible to take out motors without taking the hole gearbox apart. So my question that I have for you all is this. What ratio would give my team the best power to speed ratio for ITZ while being compact enough to be serviceable?
Generally speaking, the easier way to change the torque/speed of a drivetrain in VEX is to just modify the internal gear set of the motors to one of three options: torque (default), speed, turbo. This lets you avoid complex multi-layer gear setups that take a bunch of space in your chassis.
1:1 direct drive with a torque motor to the wheel is usually a safe bet. That (on 4 wheels) should be able to push even the heavier robots without stalling and still provide some reasonable speed. You also expierence less losses from friction of gears or chain and losses from slippage since the wheel shaft is directly in the motor. This is safe, takes up very little space, and efficient.
If you want a slightly faster option, 1:1 direct drive with a speed motor is an option. However, you’re robot needs to be pretty light (search VexForum for estimations). You can test that, or you can also do 6m speed drive with some minimal gear setup so you can have the high speed advantage but not stall with a heavier robot.
If you plan on running turbo motors, you better be allocating 8 motors plus to that drive.
Given what you’ve said, 4m torque or 6m high speed is probably best for you.
Would it be possible to do a 4m high-speed drive with a bit of external torque gearing? I’d love to do six, but we only have 4 motors allocated to our drive and reallocating two could be a bit of a challenge.
You could do 4m high-speed 1:1 with the 3.25" wheels to lower the chances of stalling. The only disadvantage of using those wheels is that you’ll have a lower drive train but that can be resolved by using pillow blocks under c-channels and voila. Also, a bit slower but you’ll be using high speed internals.
To do a little bit of external gearing for torque would probably be literally more trouble than it’s worth. Complicated gears to get a drive gear ratio with slightly less torque is going to give you more frictional losses than the torque you would trade off your speed for. For that reason, I always just keep my ratios simple. You can also change wheel size to reduce speed/increase torque and vice versa.
@Aponthis & @Yerayrobotics I never considered the wheel size actually having an effect on speed/torque values for the system. Thanks for the info.