I am a newbie to High School Vex. (7 years of Iq though.) Just putting that out there, so if this is dumb please understand.
My team has settled on building a 4 inch wheel drivetrain with 2 11 watt motors on each side and one 5.5 watt motor on each side, with a red cartridge motor on a 2:1 gear ratio for 400 RPM. Note that we will also be using a transmission to switch between a 2:1 ratio and a 1:2 ratio. From all that I have seen, all 400 rpm drives have been on the smaller wheels. Before we go through with finishing it, would the motor counts/gear ratios and wheel sizes actually work? Or do we need do switch to smaller wheels if we want 400 RPM?
firstly, a 400 rpm drivetrain is insanely fast for 4inch wheels, given the fact that the field limits your maneuverability. also, red cartridges are 100rpm, and you would therefor be running at 200 rpm on a 2:1 ratio. also, the 5.5w motors are locked at 200rpm. for a drive of this speed i would recommend moving to at least 6 11w motors, or just running a lower speed or switching to smaller wheel size.
My team made a 66 watt 360 rpm drivetrain on 4 inch wheels and that is plenty quick for this year. I think anything faster than that and you’re just throwing defensive capabilities and torque out the window for no reason. Especially with how limited space is on the field you would need a very skilled driver to navigate the field and it would be very hard to actually use a drivetrain like that at full speed.
Edit: I want to also add that yes you could use smaller wheels if you really wanted 400 rpm but ideally just make it a slower rpm and keep the four inch wheels because generally the bigger your wheels are the less of a problem you’re going to have with the middle barrier.
Another thing i would like to add is that I would usually stick to a maximum 180 rpm per motor on each side of a drivetrain with 3.25 inch wheels. so if I had a 2 motor drive I would do 180 rpm max and with four that would be 360. Now with 4 inch wheels maybe make that number 150-160 because this is the point before you have overheating and torque issues. And you can push these numbers dep[ending on the weight of a robot in some cases.
It is finally time for me to break silence on this thread.
One of my sister teams uses a speed around 400 with 4 motor drive on 4 inch wheel and it works well for them. I think you will just need to keep it relatively lightweight.