- Sun Oct 01, 2017 10:56 pm
The big problem with that strategy with trying to reuse the factory motors/gearbox (or similar) is that you need pretty massive amounts of reduction to get the right speed & torque. The 16T/19T boxes are in the 120-150:1 range. A typical pulley arrangement would require 3 stages of reduction minimum to get there (at 5-6:1 each). 10mph on the average power wheels (13-14" tires) is going to be 250rpm. Most people that go to a "non-plastic-gearbox" are using larger scooter motors with 2500-3500 RPM no-load speeds and then a ~8:1 speed reduction (and are shooting for slightly correspondingly higher speeds).
You can buy lower-speed motors, but I haven't seen any in the standard footprints (550/775) that run at 3500RPM AND put out 5x the torque of the 15k RPM ones -- they're always lower power and not very well suited to that type of application.
I think you could build a 2-stage metal gear gearbox with some of the parts they sell for the competition robots, but you're talking about some fabrication. If I had a lot more time, 48-60V into 3 or 4 RS775 motors per gearbox, driving a 42:1 reduction would net a good 2-3HP per side (with appropriate batteries, of course) at 15-20mph, but at that point you really want a chassis that could keep up. And the only reason to do that is if you have a lot of cheap 775s (which I do...) -- otherwise, just get a scooter/winch/other large DC motor.
F-150 - 24-36V with homebrew 100A variable-speed motor controller, 4x 775 motors (NOT all-wheel-drive), and fading color
Hurricane - 24V w/50A step-down controller, Mabuchi 8514 motors
Princess Mustang - 12V w/23000 RPM 550 motor and 23T gears