I’ve added a safe braking system to Acorn. Normally closed relays short the motor leads together any time the motors are not enabled. Works on power failure, e-stop, or motor fault. It’s a nice system and stops the problem of potential catastrophic runaway on a hill. Now we can operate autonomously on hills! More details incoming but I wanted to share this little tidbit.
Also that system does not completely immobilize the vehicle, just solves the risk of runaway (the unpowered motors have next to zero rolling resistance). We might implement a “parking brake” where it turns the wheels inward (opposing angles) to make a zero power complete stop on a hill.
Gear and motor and brake: Have you considered a worm drive?
All your gearing in one step.
No need for additional brakes, since they usually can’t be backdriven, the wheel is locked
Some example numbers: Did I get them right? Larger wheels = lower ratios than I’ used to.
3000rpm motor, 26"dia wheel is ~72" circumference = 6’ per rev
10mph ~= 15f/s x 60s/m = 900 f/m x 1rev/6ft = 150rpm vs 3000rpm motor = 20:1 worm gear
Worm gears from 10:1 to 120:1 are available from that website for example.
The torque is probably fantastic.
The efficiency may be too low.
Need a custom worm gear box since alignment between worm and wheel is critical, and needs good lubrication supply.
A worm gear with a splined bore to fit the single speed wheel hub would have the fewest parts and the most precision, but is custom.
Motor Controllers: On brushed DC motor drivers using PWMenable for speed control, it seems like you can provide arbitrary alignment between the phases.
Either align them in pairs where one motor turns off as the other turns on, or just make sure all the rising edges are spread out.
Can brushless motor controllers do the same thing?
Hi,
What about using a cycloidal drive or a strain wave/harmonic drive. I found some open source solutions that seem reliable.
(This is a playlist)
There are many other videos about these drives on youtube.
They are very compact and have high torque and with the right materials maybe good enough in 3d printed plastic. At least to go further, later this can be made from metal if it works in general.