Today reminded me of why I’m glad to have done a 4wd build, instead of sticking to 2wd. I have stated before, that my goal in electric skateboarding to create a serious mode of transportation rather than something to play around with. To do that, we need to create redundant systems, so when (not if) something fails, fail safes are in place.
Today while riding home from class, I experienced a failure in 1 of my 4 motors while traveling down a rather steep hill. I immediately noticed the reduced braking power, as it went to 3wd. However, 3 motors is still more than enough to stop me (200 lb plus my backpack with my laptop weighted 20 lb, so 220 lb total) without any incident. Had I been on 2wd, I can’t say the results would have been the same, considering the steepness of the hill I was going down.
One of the major benefits of 4wd is you create redundancy. If one motor fails like it did in this case, you have 3 more to make up for it. I was able to ride the rest of the way home (about another mile or so) home without any issue with the only effect being I was limited to 20 mph instead of 24 mph (I noticed the board feeling more sluggish, so I pulled my phone out and started measuring my speed on flat straights of my route. I didn’t know the motor was not working at the time). I found the motor not spinning when I got home.
The issue was not the motor broke, but 2 of the 3 cables between the vesc and motor broke. This was because where I soldered the 3 motor cables to the vesc, I stripped away too much wire. As a result, too much wire was exposed, and vibrations mixed with the concave of my board put too much tension forces on the wires and they broke. It was a simple fix and their is no permanent side effects. But having the extra motors added extra safety that allowed me to stop on a hill I could of had a run away into traffic and allowed me to keep riding with little side effects.
There is one flaw in my design, which is if the master vesc fails, I would be just as screwed as a 2wd board. That, I want to find a way to make more redundant (Ideas?). But the same can be said if one of the slave vescs fails. It’s not a big deal, and doesn’t impact safety to have a slave vesc fail.
No one can expect a failure, but they do occur, and we need to be ready for when (not if) this happens. Our boards won’t last forever (nothing does), and cars and airplanes create redundancy and fail safe systems to attempt to avoid catastrophe.
This incident today helped me refocus my energy into creating the safest electric skateboards possible. My vision is to create boards capable of safely commuting electric skateboarders at speeds of 45 mph+ without loosing torque due to hills. 4wd really helps get me closer to this goal. Hills slow me down from 24 mph to 20 mph at worst. With 1 or 2 motors, I would slow down to 12 mph or even less on hills, depending on the steepness. Today, I tackled my first 20% grade hill. I was able to travel 18 mph up that hill.
I don’t want to build toys to play with (of course I still play with them), but a real option that can travel as fast as a car and get me from point a to point b in the same time or less than a car, as safely as physically possible. I’m getting closer to that goal thanks to 4wd, as I no longer slow down significantly on steep hills (which I am surrounded by living in San Francisco) and a single motor or vesc failure does not mean I lose control or the ability to keep trucking on.
(I don’t want you guys to get the wrong impression, this thread is not about bragging. I want to share my experience of riding 4wd for the past week 10 miles a day for the past week (including my first hardware failure which could have resulted in an accident. And why I think 4wd, especially 4wd hub motors, are the future of electric skateboarding.)