Saturday, March 8, 2014

Scooter Recap


After having a working scooter for nearly a week, I can conclude that, while definitely delayed, there was gratification.

Further, it's worth noting that after thoroughly testing said vehicle, I can accurately report some of its idiosyncrasies.

1) RPM limit

Using the sensorless jasontroller (350W yiyun yk85s) definitely has its benefits: it costs next to nothing, is very small, and is extremely easy to set up. However, as I discovered only after several motor cutouts, its commutation frequency is limited to 550Hz (electrical). Check out Charles' blog post for details. And while scooters with larger, lower kV motors may graze this limit, my spunky 280kv motor is well above it, eliciting many a drivetrain failure early on in its derpy little life. (Sounds like a job for custom motor controller  Hobbyking airplane ESC man!)

2) Controller modding is almost definitely required

350W out of the controller is boring. Heck, 500W was too. In fact, to get the acceleration to something usable on a day-to-day basis required that I decrease the shunt resistance with solder globs. Controller output currently sits at ~800W.

It's as easy as popping
open the controller...
Finding the shunt resistor
(in this case, a piece of wire)
And globbing on some solder. 

Note: for a slightly more legitimate solution, you can cut the piece of wire and solder in an SMD resistor on the traces on the bottom of the board.

3) Hot motor is hot

Among the many valuable skills an EV builder must have, being able to translate sketchy Hobbyking ratings to IRL ratings is necessary. As it stands, the current motor is rated for 1.5kW*. It's important to remember that this motor is meant for R/C plane duty, which has a significantly lower inertial load as compared to that of a vehicle. Further, the typical outrunner is exposed to much greater airflow when not mounted to the inside of a piece of u-channel.

*kiloWalruses

Le Result:

In the end, with a 10S2P pack, I ended up getting 4 miles of range (the distance between my dorm and MITERS) with an average speed of 14 mph.

After-trip charge revealed an effective capacity of 3.1Ah

These are quite reasonable numbers considering the route there was very hilly, and that my downhill speed was artificially limited by the commutation frequency and my rolling resistance (no throttle going downhill).

The average grade was found to be 0.2%, so my mileage wasn't too far off from what I'd get on a reasonably flat route.

If I were to stay with the same motor, I'd probably go for a lower voltage pack at a higher capacity (I can only utilize so many rpm), choose a lower gear ratio (currently 11:55), or just go for a lower kv motor.

It also turns out that it take less time to get to MITERS on the scooter than it does to train.

Yay!

And on that note, happy scootering!