In my previous post, I covered the setup configuration of the BLDC skateboard wireless remote control. Now that the remote is working, the drive is working, the motor is mounted, and the motor is attached to the wheel, I need to find a power source and go for a test ride.
Lithium Ion, LiPo, and LiFePo batteries are quite expensive, when looking at the energy the board will require, and need special chargers. Since I am still not sure this motor will even move me and the board adequately, I decided to use a 12V 5Ah SLA battery that was in an old alarm system as a test. It can be charged using the same charging system I use to maintain the lead acid batteries in other vehicles and uses simple crimp faston connectors.
The downside of the SLA battery is that it is large enough that it must sit on top of the board. I do not love this configuration. So, if the motor proves capable of moving the skateboard the way I want, I may try some 18V lithium ion batteries that I use in cordless tools. Those batteries should be able to fit underneath the deck and will give a bit of a speed boost compared to the 12V battery.
The last bit to figure out is how to mount the electronics to the skateboard. I decided to put the C2000 launchpad setup in a plastic project box and industrial velcro to attach it to the bottom of the board. This is just a proof of concept!
I ran some 18AWG duplex wire from the battery to the C2000 launchpad, tested that everything worked as I hoped, reduced the speed command using the potentiometer, and jumped on!
First, the motor has plenty of torque and even at reduced speed was not too slow. There is still a bit of tuning that needs to be done to the speed regulator and ramp for a smoother takeoff. The timing belt and pulleys could all handle the load and did not slip.
Second, the DRV8323 boosterpack is limiting the full amount of torque available from the motor due to the current feedback burden resistor size. The MOSFETs on the boosterpack are also a small package and situated in a location where it is difficult to heat sink them. After riding the board uphill for a bit, the MOSFETs were very hot. This initial configuration is not something that is ready to use for reliable transportation.
Third, the remote works well, but I would like something that frees up my hands. I might experiment with some Flexiforce sensors placed on the top of the deck as the torque command.
My plan moving forward is to design my own motor control board. The TI development boards are fantastic for evaluation, but take up a good amount of space and limit the performance of the motor. This might be a good time to compare the performance of a few different popular MCUs targeted to motor control. I also plan on evaluating sensorless FOC control of the motor for smoother torque application and better dynamics (at the expense of a little top speed).
Keep checking the blog! I will cover the custom board design, MCU performance comparisons, sensorless FOC control using a sliding mode observer, and Flexiforce sensor experiments in future posts.