Sensors Adding the Burtie optical sensors to a sensorless Astroflight 3210 RC motor

by Warren Beauchamp

I had been using this Astroflight 3210 RC motor with an RC controller (ESC). RC controllers do not use sensors, because RC motors are designed to always run at high RPMs. E-bike motors on the other hand run at low RPMs when starting. It always annoying me that the motor would cough and hiccup until I got up to about 10 MPH (at which point it would of course launch my bike like a rocket).

Sensors tell the controller when to send a pulse of power to a particular phase of a brushless motor, which makes the motors run much better at low RPM, and can make them run more efficiently at high RPM. Ian (Burtie) has been making optical sensor conversion kits for sensorless RC motors. I will use this kit along with a MKII-LYEN EDITION-12 FET 3077 MOSFET Mark II controller to convert this motor to be a sensored motor. This controller is rated at 45 amps continuous, but can support the higher currents consumed by RC motors, especially after the circuit board traces are beefed up. This motor can draw 80 amps, but only for short times, so I think the controller should be fine. This controller can be programmed to limit current, change low voltage cutoff, and other stuff.

Bertie's kit comes with a circuit board, a washer, a sheet of paper with the black/white patterns on them, and a piece of balsa wood.

The idea is to space the washer out about 5mm from the rotor on the axle. Instructions said to use the balsa and silcone, but I decided to make a washer out of Lexan (polycarbonate) for a spacer, and use JB Weld  to glue it all together.

The Astro motor has an aluminum spacer between the rotor and the bearing. The washer and Lexan spacer sit on this 1/2" OD spacer.

Because the washer has a bit of slop on the aluminum spacer, I used a punch to make a series of dents close to the ID of the washer, which closed the gap.

Here's the spacer and washer glued to the rotor. I roughed up all surfaces with fine sandpaper before glueing.

I cut out and glued the sensor pattern to the washer.
Added the wires to the sensor board and mounted the circuit board to the inside of the motor cover. Right now it is just a friction fit.
Adjusted the circuit board until there was about 2mm between the sensors and the pattern.

Sealed up the motor temporarily as the circuit board will probably need to be twisted a couple degrees to adjust the sensor timing.

Used a 5V power supply connected to the 5V and Gnd wire of the sensor board to ensure that the sensors switch between about (about) 0V and 5V.  It works!

I got the wiring right the first time, but the motor was running counter-clockwise (when watch from the driveshaft side). After re-wiring to get it turning clockwise (for output shaft on right side of bike), I adjusted the timing for minimum current, then advanced it just a bit.

When timing is adjusted for max RPM, no load current at max RPM is 650 watts
When timing is adjusted for min Current, no load current at max RPM is 50 watts

I advanced the timing so no load current at max RPM is 70 watts.

Advancing means that after you adjust the timing for minimum current, you turn the circuit board in the opposite direction of motor rotation

The max RPM at 650 watts is way higher than when adjusted for min current, but the motor gets hot...

The low speed performance seems similar across the range of timing adjustments that I tried.

Here are the sensor wire colors I used with the Lyen / Infineon controller, with the motor running clockwise. To run the motor counter-clockwise, flip the green and yellow wires. Burtie says that the wiring may vary depending on how the pattern lines up with the rotor magnets.

I adjusted the circuit board until the timing was set correctly (I hope), and then glued the circuit board in place with high temperature silicone RTV glue. I'll clean up the stringy bits before reassembling the motor.

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