>>>Seeker Of Ways B: Test DC Motors<<<
1Seeker Of Ways-B Test Motors
With the Regulator, Microcontroller and Raspberry of Seeker Of Ways-B operational the next step is to test the DC Motors.The H-Bridge used by the board is a BD62321, an integrated full half bridge that handles up to 3A with a PWM frequency up to 100KHz. Perfect for small DC motors like the ones installed in Seeker Of Ways-B
2Wiring
Upgrade the wiring of Seeker Of Ways-B2.1Motor Wirings
The motors installed have been through a lot and the wires are worn out and the colors made no sense.
The wires of the motors have been replaced.
- Thicker red and black wires for the actual windings
- 4x2.54mm female connector for the integrated encoder
2.2Cable Management
Routing of wires on the platform. use zipties to hold the wires in place. Label the wires based on the motor (Left/Right)
3Test Power
A power test was conducted and failed. The regulator died again for unknown reasons.This PCB is too compromised so the on board regulator has been replaced by a few switching regulator modules I had laying around. The regulator was due to a redesign anyway for the next platform.
With the regulator replaced, everything was working again thanks to the embedded protections inside the RPI Hat.
4PWM Test
With power sorted out, next step was to write a test firmware and test both motors in both directions with a soft bidirectional PWM ramp.4.1Firmware
The AT644 is capable of generating a phase corrected PWM signal at about 39KHz, well above ultrasound, ensuring a silent operation of the motors.
This program uses the Timer0 to schedule both the led blinking and the update of the PWM signal.
Timer1 and Timer2 are used to generate a two slope, eight bit, 39.06KHz PWM signal on two channels, connected to the H-Bridges.
A general I/O is used to connect or remove the H-Bridges from power.
The full firmware can be found in this GitHub Repository
>>>Firmware GitHub Repository<<<
The test failed failed for the right motor counter-clockwise direction. The problem was a cold solder on a protection resistor that was easily fixed.
With the cold solder taken care of, both motors run in both directions safely.
5Conclusions
The H-Bridges work as intended.Next steps are:
- Acquisition of two quadrature encoders
- Speed PID control
- Control from UART from the Raspberry Pi
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