Citizen

Last updated on Nov 27, 2020

A balancing robot written in Go and running on ARM Linux.

Mod list

Changes to make:

Move the gyro down between the wheels. Reduces the acceleration seen due to falling.

Other robots

There’s a ton out there.

lil-bot uses the same motors (MG-6-48) but with encoders. 7xAA so 8.4 V to 10.5 V. 100 Hz control loop. MPU-6050 with 2 % complementary filter. Has a err**2 term as well.

v1

v1 can balance but poorly. The big differences were:

Better pitch measurement through a complementary filter. Gives the absolutes of the accelerometers and noise rejection of the gyros.
Integral control to respond quicker to small offsets.

Things I also changed:

PWM rate up to 10 kHz
Control loop up to 100 Hz
Gyro bias removal. The gyro had a 0.34 deg/s bias.

Things to check:

The gyro scale might be wrong and might be over reporting the angle.
The deadband on the motors is quite bad and is probably hurting the small tilt response. I might be able to kick the motors to start things turning then return to the demanded speed.
Is the gyro saturating?
I2C speed
Add voltage compensation?

v0

v0 is done but doesn’t really work. Issues:

The motors have a high deadband and are too high speed.
The pitch is based off the accelerometers only and seems very noisy.
The motors are independant, so at low drive sometimes one will start and the other stay still.

Next steps:

Measure the CPU load
Measure the pitch while standing upright and steady
Investigate complementry filters to combine the gyro and accelerometers
Investigate the IMUs advanced features to see if it already gives a good pitch
Profile the motors to see if I can lower the deadband (dither?)
Check I2C rate is 100 kHz or higher.

Notes:

The 20 ms timer fires at ~16 ms and ~24 ms. HZ is 128. Turn on TCB as a clock source, switch to low latency, switch to tickless.
IMU has:
DLPF, a low pass filter. Use to filter accelerometers?
Default accelerometer range is +-2G (as the default reading is ~16000)