+++
date = 2014-11-02T00:00:00+00:00
title = "Citizen"
summary = "A balancing robot written in Go and running on ARM Linux."
tags = ["machines"]
+++
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)

  -