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Assembly and calibration

There are a number of great resources for the assembly of the Spot Micro. For this reason, I refer to these, as the steps are the same for this version:

Calibration

Discussion about Calibration

Assuming the servos are connected to the PCA9685 and are powered on:

Calibrate in servo frame

  1. Navigate to /controller and click on "Calibrate". This will set the servo to the center pwm value.
  2. Navigate to peripherals/servo - Here you can control the servos individually.
  3. If all your servos are the same kind, you can calibrate one and copy the configuration to the other ones.

We have to find a couple of values: min pwm, max pwm and conversion ratio.

Min Pwm

  1. Select the servo you want to calibrate and move the pwm slider to where the servo stops moving. Then move it up and note the value where it starts moving again as $p_1$.

Max Pwm

  1. Move the pwm slider up to where the servo stops moving. Then move it down until the servo starts moving again and note this value as $p_2$.

Conversion ratio

  1. Now we have to find the conversion ratio, by looking at how much the servo move in deg per pwm. Move the pwm slider to the min pwm. Then mentally mark this as 0 deg. Move the pwm slider until the servo has moved 180 deg. Mark the pwm value $p_3$

Center pwm $=p_2 - p_2$ Conversion ratio $=(p_3 - p_1) / 180$

You now have the values for the servos.

Calibration in body frame

They now have to be calibrated to the body frame. It is assumed they have the center PWM pointing straight down.

  1. Navigate to /controller and click on "Calibrate". This will set the servo to the center pwm value.
  2. Navigate to peripherals/servo - Here you can set the servo angle offset.

All the legs should be pointing down. If they are not, you have two options. 1. Physically move the servos to the correct position by unscrewing the servo horns. 2. Update the servo offset in the servo table.

Circuit diagram

Electronics diagram

PCA9685 Servo PWM numbers to joint:

PWM_0 Front Left Shoulder
PWM_1 Front Left Upper-Limb
PWM_2 Front Left Leg (Lower-Limb)
PWM_3 Front Right Shoulder
PWM_4 Front Right Upper-Limb
PWM_5 Front Right Leg (Lower-Limb)
PWM_6 Rear Left Shoulder
PWM_7 Rear Left Upper-Limb
PWM_8 Rear Left Leg (Lower-Limb)
PWM_9 Rear Right Shoulder
PWM_10 Rear Right Upper-Limb
PWM_11 Rear Right Leg (Lower-limb)