Mouse-wheel speed controller

An add-on that gives the experimenter control over a running wheel's timing and minimum speed. It enhances the open-source KineMouse wheel with a motor and clutch, so a mouse can run faster than the motor and keep running when the motor is off — supporting the 3Rs by reducing session count and duration.

Ingredients

BeeHive boards:

Other components:

How it works

The KineMouse wheel is a lightweight open-source running wheel. This recipe couples it to a NEMA 17 stepper through a clutch:

• The motor sets a minimum running speed and controls when the wheel turns, so the experimenter — not the animal — decides the timing.
• The clutch decouples motor and wheel one way: the mouse can always run faster than the motor, and can keep the wheel spinning when the motor is off.
• Wheel speed is set live by an analog potentiometer read on a mainboard analogue input; the mainboard translates that into a stepper rate.

By letting the experimenter enforce running periods and a floor speed, sessions can be made shorter and fewer — aligning with the 3Rs (replacement, reduction, refinement).

Wiring

• Potentiometer wiper to a mainboard analogue input; ends to 3.3 V and ground.
• Adafruit DRV8833 control inputs to mainboard data lines; motor power and ground from the appropriate rail.
• NEMA 17 stepper to the DRV8833 outputs; the stepper shaft drives the wheel through the clutch.

Code

Controlled via MicroPython. A minimal potentiometer-to-stepper loop:

# TODO: pins are placeholders — set to your wiring and stepper coil order.
from machine import Pin, ADC
import time

pot   = ADC(Pin(34))                               # speed potentiometer
coils = [Pin(p, Pin.OUT) for p in (12, 13, 14, 15)]  # DRV8833 inputs
SEQ   = [(1,0,1,0), (0,1,1,0), (0,1,0,1), (1,0,0,1)]

step = 0
while True:
    speed = pot.read()                             # 0..4095
    if speed < 40:                                 # near zero = motor off
        for c in coils: c.off()                    # clutch lets wheel free-run
        time.sleep_ms(20)
        continue
    delay = 40 - int(speed / 4095 * 38)            # higher pot = faster
    step = (step + 1) % 4
    for c, v in zip(coils, SEQ[step]):
        c.value(v)
    time.sleep_ms(delay)

Results / notes

Adding a motor and clutch to the KineMouse wheel hands timing and minimum-speed control to the experimenter while never restraining the animal's ability to run faster or coast. The shorter, fewer sessions it enables support the 3Rs.