Help with Overheating FS90 Servos in Random Positioning Machine
 

Hi,

I’m replicating a random positioning machine prototype from GitHub, but I am a complete beginner:

I’ve built the setup as described, but I’m facing an issue where my FS90 continuous rotation servos overheat and stallafter running (empty) for less than a day. When this happens, I can manually nudge them, and they will restart for a few minutes before stopping again. When the servos are off the machine they seem to work normally.

Setup Details

• Servos: FS90 (continuous rotation)
• Power Supply: 5V, 4A (servos connected in parallel)
• Code: (see below) – based on the original repository

I suspect the issue could be due to excessiveload, but in the original project videos, their machine runs for a week without any problem. Could there be another reason why my servos are overheating?

Any help, tips or theories would be greatly appreciated!!

Here’s the code I’m using:



import time

from servo import Servo

import math

from random import randrange, random



# Create our Servo object, assigning the

# GPIO pin connected the PWM wire of the servo

outer_servo = Servo(pin_id=16)

inner_servo = Servo(pin_id=15)

delay_ms = 100









def modified_sine_wave(amplitude, deadband, t):

'''removes the dead band from the centre of the sinewave. useful for driving DC motors that stall at low speeds'''

value = amplitude * math.sin(2 * math.pi * t)

if abs(value) < deadband:

value = math.copysign(deadband, value) if value != 0 else deadband

return value



frequency = 0.05 # Hz

amplitude = 25 # servos accept "speeds" between 0 and 180. most of the speed change is at low amplitudes

dead_band = 12 # dead band around where the servo changes direction. Must be smaller than amplitude



duration = 10000 # time between speed changes

last_update_time = -duration



speed_inner = setpoint_inner = 0.5

speed_outer = setpoint_outer = 0.5



try:

while True:

# Periodically update the speed setpoint

if time.ticks_ms() - duration > last_update_time:

last_update_time = time.ticks_ms()

setpoint_inner = random()

setpoint_outer = random()



# Update the current speed (-1 -> 1), moving towards the setpoint smoothly

speed_inner = speed_inner + 0.01 * (setpoint_inner - speed_inner)

speed_outer = speed_outer + 0.01 * (setpoint_outer - speed_outer)



# Convert speed (-1 -> 1) to a servo drive signal (angle 0 -> 180), and scale down to the desired amplitude.

drive_inner = 90 + modified_sine_wave(amplitude, dead_band, speed_inner)

drive_outer = 90 + modified_sine_wave(amplitude, dead_band, speed_outer)



# Drive the continuous servos

inner_servo.write(drive_inner)

outer_servo.write(drive_outer)



time.sleep_ms(delay_ms)



except Exception as e:

print(e)

finally:

outer_servo.off()

inner_servo.off()