Guide to Troubleshooting and Preventing Servo Port Failures on Wombat Controllers
Understanding the Problem
Servo ports on Wombat controllers can fail, resulting in reduced or no power being delivered to connected servos. Common symptoms include:
Servos failing to move or stopping mid-operation.
Servos entering a failsafe state, requiring manual reset.
Some ports working while others do not.
Even unused ports have been observed to fail. This guide explores potential causes and practical solutions.
Common Causes of Servo Port Failures
Excessive Power Draw: Servos under heavy load draw more current, potentially tripping fuses that protect the controller.
Repeated Fuse Tripping: Over time, internal resistance increases, degrading performance.
Servo Torque Exceeding Limits: If a servo attempts to move or hold weight beyond its capacity, it strains both the servo and controller port.
Improper Power Supply: Voltage irregularities or unstable power can damage ports.
Mechanical Stress: Improper mounting or excessive tension on servos may cause instability and overdraw.
Diagnosing the Issue
Test the Servos:
Plug suspect servos into known working ports on another Wombat controller.
Use new servos in suspected faulty ports to confirm behavior.
Inspect Fuses:
Look for small fuses (likely surface-mounted) protecting each servo port.
Check for Overloading:
Calculate the force and torque required (explained in Section 7). Compare it to the servo’s datasheet specifications.
Power Supply Check:
Ensure stable voltage from the power supply. Use a multimeter to test output.
Technical Explanation: Fuses and Power Overload
The Wombat controller includes self-resetting fuses to protect servo ports from excessive current draw.
Why Fuses Trip: When a servo encounters excessive load (e.g., lifting too much weight), it draws too much current, causing the fuse to trip.
Degradation Over Time: Repeated tripping increases internal resistance in the fuse, reducing power to the port and eventually making it unusable.
Identifying Burned Ports
If a port delivers little to no power but hasn’t been permanently destroyed, it’s likely due to accumulated fuse resistance.
Solutions for Burned-Out Ports
Replace the Fuse
Identify the fuse part number (check KIPR’s GitHub or Wombat schematics, but it seems like it's the fuse 0603l100slyr).
Purchase compatible surface-mounted fuses.
Carefully desolder the old fuse and solder a replacement.
Workaround: Use alternate ports or redistribute servo load across multiple controllers.
Preventive Measures
Avoid Overloading Servos:
Calculate torque and force requirements (Section 7).
Use servos rated for higher torque if necessary.
Reduce Load on Servos:
Add counterbalances or rubber bands to reduce mechanical strain.
Replace heavy components with lightweight materials (e.g., LEGO, 3D-printed parts).
Use Multiple Servos:
Distribute load across two or more servos when possible.
Monitor Voltage and Current:
Use power regulation to maintain a stable voltage supply.
Optimize Mechanical Design:
Minimize unnecessary forces acting on the servo. Ensure smooth and precise movements.
How to Calculate Force and Torque Requirements
To avoid overloading servos, calculate the torque and force required:
Torque Calculation
The torque T is given by:
Where:
T = Torque (Nm)
F = Force applied (N)
d = Distance from pivot point (m)
Find Center of Mass: Determine where the load acts relative to the servo arm’s pivot point.
Calculate Force: Use the formula
, where m is mass (kg) and g is gravity (~9.81 m/s²).
Compare Torque: Check the torque value against the servo’s datasheet rating.
Practical Example
A servo arm 10 cm long (d = 0.1 m) holding a 500 g object (m = 0.5 kg):
Ensure the servo’s rated torque exceeds this value.
Motors are modified Servos
Motors in Wombat kits may be modified servos (e.g., MG996R). Treat their specifications similarly.
Additional Resources
KIPR Documentation: KIPR GitHub Docs
Servo Datasheets: MG996r
Troubleshooting Forums: KIPR forums, robotics communities like Reddit, or FIRST Robotics groups.
Conclusion
Servo ports burning out is typically caused by excessive current draw, often due to mechanical stress or torque overload. By calculating force requirements, replacing damaged fuses, and optimizing mechanical design, teams can minimize or prevent failures.
This guide provides a systematic approach to troubleshooting, repairing, and improving servo usage, ensuring reliable performance in competition settings.
Authors
Tobias Madlberger