Recently we have purchased an Aluminum 4WD1 Rover Kit (http://www.lynxmotion.com/p-603-aluminum-4wd1-rover-kit.aspx). Strangely, the two front motors got damaged. The motors are not rotating initially but rotate slowly only when we give small excitation like rotating the wheel with hands.
It seems like there should be some problem with the coil, gearbox or bearing setup.
Initially, we suspect the problem might be due to overloading.
The chassis is claimed to support 5 lbs(2.26 kg) of payload. But we have loaded only 3.96 lbs (1.8 kg) of payload. But ground friction might play a role.
Further, we are not sure why only the front motors got damaged. We have designed the loads in such a way that it should evenly spread across four motors.
What motor controller are you using?
What are you powering the motors with (LiPo/NiMh…)?
What voltage and mAh are the batteries?
Have you tried putting 12V power directly to the “damaged” motors?
Did you try to disconnect the good motors and only running the “damaged” motors?
Or have swapped the leads with the good motors and the 'damaged" motors on the controller?
What motor controller are you using?
RoboClaw 2x15A Motor Controller
Designed to control two brushed DC motors at 15 Amps continuous with up to 30 Amps peak per channel
Front motors and Back motors are tied together.
What are you powering the motors with (LiPo/NiMh…)?
LiPo battery (3DR Solo Smart Battery)
What voltage and mAh are the batteries?
voltage : 14.8V
mAh : 5200 mAh
Have you tried putting 12V power directly to the “damaged” motors?
No, We have operated the motors only through the motor controller. If required, we will try it too.
Did you try to disconnect the good motors and only running the “damaged” motors?
Yes, We tried it. But, the results were same.
Or have swapped the leads with the good motors and the 'damaged" motors on the controller?
Yes, We tried swapping. But the results are same.
It has to be noted that front and back motors are tied together on each side( right and left ). But only the front motors got damaged.
It’s very difficult to spec a payload for a robot given the infinite variation in conditions. For example, does the “payload” mean how much it can support moving forward on a low friction surface? Or instead, how much it can support when trying to climb a 45 degree high friction angle? Turning on the spot is the hardest thing a 4WD robot can do, and when it’s at maximum payload, it’s even more difficult. For this reason, it’s best to turn in an arc. As such, you might be correct that the payload and environment contributed to the events.
Note too that the motors are really intended to be used at up to 12V (as spec’d by the manufacturer). Using charged 4S batteries (could be 4.2V per cell when fully charged) might have also been problematic.
Q1. What may be the reason for this motor damage?. Is it correct to suspect overloading ?
A1. It sounds like it might be:
“Overloading” in that the motion + payload might have been too much for the motors (need more details)
High voltage which then also drew higher current
Q2. Why only the front motors got damaged?
A2. Honestly do not know. Perhaps the rear motors lost traction and were able to slip? Don’t have many theories about that.
Q3. Which part of the motor might have got damaged like the coil, bearing etc?
A3. If it was over-current, it might be the coils. If the torque was too high, it might be the gears / bearings etc.
Q4. Will this issue get fixed if we replace these motors with the high torque one (thus high payload)?
A4. The tires become the next restriction in that they are air-filled (a bit of foam), so they squash flat quite easily. This causes higher friction between the wheels and the surface, and significant problems when turning on the spot since that requires pushing sideways on a surface. Can you explain a bit more about how you’re using the rover and the operating environment?
Q5. Is there any rule-of-thumb available to select a motor based on the payload?
The fourth question in the above reply is the most important one.
Let us narrow down to it.
Q4. Will this issue get fixed if we replace these motors with the high torque one (thus high payload)?
A4. The tires become the next restriction in that they are air-filled (a bit of foam), so they squash flat quite easily. This causes higher friction between the wheels and the surface, and significant problems when turning on the spot since that requires pushing sideways on a surface. Can you explain a bit more about how you’re using the rover and the operating environment?
We are using the rover on a normally flat surface (office environment). So, I feel comparatively it shouldn’t have caused more friction.
We have planned to procure high torque motors. But still, we can’t be sure that this issue won’t occur in the future.
If the motor damage was caused by any reason other than overloading, this issue will occur again.
Further, we attached wheel encoders to the front motors only. And only the front motors got damaged. Will there be any link between wheel encoder and this type of motor damage?
