We are having kind of a strange behavior in one of our MAXSwerve modules, and need help trying to figure out possible causes and solutions to this.
The steering motor (NEO 550) of this specific module is drawing some current even when it is stopped. This seems to happen because it is not reaching the angle setpoint by very little, < 0.1 rad, and the current being drawn isn’t enough to make it move (if i turn it manually to the setpoint it stops drawing current). It could be a software issue, but the thing is this behavior only happens with this specific module, and it requires more strength to steer manually (spinning the outrunner motor or steering the wheel by hand) than the other modules, which may indicate a mechanical problem in the assembly. We disassembled the module, and the motor and UltraPlanetary seem don’t seem to be the problem. The steering gears have a little wear, but also dont’t seem to cause this. Has someone experienced a similar issue, or has any guess on what could be causing that?
What you seem to be experiencing is steady state error.
This is most likely caused by the force the motor is outputting not being able to overcome the friction of the wheel against the ground/the resistance in the gearbox. One way to solve this issue would be to apply a constant additional voltage to overcome the steady state error, also known as kS
A few questions:
Does it feel stiff both with power and without? If it still feels stiff without power there could be an issue with overtightening / too long bolts in the ultra planetary. Also ensure that the bolts are not stalling the NEO550. This could be causing the extra resistance.
Less likely based on your description, but does the motor snap back to approximately the same position if manually twisted while under power? Does it jitter and skip? Check the phase wires if it is doing this as it could indicate a bad connection.
Yes, it feels stiffer than the other modules both with power and without.
When we reassembled the module, i noted that with the bolts overtightened the stiffness increased, so we loosened them and it felt less stiff, but still not normal like the other modules, maybe we did something else wrong in the process.
For the second question, it seems to be behaving normally as it should, he issue is probably not caused by electrical problems
Try taking it apart one stage at a time to see where it is sticking. i.e remove the output stage and test, repeated until you get to the motor.
we actually did test spinning the motor + ultra planetary separately from the rest of the module and i had the impression that there wasn’t any stiffness problem (could be just an impression, we’re going to test it again). Do you think there could be something wrong with the rest of the steering mechanism?
That is entirely possible. Have you tried rotating it from the wheel both with and without the UltraPlanetary? It might not be possible to rotate from the wheel though; I do not remember if you can.
I will touch base with our chassis sub team from last season. What you are describing happened to us for at least one module upon initial assembly for our competition and practice bots . There was a minor assembly error that caused it. I will follow up here when I hear back from the students about which step was the root cause. In the interim, I agree that taking apart the module and reassembling it with extreme care might be the best path forward.
As far as I remember we did not make this test, but we’re going to try this to see if there is any problem related to the rest of the steering mechanism.
Great! We’llLimelight, an integrated vision coprocessor be very greatful if they can give us any idea on the cause of this so we can check that more carefully.
The students don’t recall the exact step, but there were two common assembly issues they ran into:
- There is a shaft key that must be inserted in the correct orientation. If it is upside down it won’t cause module binding until the assembly is tightened down to the chassis. So you can’t tell until the last moment!
- They recall a bearing being inserted upside down. Causing a similar issue.
We had folks that assembled 8 plus modules that still ran into issues with missing key steps!
double check the assembly of the NEO550 stack itself. especially within the Ultraplanetary Gear Stacks. For us, couple students used a ‘socket head’ screws instead of the ‘button head’ screws when they screwed together the Motor to the Gear Plate itself. The small enough of the differences made the screw heads pushes into the gear stage. Now when the outer screws that locks the entire Steering Assembly is tighten, this will pushed those screw heads more into the gear plate and essentially pin the stage. We notice this when we saw couple of our assembly’s outer screw wasn’t screwed down by the students. When we asked why, they said if they tighten them, it’s nearly impossible to turn the motor/steering gear at all. So after full disassembly, that’s when we find these issues.
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