We are having a strange problem with the Motor Fading on a VEX Claw.
The claw works fine and then (3 to 5 x open/close) it starts to slow down to where it doesn’t move at all. Then after 5s it runs fine then repeats pattern.
We’ve tried changing controllers, motors, ports and the Cortex !!
Yes, the VEX connectors are (always) weak & suspect. We have the VEX-approved thingies that hold connectors together and ‘jiggling’ connectes makes no difference.
Mechanically the motion seems fine - no apparent binding or ?? that may cause the motor to go into overheat mode.
We’re using the same code as the ClawBot sample (IF…THEN…ELSE) Debug shows the motor speed correlates with the button being pushed so I’m guessing the code/remote works as planned. (attached ZIP)
#Clueless here & hoping some can help! 01-17-2018.zip (2.51 KB)
Too much stress on a motor can cause this sort of thing. Our bot does the same thing where it runs fine for a short period then dies. Always make sure that you have fully charged batteries that have been charged on “safe” mode. “Fast” can set them on fire. Let the motors cool down for a few seconds then resume usage. Try using a power expander if you aren’t already.
What you are describing sounds like PTC tripping. The way a PTC works is the hotter it gets, the less flow of electricity it allows until it cuts it completely and then it will cool, recover (at least partially) and start over.
Check to make sure the motors are not trying to move when they are physically stopped from moving. Also, make sure to reduce friction.
We had the same problem. You’re most likely burning out. The motor doesn’t necessarily have to be warm to have burned out.
As far as I know/understand, the claw opens/closes, hit’s it’s physical limit and keeps straining. As it tries to turn, it draws more power from the cortex, and trips the PTC, burning out.
Potential solutions:
We put ours on a partner joystick so we could slow it down as we neared full open. This was a solution needed for our robot in particular because our claw would bounce back at full speed.
You could tell it to go no further at a set potentiometer distance.
One idea I had was to press a button to open it to a set value and press another to close it to a certain value.
Yes, it was PTC tripping. We solved this by a few ways:
1 - used floor/ceiling values to keep max power ~100 (read where motor power = 90 is optimum)
2 - on_Button() we closed the gripper motor @100 for 1/2s then shut it off
These two changes seem to eliminated most of the stalling and secured us a place in state & nationals!
The only place we see stalling now is on the H-bridge (ports 1 & 10). I guess just another reason to stay away from them I reckon.
WOW @bigleslip - another VEV Icon! I’ve found myself going to renegade’s website a lot! So much so that I learned of & downloaded JPearman’s SmartMotorLib last night (small world of VEX)!
Do you know if it still works? I haven’t heard anyone suggesting it and the code is pretty old…
My team does use the Smart Motor Library. It’s of course impossible to know how much it helps us (we don’t have the manpower to run extensive tests to figure that out). I put it in the “might as well” and “couldn’t hurt” categories. It does still work; I emailed jpearman when I was writing my article about the library to ask him a question and he didn’t say anything like “don’t bother using it”. He did say that he wrote the code long ago and hadn’t looked at it in a while, and that he was spending his time focused on things to come.
P.S. Aww. Thanks. I’m very glad when I hear that stuff I put together is helpful.