I’ve recently built a new robot, with a motor configuration as follows:
11W Hooks
5.5W 1st stage Intake
66W Drive
5.5W Lift
When the robot scores on wallstakes, It drives up to the wall, and both the 5.5W lift and the 11W Hooks engage.
If I push the robot into the correct position by hand, and then activate the scoring sequence, both the 5.5 and 11W motors perform optimally. However, if I drive up to the position and push against the wall, and while pushing activate the scoring sequence, both the lift and the hooks do activate, but with lower speed and torque.
I have done a number of tests, and I am 100% sure it is not a mechanical problem, but potentially a software or vex hardware problem.
My theory is that the robot is activating “VexU” mode whenever all the motors are engaged, and cutting the power per motor as there are technically 9 motors on my robot, instead of 8. However, Im not confident in this theory because the bottom stage of the intake does not engage, meaning just 8 motors are active, and I’m pretty sure that it is supposed to cut power only when the demand exceeds 88 watts, not 8 motors plugged in.
Me and the whole club (30 people) have no idea how to fix this or if its even fixable, and I would love some help solving this issue, or at least finding out that solving it isn’t possible so I can spend the troubleshooting time on something useful.
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Check the brain event log for error messages. We reduce motor power if excessively high battery current is detected,
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I did actually notice that message happening occasionally, however it wasn’t 100% matching with the issue every time, so I assumed it was incidental. How would I go about fixing this?
There is no fix as such other than to not stall lots of motors at the same time.
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The reason I’d see (similar to what J. Pearman above) is the way a smart motor work. VEX’s smart motors don’t draw the full power most of the time, they leave a bit of extra power possible to draw. This makes it so when the VEX motors are under performing, stalling, or accelerating they can get extra power to help level things out. However when you drive up to a wall all 66 watts of motors end up stalling, meaning all of those motors end up drawing using the actual 100% not the regulated 100%. This makes a large draw, which the brain doesn’t like. Then the VEX brain turns the rest of the bot to low output mode so that they can try to bring the other motors up to the full RPM. This is why you either need to stop running the motors while against the wall bringing up the lift or bring the lift up before you contact the wall (although I believe your should be able to bring it up while driving if none of the motors are stalling). If it does stall then your probably running a fast gear ratio on that drive that naturally dips into that power reserve a little.
TL;DR If the motors are stalling because its being raised while driving into the wall its going to draw too much power. It will probably work if you preemptively lift it though.
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