1. 5 weeks ago

    AryanG

    Dec 10 Mississauga, ON, Canada 60006X

    Hello, our robot currently keeps stalling on the drive. We use the cortex system. We used to have a 4m torque drive(100 rpm) but we changed to a 6m torque drive sprocketed for speed (150 rpm) which has the exact same stall torque. For some reason the bot kept stalling out even after we changed to a 6m torque drive(100 rpm). We have checked for friction and made sure everything is smooth. Could someone help us out with this?

    Pictures will definitely help - when you check for friction, make sure your include the motors - these being misaligned can cause a lot of friction. Check to make sure that you aren't overloading the motors, and try double checking with different motors and controllers.

  2. NyQuil

    Dec 10 Ashburn, VA 80508X

    Hm, pictures would help, your gear ratio isn't aggressive enough to where it would burn out.

  3. AryanG

    Dec 10 Mississauga, ON, Canada 60006X
    Edited 5 weeks ago by AryanG

    I can get pictures on Tuesday. I think its weight but last year the bots that we built were of nearly equivalent weight when carrying the mogos which is why this issue is confusing.

  4. I know it seems obvious but check for friction.
    Also, and this seems dumb but make sure that all the motors have the same internal gearing (aka high speed ,turbo, tourqe

  5. squirrelman777

    Dec 10 Fairmont, WV 20610N
    Edited 5 weeks ago by squirrelman777

    Try running it with new motor controllers. Whenever we have a problem with motors not behaving we always try that first. Over the past two years, motor controllers have caused our robots to attack us and to drive away.

  6. JDeuter

    Dec 10 South Dakota 6844B

    Do you have the front wheels chained to the back? This causes some friction. Also are you using all omni wheels?

  7. Rick TYler

    Dec 10 Teachers/Coaches, Event Partner, V5 Beta Moderator Redmond, Washington Founder of Exothermic Robotics
    Edited 5 weeks ago by Rick TYler
    1. Too much friction
    2. Over-geared <and/or> overweight
    3. Bad motor controller
    4. Bad motor
    5. Chains that are too tight (leads to high friction (see #1)
    6. Other weird stuff (motor not plugged in)

    Listed in order of occurrence after watching VEX robots for 12 years.

  8. Do you have your drive hooked up to your Cortex or Power Expander. After over a year of wondering why my students drives would have major stalling issues, we found out that you should never, ever hook your drive up to a power expander.

  9. goofnrox

    Dec 10 Jenison MI Jenison Robotics

    Using a power expander for drive motors is just fine, just not ALL of the drive motors.

    OP didn't specify if there is an expander on the robot. If there is the best wiring configuration will be to have two motors on each PTC channel. Otherwise split the motors evenly between the two PTCs in the cortex.

    Cortex 1-5 is one channel
    Cortex 6-10 is one channel
    Expander is one channel

    @AryanG how is the bot wired?

  10. Vyx

    Dec 10 Florida 82987A

    From your description, I would check to make sure each motor is functional and spinning at the same speed and then check the sprocket chain for friction when on the ground with the weight of the robot pressing down

    When two motors are chained and one of them is underperforming, it creates more issues than if there wasn't even one there

  11. AryanG

    Dec 10 Mississauga, ON, Canada 60006X

    @squirrelman777 Try running it with new motor controllers. Whenever we have a problem with motors not behaving we always try that first. Over the past two years, motor controllers have caused our robots to attack us and to drive away.

    We really can't change motor controllers as vex has stopped shipping them and we only have around 12 all of which are on the bot.

    @goofnrox Using a power expander for drive motors is just fine, just not ALL of the drive motors.

    OP didn't specify if there is an expander on the robot. If there is the best wiring configuration will be to have two motors on each PTC channel. Otherwise split the motors evenly between the two PTCs in the cortex.

    Cortex 1-5 is one channel
    Cortex 6-10 is one channel
    Expander is one channel

    @AryanG how is the bot wired?

    We do have a power expander specifically for the drive but it is wired on the correct cortex channels to split them between the PTC's on the cortex.

    @Rick TYler 1. Too much friction

    1. Over-geared <and/or> overweight
    2. Bad motor controller
    3. Bad motor
    4. Chains that are too tight (leads to high friction (see #1)
    5. Other weird stuff (motor not plugged in)

    Listed in order of occurrence after watching VEX robots for 12 years.

    We have checked through 1,5 and 6 we are strongly suspecting it to be bad motors or MC23's. We shouldn't be too overweight as the bot is approximately the same weight as a bot with a mogo on it from itz.

  12. JuiceBox

    Dec 10 Ohio 6741E

    @AryanG We really can't change motor controllers as vex has stopped shipping them and we only have around 12 all of which are on the bot.

    I would talk to teams in your area that have made the switch to v5, they could possibly be able to hook you up with some motor controllers that they no longer need.

  13. sazrocks

    Dec 11 Arizona 2114V

    @AryanG We do have a power expander specifically for the drive but it is wired on the correct cortex channels to split them between the PTC's on the cortex.

    You mean that your entire drive is going through the power expander? That would be your issue. It doesn't matter where the control wires are hooked up because power expander motors do not draw from the cortex; it's the whole point of the power expander. They instead will load the lone PTC in the power expander and trip it much more easily.

  14. JuiceBox

    Dec 11 Ohio 6741E

    @sazrocks You mean that your entire drive is going through the power expander? That would be your issue. It doesn't matter where the control wires are hooked up because power expander motors do not draw from the cortex; it's the whole point of the power expander. They instead will load the lone PTC in the power expander and trip it much more easily.

    Speaking from experience at the beginning of the season we had a 4 motor high-speed drive and all 4 motors were on the power expander and we never had problems with it burning out due to it all being in the power expander.

  15. JDeuter

    Dec 11 South Dakota 6844B
    Edited 5 weeks ago by JDeuter

    @JuiceBox Speaking from experience at the beginning of the season we had a 4 motor high-speed drive and all 4 motors were on the power expander and we never had problems with it burning out due to it all being in the power expander.

    Power expanders vary depending on how well they have been taken care of, I had some trip easily and others not trip under a 4 motor load, also battery quality can have a bug big effect.

  16. AryanG

    Dec 11 Mississauga, ON, Canada 60006X

    Our power expander has only 2 of the 6 drive motors on it.

  17. Will Xu

    Dec 11 California 2496N

    We used to have a 4m torque drive(100 rpm) but we changed to a 6m torque drive sprocketed for speed (150 rpm) which has the exact same stall torque.

    When I hear that you guys have presumably around a 2:3 speed ratio, that's a bit concerning because normally you don't want to have a ratio in your chassis. Direct drive or 1:1 chains are enough.

    Other than that my second guess would be your chain tensioning or lack thereof. If you have a speed ratio + some standoff tensioning your chain, it's probably that issue because that standoff creates a lot of friction.

  18. goofnrox

    Dec 11 Jenison MI Jenison Robotics

    You can also try implementing jpearman's smartMotor library.

    It attempts to predict when the PCTs are going to trip and dials back the motor power. I think you'll find your robot will need to run quite slow to keep from burning out with the way it's currently geared.

  19. ranOOm

    Dec 12 Answer Ottawa, Ontario, Canada 2381

    Pictures will definitely help - when you check for friction, make sure your include the motors - these being misaligned can cause a lot of friction. Check to make sure that you aren't overloading the motors, and try double checking with different motors and controllers.

  20. AryanG

    Dec 13 Mississauga, ON, Canada 60006X

    We found out that some of the motors were misaligned and the gears in the gearbox were causing a problem. We fixed it now and it works fine so far.

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