Drive Base Died?

Hi everyone,

Today my team attended a qualifying event and experienced trouble with getting our drive train to move during a match.

It was extremely frustrating because we could run auto and teleop perfectly while connected to the competition switch on the practice field. But the second we ran on the competition fields, the drive base would fail after auto.

Our auto routine would work find and then when our driver and operator took over, the drive base would die. It would only move occasionally while the flipper/catapult would still work.

The other weird thing was that we weren’t the only team that experienced this problem. Several other teams (at least 3) had the same issue. So we approached the head ref to ask what the problem could be, and he our robotC was out of date.

We all updated robotC to the latest version and downloaded the latest firmware to the cortex, keys, and joystick but none of the robots’ drive bases moved during teleop in the elimination round.

Does anyone have any ideas on why this might have happened and how we can prevent it for the next competition?

Some information:
We have only 6 motors total with 4 on our tank drive (geared for speed) and two on our flipper
They are in ports 1-6


Numerous teams had problems yesterday at the Jay Noblesville tournament where the robots would work fine with the control switch(or not hooked up to anything), but would not work properly when connected to the field controllers. Yesterday was our third tournament with issues similar to this in Indiana. We are also using RobotC and had the most up-to-date code.

Have you named your robot on robotC?

If you haven’t, that could be a part of the issue

I don’t think RobotC let’s you download code to your robot without having your robot named, so that is probably not the case.

It will let you download the code but it does give you a warning as you download it.

We lost in the finals because of our robot losing connection :frowning:

We had three robots there and only one of the three was not named in RobotC. Both named and unnamed robots had issues yesterday.

Yes we named our robot too and still experienced problems.

Naming (or not) the robot has nothing to do with field control.

For those of you that have never read this, here is a link to my fairly comprehensive analysis of the field control system from a couple of years ago.

If the field control is disabling your robot you will see this reflected in the game led and also on the driver interface boxes. It’s essentially impossible for field control to cause VEXnet or other drive related problems with your robot.

Thanks for that. I’m wondering; when we plug in our controller to the field our robot led (on the joystick) always goes red, even when the battery is fresh off the charger and the voltage is well above 7.2 volts. Could this be caused by us plugging in to the field after our controller and robot connect as opposed to before? If so, could this be causing connection issues(i wouldn’t think so but you never know)?

We were experiencing similar things as well.

On the joystick we had the following lights:
joystick -green
robot - red (even with brand new battery)
game - yellow
vexnet - green

According to @jpearman 's field control analysis all lights should be green.
Is that the same for this year?

Do you have a backup battery? The robot light will flash red when connected to the field if you do not have backup battery.

We have a 9V back up battery and a 7.2V power expander. We were running our flipper off of the power expander.

Was the robot led flashing or solid?

We were having the exact same problem with our robot for a whole scrimmage as well! After a lot of testing, we narrowed it down to bad batteries or as we call them, badderies. Some of our batteries were old. Therefore, even if freshly charged, they would die down in the game (because of a rapid voltage drop). I know how you said that after the game the robot moves fine. This happened to us too. This happens because after the game ends, the robot gets a short period of time to rest and the battery voltage jumps back up which allows the robot to move fine after the game for some time. So, I would recommend deep cycle testing your batteries to see if they are able to hold charge well. If that doesn’t work, try switching out your brain for a new one (It could also be a connection problem because of faulty pins). I hope this helps! Good luck for your future competitions :slight_smile:


I’ll let James address the less-likely electrical and control issues.

In my experience (11 years) the most common causes of stalling drivetrains are:

  1. Over-geared drive train. If you are doing more than 2.5fps or so with four motors and your robot is not a featherweight (less than 10 pounds), you are over-geared.

  2. Friction in the drive train. Slide the motor shafts out of the motors and spin the wheels by hand. If they do not spin freely, and for a long time, you have too much friction in your drivetrain.

  3. Chain-drive drivetrain with excess friction. Serpentine chains suck power like crazy, and cause your motors to draw too much current. The best drivetrains are wheels directly connected to the motors, second best is gears, third is anything that uses a chain.

  4. Flaky motors (rare).

  5. Worn-out batteries (pretty rare).

Unless James turns up something I have never heard of, it’s not the field controller, it’s your robot.

Thank you for all of the help! I will definitely ask our lead mechanical to take the chains off of our drive base.