ok, My name is Luke Whitcomb and i am part of a robotics team of Jesse Remington Highschool. We are a small highschool and dont really have that many smart people of the robotic pursuasion. So we have our robot and its really good, but there is one problem. once we start it up, the wheels move for a little while but then suddenly stop or go reallllly slow. The drive is a chain system with the two back wheels have the motor and a chain connecting to the front wheels to power the front wheels. So i dont know what the problem exactly is because it seems that the wheel engines are perfectly fine when run alone. And all the other engines work fine when this problem occurs. So can someone possibly give me some input into what the problem could be?..thank you
I have not been a fan of the VEX chain and I do believe that is your problem. The vex chain isn’t very precise nor strong, I would have expected that the chain pops off a drive train if it meets resistance, I’m not sure if you’ve tested that.
If a chain is loose, then one side can get really tight while the other side can get really loose and then it’ll slow down the entire system. If your chain is not popping off, I would think that it would be a loose chain.
I can also attest to the weakness of the chain. They will skip fairly easily, and they can also simply un-attach under higher loads. I will usually use a pair of chains in most situations, to distribute the load.
For troubleshooting, it’s sometimes helpful to test a malfunctioning system by removing the load and/or components one at a time. If you’ve checked the batteries already and it’s still running slow:
Try running the robot while lifting it off the ground (wheels spinning in air). Observe the wheels to see if there is friction anywhere.
If it’s still slow, try removing the chain.
If still slow, try removing the wheels.
Somewhere along the way, you’re likely to find the source of drag, unless your motors are shot.
One last thing: I noticed you said, “…the motor and chain connecting to the front wheels…” Does that mean you’re using only one motor to power the whole robot, or do you have one motor on each side (total of 2)? One motor probably isn’t enough to drive a robot unless it’s really light.
The motor modules are on teh left and right wheels in the back, and chain going to the front wheels. So for the first 10 seconds its drives fine, then acts like the batteries just died, so it slowly stops, i had in fresh batteries. When lifted off the ground the wheels move fine…wait it just got solved. Sunny is right about the chain, it is not good. I just removed it and the rear wheel drive works fine, it doesn’t die at all. So thanks for everyones input…if some other crazy thing comes up…us hicks shall message out for help.
It also could be that your microcontroller speed controllers for those channels are heating up. That ususually comes from too much current through it from too many motors. If there was enough resistance and therfore load on the motors this could be the case. I cant be 100% certain but those are the same symptoms we have had with this problem. But i hope the chain was just the problem and your troubles are fixed. Best of luck!
ya, our team always has really good designs for the robotics, like ones that work efficiently and can make us win…but then some technical stuff always comes up at the last moment that we can’t fix…so hopefully it wont happen this year.
I know exactly what you are talking about. Because of the problem i described. At our first comp with it, i had to take off motors and change the gearing. We lost all of the manuvering advantage we built into it. At least there are more competitions. We wont make the same mistakes twice.
Simplest is cantilevered omniwheels driven directly from motors on the front, and cantilevered non-omniwheels driven directly from motors on the back.
4 wheels, 4 motors, no gears. 4" wheels are faster that the small wheels. Large (4") omniwheels are awesome.
Better, but slightly harder mechanically: non-cantilevered wheels, ie support axles from both sides.
Use a Y cable or send the same output to both motors on same side.
I estimate that 60% of competition teams use this, or the 6wheel 4 motor variation of it; 20% also use gears, 20% are more complex.
“Best” requires metrics for qualitative measurements, best for what purpose?
Most pushing? Highest speed? Most nimble? Most cost-efficient?
NASA Mars Rovers use 3w rocker-trailer on each side.
This might be good for climbing the platform for VEX Elevation.
In my opinion, the simplest 4 wheel drive is with 4 motors, one directly mounted on each wheel. With a very simple program, this is really easy to drive and is durable . If you want it faster you just add gearing and/or change wheel sizes. Ive tried adding aother set of motors and wheels for more power but this has just fried my micrcontroller from the current.
But it might also be your wheels. Did you lift up the robot and see how the wheels do free spinning? I would say like previously, the battery is a perfect example of something like this happening. Also, if you have the largest wheels, they create huge friction. It’s unbelievable how much friction they have. Also, check if a part of your robot is rubbing up against the ground.