Drivebase Issues

So we’ve been having some strange problems with the drivetrain system on our robot. Basically after driving for a few minutes the wheels lose power. The left side tends to stop moving altogether. We have no idea what is causong this problem. We have done everything from changing the axels to changing the motors, changing the motor port configuration ect.

For a setup we have 4 3-wire motors each driving one wheel. The wheels have a 3:1 gear ratio for speed. Programming uses 2 2-wheel arcade blocks (easyC v2). We use a pic brain, the motor port configuration is as follows:

Left Rear Wheel:5
Right Rear Wheel:2
Left Front Wheel:7
Right Front Wheel:1
Left Arm:6
Right Arm:3

your motors are most likely burning out due to over heating or too much stress. Try reducing the gear ratio a bit. Say, a 2:1 ratio for speed.

Um you definitely have a very high gear ratio. You should gear it way down depending on the weight of your robot. Usually only robots less than 10 pounds can use a 3:1 ratio and not burn down. 2:1 for around 15 pounds or less, and around 1.6:1 for 20 pounds and for a robot over 20 try around 1.4:1 or 1:1

No one on this thread has mentioned wheel size, which directly affects the effective wheel gear ratio. 3:1 speed on 4" wheels is usually uncontrollably fast.

If it is only the wheels losing power, then at least it isn’t the PIC CPU PTC protection circuits.

The thing is he mentioned 3-wire motors which don’t stall/internal PTC.

Explain? All motors stall, and I’m pretty sure the old motors had internal PTCs too…

//Andrew

I don’t believe they do. The first motors to implement them were the 2-wire motors. https://vexforum.com/wiki//t/what-is-inside-a-library-file/12260/1

Ah. Ok.

(Learning something new every day… :))

//Andrew

In addition to not stalling, 3-wire motors have not temperature sensors so they don’t stop when they overheat.

I have 2 suggestions:
-Change your gear ratio for less speed.
-Check all of your wiring. Our wheel base did some pretty weird stuff this year, including many of the same problems you have, and it turned out one of the biggest causes was some flipped wires.

All motors stall. To stall means that the motor stops turning because it isn’t strong enough. So, if you put a large weight on 3-wire motor a few inches out, it will stall–the motor isn’t strong enough to lift the weight.

I do concede, however, on the lack of the PTC (temp sensor) in a 3-wire… didn’t know about that…

//Andrew

That link doesn’t mention whether 3-wire motors have overload protection or not.
Lack of mention of feature is not assurance of lack of feature.

The page does not mention the lack of the feature because when the 3-wire motors and their info pages were made, the feature did not exist with VEX. Why mention the absence of something that didn’t exist at the time? That would be like telling George Washington that he couldn’t take the city bus anywhere.

The overload protection for a 3-wire motor is called a clutch. The teeth within the clutch grind to allow the motor to spin when its load (example, a wheel) cannot move. If a robot using three-wire motors with clutches on its wheel base drives into a wall, the clutches will grind and strip, allowing the motor to spin freely without damage. This, among other reasons is why 3-wire motors require clutches and two wire motors do not (although we have found that using clutches on 2-wire motors is an effective way to stop them from overheating).

It turns out that you are incorrect. See the seventh post in the linked thread.

Thanks. Just wondering do you think changing out the motors for 393/high torque motors would help?

393’s have 2x the torque of a 3-wire motor. It will help. However, the amount it will help is dependent on your wheel size. What size wheels are you using?

//Andrew