How to make robot faster?

We went to a qualifier this weekend and a few of my kids noticed that our bot wasn’t as fast as some of the other bots. What are some of the options that I could present to my roboteers? Our bot is a tankbot with a single motor and two wheels on each side that are geared 1:1. I guess we could have each side powered by two motors but that would mean our 4-bar link would have to be powered by a single motor instead of two (to stay under the 6-motor limit), and don’t know for a fact that a 4-motor drivetrain would actually be faster. Another option would be to gear up but I assume there’s limits or disadvantages to that as the bot feels a bit on the heavy side.

given the motors can handle it you could try using a larger sprocket to connect to the treads (larger circumference, more distance covered in a single revolution of the motor). The main limiter at the moment is likely the motor’s peak rpm, which means adding more motors wouldn’t make it faster.

Another option is to have a geartrain to have the same effect (larger end circumference per revolution of the motor).

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Are you sure your motors aren’t not defaulted to 50% in your code?

In teleop mode , the velocity is set based on the joystick position, so when we do drive at 100% velocity that doesn’t feel fast enough. We’re not doing anything specific with the torque; should we?

Since you are using joystick values it probably isn’t your code.

It really depends what you want the robot to be. tankbots are known to be slow but capable of a lot of pushing power. If you’d rather have the speed then your options are pretty much to either trade torque for speed, using something other than treads, or both.

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You could either reduce weight and use more speed oriented gear ratios on the wheels, or you could run one motor on the arm, but gear it 1:2, making the arm move at half the speed, but at the same torque. This issue can be mitigated by raising the arm while driving, so it is at the correct height when the destination is reached, thus improving efficiency.

Edit:Or switch to wheels

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First, I misspoke when I said “tank”, we’re using wheels, not tracks. I thought I had seen this kind of drive train referred to as “tank” but maybe that referred more to steering. But, yes, we’ll try putting the bot on a diet. Our arm is geared 1:3, and we’ve been running it at 50% velocity, but this weekend we ended up with a badly twisted and broken axle. That’s why we thought of adding another motor.

As @Deicer pointed out, using 2 motors on a single drive side (4 total for both sides) will not make your robot go faster. All that does is give your robot more pushing power. Your only option is to gear it or lose weight on your robot so you have a lighter robot. Gearing the robot (3:2 or 2:1) will reduce your torque but this season’s game doesn’t require a lot of torque.

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Understood, thank you!

I’d like to clarify that if the motors are already going at max rpm (as it sounds like it is) then making it lighter doesn’t make a difference in speed.

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Would it not take longer to get to that max rpm with a heavier robot? Or would the difference be negligible?

likely negligible. If it takes a noticeable amount of time to reach max speed then odds are that there’s so much weight that the motors will burn out within 30 seconds.

You would probably be experiencing motor burnouts before you reach this much weight after playing with the bot for 3-4 minutes

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You can change the gears in a normal vex 393 motor over to high speed gears. This in turn will increase your total speed by about half and you can still run them at full speed without them burning out.
*This works for v4, not sure for v5

This is IQ so that option for changing motor gearboxes is not available

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Sorry, I didn’t know. I’m afraid I can’t help you, then. Best wishes.

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A popular choice of step-up drivebase gears in IQ is 5:3, since you can easily implement that using 60t gear on the motor meshing with 36t gear on the wheel. 3:1 is waaay too steep and using 12t gear on the wheel would be challenging the part integrity. 2:1 is marginally possible, but 48t and 24t IQ gears are hard to get by.
Other gear ratios are doable using chain and sprockets, but that uses more space and typically affects programming precision more than direct gears.

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