Limit full power on victor sp

[ethan271]

So we saw with a test robot that our drive is too fast, is there a way that we could limit the victor to were if we were full on the joystick that it would max out power to 75%? We are using labview for programming.

[Oblarg]

Originally Posted by ethan271

So we saw with a test robot that our drive is too fast, is there a way that we could limit the victor to were if we were full on the joystick that it would max out power to 75%? We are using labview for programming.

I don't know labview, but you should be able to just multiply the joystick input by some constant less than 1.

[arichman1257]

Originally Posted by Oblarg

I don't know labview, but you should be able to just multiply the joystick input by some constant less than 1.

Do this ^^. I do not know how to do it in LabView but it should be a similar method to any other language.
For example, for 75% multiply the value (between -1 and 1) from the stick by 0.75 (called a scale factor). And you will want to do that in whatever function/method you are using to send signals to the motor controller. In C++ (and Java, I think) you would do

Motor_Controller_Name.Set(Joystick_Input * Scale_Factor)

[Andy Brockway]

You can never have a robot that is too fast!

We usually use one of the joystick triggers to reduce the max speed by a software scale factor applied to the y-axis when we want finer control of the throttle.

If you want a permanent reduction it could be done mechanically with gears. sprockets or smaller wheel. This will let you use the full power of the motors.

[cbale2000]

Originally Posted by Andy Brockway

If you want a permanent reduction it could be done mechanically with gears. sprockets or smaller wheel. This will let you use the full power of the motors.

This. If your drive system is faster than you ever intend to use, get a lower gear ratio. Otherwise you're wasting power and efficiency in your drive.

[arichman1257]

Originally Posted by Andy Brockway

You can never have a robot that is too fast!

We usually use one of the joystick triggers to reduce the max speed by a software scale factor applied to the y-axis when we want finer control of the throttle.

If you want a permanent reduction it could be done mechanically with gears. sprockets or smaller wheel. This will let you use the full power of the motors.

Even though this is harder than the code thing, this is a better solution.

[GeeTwo]

The question is, in what way is your drivetrain "too fast"?

Is the top speed more than your driver can handle/control? If so, either more drive practice, or gear lower as suggested above so that you will use less current accelerating and/or accelerate to top speed faster.

Is the acceleration (particularly at low speed) too great, causing you to fall over backward? If so, less grippy wheels or voltage ramping (programming so that you are only increasing the voltage at a maximum rate, e.g. 20% throttle per 100ms) may be the answer.

If the joystick is too sensitive in "parking" maneuvers (e.g. lining up to get or score game pieces), you could have a switch to go between two throttle modes, or program a nonlinear response to the joysticks. Ether's paper on joystick sensitivity is a great resource for the last.

Edit: I've never written any LabView, so forgive me if my terms are way out of whack, but if you really still want to do what you asked at the beginning, you would add two "multiply" operators. Break the wire connecting your joysticks (or arcade operator) to your motor controllers. Feed the joystick output to one input, 0.75 to the other, and the output goes to the motor controller input.

That throttle switch idea would give 1.0 at one throttle setting and (for example) 0.5 at the other where I had 0.75 above.