Use a button to make a motor move a certain number of rotations

[Levansic]

What is the number of pulses per rev for the built-in encoders? I think the only legal motors that have built-in encoders have 7 pulses per revolution and a 71:1 step down through the typically attached gearboxes. Are these the ones that you are using?

If so, that could correspond to 7 x 4 x 71 = 1988 counts per revolution. The factor of four is because the encoder is quadrature, and has four registered pulse edges per pulse cycle. That means you would be seeking a count of approximately 7475. The math changes if you are using a different gearbox. Note that the numbers I am using are integers. You can't have fractional pulses.

All of this assumes that you set the output type as position in Begin.vi, and that you have appropriate PID terms.

[RoboBucs]

Originally Posted by Levansic

What is the number of pulses per rev for the built-in encoders? I think the only legal motors that have built-in encoders have 7 pulses per revolution and a 71:1 step down through the typically attached gearboxes. Are these the ones that you are using?

If so, that could correspond to 7 x 4 x 71 = 1988 counts per revolution. The factor of four is because the encoder is quadrature, and has four registered pulse edges per pulse cycle. That means you would be seeking a count of approximately 7475. The math changes if you are using a different gearbox. Note that the numbers I am using are integers. You can't have fractional pulses.

All of this assumes that you set the output type as position in Begin.vi, and that you have appropriate PID terms.

Ok, that definently helps me with understanding these encoders, thank you, I just don't know where I would put that 7475 number in labview at, do you know?

[Levansic]

You would put it as an input to the drive (where you have it), but you have to have the drive motors properly configured. One other thing, is that you need a little more logic to latch the value. The Teleop.vi runs approximately every 20 ms. As soon as you let go of the button, your input will be to drive the motor back to the 0 position. This isn't what you want.

If you intend to drive your robot completely with position commands, you will need a state machine that keeps track of the current values, incrementing and decrementing the intended position.

It is much easier to drive in speed or voltage mode.

[RoboBucs]

Originally Posted by Levansic

You would put it as an input to the drive (where you have it), but you have to have the drive motors properly configured. One other thing, is that you need a little more logic to latch the value. The Teleop.vi runs approximately every 20 ms. As soon as you let go of the button, your input will be to drive the motor back to the 0 position. This isn't what you want.

If you intend to drive your robot completely with position commands, you will need a state machine that keeps track of the current values, incrementing and decrementing the intended position.

It is much easier to drive in speed or voltage mode.

It won't be completely, it's only with this specific arm, we can use joystick movement for it rather than buttons, it would just be easier for our driver to put a button and have the motors move that amount for that arm every single time. I also have 2 questions, what do you mean by speed or voltage mode and what's wrong with the way I have the drive motors configured? It's probably something stupid, I'm still used to using unbundle by name for buttons from last year rather than arrays, thank you so much for your help so far!

[RoboBucs]

Ok I think I'm starting to understand this, so would I put the 7475 number as distance per count in begin for the encoder? Past that I'm not sure how I can assign a button to work under that motor count for the encoder and the motor in teleop

[Levansic]

Can you post the snippet of code from Begin.vi where you setup these motors?

[RoboBucs]

Originally Posted by Levansic

Can you post the snippet of code from Begin.vi where you setup these motors?

[RoboBucs]

Originally Posted by Levansic

Can you post the snippet of code from Begin.vi where you setup these motors?

Would I have to set it up like this? (I just forgot to rename the second encoder in begin)

[Levansic]

Your snippets are illuminating.

OK, here's the rest of the story. Unfortunately, you won't have a simple way of just sending a number to the motor controller, as you are using PWM Victors, which have no understanding of encoders or close loop modes.

You will need to implement a PID control in LabView, where the encoder inputs are compared to your desired position. The outputs will drive the motor voltages up and down, until the desired position is realized.

LabView has several built-in PID functions, and there are many threads here about how to use them.

[Ether]

Originally Posted by Levansic

Your snippets are illuminating.

They're not snippets. They're just screenshots.

[Levansic]

Originally Posted by Ether

They're not snippets. They're just screenshots.

You are quite correct. Those chunks of screenshot carry the same human-readable info, which is what I was after.

[RoboBucs]

Originally Posted by Levansic

Your snippets are illuminating.

OK, here's the rest of the story. Unfortunately, you won't have a simple way of just sending a number to the motor controller, as you are using PWM Victors, which have no understanding of encoders or close loop modes.

You will need to implement a PID control in LabView, where the encoder inputs are compared to your desired position. The outputs will drive the motor voltages up and down, until the desired position is realized.

LabView has several built-in PID functions, and there are many threads here about how to use them.

How do they have no way of understanding encoders if the encoders are built in?

[Levansic]

Originally Posted by RoboBucs

How do they have no way of understanding encoders if the encoders are built in?

Encoders, built in or otherwise, have to plug into something that can understand their signals. The Victors have no such facility. They are not "intelligent", meaning they don't take any external feedback.

The motors themselves don't have any intelligence. Their inputs are only the voltage applied to the wires. The encoders are not linked in any way to the windings in the motor.

You have setup some DIO channels to take the A and B data from the encoders. This information goes straight into the roboRio, which has to do something with it, to control the input to the victors. The roboRio is the brain in this case.

The new Talon SRX's are intelligent, and can do the work onboard with no involvement of the roboRio. The older Jaguars had promise of this, but in practice, they rarely worked as designed for encoder-driven closed loop feedback. I have trouble finding the right words to describe how much I LOVE the Talon SRX's closed loop modes.

[RoboBucs]

Originally Posted by Levansic

Encoders, built in or otherwise, have to plug into something that can understand their signals. The Victors have no such facility. They are not "intelligent", meaning they don't take any external feedback.

The motors themselves don't have any intelligence. Their inputs are only the voltage applied to the wires. The encoders are not linked in any way to the windings in the motor.

You have setup some DIO channels to take the A and B data from the encoders. This information goes straight into the roboRio, which has to do something with it, to control the input to the victors. The roboRio is the brain in this case.

The new Talon SRX's are intelligent, and can do the work onboard with no involvement of the roboRio. The older Jaguars had promise of this, but in practice, they rarely worked as designed for encoder-driven closed loop feedback. I have trouble finding the right words to describe how much I LOVE the Talon SRX's closed loop modes.

Man this stuff is so beyond my level of experience with this stuff. I may just have to work this with the joystick like we have been so far, unless you have some way around this:/

[RoboBucs]

Originally Posted by RoboBucs

Man this stuff is so beyond my level of experience with this stuff. I may just have to work this with the joystick like we have been so far, unless you have some way around this:/

Ok, I think we're just gonna have it where when we press the button it will just run for however long we need it to run, will that work?