how do I ramp up the wheels slowly

[seanl]

I am trying to create some code in Labview so i can ramp up and ramp down the speed of the wheels but i don't know where to start. like to slowly go from the value of 0 to the max speed of -1. i tried to do this with a while loop but failed because i could not find a variable such as x. any suggestions?

[EricVanWyk]

http://thinktank.wpi.edu/article/140

Hopefully this document will help.

[seanl]

this is for the drive of a motor without the use of a joystick, i am using a button to drive the whole robot forward but i need it to ramp up. but thanks for the information on making the joysticks smoother.

[Russ Beavis]

I haven't read Eric's article but the use of filters isn't limited to floating point joystick position readings. You can also take a boolean value, convert it to a floating point 1 or 0 ("boolean to 1:0") and then pass the value through a point-by-point or similar lowpass filter (this is probably one of Eric's suggestions). The filter cut-off frequency would dictate the response time.

You could also pass the 1:0 value through a leaky integrator (if 1 then add a little bit (clamp to max value), else decrement a little bit (clamp to a min value)).

Russ

[EricVanWyk]

I've attached a picture of a leaky integrator.

I used the boolean select to convert a boolean to one of two floating point values - in this case, how much to add or subtract each time the code is executed.

I used a feedback node (the arrow) to remember the last value.

I used the coerce and in range to limit the max forward or reverse speed.

[seanl]

Eric, i tried what you stated in your paper and it looks like it could work, can you or someone else check and see if it is right. i put a constant of 1 instead of the "input from joystick". theoretically this should allow the robot to slowly back up.

P.S. the code is attached to this post.

[dmcguire3006]

Use a PID Controller:
http://en.wikipedia.org/wiki/PID_controller

There provided as a VI in Labview.

[seanl]

Originally Posted by dmcguire3006

Use a PID Controller:
http://en.wikipedia.org/wiki/PID_controller

There provided as a VI in Labview.

are there any documentation on using a PID controller being that i am a novice at labview programming. And is there an advantage to using a PID controller over the method stated above?

[EricVanWyk]

Originally Posted by seanl

are there any documentation on using a PID controller being that i am a novice at labview programming. And is there an advantage to using a PID controller over the method stated above?

PID controllers are very powerful, but in this case they are probably over-kill.

I would recommend using one here in place of a leaky integrator only for the learning experience - you will find it very helpful in the future. That being said, leaky integrator is probably the way to go here if you are aiming for simple.

[chmp09]

Originally Posted by seanl

are there any documentation on using a PID controller being that i am a novice at labview programming. And is there an advantage to using a PID controller over the method stated above?

I use a lead-lag PID controller to control our ramping, and it works really well. It will take some tweaking, but it is not that difficult.

For basics, just set you [EDIT] output range to -1 and 1. Set you gain to 1. Set your lag time to whatever you find is best (ours is .2); this changes how fast it ramps. Set lead time to zero. Set dt to -1(sets it to milliseconds). [/EDIT] You may want to tell it to reinitialize at values of zero because it will also ramp down.

The code attached was made for ramp code on a tank drive robot.