Frictio v/s Precise Movement!

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Joined: 27 May 2013, 16:50

Frictio v/s Precise Movement!

Post by ragrover » 31 May 2013, 23:06

NXT 2 Educational Set-- Programming using RWTH toolbox in MATLAB.

How much is the effect of friction on a surface on the movement of the bot. Say I want to move the bot take ten 360 degree turns on an unknown surface having some friction on a given spot and be back at its original orientation and I am using DirectMotorCommand to sync motors in opposite direction. How can I precisely determine the TachoLimit for doing so? Are there any other methods apart from hit and trial. Assume the radius of wheel=1 inch and distance between wheels = 4 inch therefore on an ideal surface a TachoLimit of 720 would do the job!

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Re: Frictio v/s Precise Movement!

Post by tabbycatrobots » 01 Jun 2013, 00:30

I would say to plan on some experimentation - hit and trial. If you start the motors at high speed / high power,
there is more chance of tire spin. I suspect a bigger softer tire will give better results. I have also found
some power / speed variation between motors, and I use a #define (determined by experimentation, which
I still need to do more of), for motor pairs in my code. I can then use the same code for various motor pairs.
Also, if the motors run at slightly different speeds, this will move the center of rotation of the robot.
And if you run on a soft surface like a carpet, a small wheel will sink in more and require more power than
might be theoretically expected. And you may see some variation as the batteries run down. So, I think the
short answer is the theory and math give a good starting point, but expect to do some experimentation.

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Re: Frictio v/s Precise Movement!

Post by jwiger » 05 Jun 2013, 12:34

This is just a random idea, but have you looked at how large walking cranes move? They have a big round foot suspended between their landing gear that drops down and lifts the crane up, then rotates to move the large crane in a very precise way along the rough rocky/dirt base of a mine or quarry. It would be pretty agnostic to hard floor or carpet, although slower and more complicated. Yet the cool factor is definitely there!

Here is a video of it walking: ... P4PuhywXm8[/youtube]

Here is a good video of it turning: ... 09DuGsk_z4[/youtube]
"The more you know, the more you know, the less you know."

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