Society of Robots - Robot Forum

Mechanics and Construction => Mechanics and Construction => Topic started by: HadeBe on July 07, 2009, 03:24:38 AM

Title: Mecanum
Post by: HadeBe on July 07, 2009, 03:24:38 AM

I want to build an autonomous robot with mecanum wheels. Andymark is a company where you can buy these wheels, so thats not the problem..

My discomforts are about the control system. I can control the turns with a compass.
But my question is about the encoders. I know that lateral movement is not possible when only using encoders for position control. but if the robot moves just forward, is slippage then a problem?

Title: Re: Mecanum
Post by: Ro-Bot-X on July 07, 2009, 05:25:16 AM

I would suggest the use of an optical mouse sensor instead of encoders. This way you get movement in all directions regardless of wheel slippage. Search the forum for mouse optical sensor hack. It has been done and documented.

Title: Re: Mecanum
Post by: Admin on August 25, 2009, 08:37:45 AM

Optical mouse sensors are horrible, actually. Lift your optical computer mouse above the table about 1mm, and watch what happens. You'll see error gets really large if its not always perfectly flush with the table.

Title: Re: Mecanum
Post by: Joker94 on August 25, 2009, 05:56:22 PM

Optical mouse sensors are not good like admin said. I just mounted the one i had lying around on my robot and it didnot work well at all.

Title: Re: Mecanum
Post by: Ro-Bot-X on August 25, 2009, 07:26:02 PM

Quote from: Joker94 on August 25, 2009, 05:56:22 PM

Optical mouse sensors are not good like admin said. I just mounted the one i had lying around on my robot and it didnot work well at all.

Of course it doesn't work. The lens is made so the beam is focused on the mouse pad (really close distance). So at a greater distance, you need to modify (change) the lens. Please look up the optical mouse sensor on this forum, there is someone who did it and it worked.

Title: Re: Mecanum
Post by: Joker94 on August 25, 2009, 07:30:33 PM

i had it mounted skimming the floor. not hovering in mid air but i get what your saying

Title: Re: Mecanum
Post by: wil.hamilton on August 27, 2009, 05:18:45 PM

you could always use gyros and accelerometers to get relative motion.
you can get ones that are accurate within a few degrees for not too much.

Title: Re: Mecanum
Post by: FingerTech Robotics on August 28, 2009, 01:23:04 PM

I would like to offer a link to FingerTech's Mecanum Wheels.  They are much cheaper than others and might be a more manageable size (2.125" diameter).
http://www.fingertechrobotics.com/products.php?cat=Wheels+%26+Hubs (http://www.fingertechrobotics.com/products.php?cat=Wheels+%26+Hubs)

[youtube]http://www.youtube.com/watch?v=DhNm0FOIiG0[/youtube]

Hope that helps!

Title: Re: Mecanum
Post by: blackbeard on August 28, 2009, 03:46:57 PM

i'd so buy those wheels if you mounted a flame thrower on that robot while it passed through the buildings :P