3 0r 4 Wheel Omniwheel robot with BS2

Prettybird

·· I was looking at another forum and found I have enough parts to make a Omniwheel robot in the near furure. Does the BS2 series stamp have enough memeory to run one of these with mabe 3 sensors.I am thinking mabe a ping and 2 IRs or 3 IRs or a ultrasonic motion sensor and 2 IRs. I know a stamp can handle 4 servos. Anyone with experience with this type of Bot? It does look a little more complicatted then my first boe still in progress. Any input as usual would be appreciatted as usual.· I have a new BS2P and BS2PX· I haven't touched yet,·along with a regular BS2.

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Timmoore

I have built an omniwheel bot but I used the prop not a bs2. The prop has no problems. Couple of comments from my experience, the traction of the wheels needs to be correct otherwise you get problems. I had 3 issues with traction
1. The base needs to keep the wheels flat on the ground, any slight imperfections cause uneven traction.
2. Most omniwheels are made of very hard plastic which slips very easily, I ended up using http://omniwheel.com/transwheel/transwheel-2000.htm the 2052BX (near bottom of page), the BX version has a rubber coating on the rollers which helps traction.
3. I ran the motors with front 45degrees from the motors so all 4 wheels run to go forward. So all wheels are providing traction for forwards.

Prettybird

·· Omniwheel Growbot update:

This is my first attempt to write a simple program to make the Quad Omniwheel robot move in 10 directions. The program seems sound but the mechnical problems are as much to be expectted. I guess it is time to design a sound body. According what I have observed on U Tube clips, it seems that 3 wheels are more stable but the programming would be more complex. I also don't know if 2 wheels per axis are any better then 1 wheel per axis·thinking more surface area contact vs more drag.·That is another issue down the road for later. It dosen't seem the Parallax (Futuba servo ) has ·enough RPM. I don't think tweeking it would make much difference. I was wondering if anyone knows the RPM of a Parallex servo settup? Any input is appreciatted as usual. Oh well, back to the basement robotics lab. Includded is test #2 short clip and the Omniwheel X 10 direction program. Thanks in advance as usual.


http://www.metacafe.com/watch/3180611/omniwheel_growbot_test_2/

Timmoore

The maths for 3 wheels isn't particular hard (trig), if you point 1 wheel forward. The wheels are 120degrees, so you need to change the forward/sideways speeds to sin30/cos30, sin30 is 1/2, cos 30 is .866 which is 1024/1183
so if 3 motors m1, m2, m3
m3 = -sidespeed
sidespeed = sidespeed * 1183/1024
forwardspeed = forwardspeed*2
m1 = sidespeed - forwardspeed
m2 = sidespeed + forwardspeed

Prettybird

·Omniwheel Growbot update. I finally made a Flexable use body for my bot. It is made of 2 peices of plexaglass with the servos sandwitched in between.Very easy to align and·add or subtract servos. I tried several combinations and am getting ready to scrap the hard plastic omniwheels. I do have a Board of Education board but saving it for another project or resale. Let the buyer beware. Rubber or silicone coated omniwheels seem to be the ONLY way to go. I found single wheels work better then double wheels and a bigger wheel base works beter then a shorter wheel base. They are terrable at pulling dead weigh servos ( servos not running). My next attempt will be with 3 wheels. May work a little better but pricing better wheels. I am not going to loose myself in programming until I get the·wheels to work. At least it can easily be changed back to the original Boe Bot style so the body is not a waste. Flexability is the future especially on a short budget. As the video shows, not very impressive.

http://www.metacafe.com/watch/3207262/omniwheel_growbot_flex_body_test_5/

http://www.fingertechrobotics.com/proddetail.php?prod=ft-mecanum-set· These my dream wheels for now, but a bit pricey.

Post Edited (Prettybird) : 8/24/2009 9:47:27 PM GMT

Timmoore

I would second the coated wheels. I haven't tried the same wheels as you. I used these http://omniwheel.com/transwheel/transwheel-2000.htm. I tried 3 different types
1. Single wheel - non-coated - doesn't work at all
2. double wheel - non-coated - slightly better
3. Double wheel - coated - much better
I haven't tried a single wheel coated. I am running it on a smooth hard floor. I have attached a picture of my version.

Prettybird

Good to see your version. At least I am on the right track. You version is alot lighter, but I have seen big ones on U Tube so I know it is possable. So far I have seen more 3 wheel versions then 4 for some reasion. I would think 4 are easier to program and have an extra motor for some extra push.