Oct 16, 2006

New MDP profile

1 MDP profile has been recently (??) added.

Rob Torok

5 comments:

Brian Davis said...

There's some interesting things to be seen on those models. First, an omniwheel on the Trent, and what is the custom board for (mounted above the NXT)? He seems to be using the stock light sensors for "vision", which is surprising to me (wide FOV on those, I would think). On Dribbler, where did he get those cables? Interesting...

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Brian Davis

Rob Torok said...

Thanks for the comments Brian. (BTW, thanks for your comments a while back defending MDPers for not having contributed to the Profile pages... you exactly described my situation.)

The omniwheel is something that I probably shold've mentioned in my description. It's not LEGO, but it's something that I would dearly love to see LEGO manufacture. Given the constraints of designing a compact and robust robot, I found that a dolly wheel was not nearly as effective as an omniwheel.

The board sitting on the NXT is a Wiltronics RoboBall Compass sensor (http://www.wiltronics.com.au/news.php?newsid=6). They're very commonly used in RoboCup Junior Australia.

Wide FOV can certainly be an issue with both the RCX and NXT light sensors. What alternatives would you suggest for vision?

The cables from the Dribbler version were ones that I built following Philo's instructions (http://www.philohome.com/nxtplug/nxtplug.htm).

Rob

Brian Davis said...

I agree that a good LEGO omniwheel would be a wonderful thing for robotics. Approaches like Steve Hassenplugs or third party ones like yours are good (where did you get it, BTW? How well does it mount? Any wiggle? is it free-spinning, or can it be driven by the axle to use as a drive wheel?), but I'd still really like to see a LEGO version.

As to the wide FOV, you can always narrow it with structures. For the old-style RCX light sensor, one technique ("technic"? ;-) ) was to aim the phototransistor through the hole in a 1x2 Technic brick, or to overwise construct "blinders" out of plates or bricks. I've not tried this on the NXT version yet (haven't needed to), but I probably will when I get back to detailed line-following.

I'd love to see videos of the dribbler in action.

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Brian Davis

Rob Torok said...

I purchased the omniwheel from Educational Experience (http://www.edex.com.au/) in Australia, but I couldn't seem to find it when I looked in their online catalogue just now. I've no idea where it was manuactured, but I could check.

The best thing about this particular omniwheel is that a pair of LEGO bushings just happen to fit snugly within the central shaft. A small amount of pressure was required to get them in there, but with an axle to help guide and align the bushings, and a table top to press against, I've now go a LEGO-friendly omniwheel. There's no wiggle on the bushings/axle and I didn't need any glue. (I'd better not want to get those bushings back out though...)

I haven't used it as a drive wheel (yet), but I think it will work for this quite nicely.

It didn't occur to me to include a video (duh!). I'll put that on my 'to do' list as well... along with the building plans...

Rob

Anonymous said...

You know, you can make a lego omniwheel without too much difficulty. I am eighteen and no genius, but i made one just yesterday and it's sitting in front of me. It's my second version, so i'm sure that other people have figured it out. It's got six wheels on it because i used two of those three bladed rotors from old legos. I have video (i think) of my old robot that i made with four wheeled omniwheels using them for drive and it worked ok, but it bounced around a lot because it only had four wheels per omniwheel. I'm planning on buying more rotors so i can remake that robot with the new six-wheel omnis. email me if you want to see pics. drew@vosburgs.org

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