Let's Make Robots!

TOW - TriOmniWheeler

 
Holonomic Rover

Here's the latest from BOA-Labs: My first omni-wheeler.

It draws very little from the suggestion here. Most roving robots must turn to face their direction of travel. The plan with this one is that it should be able to move around in 2D space without having to turn to face "forward." It's called "holonomic" motion. It's annoying that so many variations on this have already made it to market. Other omni wheelers have a perceived flaw where they might slide off the sloped roof of your house. Not this one.

Programming it is going to be the entertaining bit. Have barely contemplated it. All ideas welcome.

I have reused the the controller from Harmenszoon. This controller was also used in my first biped. In fact, in modifyig the software to operate continuous rotation servos, I found a glitch in the biped code which may well re-ignite the project.

I'm seriously considering my old Psion Series 5 as a controller because it's got an RS-232 port and its own built-in high-level programming language (OPL). It looks like some clever bugger has already thought of that, although they use a Palm Pilot.

Video

The second video show the first signs of life. You're thinking "Cool, all he has to do it flip it over!" Not just yet. First I have to do the next bit....

The first video is the last video. It "does stuff."

Closeup Pictures

Some pics of the chassis. Here's the underside, showing the arrangement of the three continuous rotation servos.

TOW02_Bottom.jpg

Detail of the servo mounting.

TOW03_Mounting.jpg

The Maths

All the maths (discussed later in the threads) boils down to this:

d = SQRT(3)/2 (this also happens to be COS(30). Useful because 30+90 is the relative angle of each wheel to the chassis.

N1 = w - x

N2 = x / 2 - y * d + w

N3 = x / 2 + y * d + w

N1, N2 and N3 are the wheel speeds. w is the angular velocity (it can rotate as it travels).

The Conclusion

It's time to take this one apart for the motors. I wanted to get it to do "something" first, though, so here it is moving around in all the prescribed ways on the floor.

The wheels weren't good - they were too slippy.

The servos in continuous rotation mode were extremely difficult to control accurately for speed.

A pity, really. I will try coating them with liquid latex or something at some point to make 'em more sticky.

Case closed.

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I quite fully grasp the concept :)

It was only a (bad) joke, refering to this thread question that you asked me ;)

Ah. You were practising your irony. I can take it. Might need a bit of notice next time...
My bad, completely, sorry :)

You can be such a techy sometimes ;-)

Apearantly, Wowwee built a similar base for one of their's, proving it can be done.

nice! i like those wheels and base.
very clean mounting technic!!  good start!
want to see what you will do with ti  ;)
I found a piece of soft plastic rod (dunno what it is, but it's about as soft as a stick of hotmelt glue). I found that a 5.5mm hole would press-fit quite nicely onto the splined head of a servo motor. I turned the rod down on the lathe to the right diameter. The wheels have a keyway in them. I cut a V groove up the length of the rod, inserted it in the middle of the wheel in line with the keyway and filled the gap up with hotmelt glue.
Good Luck and will be interested how you finish the tophalf

I cant believe it - i just ordered parts with same idea in mind - fantastic............. cant wait to see it in motion.

I agree with Rik - the maths to calculate Tri-Motion is a bit right/left brain "fuzzy" .

if you want a bit of inspiration check out "TRIBOT"

What "Fuzzy Brain" are you going to drive it with? .(i hope Arduino)

I think I can make it move in ANY direction. The only unknown being the effect of friction. It's a pretty big factor, actually.Does teh tribot have rubberised wheels? That would make it a good deal more predictable.

The controller is reused from a different project, so it's PIC based, but I'm thinking I should just simplify it a bit so that it purely provides a serial interface to the motors. That way I can control it using a higher-level computer. The most likley candidate at the moment is my old PSION series 5 organiser as it has an RS-232 port and its own built in programming language.

DAMN! I hate that someone has already done this commercially. When I think of the number of things I've invented, just to be outdone by someone with cash. I invented freeze-dried instant tea when I was about 6, you know. Someone else beat me to market, though.