Omni Mania

[SpaceOsc]

Nice

[troy_573]

Originally Posted by SpaceOsc

Nice

I have a quick question. Ok, of all the research ive been doing on omni drive systems i like the holonomic the best ... but since 2002 FIRST has only given 2 matching motors ... How can you accompish a true holonimic drive with only 2 matching motors ... oh yeah and i hate the 4 wheeled holonmic drive, it limits manuverability to fowards/backward and side to side

[greencactus3]

Originally Posted by troy_573

I have a quick question. Ok, of all the research ive been doing on omni drive systems i like the holonomic the best ... but since 2002 FIRST has only given 2 matching motors ... How can you accompish a true holonimic drive with only 2 matching motors ... oh yeah and i hate the 4 wheeled holonmic drive, it limits manuverability to fowards/backward and side to side

with only 2 motor i dont know but it can definitly go in front/back and right/left and anything inbetween.... just dont know how to turn tho. with simply two omnis in 90degrees apart. and 4wheeled omni drive is true holonomic. which means it can go front back right left anywhere inbetween and rotate similtaniously.

[George1902]

Originally Posted by troy_573

I have a quick question. Ok, of all the research ive been doing on omni drive systems i like the holonomic the best ... but since 2002 FIRST has only given 2 matching motors ... How can you accompish a true holonimic drive with only 2 matching motors ... oh yeah and i hate the 4 wheeled holonmic drive, it limits manuverability to fowards/backward and side to side

All you're concerned with is that the output speeds match eachother. This can be done with gear ratios to get them close to the same speed and shaft encoders to take care of minor variations. It's very similar to the way teams use shaft encoders to make sure their tank-style drivetrain goes straight.

"Limited maneuverability" isn't in the vocab of a holonomic drivetrain. Both our and SPAM's 'bots were of the 4-wheeled variety last year and they sacraficed nothing in terms of maneuverability.

Take a look at Evette and SAM if you'd like.

[ajlapp]

before the 2002 season we built our prototype kiwi drive with two drills and one fisher price motor. as with any other motor matching we geared the fisher price to meet the drills free speeds. we had never recieved three matched motors before but were determined to use our kiwi drive and controls. when the kit arrived and we had three matched drills we were psyched........but our prototype worked awesome even with one odd man out.

because of the nature of the kiwi drive the slight differences in motor matching didn't affect performance, you're constantly using all three mtors and wheels and it just buzzes along. we've never used it again, but neither has anyone else. it's a really great drivetrain....we've built all kinds and the kiwi is still my favorite.

[SpaceOsc]

Originally Posted by ajlapp

before the 2002 season we built our prototype kiwi drive with two drills and one fisher price motor. as with any other motor matching we geared the fisher price to meet the drills free speeds. we had never recieved three matched motors before but were determined to use our kiwi drive and controls. when the kit arrived and we had three matched drills we were psyched........but our prototype worked awesome even with one odd man out.

because of the nature of the kiwi drive the slight differences in motor matching didn't affect performance, you're constantly using all three mtors and wheels and it just buzzes along. we've never used it again, but neither has anyone else. it's a really great drivetrain....we've built all kinds and the kiwi is still my favorite.

is the kiwi drive defined by the fact it has three omni wheels? does that seperate it from other omni drives? lets say using 4 to 6 omni wheels. or is it something else that makes it kiwi

[Elgin Clock]

Hmm.. even I too am victim of misreading thread titles.

I thought this was a thread about potential guests during the Championship event of the Omni hotel in Atlanta.

Oh well...

Carry on.

[EricS-Team180]

Originally Posted by troy_573

... oh yeah and i hate the 4 wheeled holonmic drive, it limits manuverability to fowards/backward and side to side

Let me add this little experiment to George's comments:

Start with omni wheels that have the rollers in the plane of the wheel.

Build a rectangular chassis with a pair of omnis "front and back" - aligned with the chassis's latitudinal axis - and a pair "side to side" - aligned with the logintudinal axis. (we created a prototype with a piece of plywood and 4 rechargable Ryobi drills ... with a little creative soldering to wire the speed controller outputs to the battery contacts)

Load the IFI default single stick code into the FRC

Rotate your chassis 45deg AND rotate your single joystick 45 deg.

Now try out the maneuverability of 4-wheel omni

OK, now, rotate the joy stick back, and do the rotation in software


Finally, add a second stick, that will superimpose rotation left or right on top of the translation stick output


Add a yaw rate sensor to detect drift (rotation) due to drivetrain irregularities and output additional "opposite rotation" for correction ... and viola!

That is the essence of what we used last year...
eric

[ajlapp]

is the kiwi drive defined by the fact it has three omni wheels? does that seperate it from other omni drives? lets say using 4 to 6 omni wheels. or is it something else that makes it kiwi

kiwi was a code word we used to refer to a killough drive base. the original killough base has three wheels 120 degrees apart. it is the simplest configuration for true holonomic function, at least in terms of quantity of motors and such.

though building a true killough is often considered too challenging, mainly due to programming complications, control can be solved in many novel and simple ways.....our solution in 2002 required no software whatsoever! i'd love to build another, only time will tell. perhaps in the meantime another team will attempt it......no one has fielded a true killough since ours in 2002.