Chief Delphi - mecanum vs. omni

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- - mecanum vs. omni (http://www.chiefdelphi.com/forums/showthread.php?t=57282)

Re: mecanum vs. omni

Quote:

Originally Posted by JesseK (Post 626226)

If you prototype something on limited resources and then realise after the game is announced that your prototype concept has little chance of success in the game, then you have 2 choices: 1. Come up with a creative way to implement your prototype or 2. (more common) Adapt your prototype so that it fits into the current strategy, therefore introducing (sometimes) very complex integration issues or unforseen behaviors --

Don't forget choice 3: set aside the prototype as inappropriate to the task, and build something else that is more appropriate.

Re: mecanum vs. omni

Quote:

Originally Posted by JesseK (Post 626226)

I agree to an extent. If you prototype something on limited resources and then realise after the game is announced that your prototype concept has little chance of success in the game, then you have 2 choices: 1. Come up with a creative way to implement your prototype or 2. (more common) Adapt your prototype so that it fits into the current strategy, therefore introducing (sometimes) very complex integration issues or unforseen behaviors --

e.g. Adapting mecanum to play pure defense will really put some wear on the treads of the wheels -- enough wear to be of concern if you attend 2+ competitions with success.

Ok, so this argument probably holds little weight in the case of mecanums, as it's more likely you can adapt your strategy to use mecanums with some sucess every year. However, if you're like most teams, you'd rather adapt your robot to your chosen strategy and not vice versa. This is also good engineering practice, whereas adapting your strategy to your robot is something that's good practice for learning how to find & fight problems (namely integration problems) after the fact.

I agree. Just because you prototype something does not mean that you have to use it. Look at 488, who made considerable noise with their Mecanum prototype this fall, then promptly decided to use their 6 Wheel Drive design again when build season started.

Re: mecanum vs. omni

I finished my prototype VEX mecanum wheel this weekend. It's definitely under $20, not VEX competition legal (we can always hope the spacers come in the kit right?), and currently far from perfect since I need to file more metal down and figure out roller spacing that's off by minute amounts.

I'll post a pic tonight when I get home and put a link here.

Re: mecanum vs. omni

Quote:

Originally Posted by JesseK (Post 626765)

We made some a few years ago. Admittedly, they aren't VEX legal or cheap or extremely strong. Dad was running some SLS tests at his work and slipped a few wheels in, one of our sponsors cut the rollers and pins to hold them. They worked for testing with Edubot and so should work with VEX if we ever wanted to try.

Re: mecanum vs. omni

I'll make a full robot to run it around, but it seems sturdy enough:

http://www.chiefdelphi.com/media/photos/28608

Re: mecanum vs. omni

The forces are the same for omnis and mecanums. The programming is exactly identical, as an omni setup and a mecanum setup with the wheels in the same spot in the corners would turn the motors on and off exactly the same amount of time, and the same outputs. The vectors of mecanums in the same spot are diagonal just like the omnis, and are 100% of the omni's diagonal forces.

Theoretically, they're completely the same, just with different motor/wheel angles and thus different mounting. But like is stated earlier, mecanums' 45 degree wheel/motor angle causes lateral force on the bearings, but can be more easily switched with normal wheels.

The rollers themselves hit the ground at the same angle, push in the same direction, and with the same force. They're both just as efficient, neither moves slower. They both push with 71% force forward/backward and left/right, and 100% at a 45 degree angle. You only use two of your motors diagonally though (mecanum or omni) so you go 41% faster fwd/back/sideways.

Because the forces are the same, the two have theoretically the same traction if they use the same roller material and size and wheel diameter and number of rollers and both have circular profiles and all of that.