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Unread 04-12-2015, 11:07
Captain_Kirch Captain_Kirch is offline
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AKA: Aaron Kirch
FRC #1625 (Winnovation)
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Re: pic: 'I' drivetrain concept

This is going to be a long post, so I'm going to split it into sections here.

Semantics:
This by all means is a "H" drive. That term has already been coined and more people will know what you're talking about, so do yourself a favor call it an H drive. I would suggest reffering to this concept at the "KOP H-Drive" from now on.

Strategy:
Here's the meat and potatoes of my post. This concepts lends itself to a very unique driving strategy, one I'd like to demonstrate with hypotheticals then comment on.

-Assumptions.

For clarity sake we're going to assume the front of your robot is the top of the H and the center wheels are for side to side movement.

-Hypothetical 1 (Pushing robot in front of you)

On paper the omnis should work perfectly fine for this head on movement. The second you introduce an angle your wheels are losing efficiency. If you put this drivetrain against another head on, you'll lose the fight. That center plaction wheel won't help either, it will act as a brake if you put it down.

-Hypothetical 2 (pushing a robot on your side)

Let's put that plaction wheel to the test! A robot is driving past you and you're facing it head on. It gets on your side, you push it three feet off its path and it goes on its merry way.

-Hypothetical 3 (Front of opposing robot on your side)

That last one was a bit pessimistic, lets a assume your side is facing them. Thats where the pushing power is! You get in their way, put down that plaction wheel getting ready to push and they strafe around to the front of your bot. You're stuck there because you cant move against that plaction wheel. By the time you lift it to try again its already too late.

-Hypothetical 4 (Front of opposing robot contacting your side AND you get your wheel down quickly AND they don't strafe)

Ok ok, now for the ideal one. You have your side to an opponent, you make contact and throw down your wheel microseconds away from pushing. Let's assume your opponent doesn't try to strafe so its a straight pushing match.
Now stop and think, is your one plaction wheel powered by two cim motors going to win this? Is it going to make a dent (in efficiency not literally)? That other robot could be running twice as much power, three times at much! When was the last time you saw a drive system powered by only two cims? Even if that's what you were dealing with they will be using more wheels giving them more traction and more pushing power.

-Results
Your design is based off of that plaction wheel giving you extra traction, but it slows down a design that ultimately hinges upon speed and agility. Even if you get into pushing someone it wont be much power at all. Strong robots can afford to be slow and clunky because its tough to stop them, an H drive NEEDS to be fast and agile.

If you actually built one of these drivetrains for competitions, your drivers would stop using the plaction wheel and just switch to using the omni because the plaction wheel hinders you more than it helps.

Final Thoughts:

Its obvious you put a lot of effort into this design, and I'm betting youre a better designer for it. Just remember that not everything you make needs to completely reinvent the wheel so to speak.

A KOP H drive would be awesome, and you're awesome for coming up with it! I say ditch the plaction, put a faster gearbox in the middle, and take some time to really think "should the straif wheel be fixed or retractable like it is now?" Then publish the files, tell everyone how to make one and design on you crazy diamond!
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