First off, There is alot of past discussion on this and similar topics. Even So..
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Originally Posted by Rangel(kf7fdb)
Team 842 has been thinking of future drive trains recently and here are some of our ideas.
One design is a 6 wheel drive consisting of 2 super shifters in the center of our robot belted up to omnis in the front and back and a center traction wheel. We are also considering replacing the omnis with the same traction wheels used in the center. What are the advantages and disadvantages of doing this?
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6WD: Probably the most commonly used drivetrain (excluding some years with terrain.) This drivetrain is generally liked because it strikes a good balence between everything you want in a drivetrain and is easy to build.
Omnis on the front and back lead to really nice turning. There also is no rock in the chassis because the middle wheel does not need to be lowered. However, most people use all traction wheels. When all the wheels have traction, however, the middle wheels have to be dropped about 1/8". This shortens your wheels base (only four wheels are touching at a time) and allows turning while still being able to hold your own in a pushing match. If well built, a all traction wheel drive can be made to turn just as well or better than its omni counterpart. However, be warned if you're using the KoP chassis or another semi-flexable chassis you need to watch out for the opposite outer wheels bending down and scrubbing the ground. This is more of a problem when going fast (like Overdrive 2008) but can still make turning a bit of a chore at lower speeds too if your chassis is to flexable.
Quote:
Originally Posted by Rangel(kf7fdb)
8WD
Our 8 wheel drive train idea is entirely based off team 67's drive train. From what I have seen this past year, this drive train seemed to dominate all others. What makes this such a good drive train?
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8wd: This functions similarly to the all traction 6wd above with the 4 inner wheels lowered. It has a shorter wheel base then the above (1/3 the wheel base of a 4wd as opposed to 1/2 the wheel base with the 6wd) and a central axis of turning. It's much more stable because it doesn't rock back and forth like a 6wd. It is also much better at climbing (making it the choice of many top notch teams in 2010). However, the advantages come at a price. It is both heaver and more complex.
As to 67 having a dominate drivetrain. I wouldn't say that. 67 has built a completly different chassis for every year they have been with FIRST; their drivetrain was good, but not the best. The reason they look dominate is.. well, they are! They have AMAZING drivers! This is the result lots and lots of practice and drills with their practice robot. Team 67 would be awesome even if they were driving a tin can!
If you need an example of a really well thought out drivetrain that has been boiled down to (imo) near perfection, look up team 254. They have a set chassis design they make better every year. (and they've been at it for a long time)
Quote:
Originally Posted by Rangel(kf7fdb)
A few questions we have are what are the pros and cons of both of these drive trains and which one would be faster and which one would have more traction. I mean this on flat carpet by the way. I also have one other question, why is it that some wheels get lower? Is it only because there was a bump in last years game? One more question, what are the advantages of using the different size wheels in the 8 wheel drive train idea. If you have any ideas on how to improve these drive trains it would be greatly appreciated.
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Answering the questions above:
Outer Wheels are raised to prevent the outer wheels from rubbing on the carpet making turning difficult for the robot. Speed is relative, as are torque and acceleration. No wheel base is inhearently faster than any other; it's motor dependent. Different sizes of wheels have some various pros and cons. Larger wheels go faster than smaller wheels with the same gear ratios. However, smaller wheels are theoretically more efficent. Larger wheels don't where out as fast as smaller wheels. An 8" wheel wears half as fast as a 4" wheel. However, smaller wheels are lighter in weight. There is endless tradeoffs, one is not a naturally better choice than the other. Again, go look at 254's drivetrain.
Good Luck, Bryan