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Unread 19-03-2008, 12:57
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Billfred Billfred is offline
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Re: how does one go about making a 6 wheel config drivetrain?

Quote:
Originally Posted by jax1488 View Post
and im assuming the con factor is the extreme weight added on by all that chain?

also if using the 6 wheels on the same level configuration, wouldnt one have problems with traction, as well as weight if used omni wheels? if its a defensive game i.e. 06, wouldnt u get pushed around a lot?
Weight's never been an issue for us--neither of 1618's 6WDs have really broken 100 pounds. This year's robot weighed in around 78 pounds at Chesapeake, minus the forks we'd removed. That's all with #35 chain, and last year's robot was bolted together. A judicious application of #25 chain (or, if you're 125 this year, belts) and rivets could drive that down further.

Omniwheels don't have to weigh much either--compare the without-bearings weight of the 2007 kit wheel (0.75 pounds) and the AndyMark 6" plastic omniwheel (0.75 pounds).

I know there have been teams that have had defensive-oriented robots with omnis on the corners--488 last year comes to mind--but I'll yield to them since we've always run traction wheels in our 6WDs.

Quote:
Originally Posted by jax1488
say a robot is to come and push against a corner, wouldnt you spin and not be able to push back, if u have omni wheels for front and back?

and for the 1/8th lowered, why would u only want 4 wheels on the floor at the same time? i wouldnt think that the weight added would be worth the extra 2 wheels if u dont use them. you lose traction for the wheels that arent on the ground, say someone bumps into u around that area, you would spin

im not bashing 6wd, im trying to find out pros and cons
I'm still yielding on the omnis-on-corner discussion, but I'll bite on the other.

We actually use all six wheels on our 6WD, just not at the same time. Consider a robot that didn't have the front two wheels, with the other two left where they are. If you stop, the parts of the robot still doing 14 fps are going to want the robot to tip forward. Without those wheels, we're digging into the ground or rolling on some type of caster that affects how we turn (read: easily). The added weight is a non-zero amount--probably about a pound and a quarter or a pound and a half per side for us--but it's worth it in our determination.

As for traction, you're not really losing any. Granted, that particular wheel has zero traction with the floor if it's raised, but your four wheels in contact with the ground make up for it well enough to make up for it in most situations. Also consider that their front probably takes enough room to hit the middle wheel as well--unless they clip a corner and clip it well, you're still probably not turning.

And, since 6WD can enable easier turning, you can readjust quickly.
__________________
William "Billfred" Leverette - Gamecock/Jessica Boucher victim/Marketing & Sales Specialist at AndyMark

2004-2006: FRC 1293 (D5 Robotics) - Student, Mentor, Coach
2007-2009: FRC 1618 (Capital Robotics) - Mentor, Coach
2009-2013: FRC 2815 (Los Pollos Locos) - Mentor, Coach - Palmetto '09, Peachtree '11, Palmetto '11, Palmetto '12
2010: FRC 1398 (Keenan Robo-Raiders) - Mentor - Palmetto '10
2014-2016: FRC 4901 (Garnet Squadron) - Co-Founder and Head Bot Coach - Orlando '14, SCRIW '16
2017-: FRC 5402 (Iron Kings) - Mentor

94 events (more than will fit in a ChiefDelphi signature), 14 seasons, over 61,000 miles, and still on a mission from Bob.

Rule #1: Do not die. Rule #2: Be respectful. Rule #3: Be safe. Rule #4: Follow the handbook.

Last edited by Billfred : 19-03-2008 at 13:10.