Drive train wheels idea

[M. Mellott]

Omnis on all four corners make things difficult--more difficult to control, and lack of ability to resist being pushed or turned.

Perhaps you could put omni/trick wheels only on either the front pair or back pair of wheels and remove the 1/8" center drop. This maintains all 6 powered wheels on the ground at all times, removing the minor rocking due to the drop center, but it increases the manueverability without loosing contol. Teams 48 and 3193 did this with great success this year, using custom 4" treaded wheels (modeled after the AM peformance wheel) with 4" omnis up front. The robot was very maneuverable, very stable, and had no issues being pushed/turned.

Two notes: we made the custom treaded wheels 1.5" wide instead of the standard 1", and we located our main mast/arm at the center of the 4 traction wheels.

[Lil' Lavery]

Factors that I'm surprised haven't been mentioned yet:

Motor selection
Gear ratios
Tread selection
Wheel placement

[Micah Chetrit]

Originally Posted by Lil' Lavery

Factors that I'm surprised haven't been mentioned yet:

...
Tread selection
...

Which have teams had better success with (From andymark) as far as traction wheels go? Rough top or Wedge?

[Jeffy]

Originally Posted by Micah Chetrit

Which have teams had better success with (From andymark) as far as traction wheels go? Rough top or Wedge?

Here: http://www.andymark.com/product-p/am-0014.htm
it states that roughtop has slightly higher CoF. As far as tread wear goes, hopefuly someone with more experience with both treads can chime in.

[,4lex S.]

Tip of the day: Do not waste your time trying to improve drivetrain performance when the kitbot is so good!

My team ran a 6WD Kitbot with 4" Plaction Wheels and Supershifters from Andymark. It was the most reliable and effective drivetrain I have ever been involved with. If you preped the parts prior to build season, it literally takes a couple hours to put together and build (lead times for parts were the only reason we were just driving in week 2). I have seen lighter drivetrains, but the weight we had on it was only 2" off the ground, dropping CG of the robot.

Focusing on the mechanisms that get you points will make you more competitive than building what is essentially the kitbot, but lighter. Engineering is all about picking the most efficient areas to make gains.

[PAR_WIG1350]

Originally Posted by ,4lex S.

Tip of the day: Do not waste your time trying to improve drivetrain performance when the kitbot is so good!

My team ran a 6WD Kitbot with 4" Plaction Wheels and Supershifters from Andymark. It was the most reliable and effective drivetrain I have ever been involved with. If you preped the parts prior to build season, it literally takes a couple hours to put together and build (lead times for parts were the only reason we were just driving in week 2). I have seen lighter drivetrains, but the weight we had on it was only 2" off the ground, dropping CG of the robot.

Focusing on the mechanisms that get you points will make you more competitive than building what is essentially the kitbot, but lighter. Engineering is all about picking the most efficient areas to make gains.

The kitbot this past year wasn't as good as it has been from 2010 back to when andymark started providing it. They stopped including toughboxes in favor of the lighter, cheaper CIMpleboxes, which is fine, but they still gave teams 8" wheels. The since there is less torque due to less reduction, the 8" wheels required the motors to work harder and at a less desirable point on the performance curve. This can cause power failures, especially during turns, since the voltage drops far enough for some parts of the system to brown out or otherwise lose power.

My tip of the day: match you wheels to your transmissions and regardless of whether or not you use the kitbot and/or its frame.

[Lil' Lavery]

Originally Posted by Micah Chetrit

Which have teams had better success with (From andymark) as far as traction wheels go? Rough top or Wedge?

I generally prefer roughtop to wedgetop for carpet driving, and haven't really giving much effort into determining whether or not that would change if we were driving on another surface (such as different carpet, aluminum, polycarbonate, PVC, or HDPE). Keep in mind that there are also alternative tread materials, in addition to the roughtop vs. wedgetop distinctions.

McMaster has numerous options. So do other places (Brecoflex, Gates, etc).

[slijin]

Originally Posted by Jeffy

Here: http://www.andymark.com/product-p/am-0014.htm
it states that roughtop has slightly higher CoF. As far as tread wear goes, hopefuly someone with more experience with both treads can chime in.

Wedgetop tends to wear out much faster in my experience; on our 2010 bot, we had a 1/8" center drop, roughtop centers, wedgetop corners. Wedgetop tread had to be constantly replaced, about every 4-5 matches. The roughtop was placed in the center for traction; wedgetop on the corners to facilitate turning.

[Jeffy]

Originally Posted by slijin

Wedgetop tends to wear out much faster in my experience; on our 2010 bot, we had a 1/8" center drop, roughtop centers, wedgetop corners. Wedgetop tread had to be constantly replaced, about every 4-5 matches. The roughtop was placed in the center for traction; wedgetop on the corners to facilitate turning.

I don't think the problem discussed above has to do with the normal tread wear properties. It probably has to do with your weight distribution. I'm going to guess you have most of your weight on the center wheel and rocked quite a bit during the match. And with a 1/8" drop the wedgetop on the corners would most defintely be scrubbing. Especially because wedgetop is a tiny bit thicker than roughtop (making the effective drop even less).

Let me know if I'm right.

[Chris is me]

Originally Posted by Jeffy

I don't think the problem discussed above has to do with the normal tread wear properties.

Maybe, but I do know that wedgetop seems to wear faster than roughtop.

[PAR_WIG1350]

Wedgetop wheels have narrow, tall ridges which means less of the tread transmits the same force compared to roughtop. This seems to fit the anecdotal accounts of wedgetop wearing out faster.

If wheels were a dirt road, roughtop wheels would be a dirt road where the cars pass over all of the surface evenly resulting in even ware; Wedgetop, on the other hand, would be a road where cars only travel down the center resulting in ruts in the road.

[jspatz1]

Originally Posted by Hawiian Cadder

.....if you want to make a tunable robot, i would take a look ate 1986 team titanium's robot from this year, they used an 8 wheel tank drive, with omni wheels on the ends, and were amazing, because it still has 4 traction wheels, it doesnt turn too easy, but turns better than a standard tank drive.

you might try reducing your gear ratio some if you want to turn better, even just 5 percent will make all the difference in the world.

in summary;
if you want to use omni wheels on the ends, use 8 wheels total, 6 turns way to easy and its easy to get spun, and the plastic omni wheels are the best option as far as cheap, versitile, durrible, and lightweight.


Edit: here is a video showing 1986's drive train, if you want an drive with omni corners to learn from, theirs is very good.

http://www.youtube.com/watch?v=DdnYpgoClW4

Here's a much better view of our 8-wheel in action.
http://www.youtube.com/watch?v=WPD82b-y6dc