6/8 Wheel Extra Features

[JamesCH95]

Originally Posted by MICHAELABICK

My guess is that because they were using 2 in thich wheels, they had an amount of turning scrub that they didn't like. By increasing the drop, they decreased that amount.

If only two axles are touching the ground, how does lifting the remaining axle further off of the ground help?

I'd bet it's more of a wheel wear concern.

[PAR_WIG1350]

Originally Posted by JamesCH95

If only two axles are touching the ground, how does lifting the remaining axle further off of the ground help?

I'd bet it's more of a wheel wear concern.

Sometimes, the drop is slight enough that the center wheels can sink in the carpet a bit and the wheels which are "off the ground" will make slight contact which can degrade performance slightly.

[IanW]

Originally Posted by PAR_WIG1350

Sometimes, the drop is slight enough that the center wheels can sink in the carpet a bit and the wheels which are "off the ground" will make slight contact which can degrade performance slightly.

We actually ran into this problem this year. We designed a .125" drop into our 6WD drivetrain, but found that we didn't like the turning once we actually got it running. Swapped out a pair of plactions for a pair of omnis on our competition and practice bots and it worked much better.
I'm not sure what exactly caused it to behave so poorly turning. My guesses were either the drop was insufficient and the wheels still scrubbed because the robot sunk into the carpet, or our chassis flexed, allowing all 6 wheels to contact the ground.

[JamesCH95]

I'd buy the chassis flex argument, or maybe if the target 1/8" drop was not reached for whatever reason. We've never had any issues using a 1/8" drop with 1in wide plaction wheels in a 6wd setup over the past couple years.

In the past we've seen the center set of wheels (skyway wheels FWIW) wear down to the point of negating whatever drop they had, and that was an issue.

[jwfoss]

Originally Posted by MICHAELABICK

This year, we really like our 6 wheel drive. We wan't to improve it for next year, including increasing performance in general, and by maybe adding some extra features.

What I quoted above is one of the most important things a team can do. Setting a baseline, and improving from it each year.

On FRC2168, we did the same thing this year, and intend to improve again on it for next year.
Things we improved on from 2011-2012:
- Moved from a 6WD to a 8WD to gain some stability (and to go over the barrier)
- Designing for Center to Center distance between axles to have exact chain or belt length
- Designing the tensioners in as standoffs as well (A 1" nylon rod with an off center thru hole, rotate to add tension)
- We continue to use 1.5" wide Colson Performa wheels with a WCP hub and dead axles as we like the grip and the wear properties

Things we are looking to improve/add in the future:
- An Integrated braking system
- Belt Drive
- Reduce weight
- Increase efficiency (less gear reduction/better gearing selection)
- Attempt to decrease wheel diameter
- Improve packaging/modularity

About you question in wheel width, this topic has been discussed a number of times, with different answers. For us we have noticed that while our traction seems to be about the same, our tread seems to wear better with a wider contact patch. It's for this reason, and the amount of space they take up that we settled on using 1.5" wide wheels.

There are a ton of options out there in terms of wheel options, and even more for tread material. I strongly suggest exploring them.

[topgun]

Originally Posted by MICHAELABICK

Drop down casters
(I heard that 987 has done this previously. Correct/incorrect?)

• How effective is it at getting out of t-bone pins?

Drop Down Outer Wheels
(I heard that 469 has used this previously. Correct/incorrect?)

• Is the increased traction noticable
• Have you found that it imroves your offensive/defensive performance?

I am confused on this. Can someone explain why having drop down casters would help with defense? Also, what do Drop Down Outer Wheels provide? Some pictures would help if possible.

Thanks.

[Peter Matteson]

Originally Posted by topgun

I am confused on this. Can someone explain why having drop down casters would help with defense? Also, what do Drop Down Outer Wheels provide? Some pictures would help if possible.

Thanks.

It changes your center of rotation allows you to spin about 2 outer wheels rather than the middle wheels. This prevents you from getting t-boned by allowing you to spin out of it.

[thefro526]

Originally Posted by topgun

I am confused on this. Can someone explain why having drop down casters would help with defense? Also, what do Drop Down Outer Wheels provide? Some pictures would help if possible.

Thanks.

Traditional Skid Steer Drive trains are very susceptible to 'T-Bone'* pins. Because Most Skid Steers rotate around their center, or somewhere close to it, they cannot simply spin out of the pin - if you draw a simple sketch, you'll see that while you're rotating one end of your robot away from the defender, you're also rotating a side into the machine.

Dropping a caster/omni-wheel/skid on one end helps to move the pivot point of the drive to the opposite end, which allows the robot to simply spin out of the pin.

*T-Bone Pins usually refer to an instance where a robot is hit perpendicular to it's drive train's motion - these usually happen on open field, essentially pinning a robot without needing a wall/object.

[JesseK]

I'll make a plug for WCD ("West Coast Drive") here. The concept of the frame setup, wheel blocks, live axles, cantilevered wheels and tensionless chains all cobmine to make it a great, versatile drive setup. Our team will do this next year since we proof-of-concepted the first sliding block in March. It took 2 hours to make the block on a manual mill, but we feel confident we can get that time down.

WCD itself isn't the answer to everything related to drive train -- yet it is the one "baseline" drive train that allows for the most design adjustments (# of wheels, wheel diameters, wheel types, tread types, which gearbox, etc) in the least amount of time. Adding extra features (like a drop-down caster/omni) is very easy as well.

[Clayton Yocom]

Originally Posted by topgun

I am confused on this. Can someone explain why having drop down casters would help with defense? Also, what do Drop Down Outer Wheels provide? Some pictures would help if possible.

Thanks.

Watch this http://www.youtube.com/watch?v=mhtdk...e_gdata_player video of us (45) and 111. We play defense so they cannot deploy their minibot. Interestingly enough, the T-Bone pin is crazy effective, and because we were soo good at pushing last year, they just could not get out of it.