Mount Middle Slide Wheel

[sasha831]

For teams considering a slide/H-drive, how were you planning on mounting the centre wheel?

[TankerRed101]

We were going to put a spring or something else as a shock so when it hits the ramp the wheel doesn't bust.

[Skyehawk]

Originally Posted by TankerRed101

We were going to put a spring or something else as a shock so when it hits the ramp the wheel doesn't bust.

This is indeed a very good point, what about teams considering kiwi drive? There will be some similarities w/ the problems of slide like you mentioned.

[Mike Marandola]

Originally Posted by Skyehawk

This is indeed a very good point, what about teams considering kiwi drive? There will be some similarities w/ the problems of slide like you mentioned.

I don't know how well you'll be able to go over the ramp with kiwi in the first place.

[ratdude747]

Originally Posted by Mike Marandola

I don't know how well you'll be able to go over the ramp with kiwi in the first place.

Easy. Just drive up (a little momentum might help). I do know 1501 ran a small wheeled kiwi drive in 2010 and was able to get up the ramp to the goal... sure they couldn't do the bumps, but that was 45 degrees and much higher than the 16 degree 2" scoring platforms we're talking.

I think people seem to underestimate the ability of rollered wheels (omni and mecanum) to go up ramps and the like... if anything in the "slow" modes act like a gear reduction, similar to how pulleys work (trading speed for transitional force). Sure, wheel contact is an issue... but on a kiwi, unless you bottom out and drag the frame (could happen with lower ride heights), being a 3 point system, all 3 wheels will always be in contact with something.

This is an old argument... people said the same about mecanums in 2010 and 2012 (Bumps and bridges respectively)... and I saw examples of such drives work pretty much flawlessly both years. If you design the drive right, mecanums are plenty capable of ramp handling.

[GeeTwo]

We're modifying a KOP drive chassis to H-drive, using a spacer instead of the center wheel. We were thinking about just using a couple of angle aluminum brackets to hard-mount another copy of the same gearbox 1/8" higher than the built-in gearboxes. We aren't planning to drive up the ramp, but makes me realize we either need to provide suspension to let it happen, or provide some safeties so that we don't slam the wheel into the platform.

[dradoxen]

Correct me if I'm wrong, but if you were to move your center wheels to be in between your other two sets at 90 degrees, you would not need a suspension.

This design does require extra weight, with an extra gearbox, wheel, and support, because you need a center wheel on both ends of the robot but as a team with less build capabilities we found it to be easier to implement than a suspension.

Am I missing anything with this?

[Jarren Harkema]

Originally Posted by dradoxen

Correct me if I'm wrong, but if you were to move your center wheels to be in between your other two sets at 90 degrees, you would not need a suspension.

This design does require extra weight, with an extra gearbox, wheel, and support, because you need a center wheel on both ends of the robot but as a team with less build capabilities we found it to be easier to implement than a suspension.

Am I missing anything with this?

This was our thinking. Though we are concerned with all 3 wheels being in contact with the ground at all times. So perhaps still having a passive system that provides some force downward on the slide wheels, but has enough travel to be compressed if need be over the platform? We still need to figure out how to mount these the kit chassis. If anyone has any ideas it would be appreciated.

[jeremylee]

We are going to try putting our strafe omni in line with our front drive omnis. This should work well when holding totes as most weight is on the front. Without totes, we will use a gyro and compensate for turn by diff steering the outer wheels a little. Might not be perfect, will see how it works.

For mounting, I'm thinking we purchase another inner rail to bolt in place and mount gearbox to with live hex and a bearing in the front rail. Probably need to drill out a wheel bolt hole to a hex bearing as we won't want any drop.

[Arpan]

3061 is using a 'fork' style suspension where the gearbox drives one of two wheels into the ground. We like it because unlike spring systems it does not take weight off of our drive wheels when the strafing wheel is unpowered.

[RonnieS]

It is not necessary to have the strafe wheel on a suspension. That being said, make sure you have a very good way to drive around the field and not hang up. We have gotten away without one so it eliminates complexity.
-Ronnie

[Joseph Smith]

Originally Posted by Arpan

3061 is using a 'fork' style suspension where the gearbox drives one of two wheels into the ground. We like it because unlike spring systems it does not take weight off of our drive wheels when the strafing wheel is unpowered.

Sounds like what 148 did in 2014. https://www.youtube.com/watch?v=oRwvQ2D_B-c
very cool design, my biggest concern would be keeping the strafe straight with only a single strafe wheel contacting the ground.

[GeeTwo]

Originally Posted by jeremylee

We are going to try putting our strafe omni in line with our front drive omnis. This should work well when holding totes as most weight is on the front. Without totes, we will use a gyro and compensate for turn by diff steering the outer wheels a little. Might not be perfect, will see how it works.

For mounting, I'm thinking we purchase another inner rail to bolt in place and mount gearbox to with live hex and a bearing in the front rail. Probably need to drill out a wheel bolt hole to a hex bearing as we won't want any drop.

Unless you're about to tip over, this will always introduce a torque so that the front will turn in the direction of the strafe. You can correct, but it's better to have a system that almost works without the feedback loop than one which is uncontrollable without it. The COG is the best place - the question is, with how much load to you optimize? We're looking to mount our strafe wheel onto a piece of aluminum angle or two which bolt to the holes on the top and bottom of the side rails (we're using the KOP chassis). Then, we can adjust this placement relatively easily when we find the COG. This could still be used with sprung suspensions.

[jeremylee]

Originally Posted by GeeTwo

Unless you're about to tip over, this will always introduce a torque so that the front will turn in the direction of the strafe. You can correct, but it's better to have a system that almost works without the feedback loop than one which is uncontrollable without it. The COG is the best place - the question is, with how much load to you optimize? We're looking to mount our strafe wheel onto a piece of aluminum angle or two which bolt to the holes on the top and bottom of the side rails (we're using the KOP chassis). Then, we can adjust this placement relatively easily when we find the COG. This could still be used with sprung suspensions.

Agree it's not ideal, but we want to cross the scoring platform without getting hung up and wothout the complexity of a raiseable wheel. If it becomes a problem even with a gyro, we may add another omni on the other side.

[XaulZan11]

Originally Posted by ratdude747

Easy. Just drive up (a little momentum might help). I do know 1501 ran a small wheeled kiwi drive in 2010 and was able to get up the ramp to the goal... sure they couldn't do the bumps, but that was 45 degrees and much higher than the 16 degree 2" scoring platforms we're talking.

Just as another data point, here is a kiwi drive attempting to drive up a non-carpeted incline: http://www.thebluealliance.com/match/2007il_qm37