Different Drivetrains

[3072Cap]

It seems this year, most people went with either a 6wd/8wd pneumatic or tank treads to get around everything. Show off what your team did differently and why!

Team 3072 went with pneumatic tires in the center, with omnis on the corners in a 6wd configuration. We also used Bimba pistons and custom designed plates to give our omni wheels suspension. We can raise and lower the wheels to give us better angles at things, and to help with shooting. We decided that this would give our robot an advantage, considering how high the RW is, not getting stuck in the moat, and helping absorb impact when ramming into things.
https://i.imgur.com/wRrIXRwh.jpg

[M217]

This year, our team went with a pneumatic-tired swerve drive. It certainly presented a lot of engineering challenges to make, but it also offers us a lot of advantages in competition -- for example, the use of an omnidirectional drive allows us to easily align in front of the goal with vision tracking, and the pneumatic tires mean we don't sacrifice any traction or defense-crossing ability. It also opens up a lot of new possibilities for defending/avoiding defense.

https://www.youtube.com/watch?v=SZ9sYcAYBzo

Our team is very proud of how successful we were in pulling off such a unique drivetrain, and we hope to showcase more of its capabilities at champs tomorrow!

[emeraldstorm]

That's a rather interesting drivetrain.

Did your bot turn easily with the grippy wheels in the center? Did it move quickly? Did you have to worry about the omnis taking the force of hitting the obstacles?

I feel like I'm missing an obvious design cue with this. My first thought was "they should've put the pneumatic wheels on the ends and the omni in the center so it could absorb the hits while still being able to turn (with the raising and lowering of the front and rear)", then I wondered if rotation would still be feasible with the friction.

Still, very innovative design. I like it!

Answering the question, we went with the standard-ish AndyMark Rhino module treads. We're definitely making our own drivetrain next year.

[Tom Ore]

Just three wheels for us...

http://www.thebluealliance.com/team/525

[JR0405]

I don't have a picture but we have a total 6 wheels 2 six inch wheels in the front and 4 eight inch wheels in the middle and back so the 6 inch wheels don't touch anything until we go over a defense and then they make it easier to get over the defense.

[Arkive]

Just three wheels for us...

http://www.thebluealliance.com/team/525

What was the benefit of using only three wheels? It looks like a very interesting concept!

[emeraldstorm]

What was the benefit of using only three wheels? It looks like a very interesting concept!

It looks to be 3 pneumatic wheels, two bidirectional and one omnidirectional, similar to a swerve drive. I wonder how it would perform with two omnidirectional wheels on the front instead of one (eg. rectangle instead of triangle).

[Tom Ore]

What was the benefit of using only three wheels? It looks like a very interesting concept!

It crosses the defenses rather easily. We can mostly crawl over them - don't need to ram and fly over. The single wheel end is a swerve module - we use that to aim. When on the batter, we turn it sideways to use as a park brake. It will drive over one or two boulders easily (it will get stuck if we try to drive over three boulders.)

[C.Lesco]

Triwheels, since we wanted to do something different
https://www.thebluealliance.com/team/5870/2016

[EricH]

I don't have a picture, and I wish I did, but there was a team at Orange County with 4 wheels, looked to be about 10"-12" range. They weren't necessarily round, though... They were squishy and spongey--might have been some sort of filter in another use case. That team went after a driving defense, they'd go right over it. Can't remember the number.

[Darkseer54]

I don't have a picture, and I wish I did, but there was a team at Orange County with 4 wheels, looked to be about 10"-12" range. They weren't necessarily round, though... They were squishy and spongey--might have been some sort of filter in another use case. That team went after a driving defense, they'd go right over it. Can't remember the number.

By chance, do you mean 3953? If you do, they have a good picture of their wheels on TBA. (http://www.thebluealliance.com/team/3953/2016)

[EricH]

By chance, do you mean 3953? If you do, they have a good picture of their wheels on TBA. (http://www.thebluealliance.com/team/3953/2016)
That's them.

[juju_beans]

We had two 10" pneumatic wheels in the front, two 6" colsons in the middle, and two 8" omnis in the back. We originally had 6 10" pneumatic wheels then found that if the center wheel was smaller, it went over defenses much more easily, but with 4 3" wide pneumatic wheels it couldn't turn so we ended up putting omnis in the back and it goes over defenses wonderfully

[Everett33]

There was a team (5183) at Kettering #1 that had tracks off of a snowblower for their drivetrain.

https://www.flickr.com/photos/131241717@N05/25449685443/in/album-72157666413129205/

[3072Cap]

That's a rather interesting drivetrain.

Did your bot turn easily with the grippy wheels in the center? Did it move quickly? Did you have to worry about the omnis taking the force of hitting the obstacles?

I feel like I'm missing an obvious design cue with this. My first thought was "they should've put the pneumatic wheels on the ends and the omni in the center so it could absorb the hits while still being able to turn (with the raising and lowering of the front and rear)", then I wondered if rotation would still be feasible with the friction.

Still, very innovative design. I like it!

Answering the question, we went with the standard-ish AndyMark Rhino module treads. We're definitely making our own drivetrain next year.

It turns great, never had a single problem. Turning easily was actually one of the reasons we went with this design. Ex 1 (http://www.thebluealliance.com/match/2016vapor_qm4) Ex 2 (http://www.thebluealliance.com/match/2016vapor_qm59) Just a couple matches from Hampton Roads to showcase. (Our shooter was shut down due to bumper rules, or we would be doing more than breaching. :( )

This thing was actually pretty quick, way quicker than the mecanum drive we had last year.

We never had a problem other than one of the axles on the pneumatic wheels bent in Blacksburg. (Weird, huh?) That was probably the worst that happened. We had the pressure set wrong in Hampton Roads, so we were really bouncy and had to take it slow, but since we had the pistons taking most of the shock, they never had any problems. We inspected them after every match to make sure they weren't cracked or broken.

I really enjoyed the challenge, and it won us the Innovation in Control Award in Hampton. I think custom frames and drivetrains will be in our team for years now.

[GeeTwo]

It's not nearly as cool as a swerve, but we did not use pneumatic wheels, nor treads. We beefed up the usual 6WD to a 10WD, featuring three different wheels (2 2015 KoP wheels, 4 2010 KoP wheels, and 4 8" plaction wheels with pebbletop tread). They were staggered into four lines because they were too big to put ahead of each other. Here's a pic of the drive train before we installed any manipulators. (https://twitter.com/slidellrobotics/status/698593651497144320) The pebbletop does most of the work on the carpet and the slicks do a fair share of the work getting over the defenses.

[Steph342]

Not the best picture but here is what we did on Team 5508. It is 2 drive trains. One with treads and one with 4 wheel (2omnis and 2 traction). It worked good and only broke a tread once.

[ahartnet]

A pretty good picture of all our wheels + chain. It did pretty well for us, and I was amazed at how easy it was to turn the wheels by hand on an unpowered robot. Base team did a great job of chaining it. essentially 6WD, center drop, but each side had an additional 4 raised wheels to help with rockwall/moat/ramparts. We used the vex wheels in a 1.5" configuration so they couldn't get stuck in the rough terrain.

[emeraldstorm]

A pretty good picture of all our wheels + chain. It did pretty well for us, and I was amazed at how easy it was to turn the wheels by hand on an unpowered robot. Base team did a great job of chaining it. essentially 6WD, center drop, but each side had an additional 4 raised wheels to help with rockwall/moat/ramparts. We used the vex wheels in a 1.5" configuration so they couldn't get stuck in the rough terrain.

That paint job is sexy. 1x1 steel tubing I assume?

[ahartnet]

1x1 steel tubing I assume?

1x1x.125 aluminum tubing, welded, powder coated. We have a sponsor that can do welding for us so we were able to get by with 1/8" aluminum.

Also, this powder coated frame became our practice bot because we didn't come up with a rig for keeping axle holes aligned during the welding process =(. It was late in the season so we tried a fix by match drilling some plates and drilling out the axle holes on the inside runner for our practice bot (I'm surprised, but I can't find a good picture of it). Since it worked, we spray painted our frame originally intended as a practice bot frame and implemented the fix on the powdercoated frame during/after bag and tag. I liked to refer to our comp bot frame as the Ugly Duckling.

[emeraldstorm]

1x1x.125 aluminum tubing, welded, powder coated. We have a sponsor that can do welding for us so we were able to get by with 1/8" aluminum.

Also, this powder coated frame became our practice bot because we didn't come up with a rig for keeping axle holes aligned during the welding process =(. It was late in the season so we tried a fix by match drilling some plates and drilling out the axle holes on the inside runner for our practice bot (I'm surprised, but I can't find a good picture of it). Since it worked, we spray painted our frame originally intended as a practice bot frame and implemented the fix on the powdercoated frame during/after bag and tag. I liked to refer to our comp bot frame as the Ugly Duckling.

That stinks. Very few teams powdercoat their chassis, and it's a shame that yours couldn't be displayed in-comp. Performance over looks anyway, right?

It's a shame you guys couldn't make it to St. Louis, you've got a fine looking bot.

[Paul Richardson]

Did your bot turn easily with the grippy wheels in the center? Did it move quickly? Did you have to worry about the omnis taking the force of hitting the obstacles?

I feel like I'm missing an obvious design cue with this. My first thought was "they should've put the pneumatic wheels on the ends and the omni in the center so it could absorb the hits while still being able to turn (with the raising and lowering of the front and rear)", then I wondered if rotation would still be feasible with the friction.

When you think about turning scrub (the resistance to turning from friction), it helps to look at the path each wheel will take when the robot pivots, because this determines the friction force you'll see.

To start simple, imagine a Segway rotating in place about its center. If you traced the path of the wheels, they would draw a circle, right? If you looked at the wheels at any point along that circle, they would be pointing tangent to the curve. In other words, in order to follow the curve, the wheel just needs to roll forwards as the Segway rotates, and there is no sideways movement (which would cause friction). So you can see that the center wheels of a robot have almost no contribution to turning friction.

However, if you switch to a 4/6/8 wheel robot and imagine the circle traced by the corner wheels, you see that the wheels are not tangent to that curve. The corner wheels can't just roll along, they have to slide sideways, too. This is where nearly all turning resistance comes from.

[emeraldstorm]

When you think about turning scrub (the resistance to turning from friction), it helps to look at the path each wheel will take when the robot pivots, because this determines the friction force you'll see.

To start simple, imagine a Segway rotating in place about its center. If you traced the path of the wheels, they would draw a circle, right? If you looked at the wheels at any point along that circle, they would be pointing tangent to the curve. In other words, in order to follow the curve, the wheel just needs to roll forwards as the Segway rotates, and there is no sideways movement (which would cause friction). So you can see that the center wheels of a robot have almost no contribution to turning friction.

However, if you switch to a 4/6/8 wheel robot and imagine the circle traced by the corner wheels, you see that the wheels are not tangent to that curve. The corner wheels can't just roll along, they have to slide sideways, too. This is where nearly all turning resistance comes from.

That's some interesting information. On my way to redesigning my concept drivetrain due to this; Thank you! (is it ok to mention that I repped?)

[Thayer McCollum]

We built a pretty interesting drive-train this year, it was a 8 wheel, drop center, articulated tank drive. The articulation was what made it really interesting. One side of the drive-train (4 wheels-2 CIMs) was solidly fixed to the frame, but the other side was on a pivot underneath the frame. This meant that the sides of our drive-train could be in different planes at the same time. This was really effective at getting over the ramparts specifically because we could drive right up the middle and have both sides of our drive-train flat against both slopes of the ramparts.

https://www.thebluealliance.com/match/2016code_qm3

You can see in this video our robot really bounced back and forth, this was because it would rock on the pivot point due to it not being perfectly balanced.

[happyWobot]

We went with a 35" long x 24" wide perimeter with 4 wheels, 12.5 inch pneumatic configured with #35 chain and two AM Tougbox Minis at 12.75:1 with all wheels dead axle and using Tank Drive as the logic. Wheelbase was about 20 inches axle to axle with a 7 inch separation between tires. This might seem fairly straightforward but here is what we did different.

Chassis floor was 7 inches off the ground to mount the wheel axle below the chassis and bumper was 6 inches off the ground to clear the rock wall. However, while crossing most defenses was silly easy, turning was a problem with significant shudder. The wheels were plastic frame and would bend on turning while the tire shell had knobbies with a lot of grip. The wheel frames would bend so much in a turn that significant energy would get released when the tire knobbies released from the carpet causing the bot to literally bounce several inches off the floor on carpet.

So we tried something different, we dropped the front left and back right wheels 1/8 inch simulating a drop wheel config but on the diagonal. This was highly effective in taking a lot of the shudder out. The diagonal list was barely noticeable and proved not an issue in driving straight. But since the wheels were pneumatic and flexed enough to still maintain some contact with all 4 wheels, the bot still shuddered some, just not violently anymore. We found a slick black duct tape and covered the rear wheels to permit them to drift. Turning was no longer a problem and the config was ridiculously effective at crossing defenses permitting us to avoid the Evel Knievel breaching method.

The diagonal wheel drop and tape cover worked remarkably well even on wheels that have a lot of surface contact due to their diameter and any rocking action was practically unnoticeable. I spent significant time trying to find some reference to someone else having done it before to see if there was any insight on the best wheelbase separation and drop height. Could find no evidence that it had been tried before. I joked a couple times that we should call it the East Coast drive.