pic: Jester Drive:Mecanum Wheel Drive Train

[EricH]

Originally Posted by Alex357

-Our wheels require a significantly less amount of parts

Keep the questions rolling...

How many parts did you need per wheel?


We only needed 30 parts per wheel total. 8 rollers, 8 shafts, 8 screws, hub, Lexan piece, 4 bushings in two sizes. This does not include the sprocket or its attachments.

[EricH]

Originally Posted by techtiger1

as the engineer from beach bots said think and have a back up plan before u get into doing this. Making these is extremely labor intensive and you have to make them from scratch I have seen prints for wheels like 357 and there a whole off season's worth of work as Alex stated.

I'm not an engineer, I'm a student. Thanks for the compliment.

Making the wheel we had at nationals (for display only) took about 2 years from initial concept through prototyping to the wheel. The first year: After seeing the ones used to remove containers from airplanes, my dad decided to try to make some. By the end of the summer, we had a set for the Robovation kit. We also had the programming to operate it. The second year: two experimental wheels were made, similar in design to the current ones. When we decided to try them this year and keep six wheels as a reserve, we had a set made. However, when we tested that set, we found that it did not have enough traction, and we could not get another set of rollers designed and built in time to test them before ship, so we went with six wheel drive. We had the textured rollers made before ship day, but have not tested to find out which roller tread is best. More testing to come at a later date.

One set of wheels can be made in about 3 days, from part production to assembly to mounting on a robot.

[Alex357]

Originally Posted by EricH

How many parts did you need per wheel?

i'd like to see a picture of what you've done. Have you driven with it or anything yet? no bearings? how are you're rollers attached to the hub? is that even more parts? did you mold any parts inside the rollers? are these mecanum wheels or omni/grenade wheels?

[ConKbot of Doom]

When I first saw 357 strafe, I was driving in a match in Philly, and I don't know if they were on our alliance or the other, but I was amazed. Especially since how it worked wasn't immediately visible. I had a look later, and loved what I saw. Very nice job guys.

As for control's why not go for a keyboard and a joystick? make the keyboard be WASD, for strafing and forwards/backwards, and joystick for turning. A mouse would be even cooler, but a bit harder to implement. Would be neat to see...
I mean it works for First person shooter's, why not a robot

[BrianBSL]

Originally Posted by ConKbot of Doom

When I first saw 357 strafe, I was driving in a match in Philly, and I don't know if they were on our alliance or the other, but I was amazed. Especially since how it worked wasn't immediately visible. I had a look later, and loved what I saw. Very nice job guys.

As for control's why not go for a keyboard and a joystick? make the keyboard be WASD, for strafing and forwards/backwards, and joystick for turning. A mouse would be even cooler, but a bit harder to implement. Would be neat to see...
I mean it works for First person shooter's, why not a robot

A keyboard limits you a lot - allowing you to only move in 4 directions rather than an infinite amount that the joystick allows you. A mouse doesn't really give you anything that a joystick doesn't, and you have to worry about running out of room on the mousing surface. We (190) use a joystick for the direction vector (relative to the driver) and a 2nd joystick for rotating counter clockwise or clockwise. We're probably going to set it up with a single 3 axis joystick to make it more intuitive, however. The second joystick also has the issue with more experienced drivers, when they start driving it tank-drive style.

[Alex357]

Originally Posted by BrianBSL

A keyboard limits you a lot - allowing you to only move in 4 directions rather than an infinite amount that the joystick allows you. A mouse doesn't really give you anything that a joystick doesn't, and you have to worry about running out of room on the mousing surface. We (190) use a joystick for the direction vector (relative to the driver) and a 2nd joystick for rotating counter clockwise or clockwise. We're probably going to set it up with a single 3 axis joystick to make it more intuitive, however. The second joystick also has the issue with more experienced drivers, when they start driving it tank-drive style.

The three axis joystick is definately what we have been looking at, but there's one problem with it - it's designed to be used from vehicle persepctive. Even in talking with Airtrax, they use the joystick for their drivers, and they said that doing it without having that first-person perspective would be difficult. so if we do, indeed give it a try, i suspect we'll be training with the joystick for a few months.
as for our current controls, we only use a single joystick.
normal: front, back and spin
trigger: direct motion in the direction the joystick is pointing
-it's actually a lot easier than dealing with two joysticks

[Andrew Rudolph]

We use 2 joysticks on 1083 with our omni wheeld holonomic bot. Its really easy to drive, much like what 190 does.

[i_am_Doug]

Originally Posted by MrToast

Ditto!

Dave

double DITTO!

[Alex357]

Originally Posted by Andrew Rudolph

We use 2 joysticks on 1083 with our omni wheeld holonomic bot. Its really easy to drive, much like what 190 does.

Controlling an omni wheel is much different than controlling a mecanum wheel. Since the rollers are perpendicular on omni-wheels, the direction produced has almost no similarities with controlling mecanum wheel motion, which depends on the rotation and speed of each individual wheel.

[BrianBSL]

Originally Posted by Alex357

Controlling an omni wheel is much different than controlling a mecanum wheel. Since the rollers are perpendicular on omni-wheels, the direction produced has almost no similarities with controlling mecanum wheel motion, which depends on the rotation and speed of each individual wheel.

Omni wheels all 45 degrees apart from each other produce exactly the same effect the mecanum wheels do, and you can control the robot exactly the same way. This is how we prototyped the code for our field relative drive and found that we needed to have the split in the chassis to have equal wheel pressure.

[Tytus Gerrish]

the control system that i came up with for mechanums was to have 2 joysticks pitched on 45's with open loop programing. you could have a noormal tank drive hangling with the abilty still to go left and right. however your driver would have to be realy $@#$@#$@#$@# good. Of course i came up with this because im complletely useless with programing things of any nature except in legos.

[Andrew Rudolph]

Originally Posted by Alex357

Controlling an omni wheel is much different than controlling a mecanum wheel. Since the rollers are perpendicular on omni-wheels, the direction produced has almost no similarities with controlling mecanum wheel motion, which depends on the rotation and speed of each individual wheel.

As BrianBSL said, its exactly the same. Mechanum wheels have rollers at 45 degree angles, for the omni holonomic drove you put the entire wheel at 45 degrees. There are slight differences but its still the same.

Originally Posted by BrianBSD

This is how we prototyped the code for our field relative drive and found that we needed to have the split in the chassis to have equal wheel pressure.

We shimed our wheels so that all the wheels are touchign at the same time. Also we have encoders on everywheel to track how fast each wheel goes. We had a suspension of sorts on our mini bot we prototyped on last year and found it wasnt super important since the field is relatively flat.

[Alex357]

You're completely right... I thought he was referring to omni wheels set in the same frame as our mecanum wheels. In fact, we were encouraged early on to try using the 45 degree omni-wheel set-up because of the complexities of the mecanum drive system. However, there is a disadvantage in the 45 degree omni-wheel drive train when it comes to driving over obstacles. Correct me if I'm wrong, but I think the set-up also has a harder time adapting to different surfaces.

Sorry for the lack of posts lately. I'll be answering questions more quickly more often.

[John Gutmann]

it looks like the wheels are set up so they are just easier to turn, ie less resistance for more maneuvarbility

[EricH]

Originally Posted by Alex357

i'd like to see a picture of what you've done. Have you driven with it or anything yet? no bearings? how are you're rollers attached to the hub? is that even more parts? did you mold any parts inside the rollers? are these mecanum wheels or omni/grenade wheels?

Sorry I took so long to respond, but here are the answers.

Have you driven with it? I only drove the EDUbot prototype. Others have driven the real thing.

No bearings? Two bushings pressed together (one was smaller than the other) formed the bearing on each side of the wheel. Nylon is slippery enough that the rollers didn't need bearings.

How are your rollers attached to the hub? The hub looks something like two thin Skyways with a connecting bar between the hubs. The rims have holes in them to hold steel axles, which are kept from falling out by a piece of lexan screwed to the outside.

Is that even more parts? No. The roller axles were labeled as shafts in the parts list.

Did you mold any parts inside the rollers? Nothing in the wheel was molded. It was all formed using SLS (a laser drawing patterns in powder). There are no parts inside the rollers.

Are these mecanum wheels or omni/grenade wheels? Mecanum, something like what some airlines use to unload containers from airplanes.

The only picture I have is of the side of the hub, nothing else was attached.