09-12-2004 19:38

Tytus Gerrish

Re: pic: "Omni Grenade" Wheel

sweet, kinda looks like mecanum wheel rolers

09-12-2004 19:41

Max Lobovsky

Re: pic: "Omni Grenade" Wheel

Jesus, that's beautiful. I wish we had the time and resources to undertake a project like that. Are you planning on using them in a holonomic design for the coming season?

09-12-2004 19:42

Hinkel Y.

Re: pic: "Omni Grenade" Wheel

Looks awesome! Guess you guys made it using a CNC machine. What materials did you use for those wheels? Have you tested them out yet? If so, how's the traction on them?

[edit] Ooops didn't read the captions on the other pictures for material and how it's made*slams head on desk* [/edit]

09-12-2004 19:51

Arefin Bari

Re: pic: "Omni Grenade" Wheel

To answer your questions...

What Machine did they use for this project?

"Sam Elzarian, a Nw Horizons Governors School mentorship student with prototype omni wheel. He and I designed and produced this with the help of a few other NASA Langley technicians. The project involved rapid prototyping techniques, CAD, solid modeling, waterjet, stereo lithography, mold making, and a conventional mill and lathe."

What Materials did they use for this wheel?

"The rollers are soft urethane with a brass sleeve cast-in to serve as a bearing. The rollers can be made in ten minutes flat! The mold has a flexable rubber liner with the tread pattern on it's inside surface, this is peeled off the roller when the roller is solid. The wheel is strong, probably stronger than it needs to be. The frame is waterjetted 1/2 inch thick aluminum."

...And this is how it is put together

"The "half grenade" configuration allows the rollers to be very close to one another. Also helping this is that the roller mounts extend into the roller to lengthen the roller. Button head bolts were intended but not available. A keyway is currently the drive method to be used, although it would be easy to add sprocket mounting hole areas on the frame.
Sam was responsible for all machining and CAD for the waterjetting of the frame and all fixtures."


Posted by Dave... "Not a Team 122 project"

I would guess no.

To Dave and Sam, You guys did a Great job getting this project done.

09-12-2004 20:09

Rich Wong

Re: pic: "Omni Grenade" Wheel

WOW........ it's the BOMB!

(finally I got to said that.... hehe)

That is a WHOLE NEW level of FIRST engineering and innovation. Congrats!!

Question: Is there an advantage in rolling clockwise vs. counter clockwise?

09-12-2004 20:34

Kyle Love

Re: pic: "Omni Grenade" Wheel

I hope that thing isn't loaded!!!! ha That thing looks great!

09-12-2004 20:49

D.Fahringer

Re: pic: "Omni Grenade" Wheel

Quote:
Question: Is there an advantage in rolling clockwise vs. counter clockwise?

Yes, I think the wheel would climb up 2X4's and steps better with the roller big end leading...that is viewed from the side, looking at the roller in contact with the ground, the big end of the roller is to the left when the wheel is turning clockwise. That side is so beefy you couldn't hurt it!

It is amazing to me how much less work this would be to make than our previous omni wheels from 2001 to 2002. Those wheels were student machined except for the rollers and axles. This wheel could be totally machined, except for the waterjet work, by students and the rollers cast
using the mold, add some off the shelf bolts...done!


Quote:

"look kind of like mecanum wheels":

Aren't Mecanum omni wheels the ones with angled axles? Ours are inline with the wheel. Those Mecanum type omnis are cool too!

We can provide all details on this design if desired,

Thanks to all!!!

Dave Fahringer

09-12-2004 21:06

Arefin Bari

Re: pic: "Omni Grenade" Wheel

Here is a good picture of some mecanum wheels...

09-12-2004 22:25

JVN

Re: pic: "Omni Grenade" Wheel

Hmmm...
Everything I've heard makes me think these wheels are being mass produced.

Umm.. "Not a Team 122 project"
Interesting...

Dare I speculate? Will you be selling these?

-JV

09-12-2004 22:40

Max Lobovsky

Re: pic: "Omni Grenade" Wheel

I was wondering that, too. If the price is right, there is at least one team that is in the market.

09-12-2004 23:12

Tytus Gerrish

Re: pic: "Omni Grenade" Wheel

i ment those rolers look strikingly similiar to my mecanum wheel rolers shown attached,

Ps: this is also not a team 179 project this wheel's OD is 2" it's for my oun project

09-12-2004 23:13

D.Fahringer

Re: pic: "Omni Grenade" Wheel

John and Matt,


Ha Ha! Thats a good one! I would love to get the procedure out to make it possible, I don't know if it is possible to have NASA recieve Fabrication hours to produce the rollers and frames for FIRST teams use...as a kit or finished....

I could (I think) release the solid models of the mold, and the DXF files for the waterjetted frame...and instructions, then any team could make the mold for the rollers and get the frames made, I am not sure if I could.

Sam is making a Powerpoint of this project for the first of three presentations for his NASA mentorship. There is no shortage of pics documenting the construction of the Omni Grenade!

If left to me to decide...I would share it freely. I can find out about this subject and anyone with prior experience can respond with advice.



Dave

09-12-2004 23:26

Max Lobovsky

Re: pic: "Omni Grenade" Wheel

I know nothing about molding polyurethane. Can you give me some idea of whats involved in making the mold and molding the rollers? Are there companies that will do small runs of molded parts like these? Do any teams have the proper materials.

If I can figure out how to get a hold of some of these rollers, I'm pretty sure we can get some waterjetting services donated to us and this may be possible for my team.

09-12-2004 23:44

D.Fahringer

Re: pic: "Omni Grenade" Wheel

The casting is easy but you have to have the mold treated with a spray on release agent (like pam for plastic) every run so nothing sticks, you mix the resin and hardener in a dixie cup and pour it in the mold to the top of the brass sleeve then stop and pour the remainder into the syringe then after your helper has placed the top of the mold on place the syringe into one of the 2 holes on the top of the mold then squirt the urethane into the mold and the excess will pop out of the other hole....hold the mold still until it solidifies.
The rollers you see were made of urethane that had a VERY fast cure time...about 2.5 minutes! you would want to use a resin that is slower like 15 minutes. Do you want to see the mold?


DF

09-12-2004 23:54

Stu Bloom

Re: pic: "Omni Grenade" Wheel

I am definitely interested an any CAD files you have available. If you can "publish" them - and post to the white papers it would be greatly appreciated!

GREAT looking wheels!!

10-12-2004 09:37

D.Fahringer

Re: pic: "Omni Grenade" Wheel

Thanks, I will get the files together, and zip them up.

Here is the Mold and drill fixture used...the brass sleeve (not shown) fits on the center pins. The drill fixture assures a good hole location every time!
The holes were finished with a flat bottom before tapping. The 5/16-18 tap was modified to get thread all the way to the bottom. The bolts were faced on the ends and completely bottom out in the hole.

10-12-2004 19:54

artic_raven

Re: pic: "Omni Grenade" Wheel

looks like a good idea. but what will happen if you are forced into a pushing match? those wheels look like they will turn like no other but whats the coefficient of friction? turning isnt the only thing that you have to look out for.

10-12-2004 20:22

Cory

Re: pic: "Omni Grenade" Wheel

They aren't using them for a FIRST project. And rubber has a pretty high coefficient of friction... you're going to have a problem with durability though, more likely.

10-12-2004 20:55

Max Lobovsky

Re: pic: "Omni Grenade" Wheel

Its "soft polyurethane", not rubber, if I'm not mistaken. Soft or not, polyurethane definitley is not as good as some nice rubber treads. I wonder if a finer tread pattern, rubber coating, or a different material can be used to make the rollers.

11-12-2004 13:02

D.Fahringer

Re: pic: "Omni Grenade" Wheel

Two points well taken...Pushing vs steering: I would want to use omnis on the front and good pneumatic treaded tires on the rear, the steering input would for the most part revolve around the rear wheels. The other point about using rubber: I like the thought of being able to use real rubber. It would be neat to have little air-filled omni rollers with real rubber tread too, but we have to work with what we have, and soft urethane is workable, you have probably seen the clear pencil erasers... thats how soft a compound I would be wanting to use. When you push with the front of your robot most of the traction is at the rear wheels, when pushing with the rear at least you are getting reasonable traction out of your Omni wheels. Different tread patterns are possible of course, I had considered using the black rubbery adhesive they use to seal windshields in cars. I would coat the inside of the tread pattern part of the mold and let it set up then assemble the mold and inject a harder urethane to make a soft reinforced treadded roller.


As for not being used by a FIRST team....it certainly was designed to be!

The goal was to make this prototype and present the construction tools and techniques to New Horizons Robotics Team 122. Teach the Team 122 students about the current prototyping methods used in the current day industrial world. The wheels were to be built completely by the students on the team during the build season except for running the waterjet machine. The wheel was accepted by the mentors and students but the teacher would not because it was not a Team 122 student concept.
This year all concepts, designs, construction, must be that of the students only. I realize that all teams are run differently, at least Sam Elzarian has learned a lot about these current rapid prototyping techniques, and about Omniwheels as well!

IT would need to be tested to see how durable the wheel would be...robotics is hard on wheels and just about everything else. One good thing is that if you bent an axle bolt it would be so easy to replace.

I assembled all the CAD files and Stereo lithography files, it comes to less than 50 megs...where could I store it to be used by the FIRST community?