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.
All CAD files required to produce the Omni Grenade wheels are in the following location thanks to the the generous offer of a storage area on Team 1257’s website of the Magnet Robotics (Parallel Universe)
Thanks Max and Team 1257!
“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.
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!
“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,
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.
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.
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?
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.
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.
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.