Hemispherical Omnidirectional Gimbaled Drive
 

Just saw this Gizmodo.com and found it most interesting.
Youtube video: http://youtu.be/uaT7M3Nwj7c

I'd love to see someone scale this drive system up to FRC size. The popularity of swerve drive, and other omnidirectional drives, isn't going away anytime soon. It seems that a major technical hurdle facing teams is building the wheel units and linking them all together... and having multiple transmissions.

The maneuverability looks promising.


Oh, yeah, is this the correct forum for this topic? I don't post much :o

Re: Hemispherical Omnidirectional Gimbaled Drive
 

http://www.chiefdelphi.com/media/photos/15197

Similar, though the angle of the hemisphere with respect to the ground is static.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

There's a pretty significant difference between a ball drive and what this does. This doesn't have to change the speed of the motor(s) to change direction, only the angle of the "wheel." The ball drive has to decelerate and accelerate the motors controlling the balls in order change directions.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

cool, but one of the issues I see with scaling this up to frc size is that each drive unit would require 2 steering motors, on the other hand, a common shaft could be run through the robot from which all wheels are powered through chains and universal or cv joints. But still,the minimum number of motors for a robot supported entirely on its driving wheels is seven if three wheel units fed from a single motor driving a common shaft. if only two driving units are used, that drops down to five motors, but you now must support part of the robot on non-powered wheels which reduces available traction.

The greatest disadvantage would be that both the seven and five motor versions that I mentioned use only one motor for actually driving. in comparison, a six motor swerve drive configuration uses three of the six motors to drive and a four motor meccanum system uses all four motors to drive, but at reduced efficiency due to canceling vectors.

The final concern would be wear on the field and on the hemispherical wheels, the sliding motion that occurs when the wheels pivot on the gimbals would result in a lot of wear on the tread. Also, when a wheel is idling (when its axle is vertical and it is not contributing to motion) that part of the hemisphere, not to mention the carpet under, could experience accelerated aging and wear due to the friction and heating that would occur. The solution to this problem would be to use a low friction material like acetal (2009 wheel tread material) form the hemispheres' surfaces, but then you would have little to no traction. [In the video, he is driving on a slick floor which reduces this issue].

if these issues could be dealt with (if a team can devote 9 motors to drive and implement a weight transfer system to reduce high-wear interactions with the floor by unloading drive wheels while idling (pivoting could still pose issues, just have spare wheels to replace worn ones I guess), then it could be done and would likely win an award (specifically innovation in control). But the question is, who is willing to face the challenge*?






*probably not us, we tried an 'innovative' {read "complicated"} drive train in 2010, it wasn't pretty. On the other hand, watching a robot drive across the field as parts of the drive system fall out behind it leaving a trail of parts while it continues to drive is rather comical.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

seems like it would've been good in 08'

Re: Hemispherical Omnidirectional Gimbaled Drive
 

It seems that it would be hard to scale up. Scaling up to FRC level would be fine, but to a commercial level would not be all that easy. What I imagine is that the wheel platform would just snap. It's like trying to stand on one leg and trying to rotate your foot. I think there would be too much torque acting on that to be safe.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Do you have any calculations, even first order estimations, to support this hypothesis? And since when was "commercial level" automatically larger than FRC scale?

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Great link, thanks for posting! It's a very simple method, construction wise, of creating a drive module capable of moving in any direction.

Just because the drive modules used in the video each use two actuators doesn't mean you'd have to implement it like that on a FRC robot.

For some systems it's easier to think about it in terms of degrees of freedom (DOF); for example, the typical "full swerve" drivetrain is able to move in x, move in y, and rotate... a total of 3 DOF. 3 DOF can ideally be obtained with just three actuators.

As an example, the Robonauts have effectively used a full swerve drive system in the past by using a crab drive (all modules steer together with one motor, all modules are driven together with one motor) with a rotating 'top' manipulator to give rotation. 3 motor inputs = 3 DOF.

Along that same logic, a typical six wheel drive train has two degrees of freedom: rotate, and drive forward/back. This requires two inputs, left side of the drivetrain and right side of the drivetrain. 2 motor inputs = 2 DOF.

The module shown in the video is intriguing because the tilting of the module acts somewhat as a gearing system. The further it tilts, the faster you can go. This effectively gives you a high gear at full tilt, and low gear with minimal tilt, as well as every gear in between (CVT!). So, tilt in x and tilt in y = 2 motor inputs = 2 DOF for a single module, the outputs being velocity and direction of travel.

Practically, I don't see a good use for this kind of system for an FRC robot. A simple swerve module already gives directional and velocity control (via motor speed controller). Any advantage that this system has in terms of variable gearing is most likely lost in the hemisphere/carpet interface... I can't envision getting a respectable amount of traction in low gear with such a system. The fact that it effectively works as a continuously variable transmission is appealing, however. I'd like to see one made, in Robonaut fashion! 4 modules tilting together with a central power plant to drive the hemispheres... 3 DOF for a CVT crab drive. :cool:

Re: Hemispherical Omnidirectional Gimbaled Drive
 

So after seeing this drive, I questioned weather it was possible at a VEX scale.

Sooo I went and spent a few hours CADing and went through two iterations of gimbles.

This is the final version


Comments and critiques are appreciated

Thought everyone would like this!

- Andrew

Re: Hemispherical Omnidirectional Gimbaled Drive
 

That actually looks very awesome! What are you going to to make the hemisphere out of/ Where are you going to get it?


On a side note, we should call this the HOG Drive (Hemispherical Omnidirectional Gimbaled Drive)

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Is this in reference to Aperture's "Hand of God" (HoG) Or Exploding Bacon? :p

Just has to clarify

The material we don't know what it will be yet since this will be made for College Level VEX if we make it (prototyping tomorrow)

- Andrew

Re: Hemispherical Omnidirectional Gimbaled Drive
 

I made that up right now :yikes:

If you are indeed prototyping it tomorrow, video please?

Re: Hemispherical Omnidirectional Gimbaled Drive
 

To Funny! :D

We will see how far we get the only thing we probably won't get the hemispheres made we will probably try to make a makeshift version of the hemispheres. Pictures and video will be made!

-Andrew

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Would a lone drive hemisphere drive train mounted in the middle of a traditional 4 wheel omnidrive system work? The omni wheels would not be powered, but just used as castor wheels.


And Joyride, great work. I am impressed. Only critique is that it looks very back heavy, or is that a fundamental part of the drive system?

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Yes a lone hemisphere would give you the same effect I guess I personally don't like the idea of mounting a ton of omniwheels everywhere since the wheel on the gimbal changes the ground clearance making the robot need at least a form of suspension to keep all omniwheels on the ground, at least thats what I would do.

Also may I point out the Omniwheels and structure up front was for a ground test to see what angle the drive would sit when the robot was essentially in "neutral"

Re: Hemispherical Omnidirectional Gimbaled Drive
 

If you can do that in just a few hours, what can you do with the rest of your day? Seriously impressed, can't wait to see how it all turns out.

Jason

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Talk about rapid prototyping ... Bacon seems to be on top of it! John should post this on his blog...

Scaling up to large-scale applications (FRC, heavy-lift mobility, etc) has some foreseeable issues. The first and foremost is the noticeable skidding of the hemisphere as the robot changes directions. Even changing the speed/torque by rotating the gimbal causes localized skidding on each individual hemisphere due to the differences in radii that create the different "gear ratios". I don't know of every way to reduce the effect, but it implies that each individual application will have to account for the effect. The easiest way to account for it seems to be finding the best balance of traction & intentional slip. Another way could be to limit the rotation speed of the gimbal.

I like how it's a 'resurrection' of technology.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Very, very cool.

I would hope that someone attempts to make this happen at FRC soon. I understand there are some initial issues with making it happen, but I'm sure its only a matter of time before someone figures those out and makes it happen.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

From 1938 (not team 1938).

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Joyride: very impressed. My only critique (and this is coming from someone who will probably never build a HOG drive) is that the square frame supporting the drive motor seems a bit large. This would limit the total angle of rotation. But you have two hemispheres, so you wouldn't need as much power from tilt from each wheel to get a faster speed.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Absolutely true. I wasn't questioning the notion of there being issues with scalability of the concept, but rather that the statement was made without even a modest attempt at calculations to prove his (very different) reasoning.

But building off of what you said, I'm curious as to how this would behave with softer tread materials on a soft surface (as likely to be the application in FRC). The deformation of both the tread and carpet under the weight of your robot would result in a contact patch larger than a single point (obviously). Because of that, different points in contact with the carpet are going to be moving at different speeds (and with different torques), meaning that there's going to be some slip in the drive of the wheel on the carpet. Depending on the radius of the hemisphere, the difference in speeds from one end of the contact patch to the other may or may not be marginal. It's possible that portions of your contact patch might interact with the carpet at closer to their coefficient of kinetic friction than their static friction.

In order to mitigate that, larger hemispheres could be utilized. But then the size and range of motion of your gimbal must increase accordingly, as well. Pretty soon that's eating up a considerable portion of your volume, especially compared to traditional drive systems.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Actually (for the most part) right now the "wheel" contacts first before any metal while its tilting. The current "wheel" does need to be made just a hair bigger which will get rid of this problem entirely.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

As promised I have pictures. No video since we didn't get to running it.

If you have problems looking at the album just post and Ill upload the pictures!

https://plus.google.com/photos/10171...92528705?hl=en

You may notice some things have changed from the CAD, this is because we didnt have enough of the right metal to build it to scale so we improvised a bit!


Enjoy

- Andrew

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Very nice thus far! Keep up the good work and definitely post some videos when you get it running.

-Brando

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Hmm, you made me think of the AT&T logo when you said this. It's a sphere with ridges. Translate that to this application: if the ridges were rigid, all of the deformation would be on the floor/surface. A hard rubber might work well. Hopefully the builder wouldn't owe AT&T a royalty for every wheel made :rolleyes:.

Interestingly for VEX/VRC, if one used a hard/durable material for the tread, without ridges, all of the wear would happen on the rubber tiles.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Commecial robots vary greatly in size, one company, FANUC makes robots designed to handle maximum payloads from 5kg-1200kg, obviously if these were made mobile they would require significantly different Drive systems.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

One thing I would like to know is, where did the gimbal he used come from? Did he have to fabricate it himself, or is it COTS?

Re: Hemispherical Omnidirectional Gimbaled Drive
 

And we come full circle again....... Now in the original discussion nobody talked about changing angles to get holonomic motion but now that you see one built it makes complete sense.



http://www.chiefdelphi.com/forums/sh...ight=cvt+wheel

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Whats to say you couldn't plant a ball caster right in the middle for an FRC scale one? to idle freely

Re: Hemispherical Omnidirectional Gimbaled Drive
 

You could do that, or you could just use a nylon/acetal hubcap. But there are still other issues that must be resolved.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

I know I'm a tad late, but I just entered CD after just watching it for years. Have you decided not to attempt this? :/

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Thanks for resurrecting this! Now I want to casually slip the word Hemispherical Omnidirectional Gimbaled Drive into normal conversation and see how people react! :p

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Like this: O.O

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Our recourses have been dedicated to our College VEX bots, If we ever get enough parts for a spare robot, we will continue to persure this. But for now we can not since alot of our current metal is in use for our robots (more on that later)

Thanks for the concern

I haven't fallen completely off the cliff yet!

- Andrew

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Ok, thanks! I look forward to seeing more of your projects in the future.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

Try using HOG drive instead. Not only does it come off the tongue a little easier but it sounds like a 1902 fundraiser.

Re: Hemispherical Omnidirectional Gimbaled Drive
 

I believe the main issue with this drive system will be the motor attached to the hemispherical section. Compared to the weight of the robot in the video (and most other HOG drive robots I have seen) the drive motor is simply massive. I'm not sure a CIM motor would be a viable powersource.