pic: Planetary...Wheel?

[Jizvonius]

Hey nice design. One way to reduce the range of loading on the gears would be to find a way to support the wheel on it's own bearing. It may have to be a needle roller bearing with a large inner diameter to keep the design compact but it should work out with a bit more structure. That way the wheel loads go to the bearing and the gears don't have large time varying loads that will occur even without impact with the present design.

Also, you can get away with using fewer gears now that the loads don't have to be distributed that much. That should save a little on weight.

[Matt Krass]

Thanks for all suggestions, I'm taking them all under consideration, now I have a question for all you gearheads out there...

What the heck is a needlepoint bearing?

I'm learning, one step at a time..

[RogerR]

Originally Posted by Matt Krass

Thanks for all suggestions, I'm taking them all under consideration, now I have a question for all you gearheads out there...

What the heck is a needlepoint bearing?

I'm learning, one step at a time..

needle bearings use thin cylindrical rollers instead of a balls (in the case of ball bearings).

[Jizvonius]

Originally Posted by RogerR

needle bearings use thin cylindrical rollers instead of a balls (in the case of ball bearings).

Indeed, and for larger diameter shafts, they are generally a whole lot smaller than ball bearings that will get really huge and heavy.

Andy Baker's suggestion in the other thread was also a really good idea for taking the load off the gears and constraining the wheel motion, just depends on what you choose.

Jevawn

[dlavery]

Originally Posted by Matt Krass

Thanks for all suggestions, I'm taking them all under consideration, now I have a question for all you gearheads out there...

What the heck is a needlepoint bearing?

I'm learning, one step at a time..

Matt -

Look here for some examples of needle bearings. You can get them straight from the manufacturers (sometimes - depending on how many you want to buy), or from standard sources like MSC, McMaster-Carr (see page 1023 of their catalog), Small Parts, etc.

-dave

[Joe Johnson]

What is the purpose of the design?

It is fairly clever but without knowing what you are planning it is hard to be fair.

In generally 3 things worry me.

Others have said it already but imho, you need to get independent bearings on the wheel/sun. Gears are not intended to be bearings. You have little chance of success if you depend on the gears for support.

The thinness of the wheel. I think you will want to consider thickening up the wheel. Wheels take considerable side loads, more than I would expect a 10" dia, 1/4th thick spoke splate to be able to support.


Finally, gear tooth face width. This is 2 problems in one. I think 1/8th thick gears will be hard to keep aligned.

Without actually counting teeth it looks like you've got about a 15:1 overall reduction from the motor to the wheel. But more importantly, 2 Chiaphua motors put out a lot of torque, more than those gears look like they can hold if my gut is right.

Without actually doing the calculations to see if they are going to fail, you can get a feel for things by looking at designs you know work.

Without actually counting teeth it looks like you've got about a 15:1 overall reduction from the motor to the wheel. Thinks about it this way: Look at the face width of the gears inside a planetary gearbox. Take the Dewalt for example. Look at the 2nd stage. See how thick those gears are? Well, your ratio about the same as that second stage BUT BUT BUT... ...2 Chiaphua motors will put out 5-10 times as much torque as a single drill motor. So... you've got many times the torque trying to be supported by gears many times thinner. Something has got to give.

Just some things to think about.

Joe J.

[Matt Krass]

Originally Posted by Joe Johnson

In generally 3 things worry me.

Others have said it already but imho, you need to get independent bearings on the wheel/sun. Gears are not intended to be bearings. You have little chance of success if you depend on the gears for support.

The thinness of the wheel. I think you will want to consider thickening up the wheel. Wheels take considerable side loads, more than I would expect a 10" dia, 1/4th thick spoke splate to be able to support.

Finally, gear tooth face width. <snip, sorry its just long...>
Just some things to think about.

Joe J.

I appreciate your comments, as well as everyone else's, this design was a mere idea I came up with one day, I didn't think it anywhere near fully through and I'm not sure if it will ever be feasible. That being said, I'm currently sketching ideas to get independent needlepoint bearing support for the wheel, hopefully I can find a solution to the side load and gear load problems.

Also, The wheel thickness in this diagram is fairly thin I admit, but as stated before this is more of a conceptual model than anything to build from, same goes with the thin gears, I'm sure I could find better ones up to the job, and I will when I finish "rev 2" the "Production model" over this summer. I'm fairly busy, just starting work and handling my last summer in high school and all, so it may take some time to finish. Also, I've devoted some of my low amounts of CAD time to version 3.0 of my Omniwheel, which I'm posting right after this, based on suggestions offered in that thread to improve the design, it was a little easier and less demanding, so I figured I might as well get it out of the way. I appreciate everyone's help with this and I hope a final, workable design can be realized, and that it may be of help to a team at some point.

And now back to the wizard of Cogs...

[sanddrag]

If this turns out to be more trouble than it's worth (which I'm not saying it necessarily is) there is always the option of making a traditional fixed ring planetary, and having the output of that be your wheel axle. You'd have to take some precautions so that wheel impact doesn't happen or if it happens that it doesn't affect the gears. It would end up being a little bit long to space out the bearings (probably an inch of spacing between them will do), but you could have the wheel double back over the gearbox sort of like the MER rovers. You could have a deep dish wheel so the gearbox goes inside of it a bit.

I'm even thinking maybe a Chiaphua/Dewalt directly driving a wheel by modifying the output shaft and end of gearbox to give better support for holding a wheel. The only thing is though you wouldn't want to go any larger than about a 5" wheel straight on a Dewalt, but at least I think that is enough to clear it so the gearbox can go inside the wheel a little bit.

The thing with making planetaries is that I haven't been able to find a source of wide face internal gears. The largest I've found is 5/16 and it is brass.

[Jizvonius]

I think the internal gear idea can work if the pitch diameter is large enough. Then it wouldnt require nearly as much force on the gear teeth as it would be applied far from the center of rotation. This thread actually made me resurrect an old idea that can possibly make a very compact drive module. The gears(except the internal gear), brackets and shafts are missing from the inventor drawing, but the spacing has been worked out in 2D. The model so far should give you an idea of what I'm working towards though. The gear ratio ends up being about 15:1. The weight looks like it will end up being about 8 lbs and the size is about 8"x6"x6". The design obviously needs more thought, but I figured that I'd put it out there.

I have many variations of this design that move components around for different purposes. This one is to minimize the amount of gearing and space for the motor-gearbox-wheel system.

Jevawn

BTW i did this last night at around 4:30am so any resulting crappyness of the model can be attributed to that.