pic: 2451 PWNAGE Planetary Drive

[pwnageNick]

This is a concept I started working on last offseason. The result before build season caught up with me was a single speed drive with the wheel having an internal ring gear and pinions on the CIM motors directly driving the ring gear/wheel. The encoder is also driven by the ring gear through an idler gear.

The benefits ended up being a pretty significant gain in real estate on the chassis. This also resulted in some (albeit minor) weight savings compared to a standard single speed skid steer drive.*

I'll have gearing info, weights, etc. and more info posted once I can get the model open again. Comment any questions, etc. and I'll answer as I know it's tough to make everything out from this picture.

EDIT: The ring gear on the wheel is 72T while the pinions on the CIMs are 11T/12T. The encoder gear is 28T

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[KohKohPuffs]

What reduction is the gearboxes at?

[R.C.]

Nick can we get better pictures of the planetary setup?

[pwnageNick]

CIM motors are hidden here as well as the tread. The four screws showing are what mount the CIM to the sheet chassis.

Versa pattern cut into the plate part of the wheel to easily mount sprockets, etc.

[JohnFogarty]

Besides weight saving and real-estate gain. Are planetary gearboxes more or less efficient than regular non-planetary gearboxes?

[pwnageNick]

Originally Posted by JohnFogarty

Besides weight saving and real-estate gain. Are planetary gearboxes more or less efficient than regular non-planetary gearboxes?

Generally they are less efficient. Due to this being a custom setup, to know what the efficiency of this setup would be a prototype would need to be built to find that out. A prototype would also test any issues with loads, and how stable the wheel would be.

[asid61]

Neat idea. Your wheel looks very complex though when it looks like all you would need is an internal gear and versa key.
Have you though about how the wheel tweaking the shaft it's on could affect the Cims, if it happens at all?

[indubitably]

How long until we get the two speed version?

[s_forbes]

How is the wheel manufactured? It looks like it's designed to be several layers of plates. Do you have to cut your own ring gear?

This looks like a good way to get a high reduction single stage gearbox without having the wheel's gear teeth drag into the carpet. Pretty cool!

[pwnageNick]

Originally Posted by s_forbes

How is the wheel manufactured? It looks like it's designed to be several layers of plates. Do you have to cut your own ring gear?

This looks like a good way to get a high reduction single stage gearbox without having the wheel's gear teeth drag into the carpet. Pretty cool!

Currently the wheel is made of two parts. The one side of the wheel is a 1/4" this around plate with the inner hub area 1/2" thick to press the 1/2" wide needle bearing into. The other part is the round part that the tread gets riveted to. the ring gear profile would be EDM cut, with the rest of the machining work done on a mill and lathe.

I am debating making it so that the round part of the wheel is split into 3 parts, with he middle part being a steel ring gear and then aluminum parts sandwiching it in place. Some have expressed concern over the wheel being aluminum.

Originally Posted by indubitably

How long until we get the two speed version?

We'll see. I want to lock down the single speed design first, and I think I'd want to build prototype first to prove it works before moving to a two speed.

[ThaddeusMaximus]

<ignore this post since I'm a dumb>

[pwnageNick]

Here is an update. In the album linked below is pictures of all the custom parts necessary for this design. The majority are actually relatively simple, there are really only 2 parts with any real kind of complexity. Also in the album is an updated iso view of the module and a section view to better understand what is going on.

Album here

[Kevin Ainsworth]

Is the single offset needle bearing the only thing supporting the wheel?

[Mr V]

Originally Posted by JohnFogarty

Besides weight saving and real-estate gain. Are planetary gearboxes more or less efficient than regular non-planetary gearboxes?

Originally Posted by pwnageNick

Generally they are less efficient. Due to this being a custom setup, to know what the efficiency of this setup would be a prototype would need to be built to find that out. A prototype would also test any issues with loads, and how stable the wheel would be.

In general a planetary reduction is less efficient than a spur gear reduction. However this set up isn't really a planetary reduction and should have a frictional loss essentially a simple spur gear reduction.

The extra frictional losses occur in a planetary reduction because of the increased number of gear to gear interfaces.

In your basic spur gear reduction you have 1 gear to gear interface per stage. With a planetary set up you have 6 or 8 gear to gear interfaces as well as the friction of the pins that the planets rotate on.

This set up however does not have a sun nor really any planets, it is just the driven gear turned inside out.

[Cothron Theiss]

Originally Posted by Mr V

In general a planetary reduction is less efficient than a spur gear reduction. However this set up isn't really a planetary reduction and should have a frictional loss essentially a simple spur gear reduction.

The extra frictional losses occur in a planetary reduction because of the increased number of gear to gear interfaces.

While what you've said is accurate for these purposes in a practical setting, if I understand some of the finer points about involute gear profiles correctly, a ring gear is always slightly less efficient than a regular spur gear. Since the gear teeth of the ring gear are directed inwards, there is an increased amount of interference, which would lead to SLIGHTLY less efficiency if you use the exact same gear teeth profiles and spacing as a regular spur gear reduction.

Now, you can regain this loss in efficiency by increasing the amount of cutout in the ring gear (changing the pressure angle), or decreasing the center distance between the ring gear and pinion gear. But since both of those solutions lead to less load carrying capacity in the gear mesh, it's a trade-off. Since the OP is going with a really interesting combination of the wheel and gearbox, I would NOT risk decreasing the load carrying capacity to regain a small percentage of efficiency.

***Disclaimer***
I may be totally wrong about all of what I just said, but that's what I think is accurate.