Aluminium Gears
 

Hey CD, I'm looking for any and all COTS aluminum gears on the market. In particular, larger 32DP gears with decent face widths would be really cool. I realize aluminum gears are pricey and hard to find, but I wanna know if CD has any sources I don't know about and couldn't find on a Google search. Thanks!

Re: Aluminium Gears
 

I recently noticed that the tetrix gears are .25" face width 32DP. Using an 8T brass pinion to the 120T that's 15:1!

Sdp-si is the only place I've found aluminum gears at a reasonable price (aside from the limited 20DP selection at AM). Although I've only seem them up to 3/16".

What is this for?

Re: Aluminium Gears
 

I'm interested in prototyping various gearbox arrangements to see if I can save space or weight in small reductions. I also want to test a drivetrain with these gears. I haven't run the numbers on tooth loads, though.

Re: Aluminium Gears
 

Back when I was on 308 we did aluminum gears in the drivetrain for two seasons (2001 and 2002). I think we used 24 DP in 2002 and they lasted the entire year until the first match of the world championship finals - then they shredded. Pretty bad timing. I think you can find pictures of the gearbox carnage somewhere on this site. In fairness to those gears, we're pretty sure the shaft shifted leaving only about 60% engagement along the face width.

In 2002, those gears were 1/4 inch face width, but we sandwiched multiple gears together to increase the effective face width. I really wish I could remember the source where we bought the gears. Although, as long ago as that was they may not be in business any more.

One important note: when we were doing tooth stress calculations, I remember that 24 DP was pretty marginal in later stages of the gearbox, so I would expect 32 to not be able to withstand the loads without getting crazy with the face width. Just be sure to do all of the calculations and double check them.

In 2001, we machined custom aluminum gears because we were worried about tooth loads with small gear teeth. I want to say we made them in the neighborhood of 12 to 16 DP. They looked a little weird, but worked great.

Re: Aluminium Gears
 

Check out JVN's post about aluminum plate gears here.

Re: Aluminium Gears
 

That's the idea, but unfortunately we don't have any sponsors with a laser. The hope is to buy a bunch off the shelf and play with them.

I'm not sure if the Tetrix gearset is worth trying or not, I imagine they are probably pricy.

Re: Aluminium Gears
 

Get some sponsors then, google, phonebook, etc... It doesn't have to be laser either, could be waterjet.

The tetrix gears aren't really bad at all in price when compared to other 32DP aluminum gears. a 120 tooth for $30. Now that I know about it, we're certainly interested in doing a 32DP based gearbox for 500 sized motors as 32DP pinions are cheaply and easily available in varied sizes at EVERY hobby shop.

I think effective design and pocketing of existing steel gears would yield more bang for your buck than investigating aluminum gears.

You should also learn how to calculate gearstrengh using Lewis Bending Numbers, once you do it's trivial to determine if a gear will survive; no need to experiment to solve a problem that's been solved for a hundred years.

Re: Aluminium Gears
 

We're certainly working on it. Our economic region isn't particularly bright (Troy has 14% unemployment and I bet Latham isn't much better), but if we do we'll see. I'm just generally a fan of modifying COTS parts in house, since that's more reliable than counting on the donated services of a sponsor, plus it puts less stress on them.

That's probably true, I'm just interested in seeing if we can throw a few bucks at the problem to avoid having to pocket steel.

I've heard that Lewis numbers tend to be conservative, but I've still been meaning to learn. Thanks for the reminder. Lewis numbers do say my drivetrain application should hold up.

Re: Aluminium Gears
 

I would be extremely concerned about runout in a high speed application such as the initial reduction(s) in a gearbox, if using this method.

The tetrix gears are probably 5000 or 6000 series aluminum which is less than ideal for any high torque situation.

Re: Aluminium Gears
 

If you've found a bunch of reasonably priced 32dp aluminum gears that just aren't wide enough for your purposes, you can always just stack them. I'm no expert, but that seems to accomplish the same thing, in terms of pressure. Maybe not so much in terms of the statics of the material stress or whatever is going on there, since the gears aren't actually connected, but you're at least distributing the same load over a larger area.

Re: Aluminium Gears
 

There was a team at CMP that used anodized aluminum gears that were similar to the gearset that andymark sells, i believe they were going to try to start selling them, does anyone else have any more information?

Re: Aluminium Gears
 

That was Team 1323/973. I'll put up a pic soon.

-RC

Re: Aluminium Gears
 

And the draft angle.

Re: Aluminium Gears
 

Waterjet is probably better for this application. Laser would require plate gears since all lasers are limited in the thickness of aluminum they cut (some more so than others) due to aluminum's reflective properties. Waterjet could cut the proper thickness material in one cut.

Chris, I wish I could help you out, but our metal shop has been unresponsive recently on account of new business and tied up equipment.

Re: Aluminium Gears
 

I know it's an anecdote, but the Space Cookies (1868) had a gorgeous gearbox for their arm that didn't seem to have the same DP for more than 2 stages. It started at 32 DP on the motor pinion gear and was much much lower by the last stage (16DP maybe?).

PINK had something similar for their crazy arm rotary joint. If you didn't get a chance to see that thing in action, sometimes it would snap from one side to the other -- so lower DP on the final stages was almost necessary. Their mentor in DC told me they would gear it down some more before Championships, but I didn't get to see the effect in St. Louis.

IMO, 32 DP is a bit risky to put on all stages of a drive train for the sheer fact that 32 DP gears need more alignment precision for proper mesh than their lower DP counterparts.

Re: Aluminium Gears
 

You wouldn't want to cut direct to thickness on the waterjet anyway with the draft angle created (unless you've got a sponsor with a tilting head).

You'd want to stack thinner gears with both processes, and laser arguably is the faster process for thinner material.

Re: Aluminium Gears
 

This is pretty smart design. The FP gearbox is actually quite similar. Emulating this kind of gearbox in other applications is something I'm aiming to do.

Re: Aluminium Gears
 

It is smart design in terms of pure tooth loading, but for FRC it can be more difficult to do. It requires ordering gears of multiple varieties. This could be a nonissue for some teams, but it can take longer and be more expensive for others.

We nearly "standardize" on 20dp, and try our best to stick to AM. His gears are cheap, in stock, and ship fast. We also have a large stockpile on hand, and have sometimes grabbed stock gears off old robots to modify then replace when the real order comes in.

Also, utlizing his 50T 6061 Al gears and heavily pocketing them, you can probably get gearboxes comparable in weight. Even with using pure 20DP, our gearboxes are some of the lightest I've seen made (for drive and mechanisms).

Re: Aluminium Gears
 

The only problem is it relies on (Out of) Stock Drive Products to get the 32 DP gears. They also come in plain bore, which is no problem for our two teams since we lighten all our gears anyways and have hex broaching capabilities, but it can add up to a lot more work for the average team.

Re: Aluminium Gears
 

PIC Design is another supplier of aluminum (and other) gears that may work for you. Although their lead time was not exactly spectacular the last few times I used them, their aluminum gears are available in conveniently small sizes. (32 pitch, 0.7 module and 0.8 module, for example.)

SDP/SI's catalogue is well-provisioned with aluminum gears. However, they seem to have been slashing stock the last few times I tried to order from them. There were numerous items unavailable, which necessitated some creative choices of gears and pitches. This included the substitution of a 0.8 module gear for a 32 pitch one (0.8 module = 31.75 pitch, so they work very well together), and the use of an acetal pinion (with brass hub) on a BaneBots motor.

Incidentally, for almost every gearbox I've done, I've tried to choose the pitches based on the expected load at every interface (mesh and shaft). (That turned out badly one year, in 2004, when an underestimate of the dynamic loads resulted in gear teeth everywhere—somewhat ironically, it was partly because I was trying to standardize the pitches between the first two stages. On the other hand, once corrected with an appropriate gear set, the transmission was fantastic—this was a 6-motor, 2-speed drivetrain using three different motor types, and needed a fair bit of complexity to interface with two pinions and a shaft, all driven at different speeds.) It definitely saves weight and space, and definitely adds complexity and lengthens the design process. My opinion is: do the bulk of the design ahead of the season, so that you can concentrate on little details like optimizing the gears. Then improve it as much as the rules demand (to ensure legality), and then pull the trigger on the supply chain as soon as possible after kickoff.

Re: Aluminium Gears
 

Reported.