pic: 1382 Brazil - Gear box

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sweet looking gearbox…will there be any more pictures coming our way?
what are those gears made of?

Wow those look really professional. I bet they weigh very little as well. I’m going to take a guess and say that those are delrin or some type of nylon gears.

Its a nice sleek design…

great job with the gearboxes and especially with the polycarbonate covers. I think its a great idea when a team has covers on their gearboxes, it keeps foreign debris out and it keeps damaged parts and grease contained within the robot.

Very Nice, your machine work looks great!!

Looks very robust. Almost *too * robust…what does that thing weigh?

At least I know of a team that shouldn’t be having any drive train failures at competition!

Man, that is some really talented machining there. How did you get the edges so nice…

It’s incredible how nice a product highschool students can turn out.

I must say these look extremely professional, and quite functional. I am rather impressed. My only constructive criticism is that these look really weighty.

LIGHT!!! ARE YOU OUT OF YOUR MIND!!! Those side plates are freaking ridiculous. There seems to be a trend of this among FIRST teams. There is honestly no reason to make side plates any thicker than about an 1/8" maybie 3/16" if they are directly supporting wheels. Check out the kit gearbox, many of the team 45 gearboxes, the andymark gearboxes etc. Last year our gearboxes were made from 3/16" plate and looking back even that was overkill.

One question: It would appear as if this is a two-speed box. How does the shifting mechanism work and is it plastic?

Granted, they’re not going to be light if they’re 3/8" thick. But there is more to selecting a plate thickness for a gearbox than simply choosing 1/8". Material selection is the biggest factor, because the range of properties between (for example) 1/8" aluminum sheet metal and 1/8" alloy steel plate is enormous. Furthermore, what is it supporting–is it structural? If so, what about the rest of the frame? Some robots employ non-structural gearboxes, others tie them into the chassis as integral stiffening members. You can’t compare these equivalently.

Incidentally, I am personally a little bit curious and concerned as to the durability of those plastic gears. Without knowing the ratios, and the shifter design (if indeed, that’s what that is), I can’t say for sure–but I would definitely suggest looking for metal equivalents, just in case you run into problems during testing. (Run the hell out of it!) Maybe someone could enlighten us a little bit about that?

I, too am a little concerned about the plastic gears. The first stage may be alright, but the output gear seems a bit undersized. If you give me your ratios, gear face widths, gear diameters, and gear material I will run some quick numbers for you.

The machining is nice quality, but for everyone who is “amazed” I’d just like to say that it is typical of any professional machining. What amazes me is the lack of scratches. They aren’t anywhere to be found! The plates have not been milled and they have not been buffed, or even gone over with a scotch bright pad. How do you keep the plates from getting scratched in their raw material form?

Last, for anyone who says this is heavy, how can you call plastic gears heavy. Most teams (like 696) would use all steel gears. So I personally think this is very light, but I do have some concerns about that final stage.

As a side note the world would be a happier place without scratches of any kind

The mech guys really made a nice job in that project.

The gears are made of “polytechmil” (please, help me: I don’t know the exact word in English…).
Soon we’ll post new pics!

Correct, the covers were a terrific addition…we used LEXAN :smiley: , a sort of polycarbonate material that is one of the most widely known “plastics”. (actually, I don’t work with mechanics, so I just barely learned what Lexan was a few days ago…long story… It’s amazing the variety of things FIRST teaches us!!!)…anyway, they’re very lightweight…I’ll try to post how much they weigh exactly, but unfortunately the only scale available in our room isn’t working :frowning: . also…affirmative: it’s a dual-speed gear box.

Feel free to ask any other questions you may have…or visit our Forum at www.tribotecteam.com …there are students there far more knowledgeable than me when it comes to mechanics…I’m just the “person-that-posts-pictures-of-our-creations-on-chiefdelphi” :yikes: …

I couldn’t find any reference to that material–does it have any other trade names, or do you know the proper scientific/engineering name? (Even in Portuguese!)

For instance, we can get Delrin gears here, but that’s just a trade name for a polyacetal thermoplastic, also known as polyoxymethylene (POM).

We’d be able to give you a better idea of the durability of the gears (that is, if you need it), if you could pick the material from one of the lists on eFunda’s polymer page or on MatWeb.

The fact that it is dual-speed is nice, but it only amplifies the concerns…I’m interested to see what those other pictures reveal about the shifting mechanism itself.

lexan is polycarbonate…just more expensive since it is a trademarked name from GE…

I suspect that they’ve run some numbers and are sure that the gears will be up to the loads they are expecting. What concerns me is that as the gears wear, their strength will go down. Depending on what type of plastic it is, even exposure to sunlight could weaken it. What works now may not work a few weeks from now after some hard driving. I guess it hinges on the material. If they manage to get away with it, they’ll have a nice little advantage in not having heavy steel gears.

As an aside, I noticed the other day that aluminum gears were available, and cheap! Is there any marked difference between an aluminum gear and say a nylon equivalent? Any practical experience with them?

-Andy A.

Care to give the source?

For what it’s worth, 188 managed to break a couple aluminum ones last year… Actually, I ended up misjudging the loads on the gears a little, and ended up with too much torque on one particular pair of gears. (This was, mind you, in a very powerful transmission.) The aluminum gears above it (i.e. spinning faster, with less torque) in the transmission have worked perfectly, without so much as an unsightly mark on the teeth, after two regionals, the championship and an off-season event. For reference, the failed gears (26 & 84 T, 20° PA, 3/16" FW, 0.7 M, 2024-T4) were spinning at 3500 & 1000 (free) rpm, respectively, with around 1.2 HP driving them. The gears of the same size and composition (and the 32 P, 20° PA ones, which are very similar) at 5500 (free) rpm and above were undamaged and still function as intended. We actually bought nylon ones as spares for the upper stages, when we replaced the broken gears–thinking that the aluminum might have been unsuitable for those too–but as it turned out, they were never needed. Without knowing too much about the exact plastic properties under load, I would simply note that the tensile yield point is much lower for the nylon than the aluminum–a definite warning sign.

Both of the following stock aluminum gears, and can (theoretically) cut custom sizes of stock pitches, including the ever-popular :mad: 0.7 module at PIC; also, be wary of the stamped 5052 aluminum gears at SDP/SI–I don’t think they’re too precise:
PIC Design

We’ll be using pneumatics to make the Gear’s change.

The problem is that we’ll have to be stopped to make this happen.

I’m more into eletronics and programming so I can’t help you guys with the Gear Rations and stuff, but I’ll se if I can get someone tomorrow to answer you guys!