26-07-2006 18:11

sanddrag

Re: pic: what is cooking

Well that's one heck of a reduction (in a fairly lightweight package too). But why the (what appears to be) 1:1 gearing on the last stage? Also, you should render that thing in Inventor Studio if you have it. It will look nice.

Also, nice job filleting all your corners. However, your machinist won't be thrilled with that really pointy triangle. What do you need to get in there, like an 1/8" or 3/16" tool?

26-07-2006 18:26

Nuttyman54

Re: pic: what is cooking

hmm...how to turn your CIM into a Taigene 101? looks nice.

26-07-2006 20:42

Jeff 801

Re: pic: what is cooking

thank you very much for pointing that out i must have missded it

26-07-2006 21:49

Re: pic: what is cooking

...That's a lot of reduction. I also like the lightening method. However, as Sanddrag mentioned, you may want to make your corner filets a little larger, just to be friendly to the machinist.

26-07-2006 21:52

sanddrag

Re: pic: what is cooking

I really like how well you've done the "spokes" out from the bearing locations. It looks just great.

26-07-2006 22:12

lukevanoort

Re: pic: what is cooking

Are you sure those spokes can take the torque of the final output, I'm no ME, but they look a little small to me. The big gears look about the same size throughout the gearbox, as do the little ones. So, lets say the little one looks about 12-15 tooth and the big ones look about 60. There look to be about 5 reductions, so I'm thinking a final output of 1.7-5.2 rpms. So, either turning swerve modules (seems a bit excessive) or some sort of arm? I might be a bit off on the tooth counts (hopefully not too far) but whatever the exact number is, that is one heck of a reduction.

26-07-2006 22:16

Bill_Hancoc

Re: pic: what is cooking

Judging by Luke's calc of final output RPM which sounds about right....im guessing a telescoping arm mechanism or other arm mechanism...looks very cool tho

26-07-2006 22:18

Jeff 801

Re: pic: what is cooking

Lukevanoort you were close the large gear is 70 teeth and the small gear is 12 teeth the final out put is 2.2 RPM

26-07-2006 22:22

Jeff 801

Re: pic: what is cooking

you got it it is for a telescoping arm designed by a 8th grader

26-07-2006 23:38

Nitroxextreme

Re: pic: what is cooking

I agree with the torque concerns...

But how can you test something like that...the only thing I know of is COSMOS and that is only for solidworks.

I really like the wight reduction designs though and if there are no torque problems that is an amazing gearbox.

26-07-2006 23:42

Morgan Gillespie

Re: pic: what is cooking

Where are you counting a fifth reduction I count four... I had someone else look and they also only see four.

27-07-2006 01:47

sanddrag

Re: pic: what is cooking

There is stress testing in Inventor 11 and I believe in 10 also, but you've got to know how to use it. Testing for loads is the easy part. Predicting them is not.

27-07-2006 02:03

=Martin=Taylor=

Re: pic: what is cooking

Why not spare your machinist a tremendous amount of trouble and cut all those holes yourself with a hand drill?

Round holes will be faster to cut and stronger to boot. True, you will probably want your machinist to machine down the gears since they require balance; but the frame?

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What do you plan on doing with your telescoping arm anyways? Any cool off-season projects a-brewing?

Nice work.

27-07-2006 09:36

Jeff 801

Re: pic: what is cooking

no it is just to have if next year we need it

27-07-2006 13:48

sanddrag

Re: pic: what is cooking

Are you joking? It would take way more effort to hand drill a bunch of round holes than to throw the drawing in a CAM program and throw a plate in a CNC. I like it hoe it is and it the plates appear to be sufficiently strong (might be worried about the later stage gears though).

27-07-2006 20:58

Drew Hopman

Re: pic: what is cooking

Thanks to ASRC Aerospace we can get this cut out on the wire edm that they have, either that or the water jet.... The machining ability that we have gained is amazing! I have looked over some of the stress factors and I think it should work because it is ¼” thick plate for the sidewalls. I would like to commend Jeffery on his skills considering he is only in 8th grade but has mastered inventor and has the ability to think in a mechanical nature will be a great asset to the team.

27-07-2006 21:44

Nikhil Bajaj

Re: pic: what is cooking

I'd be more concerned about the strength of the gear teeth, especially in the later stages...if you take a CIM down to 2.2 rpm...you're going to be multiplying the max torque you can exert (it'll be around 90-100 oz-in when you trip the 40 A breaker) and if your free rpm is 2.2 rpm...then your gear ratio is somewhere around 2400...

240000 oz-in is a LOT of torque. be absolutely sure your gears can take it...you may have to step up the pitch a bit

but i totally agree...that amount of engineering proficiency and gumption in an 8th grader has the potential to be amazing...i look forward to future work.

27-07-2006 21:58

Karthik

Re: pic: what is cooking

An 8th grader designed this?!?! I'm floored. This is cool on so many different levels. Jeffrey, your design skills are phenomenal for someone your age. Secondly, it's great to see FIRST inspiring someone so young to tackle such big challenges in their spare time. This is what it's all about. Kudos.

27-07-2006 22:23

Rohith Surampudi

Re: pic: what is cooking

wait...8th grader...thats amazing wow thats really food, i was thinking you were a veteran senior...Your team is really lucky to have you

Keep up the good work

27-07-2006 22:33

Not2B

Re: pic: what is cooking

There are lots of different CAE / FEA type packages to do the testing. Of course, you could also do it old-school. Do it by hand. I don't do this very often, but... I'd check the hub, the spokes, and the teeth in different calulations. Have to estimate the forces - remember that start and stop are very much higher than forces during drive.

I know there are people out here that would do a much better job of explaining this than I would, but rest assured, you can do a good job by hand calcs. One of those things you learn in school.

28-07-2006 13:51

Jeff 801

Re: pic: what is cooking

it is not the small CIM but the large CIM to be clear.

28-07-2006 14:32

Nikhil Bajaj

Re: pic: what is cooking

ah, well then...

free speed of around 2500 rpm down to 2.2...gear ratio of 1136...at your max current of 40 A, then that's 1136*240 oz-in = 272700ish oz-in, and then considering dynamic loading you need to multiply that by at least a factor of 2 for safety one would think. 550000 oz-in is a pretty hefty requirement. Although, to be honest you will probably never ever ever see anything in FIRST that requires that sort of reduction to do something. Unless next year's game is pick up an elephant and hang your robot on the bar carrying the elephant...which WOULD be pretty sweet to see aside from animal rights issues...

Also consider that every mesh you make decreases efficiency by a few percent.

Just things to keep in mind. Keep up the good work.

28-07-2006 14:39

Jeff 801

Re: pic: what is cooking

the large gear reduction is for the speed that the arm gos up

if it has that much strength than i need # 35 chain instead of # 25

28-07-2006 15:04

Nikhil Bajaj

Re: pic: what is cooking

So are you just trying to reduce the speed of the motor? IE, is maximizing torque the concern or do you just want it to move slower?

28-07-2006 16:00

Jeff 801

Re: pic: what is cooking

both