Hi, what options have other teams explored to reduce the weight of gearboxes? How about such things as Delrin or aluminum shafts, gears, plates, etc? Thanks!
there are things…
-you could knock the hubs off sprockets
-use delrin bearings
-knock weight off the supports with holes…
YOu should without a doubt look to all of the steel in your robot before you start speed holing the rest of the robot. The picture attached is from just one of the spur gears in last years drivetrain. This modification removed about 80% of the mass from the gear, and it never showed any signs of stress.
We have done everything from hollowing steel shafts, definately remove the hubs, weld the gears, and hollow out the web on the side of the gears with symetrical holes and material removal
Keep in mind though, that sometimes it is not worth it to drill 1,000,000,000,000,000… holes in your bot, or any other component for that matter. I say this, not because it doesn’t take weight off, but that the amount that you would have to drill to make a sufficiant dent is impractical. Sometimes your better off playing with different materials (like u said delrin).
*Originally posted by DaBruteForceGuy *
**I say this, not because it doesn’t take weight off, but that the amount that you would have to drill to make a sufficient dent is impractical. **
I agree completely… for Aluminum. but for steel you can literally remove over a lb from each individual spur gear and still maintain its integrity. (More on bigger gears less on smaller) In a large gearbox, such as the technocats 3 motor air-shifter 
The amount of weight savings from the gears will be much higher than the savings from bearings to delrin bushings. I also like having nice flanged bearings when the meshing of gears is involved and important.
The gear in my post above starts life at right about 2lbs (1.93) after the mod is 0.4lbs. We used 4 of these last year that is over 6 lbs. savings on just those 4 gears alone, we did not have 6 lbs of bearings on the whole bot. Try saving 6 lbs of aluminum and you are talking many, many, many holes.
*Originally posted by Matt Reiland *
**The picture attached is from just one of the spur gears in last years drivetrain. This modification removed about 80% of the mass from the gear, and it never showed any signs of stress.
**
Matt,
I spent an hour or so last night looking for this picture! I remembered you posting it and wanted to show some of our machinists what is possible. Of course now that I went and found it, you re-posted it this morning.
Good luck to 226 this year!
You could always drill holes in your motors (maybe the battery and pnumatics as well…lol) j/k
Seriously tho, NEVER USE STEELE (unless you have no choice, in which case pump it full of holes). Aluminium is great, in some cases you can even get away with plastics (altho is this risky in gearboxes).
As for holes in general, unless its steele, it won’t save much weight/hole (maybe only a gram or 2). But, with A LOT of holes, those grams to slowly add up. And when it comes down to the wire for weighing your bot, those grams come into play. When it came time to weighing our bot last year, we were 130.1…take off a screw, and we were 130.0. Every little piece of weight you can save, save.
If you are using large sprockets, get them without the hub…If you cant, find the one with the largest hub possible, that way you wont have as much material on the sprocket…I havent tried frilling them, but that would be a good way to save weight. Matt: how did you guys figure out the pattern needed, and how many holes to drill while still having structural integrity. I’d be very interested to find out more about this.
Cory
*Originally posted by Matt Reiland *
**The gear in my post above starts life at right about 2lbs (1.93) after the mod is 0.4lbs. We used 4 of these last year that is over 6 lbs. savings on just those 4 gears alone, we did not have 6 lbs of bearings on the whole bot. Try saving 6 lbs of aluminum and you are talking many, many, many holes. **
Yea, we actually did reatively the same thing to our sprockets last year and the weight difference was much different than aluminium.
--- We were also careful not to take off too much of the "blackened stuff" (or the hardened outer surface). This is because that surface gives the steel more stability, and without it the sprocket is more brittle. This is jus a lil thing, not too important when on the bot, but if you walking with it and u drop it..... well lets not go there :rolleyes:
Have any teams had success using delrin gears or sprockets? How about aluminum shafts? Are there any components that should be steel?
That’s a great pic of the sprocket holes by the way, we’ll definitely look at that!
dont use delrin gears…please… use nothing but metal gears if you want any chance of them survivng a match, let alone a competition.
Cory
I think they mean delrin bearings which can be quite durable. Btw don’t use derlin gears. Look at the edurobot gears thats derlin gears.
The EduBot has sprockets that I don’t think are Delrin.
As for saving weight, bore out the center of your axles, drill hole in sprockets especially in the hubs.
You’d also be surprised how much those Skyway Bead-LOK wheels weigh and how much less they can weigh. You can half the weight with some well placed holes and taking off some rubber.
And remember, every little bit of weight adds up, so every little bit of material removed will bring that number down. Just don’t drill aluminum with anything smaller than like a 3/4" bit or you won’t get very far. As for steel though, drill the heck out of it.
I know for a fact that most of the plastic sprockets and bearings used in the edubot are made of derlin plastic.
I found first’s supplier.
Last year, we used the skyway wheels. We actually bored out 1"holes with a spade bit in the rubber, from the inside of the rubber tire. it actually helped a lot with the weight. You’ve just got to be careful not to plunge it thorough the other side.
*Originally posted by Cory *
** Matt: how did you guys figure out the pattern needed, and how many holes to drill while still having structural integrity. I’d be very interested to find out more about this. **
Well I will give my answer based on the knowledge gained from one of our Advanced Development ME’s that designed much of a proprietary GM robot called the PAAS/C-Flex (Now produced by Fanuc)
He takes the Diametrical Pitch of the Gear and subtracts about .300 for the area around the teeth, then we leave as much of the hub as required for it to be welded to the shaft (or other mounting method) We then take a common hole size (usually 1/2" to start) and array it radially around the face in a number that is easy to reproduce on a rotary table (16 for example) but always symmetrical using a polar array. For gear thickness he always chooses somewhere around .150-.200 for steel gears in applications like ours. As a final check he looks over the gear to see how the holes line up to leave spoked webs and sometimes we have to adjust the # of holes or the hole sizes. We have found this method easier to recreate with common milling machine tools versus having to use CNC for more elaborate ‘spoke patterns’.
I guess as a final note never underestimate the strength of the steel parts, something like a 20 pitch 20 deg P.A. 1/2" face are overkill for most FIRST applications if left full weight.
*Originally posted by DaBruteForceGuy *
**Keep in mind though, that sometimes it is not worth it to drill 1,000,000,000,000,000… holes in your bot, or any other component for that matter. I say this, not because it doesn’t take weight off, but that the amount that you would have to drill to make a sufficiant dent is impractical. Sometimes your better off playing with different materials (like u said delrin). **
I disagree
First, delrin is impractical for many applications. Say you have a 3 foot piece of 2" aluminum square tube that you need to lighten. Delrin or any other plastic would be hard to replace it with. Many times it’s easier to drill holes than to design for other materials.
And as for drilling holes, the weight does add up. Especially if you’re using 3/16" plate or larger. The weight adds up little by little, but it is worth it. Plasma Cutters can be used for larger holes and eccentrically shaped ones. Cutting unnessesarily long fastners off is also an easy way to get weight out.