Custom RS550 Gearboxes

[Orion.DeYoe]

Back with another set of questions.
This time I would like to know about custom gearboxes using RS550 motors (or similar).
My main question is: how do you "introduce" the rotation of the motor into your reduction system? These motors don't have keyed or hex shafts to lock to a mating bore on a pinion or sprocket.
Typically these motors are used in a planetary gearbox which is great in some situations and not in others. I've seen some really nice custom gearboxes on robots like 254's and 971's that use RS500s. In my experience you have to press a 12 or 16 tooth 32dp steel pinion on the end of the knurled motor shaft and mate it to a larger 32dp gear before doing anything with it. This is kinda annoying and really boxes you in design and reduction-wise. Not to mention that you can't really get these pinions and gears from anyone but AndyMark and there isn't a good selection.
Is there a better way to do this? I know 254 uses belts somehow but I can't find a good picture of how the motor transmits power to that system.

[Rauhul Varma]

Originally Posted by Orion.DeYoe

Is there a better way to do this? I know 254 uses belts somehow but I can't find a good picture of how the motor transmits power to that system.

If you want to use a belt, just press on a pulley same as you would a gear. We two 775s connected via a 3mm GT2 belt to spin our flywheel in 2013.

[Jared]

If you have machining resources and want to use 20 degree pressure angle 32 DP gears, you can order from McMaster (http://www.mcmaster.com/#standard-gears/=tbp9wu)

SPD-SI has what you need (gears->spur gears->metal) in more sizes, but they aren't the fastest supplier.

You may also be able to find it on amazon.com, but I'd recommend purchasing only from Boston Gear or Martin, and avoiding Chinese gears or gears from "Ametric", which has horrible variations between gears.

For both you'd likely need the proper size reamer, also available from McMaster.

254 belt pictures from Pat Fairbank's photos:
https://lh5.googleusercontent.com/--...o/DSC_4505.JPG

https://lh3.googleusercontent.com/-s...o/DSC_4515.JPG

https://lh4.googleusercontent.com/-6...o/DSC_5067.JPG

[Orion.DeYoe]

Where are the belts and pulleys sourced from? Gates? GT2 3mm wide?
The shaft for those motors is .125 inches if I remember correctly. Do the pulleys come with a bore this small? Do the bores have to be finished (reamed/drilled out)?

[Chris is me]

Check RC hobby shops and other related websites. You can find a ton of press fit 32DP pinions for these kind of motors and output shafts. Banebots also sells pinions (look in the accessories column for P60 and P80 gearboxes).

Knurling isn't required but it can make a press fit that is too loose just right. Even with a belt and pulley, a press fit is your best choice. I am always uncomfortable relying on something like a set screw to transmit torque.

One of the reasons the VP is so useful is that the included coupler eliminates the need for press fitting while providing flexibility in your gear ratio. I'm a fan of using a single stage VP as the input to a traditional spur gearbox.

[DampRobot]

Originally Posted by Orion.DeYoe

Where are the belts and pulleys sourced from? Gates? GT2 3mm wide?
The shaft for those motors is .125 inches if I remember correctly. Do the pulleys come with a bore this small? Do the bores have to be finished (reamed/drilled out)?

You generally ream or bore out the pulleys to get a nice press fit onto the motor shaft. Most pulleys don't come with a bore small enough to ream out for a press fit, so you have to look for the ones that do. Also, keep in mind when you're specing the pulleys that you want to be able to stall these motors against the belts without any worry about the belt slipping, so make sure to double check that the pulleys won't ratchet at stall torque.

Sourceing wise, (Out of) Stock Drive Products/Sterling Instrument has a lot of stuff. You can also check out McMaster, although they generally don't carry all the profiles you want. I've never actually ordered from Gates directly, but I believe it is possible.

Personally, when I'm designing a gearbox for a BaneBots motor, I'd just find a VersaPlanetary that did the trick. They're really quite efficient (especially compared to the previous generation gearboxes and BaneBots gearboxes), and the output shafts are really nice to work with. But if you need really high efficiency or can't use a planetary for some other reason, Gates belts or 32 DP gears are a decent way to get a reduction right off of the motor.

[AdamHeard]

Originally Posted by DampRobot

You generally ream or bore out the pulleys to get a nice press fit onto the motor shaft. Most pulleys don't come with a bore small enough to ream out for a press fit, so you have to look for the ones that do. Also, keep in mind when you're specing the pulleys that you want to be able to stall these motors against the belts without any worry about the belt slipping, so make sure to double check that the pulleys won't ratchet at stall torque.

Sourceing wise, (Out of) Stock Drive Products/Sterling Instrument has a lot of stuff. You can also check out McMaster, although they generally don't carry all the profiles you want. I've never actually ordered from Gates directly, but I believe it is possible.

Personally, when I'm designing a gearbox for a BaneBots motor, I'd just find a VersaPlanetary that did the trick. They're really quite efficient (especially compared to the previous generation gearboxes and BaneBots gearboxes), and the output shafts are really nice to work with. But if you need really high efficiency or can't use a planetary for some other reason, Gates belts or 32 DP gears are a decent way to get a reduction right off of the motor.

I'm also a fan of using the 10T 24DP 20* angle pinions banebots sells for both the 550's and 775s as a press fit. SDP-SI has a good line of 1/4" face width nylon and delrin gears to mate with. Both are cheap and easy.

[Rauhul Varma]

Originally Posted by Orion.DeYoe

Where are the belts and pulleys sourced from? Gates? GT2 3mm wide?
The shaft for those motors is .125 inches if I remember correctly. Do the pulleys come with a bore this small? Do the bores have to be finished (reamed/drilled out)?

We buy our belts and pulleys from SDP-SI. The belt we used was a 9mm wide 3mm pitch GT2 belt. We had a bunch of 16T GT2 pulleys with 8mm bores as they were used in our drive gearbox, so we pressed in an insert that would reduce the bore to the correct diameter and then pressed the pulley with this insert onto the 775s. IIRC we just drilled the insert out to the correct diameter.

[Scott Kozutsky]

Originally Posted by Jared

If you have machining resources and want to use 20 degree pressure angle 32 DP gears, you can order from McMaster (http://www.mcmaster.com/#standard-gears/=tbp9wu)

SPD-SI has what you need (gears->spur gears->metal) in more sizes, but they aren't the fastest supplier.

You may also be able to find it on amazon.com, but I'd recommend purchasing only from Boston Gear or Martin, and avoiding Chinese gears or gears from "Ametric", which has horrible variations between gears.

For both you'd likely need the proper size reamer, also available from McMaster.

254 belt pictures from Pat Fairbank's photos:
https://lh5.googleusercontent.com/--...o/DSC_4505.JPG

https://lh3.googleusercontent.com/-s...o/DSC_4515.JPG

https://lh4.googleusercontent.com/-6...o/DSC_5067.JPG

From what I can tell from the pickup photos, that isn't actually a press fit. It looks like a fairloc hub(http://sdp-si.com/web/html/newprdfairloc10.htm). I haven't checked mcmaster but Sdp-Si has a 12t .080 MXL belt pulley with a .125in bore. They also have .1875 bore for 15t and 16t and .25 bore for 18t and up.

I wouldnt be surprised if the shooter also had fairloc hubs but I can't really tell from those views.

From what I can tell the second stage of the pickup reduction also uses the fairloc hub so I'd expect them to be pretty strong (also they lasted the entire season, if there was really a problem I'd expect 254 to fix it).