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lemiant 29-05-2011 23:37

Custom gearboxes
 
What exactly goes into a custom gearbox? I am specifically interested in ones for manipulators, as I plan on using AM headboard in the drivetrain.

Thermal 30-05-2011 03:33

Re: Custom gearboxes
 
Quote:

Originally Posted by lemiant (Post 1064124)
What exactly goes into a custom gearbox? I am specifically interested in ones for manipulators, as I plan on using AM headboard in the drivetrain.

I mean, I don't want to sound like a smart-alick or anything but essentially identical components go into custom gearboxes as anything you'd buy off of andymark.com.

The thing that makes the majority of custom gearboxes "custom" is the fact they redesign the mounting plates to get motors in a more desirable location, offer easier mounting to their manipulator/frames, and get the gear ratios to something suitable for their needs.

James Tonthat 30-05-2011 03:59

Re: Custom gearboxes
 
This.

http://www.chiefdelphi.com/media/papers/2059

And this.

http://www.team1323.com/resources/ma...alculator.html

The bottom one. (Hint: 20 DP)

Enjoy.

Hawiian Cadder 30-05-2011 13:50

Re: Custom gearboxes
 
another reason to do a custom gearbox is weight. and a lot of custom gearboxes are derived from cots components. this year we made a custom gearbox for our lift. we made a new housing for a dewalt drill gearbox.

ecchorobotics 01-06-2011 21:34

Re: Custom gearboxes
 
If you're interested in making your own custom gearboxes, it would help to have access to two machines:

-Lathe (For shafts)
-Mill/CNC (For side plates/ facing-off gears)

A gearbox is simple: Side plates, stand offs, bearings, shafts, spacers, gears, and keyways/keys.

A good place to buy quality gears would be Martin Sprocket. You can use either hardened steel gears from that manufacturer or 7075 aluminum gears (from a different source). It is safe to go with 24 DP, but I believe some people have had success with 28 DP.

Stand offs you can get from McMaster-Carr as well as keystock for keys. You can make aluminum side plates from 3/16 6061 alum. or steel 1/16 sheet metal (we don't use sheet metal).

Autodesk Inventor makes it fairly easy to design gearboxes, if you are serious about making them CAD is the place to start. Inventor has gear generators, key/keyway generators, and bolted connection. If you input the right numbers into it it'll calculate the ratio and it will also tell you if the gearbox will fail or not.

Gearboxes are harder to make the smaller they are but it's not a matter of design it's more of where to get the parts; tiny bearings are easy to find but working with such small shafts and gears may be difficult. It is not impossible to create a custom planetary gearbox but it is a challenge.

When making your gearbox always pick your gear ratio based on the motor curve- look at the point where torque and speed are balanced and decide where to go from there. Perhaps for and arm you need torque but a gripper may need speed. That's probably the first step to determining how you design.

Hope this helps.

-Eric

hat_ios 08-06-2011 18:26

Re: Custom gearboxes
 
From past experience, try to use as many parts from a common gearbox. If you are looking for a shifting gearbox look at http://www.andymark.com/product-p/am-0114.htm. The super shifter is on the slightly heavy side. This season, my team built custom gearboxes, we repackaged the majority of the Super Shifter parts into a lighter/more compact gearbox.

Hope this helps

AdamHeard 08-06-2011 18:36

Re: Custom gearboxes
 
For varied reduction single speed gearboxes, we've done something that I have poorly named in CAD as "AM based lasered gearbox plates".

It's a neat concept, we decide that regardless of gearing needs, we will ONLY use andymark toughbox gears. That means spurs with a .4 overall thickness, and pinions with a .6 overall thickness. Both already have machined nubs so they don't rub on the bearings.

Then, you can machine gearbox plates by whatever means (we like waterjet/laser as it's obviously fast and allows more flexible design).

Design the plates to be 1.125" apart (we usually bolt onto a 1" face with a .125" spacer.

For assembly, press bearings in, and you can use exclusively AM shafts if you desire. We machine our own to perfectly match our needs and eliminate spacers, but this is not necessary.

Doing this allows you to create custom gearboxes FAST and with minimal machining. We've shown you can get just about any reduction, from 1:1, to several hundred to one.

For my first custom geaarbox, I would go in this direction; utilize COTS gears and shafts. Machine only plates, and possibly standoffs. Spacers should not be necessary if you design it right (standoffs as well possibly)!

If you want the CAD for these to make the concept more clear, let me know.

Oh, last little tip, we also try to exclusively use 50T spurs. this allows us to use the aluminum gears AM sells. We cut weight off with our lathe and mill and get them down to .07 lbs each (versus .5 for the stock steel!).

Nemo 27-07-2011 21:45

Re: Custom gearboxes
 
Quote:

Originally Posted by AdamHeard (Post 1065121)
It's a neat concept, we decide that regardless of gearing needs, we will ONLY use andymark toughbox gears.

Adam,

Thanks for mentioning this. You got me interested in designing gearboxes, and I'm pleased at how accessible it is to create a gearbox design that only calls for custom side plates and COTS gears and shafts. I've spent a bunch of time playing with various gearbox designs this summer, and I also showed some students how to design gearboxes. It's really fun stuff. I'm also pleased at how easy it is to come up with a gearbox that's lighter than the standard Toughbox or Super Shifter. It's really cool that AndyMark sells their gearbox components individually to make this possible.

I think I also read a post that Art Dutra (Team 228) wrote about the same general concept, so thanks go out to him as well.

I noticed that the AndyMark gearboxes are designed with an extra 0.003" added to the center distances between gears. I'm curious whether teams typically add that extra clearance when designing custom gearboxes.

NickE 27-07-2011 22:00

Re: Custom gearboxes
 
Quote:

Originally Posted by Nemo (Post 1070802)
I noticed that the AndyMark gearboxes are designed with an extra 0.003" added to the center distances between gears. I'm curious whether teams typically add that extra clearance when designing custom gearboxes.

Team 254 typically does this.

Michael Blake 28-07-2011 01:47

Re: Custom gearboxes
 
Quote:

Originally Posted by AdamHeard (Post 1065121)
If you want the CAD for these to make the concept more clear, let me know.

Adam, please send the CAD on your gearbox designs to michaelblake@insurancelabs.com

Rookie team #3481 Brandeis Bronc Botz says THANK YOU for your valuable help!

AdamHeard 28-07-2011 10:24

Re: Custom gearboxes
 
Quote:

Adam,

Thanks for mentioning this. You got me interested in designing gearboxes, and I'm pleased at how accessible it is to create a gearbox design that only calls for custom side plates and COTS gears and shafts. I've spent a bunch of time playing with various gearbox designs this summer, and I also showed some students how to design gearboxes. It's really fun stuff. I'm also pleased at how easy it is to come up with a gearbox that's lighter than the standard Toughbox or Super Shifter. It's really cool that AndyMark sells their gearbox components individually to make this possible.

I think I also read a post that Art Dutra (Team 228) wrote about the same general concept, so thanks go out to him as well.

I noticed that the AndyMark gearboxes are designed with an extra 0.003" added to the center distances between gears. I'm curious whether teams typically add that extra clearance when designing custom gearboxes.

I'm glad it worked out for you, it really takes out all the trivial work in making generic gearboxes. We still go all out for specialty gearboxes like shifters however. It certainly makes it easier for students to design gearboxes. I'd reccomend looking into easy ways for you to lighten gears, or just use the Aluminum gears w/o lightening. The 50T aluminum gears pocketed are about .07 lbs for us, versus .5 for stock steel!

The .003 is kind of a FIRST specific trick. You are actually supposed to not add to the c-c for gears, but since our run times are low and we usually don't have an adequate wear in period it works. The .003 makes up for rougher surface finish on gears, etc... The tradeoff is you're introducing backlash and slightly decreasing strength (very slightly, it's not like .020"). Neither of these are usually a huge concern.

We tried exact C-C + a wear in period on or 2010 drive gearboxes for the sake of "doing it right" and we'll never do that again, it was a waste of time for FRC purposes.


Quote:

Originally Posted by Michael Blake (Post 1070848)
Adam, please send the CAD on your gearbox designs to michaelblake@insurancelabs.com

Rookie team #3481 Brandeis Bronc Botz says THANK YOU for your valuable help!

Since that post we've posted our entire 2009-2011 robots. The kicker on the 2010 and the shoulder on the 2011 both demonstrate such gearboxes. We've made multiple other for misc projects and prototypes.

Chris is me 28-07-2011 13:29

Re: Custom gearboxes
 
Adding .003 of backlash is a plus for us mainly because of our low run time with gearboxes. These see maybe 10 hours of run time, so adding that bit of space makes things run smoother since gearboxes don't really get to break in much. It also gives you a touch of wiggle room if you can't hold thous very well.

Brandon Holley 28-07-2011 16:08

Re: Custom gearboxes
 
I feel the 0.003" adder is most beneficial in terms of artificially shifting your tolerance band. For a gearbox thats used in FRC, its better to be a little bit too far away in terms of engagement, as opposed to too close and bottoming the teeth out.

We use it on all of our gearboxes.

-Brando

mglucido 25-01-2013 10:09

Re: Custom gearboxes
 
Adam, Thanks for your clarion gear guidance. I was wondering ... Do the bearings fit with only water-jet cutting or do you undercut and ream for a perfect fit? We need to build our first custom gearbox this year and we're planning to use your workflow.

Also, if you'd send your gearbox CAD file to mglucido@charter.net, it would be supremely appreciated!

All the best,
Michael Lucido
Mentor, Team 2838 Eaglebots

Quote:

Originally Posted by AdamHeard (Post 1065121)
For varied reduction single speed gearboxes, we've done something that I have poorly named in CAD as "AM based lasered gearbox plates".

It's a neat concept, we decide that regardless of gearing needs, we will ONLY use andymark toughbox gears. That means spurs with a .4 overall thickness, and pinions with a .6 overall thickness. Both already have machined nubs so they don't rub on the bearings.

Then, you can machine gearbox plates by whatever means (we like waterjet/laser as it's obviously fast and allows more flexible design).

Design the plates to be 1.125" apart (we usually bolt onto a 1" face with a .125" spacer.

For assembly, press bearings in, and you can use exclusively AM shafts if you desire. We machine our own to perfectly match our needs and eliminate spacers, but this is not necessary.

Doing this allows you to create custom gearboxes FAST and with minimal machining. We've shown you can get just about any reduction, from 1:1, to several hundred to one.

For my first custom geaarbox, I would go in this direction; utilize COTS gears and shafts. Machine only plates, and possibly standoffs. Spacers should not be necessary if you design it right (standoffs as well possibly)!

If you want the CAD for these to make the concept more clear, let me know.

Oh, last little tip, we also try to exclusively use 50T spurs. this allows us to use the aluminum gears AM sells. We cut weight off with our lathe and mill and get them down to .07 lbs each (versus .5 for the stock steel!).


MichaelBick 25-01-2013 15:46

Re: Custom gearboxes
 
Quote:

Originally Posted by mglucido (Post 1221610)
Adam, Thanks for your clarion gear guidance. I was wondering ... Do the bearings fit with only water-jet cutting or do you undercut and ream for a perfect fit? We need to build our first custom gearbox this year and we're planning to use your workflow.

Also, if you'd send your gearbox CAD file to mglucido@charter.net, it would be supremely appreciated!

All the best,
Michael Lucido
Mentor, Team 2838 Eaglebots

973 and many other teams vary their ream based on the fit they want. If they want a slip fit they will go with the exact bearing OD ream, if they want a press fit they will ream .001 under the OD. Reamers are a very worthwhile investment. The main bearing sizes used for FRC are R6 and R8, so you would want to get .874", .875", 1.124", and 1.125" reamers(we got from maritool, and maritool doesn't sell 1.124" reamers. Does anyone have a good source for reamers this size?)

craigboez 26-01-2013 21:31

You could invest in all those reamers, or just one boring head. Its a lot more versatile and a lot less spend on tooling.

mglucido 31-01-2013 08:26

Re: Custom gearboxes
 
I see that most teams are adding the 0.003" to the center-to-center gear distance. What's the best way to calculate the starting center-to-center from which to subtract 0.003"

- Inventor Gear Calculator? ... Which seems fairly straightforward
- Something better?

Thanks,
Michael

IndySam 31-01-2013 08:44

Re: Custom gearboxes
 
Quote:

Originally Posted by mglucido (Post 1225115)
I see that most teams are adding the 0.003" to the center-to-center gear distance. What's the best way to calculate the starting center-to-center from which to subtract 0.003"

- Inventor Gear Calculator? ... Which seems fairly straightforward
- Something better?

Thanks,
Michael

(gear1 / 40) + (gear2 / 40) + 0.003

(50t / 40) + (30t / 40) + 0.003

1.25 + 0.75 + .003 = 2.003

apalrd 31-01-2013 09:02

Re: Custom gearboxes
 
Quote:

Originally Posted by mglucido (Post 1225115)
I see that most teams are adding the 0.003" to the center-to-center gear distance. What's the best way to calculate the starting center-to-center from which to subtract 0.003"

- Inventor Gear Calculator? ... Which seems fairly straightforward
- Something better?

Thanks,
Michael

(number of teeth on gear A + number of teeth on gear B) / (2 * dp)

For AM gears DP is either 20 or 32, usually 20.

FYI, for a given c-c distance, any combination of gears with the same combined number of teeth will fit. E.g. 25-40 will fit in the same c-c distance calcualted for 20-45.

mglucido 31-01-2013 09:09

Re: Custom gearboxes
 
Thanks Andy and IndySam. I was just working through the pinion relationships to understand IndySam's magic number of 40 and my calculation was off by 20 (on which Andy shines a bright light!).

Thanks!

billbo911 31-01-2013 11:37

Re: Custom gearboxes
 
We are fairly new at building custom gear boxes. his is our first year using Hex shafts in them. Aside from the lack of availability of .5" Hex bearings currently, it looks as though we will also have a need for sleeve spacers in our box. The VexPro Delrin Hex spacers are out of stock currently as well.

So, the question is, what do you use to create sleeves for your .5" Hex shafts?

thefro526 31-01-2013 13:03

Re: Custom gearboxes
 
Quote:

Originally Posted by billbo911 (Post 1225230)
We are fairly new at building custom gear boxes. his is our first year using Hex shafts in them. Aside from the lack of availability of .5" Hex bearings currently, it looks as though we will also have a need for sleeve spacers in our box. The VexPro Delrin Hex spacers are out of stock currently as well.

So, the question is, what do you use to create sleeves for your .5" Hex shafts?

Assuming that the spacers are just spacers and nothing more, you can get round stock/tubing and bore the center out to ~.580" for hex to slide through. Personally, I like ABS plastic for this, but you can use a bunch of different stuff.

Also, the ~.580" dimension isn't THAT critical, but it's something worth trying to hit. The point to point dimension (effective OD) of a .5" Hex is ~.577" so that extra .003" or so just makes everything go together smoothly.

Or if you really wanted to, you could get round stock/tube, bore it out to .5" ID and run a broach through it.... If you're just making spacers, putting a hex into them is kind of a waste since they're not torque transmitting.

FWIW, the same method will work in a pinch for making a hex bushing as well. It's not the 'right' way to do things, but if you've got a low load application that needs to be hex and you can't find a bearing or a bearing won't fit, it's worth looking into.... In 2011, the team I was on ran a 1/2" hex shaft with the points turned down to an effective OD of .5625 and then ran that shaft through a delrin bushing on a roller claw. Just something to keep in your back pocket.

sanddrag 31-01-2013 13:10

Re: Custom gearboxes
 
For spacers, we use 3/4" diameter black delrin rod from McMaster. I second the recommendation to drill it to slip over the hex. We've tried broaching them in the past and the delrin springs back making a really tight fit. We've had to run the broach through 3 or more times to get them to even go on.

ToddF 31-01-2013 13:15

Re: Custom gearboxes
 
We made our own using our Makerbot.


We also made custom gearbox covers.

billbo911 31-01-2013 13:25

Re: Custom gearboxes
 
.580" ID.
.75" rod bored/drilled out.
3D print your own.

Excellent, I think we're good to go!

Gotta love CD!!

artdutra04 31-01-2013 14:48

Re: Custom gearboxes
 
Be careful with 3D printed spacers to ensure they are only used as spacers and not a bearing/bushing surface. If any part of the 3D printed spacer acts as a bushing, it will melt and fail.

I have always been a fan of using using Delrin rod to make spacers, partially because it is low friction and partially because it machines very nicely. McMaster has both solid and hollow Delrin rod, so if you have access to a lathe, Delrin spacers are fast, cheap, and easy to make.

mglucido 20-02-2013 17:13

Re: Custom gearboxes
 
1 Attachment(s)
I just wanted to drop back into this thread to express my appreciation for all the great info here. You all helped us learn how to build a gearbox to gang two CIMs and one miniCIM and gear it appropriately while spanning the correct distance for our lifting mechanism to function.

It was our first custom gearbox and everything just fell into place after studying this thread carefully.

Thanks everyone!
Michael Lucido
Team 2838

xSAWxBLADEx 20-02-2013 17:17

Re: Custom gearboxes
 
You could use these to reference. Great gearbox's!
http://wcproducts.net/wcp-00100/


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