25-07-2013 20:42

jman4747

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

I like it so far especially for a first gearbox I just wanted to add that you could aquire CAD files for vertualy any standard gear at rushgears.com and a good practice also is to go to some place like mc master carr's web site, VEX pro, or granger find stock gears to base your designs off of. Also I had a question about what your reduction was and how heavy this box is?

25-07-2013 20:48

bardd

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

Thanks for the tip, I'll look into it when I get the time for alterations. The gearbox is 2.7lbs, I'll try and make it lighter.

25-07-2013 21:26

cbale2000

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

Trading out the middle portion of the gearbox frame for a polycarbonate version might save a bit of weight.

Honestly I never understood why so many gearboxes (like the toughbox) use metal enclosures between the plates considering its probably the most structurally insignificant part of the whole thing.

25-07-2013 21:35

HammadB

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

While I don't know which gears you're using specifically and thus their bore sizes, maybe try a smaller gear size on the second stage. You could obtain the same reduction using AM 14 and 28 tooths etc and make the box more compact and a tad lighter.

Additionally replacing the enclosure with some standoffs would retain structure but save considerable weight.

25-07-2013 21:37

magnets

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

I'd recommend replacing the metal enclosure with some standoffs, then if you need to, put thin lexan shields around it. Also, the CIM motor shaft isn't supported on both ends, so you don't really need the outer plate to be that big, and you could make it about half size. Also, you could probably get away with making some holes in both plates, depending on their thickness.

I can't tell from the image, but it looks like the CIM is held on by two screws. It's a better idea to make the top of the CIM flush with the plate, and cut a 0.75" hole in the plate for the top of the CIM to sit in.

25-07-2013 21:54

KrazyCarl92

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

From an interchangeable part standpoint, why not have the hole for the CIM shaft/boss in the side plate be on both side plates? This way, you can make 2 of the same part per gearbox and have more flexibility if you need to replace anything.

25-07-2013 22:46

Chris is me

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

How are you making the metal piece in between the plates? Machining all of that from solid seems like way overkill for what a couple of standoffs could do.

If you want an enclosed design easily, you could take a page from the Toughbox Nano and build this gearbox out of tube stock.

26-07-2013 05:52

bardd

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

I couldn't find a gear combination that can use smaller gears without altering the ratio too much. Unfortunately 14 to 28 can't work, both because in that case the output shaft will intersect the 50T gear on the first stage, and because there's no 28T with 0.5" hex bore. There is a 29T one, but still too small.

The hole exists. You can't see it in the picture though.

The output shaft sits on two different bearing sizes (0.875" in the back and 1.125" in the front), so the front and back plates have different holes for the bearings too.



Most of you recommended standoffs, I'm going to try that. I'll try and make holes in the plates too. Christ- ehh... Open profile version will be coming early.

26-07-2013 16:09

bardd

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

Made some changes, introducing BarBox 2.0:

New weight: 1.75lbs



Thanks for the tips everyone!

26-07-2013 20:03

Redo91

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

One other thing to think about when designing your gearbox is how you would mount it.

26-07-2013 20:07

bardd

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

It's a bit similar to how you'll mount a toughbox. You attach the bottom four screws to a channel with fitting holes, and have the shaft go through another hole in the channel. There are other ways to do it but that's the way I wanted to mount the gearbox so that's what I designed for.

26-07-2013 20:24

Redo91

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

What machining capabilities do you have available to make your parts?

26-07-2013 20:25

bardd

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

I don't, but this is not supposed to be manufactured, it's just for practice and fun.

26-07-2013 22:52

cadandcookies

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

I'm liking your progress so far! It reminds me a lot of one of West Coast Products' gearboxes.

Small nitpicky thing on your latest version-- the edges are looking rather sharp. Whether you're planning on manufacturing it or not, it's best practice to design for manufacture, and nearly any manufacturing method that you would use in competitive robotics is going to need to have some sort of radius where you're cutting. I personally design most of my practice stuff to be manufactured with a 1/2" endmill because our primary machining sponsor uses CNC mills. Also for sharing screenshots, you might want to use shading with edges (most CAD programs have different rendering modes-- wireframe, shading, shading with edges, etc), which would make it a bit easier to pick out the finer points of your design.

Just something to consider for your designs.
(Also, I love the color scheme-- red and black looks very snappy!)

26-07-2013 23:30

Trent B

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

Another benefit of designing for an endmill radius, is it will get rid of some of the stress concentrators in your design. The round rings and cross member meeting spots appear to be a pretty sharp angle which could be prone to failure.

27-07-2013 01:07

Adrian Clark

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

Why is this necessary?

And a note on standoffs: It's very hard to find .375 OD tube with #10 clearance ID. Rather than buying .375 rod and drilling it out I prefer to buy .0625 wall with .375 OD and put .0625 deep counterbores in the plates to capture the standoff. Makes things much lighter and simpler to make.

27-07-2013 01:13

R.C.

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

Ditto,

If your turning down the back guy currently to .375", you might as well save yourself time and just lathe it down to .500".

I know it might be lighter to go that smaller bearing but honestly, its much easier programming/making 2 of the same part then it is 2 different parts.

Adrian,

We do about the same thing, buy .375" OD Tube with a .235" ID. 1658T41 - McMaster. We go parting crazy and you can make a lot of spacers in no time, especially on a bar feed . We use this material for the gearboxes we make. Do you really need the cbores? We've noticed its incredibly harder to assemble gearboxes that way.

-RC

27-07-2013 03:11

MichaelBick

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

I agree that counterbores are harder to assemble with and unnecessary. What we've been considering for next year is buying aluminum 6063 .375" OD tube with .145" ID and still machining it out. While we will have an extra step, the ID will be closer, the hole will be centered throughout, and our drills will not gum up because we are taking out quite a bit less material. However I'm worried about the 6063 aluminum. I've heard it is a bit less strong than 6061 and more gummy. I'm assuming it will be fine but if anybody else does this I would love to know.

27-07-2013 04:24

R.C.

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

That's not a bad idea. You shouldn't have issues with 6063, it is weaker:

6061: http://asm.matweb.com/search/Specifi...ssnum=MA6061t6

6063: http://asm.matweb.com/search/Specifi...ssnum=MA6063T6

But I can't see you having an issue with loading them as "spacers". As we've been using 6063 for all our spacers since its so darn cheap/easy. We also use a handful of plastic spacers on gearboxes as well. No issues with either or.

6063 can gum up pretty badly when machining but your taking off so little that it shouldn't be an issue. We sometimes drill out the current spacers for 1/4" bolts.

-RC

27-07-2013 04:45

bardd

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

I took this into account. the edges do look sharp, but that's because of the render's angle. In reality I planned radii for the corners, so the whole thing can be milled with a 0.2" endmill.

The different sizes are necessary because of the shaft's shape: the back end is 0.375" and round, the front is 0.5" hex. The fitting bearings for each side are different in size. I could change the shaft to allow using the same bearing, but then it'll have to be manufactured instead of just buying it from andymark.
As to the standoffs, I didn't actually consider how to make them... I'll look into it.

Thanks for the comments everyone!

27-07-2013 14:09

AdamHeard

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

We do everything mentioned in this thread in various spots; counterbored, the specific 3/8" tubing above, and plastic spacers.

We choose them in different spots depending on the alignment required. Very few of our gearboxes have their alignment and spacing entirely set by the standoffs. Those that do (like our drive boxes) we generally will counterbore, but not always (as it is a more time expensive process).

The aluminum tubing we use when we just need to attach two plates together for stiffness, but aren't counting on it for any alignment. I'm a big fan of clamping frame members with gearboxes, and the frame member handles all alignment. This specific tubing size is something 254/968 found on mcmaster a while ago and have shared with others as it's convenient. There is no concern of failing this tube, even w/ it being 6063. We use it in high loaded situations no problem. The time saved over drilling is really nice.

We use the plastic standoffs for the same reason as above, but when the load is lower. This is an example; 94639A134. This ENTIRE series on mcmaster/fastenal is just awesome. I'm proud that we introduced it into FRC as it has saved us so much time. They come in standard thickness from 1/8" to inches, in varying OD's per bolt size. We use them all over the robots and save massive time. They come as an ugly nylon, but we RIT dye them black and they're beautiful.

In summary, all the ideas posted about standoffs are valid so far, but they apply to different cases. It's not a good idea to assume that because you want things to work well at the system level, all parts MUST be super precise.


Using an off the shelf is a great idea if you have limited access to fabrication. It can even be a great idea when you do have access if the shaft meets all your needs. We've got a full, capable shop for FRC and we LOVE not having to make parts!

27-07-2013 18:29

Adrian Clark

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

Like Adam said, using an off the shelf shaft is a great idea. But I would recommend using a .375 ID 1.125 OD bearing from andymark so you can make the plates identical.

01-08-2013 13:43

bardd

Re: pic: Introducing BarBox: My First Attempt at Gearbox Design

I haven't thought of that... Thanks for the tip. I'll try and incorporate this in the design.