Timing belt in drive success

[Chris is me]

Originally Posted by BrendanB

Using the SDP calculator for spacing will the belts loose tension overtime?

Not even a little bit. Use the GT2 tooth profile and do the math.

[trilogy2826]

Originally Posted by AdamHeard

We used Gates gt2 belts exclusively on our 2012 robot on nearly every system

Does anyone have experience manufacturing the GT2 sprockets? Gates specifically warns against using their CAD to make physical sprockets. The available sprockets seem inefficient from a weight perspective. We have the tools to do this, but without being able to confirm the tooth profile, it is a risk. Either way, I will make some up and let you know how they work out.

[BrendanB]

Originally Posted by Chris is me

Not even a little bit. Use the GT2 tooth profile and do the math.

Thank you Chris & RC!

[Akash Rastogi]

Originally Posted by trilogy2826

then the sprocket flanges popping off and the belts shifting over the sprocket edge

Since you mentioned this, and we had that problem too (3929's belt driven shooter), what was your fix? Our quick fix at a competition was just to loctite it in place and it held up after that.

[AdamHeard]

Originally Posted by trilogy2826

Does anyone have experience manufacturing the GT2 sprockets? Gates specifically warns against using their CAD to make physical sprockets. The available sprockets seem inefficient from a weight perspective. We have the tools to do this, but without being able to confirm the tooth profile, it is a risk. Either way, I will make some up and let you know how they work out.

We are machining some 24T 5mm gt2 9mm width pulleys currently that we will be using on a prototype. I'll update with results.

We cut 2 test items on our router that felt really nice on the belt by hand, and the full set is being cut on a production cnc so I can only a high quality.

We cut off of the sdp-si CAD.

[s_forbes]

Originally Posted by AdamHeard

We are machining some 24T 5mm gt2 9mm width pulleys currently that we will be using on a prototype. I'll update with results.

We cut 2 test items on our router that felt really nice on the belt by hand, and the full set is being cut on a production cnc so I can only a high quality.

We cut off of the sdp-si CAD.

I will be interested to see how that turns out.

Our belt system was sketchy last year, but sufficient enough to last through a regional and champs with no failures. Lots of lessons learned, primarily that the tension required in the belts necessitates a stiff frame (our fiberglass material is good stuff, but flexes way too much). Especially with a serpentine path and cantilevered idlers.

Interesting to note, we used 5mm pitch GT2 belt profile coupled with HTD sprockets. Not optimal, but functional enough to work well if the rest of the system is designed properly. We did this for cost purposes, the HTD sprockets were given to us as a sponsorship from Gates. Had we used the proper profile for the pulleys the drivetrain may have performed better, but it worked great at competition.

An entertaining video from when we were testing the first iteration of our idler system. We fixed this with a better idler design.
http://www.youtube.com/watch?v=8YQk0fjhk-o

[Chris is me]

Originally Posted by trilogy2826

Does anyone have experience manufacturing the GT2 sprockets? Gates specifically warns against using their CAD to make physical sprockets. The available sprockets seem inefficient from a weight perspective. We have the tools to do this, but without being able to confirm the tooth profile, it is a risk. Either way, I will make some up and let you know how they work out.

We bought pulley stock and machined it down at home. Not too hard to work with. You'll want a number of teeth divisible by three if you can in order to make it easier to hold in a three jaw chuck, but it machines easily and you can easily remove the hub or any other features you might not want.

This year, since we do belts-in-a-tube, we just had a single piece of pulley stock both belts ran on. Worked great.

[steelerborn]

A lot of people have a bias toward chains, and like to give belts a lot of negatives they don't really have. Just do some research and you will be surprised all of the different applications belts were used in.

I would still use a tension system only because it makes mounting much easier. I used sdp-si for all my designs my only negative is sometimes they are out of stock for belts sprockets and can take quite some time for you to get your parts, and that would be horrible if it was in the middle of the build season . Just got to be sure that you have a good selection of sprockets in stock or modify your design for what is in stock.

Just out of curiosity what width belts does every one use, I see alot of 3/8 inch belt out there. But I think you could probably go smaller without the fear of breaking a belt.

[R.C.]

Originally Posted by AdamHeard

We are machining some 24T 5mm gt2 9mm width pulleys currently that we will be using on a prototype. I'll update with results.

We cut 2 test items on our router that felt really nice on the belt by hand, and the full set is being cut on a production cnc so I can only a high quality.

We cut off of the sdp-si CAD.

We did the same thing with a few pulleys, looked pretty close. A Gates Rep said SDP-SI pays them to use their formula. So I figure the model should be super close? Maybe?

Originally Posted by steelerborn

A lot of people have a bias toward chains, and like to give belts a lot of negatives they don't really have. Just do some research and you will be surprised all of the different applications belts were used in.

I would still use a tension system only because it makes mounting much easier. I used sdp-si for all my designs my only negative is sometimes they are out of stock for belts sprockets and can take quite some time for you to get your parts, and that would be horrible if it was in the middle of the build season . Just got to be sure that you have a good selection of sprockets in stock or modify your design for what is in stock.

Just out of curiosity what width belts does every one use, I see alot of 3/8 inch belt out there. But I think you could probably go smaller without the fear of breaking a belt.

For GT2 5mm, common widths are 9mm and 15mm. We plan to use a lot of 9mm for all our non drive items. Rollers/Conveyors/Grippers etc... For Drive, 15mm would be pretty safe, but I bet you can probably get away with 9mm.

Adam can comment on the other smaller pitches of GT2: 2mm and 3mm. I believe the widths are a lot smaller?

-RC

[IndySam]

Originally Posted by AdamHeard

We are machining some 24T 5mm gt2 9mm width pulleys currently that we will be using on a prototype. I'll update with results.

We cut 2 test items on our router that felt really nice on the belt by hand, and the full set is being cut on a production cnc so I can only a high quality.

We cut off of the sdp-si CAD.

Hmmm, we may have to try and waterjet some as an experiment. Being able to cut the profile and the hex might be a huge savings in time and cost.

Wonder if we could cut them out of 1/4 stock and stack them.

[Chris is me]

Originally Posted by steelerborn

I would still use a tension system only because it makes mounting much easier.

We came up with a simple solution this year to make mounting stupid simple. I don't have any photos of it, but I can try to find one if someone wants it. Basically, we milled the bearing hole in the chassis with a small groove in it toward the center that would let us insert the axles and belts with slack. We then pulled the belts tight, riveted a bearing retainer on the outside, and placed the bearings in. This made installation super easy and after we did that, we never touched the belts again.

Just out of curiosity what width belts does every one use, I see alot of 3/8 inch belt out there. But I think you could probably go smaller without the fear of breaking a belt.

We used 15mm this year, which was strong and safe enough for our needs. Like RC said we would probably use 9mm for anything else. Always GT2 profile unless you need to save money or something.

[Brandon Holley]

Originally Posted by AdamHeard

The kop pulleys are 5mm pitch HTD. Which 125 ran in drive this season (and possibly before?).

Sorry I'm late to the party on this one, I severed myself from the internet to enjoy the long weekend.

We ran 5mm pitch HTDs, 15mm width in our drive this year with remarkable success. We assembled our tensioner-free drivetrain and didn't touch the belts or wheels all season (that includes the tread too, thanks Colsons).

The main reason we used HTD vs GT2 was to take advantage of the KOP options and save a little bit of money. HTD profiles also appear to be a lot easier to find, especially in plastic if thats something you are interested in doing.

We loved the belts this year and I see no reason we will not continue using them in our drive and in other areas for a long time. We may switch over to 9mm width GT2s just to save some real estate, but either way, belts are here to stay for us.

-Brando

[BrendanB]

Originally Posted by Chris is me

We came up with a simple solution this year to make mounting stupid simple. I don't have any photos of it, but I can try to find one if someone wants it. Basically, we milled the bearing hole in the chassis with a small groove in it toward the center that would let us insert the axles and belts with slack. We then pulled the belts tight, riveted a bearing retainer on the outside, and placed the bearings in. This made installation super easy and after we did that, we never touched the belts again.

Chris if you have a picture that would be most appreciated! Ingenious solution!

[trilogy2826]

Originally Posted by AdamHeard

We cut off of the sdp-si CAD.

Thanks for the point in the right direction. I was assuming (why do I keep doing that) that the Gates proprietary profile for GT-2 would not stray past their walls. I did an overlay of the SDP/SI 24T and the Gates 24T and they are indeed different in tooth geometry. Not much, but just enough to heed Gates warning about not using the CAD to machine.

We will be running a batch using low-voltage EDM, which will (I believe) give the most accurate resolution and accuracy. I am hoping the smoothness spec can still be met with this technique. We will probably be teflon coating these. so it should not matter. If you want to trade an EDM for a milled sprocket sometime, let me know and we can compare/contrast.


Also, if you don't go down the Shaker sprocket route and want to add flanges, what is your technique? Our current method is to laser a flange, press in the flange angle guide, and bolt it to the sprocket. If there is a way to do this without post machining the sprocket, that would be handy.

Originally Posted by IndySam

Hmmm, we may have to try and waterjet some as an experiment. Being able to cut the profile and the hex might be a huge savings in time and cost.

Wonder if we could cut them out of 1/4 stock and stack them.

We tried the following techniques in the 2011 and 2012 offseason to manufacture sprockets and gears:

1. Laminate plates riveted, glued or bolted together to a consistent thickness: Laser and waterjet 0.04, 0.08, 0.125 and 0.25 6061 AL and Steel. Result: Any thickness over 0.08 resulted in a kerf that ended up damaging the belt. 0.04 and 0.08 cut accurately, especially in steel, but the multiple laminations required for a given thickness were difficult to align, even with a complex process and a custom jig. Moreover, the laminations presented a "roughness" that drastically decreased the life of the belt. Overall, not recommended.

For what it's worth, this technique has worked very well for us in gear manufacture from small to large (thanks 148 for the inspiration)

2. EDM the sprocket profile to the desired thickness. Works great with gears and I will be trying them on GT-2 belts in the next couple weeks

I would like to do a cost/benefit analysis of make VS buy and machine Vs EDM... eventually.

[AdamHeard]

Jake, it must be awful nice to be able to get the finish from the EDM.

I'm hoping the milled profile works for us, I can't imagine it won't with how low our runtimes are (even on practice bot) compared to industry. I wouldn't be surprised if it leads to a bit of belt wear. I'd be willing to swap some down the road.

Our dream is to run 5mm pitch gt2 9mm wide in 24T with exact c-c; per the math this is marginal, so our expectations is that our prototype will fail. We would then run with tensioners.

We're machining our pulleys in one shot into a large block (as attached). We then will hold these on a mandrel to lathe the rear side to length and diameter at size. At this point a flange is generated. For the other flange we will bolt on a .032" plate (easy for us to router) with #4-40s.

987 had a very cool process for their large pulley that we plan to copy for large and less critical pulleys in the future. They picked the drillsize closest to the proper radius for the root of the teeth, and drilled all the teeth. They then used a mill cutter capable of an undercut to remove the top of this material all the way around leaving a flange.

We used the same process as you for cutting plate gears this season, in 24, 20 and 16DP. They initially look nasty, but quickly wore smooth. We LOVED it, and probably cut over 100 gears. I'm sure you guys did as well.




RC, for 2mm and 3mm pitch gt2 we primarily used 6mm wide. I really need to clean up Encore's CAD to a quality I can post so teams can see how timing belt is really easy to effectively integrate. Utilizing this smaller belts (which are still KILLER strong if you use them right) we were able to package much larger reductions in smaller packages than possible with #25 chain.