The KoP this year is using belts. Has FIRST told us where they are getting them, or if they will be available to be bought separately? Additionally where have teams bought belts and pulleys in the past (and what post-machining was necessary to get them on an FRC robot)?
We love sdp-si for plastic pulleys, and some general ones.
BB manufacturing is also decent for pulleys and belts.
https://sdp-si.com/ is a good source. In addition to a wide array of standard belts and pulleys, they sell timing belt pulley stock, which allows you to custom turn pulleys out of an extruded profile. Big money saver if you have the machining resources. They also have one of the best center-center distance calculators I’ve ever used.
The belts for the kit bot will come from Gates:
http://www.gates.com/news/index.cfm?location_id=752&id=11637&show=newsitem
All of our belts in the past have come from Gates as they usually offer a few free pulleys and belts every year.
www.bbman.com is our go-to spot. Great customer service, reasonable prices.
-Brando
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Oooh, that calculator is niiiiiiiice.
I’ll vouch for sdp-si. That’s where we get our belts and pulleys off of. I will say that some of their stock is slow to refill and sometimes necessitates the turning down of steel puppies to cut weight due to lack of aluminum pully stock
Gates has been a long-time supplier for FIRST and has donated belts and pulleys for the Kit of Parts for many years. We have used their components nearly every year for the past 6 years with excellent success. Last year was our first year using belts and pulleys in our drive train (instead of chain). The drive train belts and pulleys worked well for us last year, although they do require more precise tensioning tolerances than the #35 chain we used in prior years. We are very happy with Gates belts, but until last year had used almost exclusively the parts they had donated in the kit.
Last year, we asked Gates for a recommendation for a distributor to FIRST teams. At their suggestion, we used B&B Manufacturing. (http://www.bbman.com)
However, after last year’s experience, I cannot recommend B&B Manufacturing to other teams, and we are looking for a different supplier. More details as to why I have made this decision are below.
In our initial order from B&B Manufacturing, they incorrectly shipped us the wrong size pulleys for part of our order. They had the correct part number on the invoice and shipping list, but had simply picked the order incorrectly. This was a completely honest mistake that is fully understandable. After receiving the incorrect parts, I called and spoke with a very friendly customer service representative. She agreed to send out the correct parts, but needed credit card information to charge me for the additional parts, since I had not yet returned the incorrect ones. This didn’t alarm me too much, either, although many companies, when they make a mistake like this, will trust their customers to return the incorrect parts without requiring advance payment in the meantime. My thought was, “Whatever, maybe they’ve had bad experiences with other FIRST teams and are being extra careful.” We soon received the replacement parts, which were exactly as they should have been. I did not yet return the incorrect parts, since we had already paid for them, I thought they might come in handy in a pinch during the last weeks of the build season, and during the height of the build season anything that can be postponed until after ship day gets deferred!
A few days later, our mechanical team more closely examined the belts that had arrived in our order. We found that some of the sizes were genuine Gates HTD belts with a round tooth profile as we had expected, but that other sizes were instead similar Optibelt timing belts with a rectangular tooth profile. We were very concerned about the substitution, as these belts were for our robot drivetrain. I called Gates to inquire about the appropriateness of using these belts as a substitute. The Gates engineer helped me find the appropriate load ratings for each of the substitute belts so that we could figure out if they would work in our application. We learned that our “margin of reserve” would be significantly less with the replacement belts. We weren’t comfortable with using them, although they might be okay. I then called B&B Manufacturing to inquire about the product substitution. They said that they had substituted the Optibelt parts since they had no stock remaining on the Gates belts and that they should be the same as the Gates belts. I explained my call with the Gates representative and the B&B Manufacturing technical representative then agreed that I could return the belts for a refund when I sent back the pulleys which I had not yet returned. I then ordered HTD profile belts from Stock Drive Products / Sterling Instrument (http://sdp-si.com) to fill our immediate need. For the time being, I also held on to the Optibelt belts from B&B Manufacturing until I received the SDP-SI belts.
Fast forward a couple months later until after the end of the FRC season. The Gates belts I had received from SDP-SI worked fine all season, and I no longer needed the “safety net” of having the incorrect-size pulleys and Optibelt belts, so it was time to send the order back to B&B Manufacturing.
Since none of the items I needed to return had been used at all (not even for a “test-fit” installation), I packaged up all the items in a box, completed the RMA form for the incorrectly-picked pulleys, explained everything in a letter, returned the items to B&B Manufacturing, and expected all to be well. (At this point, I was still a happy, satsified customer – a little frustrated at the unauthorized product substitution, but still planning to come back this year as a repeat customer.)
Then, however, I received an email from B&B Manufacturing acknowledging receipt of my shipment, but with the following note associated with the line items for the Optibelt rectangular profile belts I had returned:
I called to follow up and protest. I spoke with the same customer service representative as I had for my initial pulley issue, and she said that this was the best that they could do. They had no record of my previous call with their technical department that said to return the Optibelt belts for a refund and insisted that the Optibelt belts were exactly comparable. I explained that the tooth profiles and load ratings were different for the two belts and that the difference was significant in our application, but to no avail. Oh well, I figured, the difference in money wasn’t huge – even a full refund of the belt price would have been only $71.36
Then, however, another few weeks went by, and it was time to reconcile our end-of-year financial reports. I was surprised to see that we never actually received any parts credit from B&B Manufacturing. Both of our payments (the original order and the “replacement” order to fix their mistake) were charged, but no credit for our returns.
I wrote a new letter explaining the entire saga, attached it to an email, and sent it off to B&B Manufacturing. Within a day, I received a brief reply from the customer service representative saying that my letter would be given to accounting and that I should see a credit in a day or two. Approximately one week later, I received a partial refund to my credit card. The amount was about 75% of what I expected ($120.77 instead of $163.16) and I haven’t been able to figure out how they came up with that total. No explanation or correspondence came to me from B&B Manufacturing. At this point, I’ve decided to “cut my losses” and just look for a different supplier next year – it doesn’t seem to me that B&B Manufacturing gets “Gracious Professionalism.”
In all honesty, the “product substitution” issue upsets me the most. When I’m referred by a manufacturer to a distributor to buy that manufacturer’s parts, I expect to get the parts I ordered. In my day job on government contracts, this kind of product substitution is called “counterfeit parts” and is a big no-no. Substitutions of parts that are similar, but not the same, are the kind of substitutions that can result in airplane crashes when prime contractors aren’t properly notified. If I were Gates corporation, I’d be furious that a distributor I recommended were instead selling a competitor’s products to a customer I had pointed their way!
We’ve had no problems like the above ones with a “premier vendor” such as MSC, McMaster, or AndyMark. Sure, we’ve had mistakes in shipments from all three of these “premier vendors” but they always fix the problem quickly and efficiently without any hassle. If only such suppliers carried the range of Gates products at good prices, we’d be all set!
Can anybody out there recommend another Gates distributor? We’re generally happy with SDP-SI, but they are expensive (we don’t get any discount from them), often have limited stock, and seem to charge a lot for shipping.
What do you do to Gates belts in order to allow power transfer?
Ditto,
We have made our own pulleys from SDP-SI models as well. It seems to work well and so far no issues. Its a super low cost option to buying them but it requires a CNC mill/laser/water etc…
-RC
I’m curious as to how you “make” a pulley. Does this involve not having a flange on the edge, or somewhat complicated machining?
Its not bad at all really.
We plan for the 2013 season to just buy .375" plate. Router out the shape and do the bore at the same time (not out the corners of the hex). Create a bolt flange pattern similar to the bolt pattern AM/IFI uses. And just rivet on 1/32 flanges out of polycarb or 1/16" polycarb.
Our biggest gripe is normally just getting the pulleys along with changing ratios down the road with belts. So having the ability to make whatever size pulley we want is awesome. I’ve contacted the FIRST gates rep about models before and they’ve been happy to send pdf’s or coordinates of the belt/pulley profile. I’d love to just find a generator, but no luck so far.
-RC
Huh. That makes more sense than I thought it would.
What do you mean by this?
So instead of broaching later, you can just mill out the corner of the hex. Allowing you to fit the part over hex shaft without broaching. Used this technique on our shooter wheels last year and our arm sprocket.
-RC
Is it possible to design a pulley of any size with just the belt profile?
We made some pulleys of weird sizes out of acrylic for the 2012 season that were light and cheap, but it took some tweaking to get it right.
-Mihir
We don’t use the belt profile but instead the actual pulley profile.
We use only GT2 5mm x 9mm wide. But you can use other sizes: 2mm/3mm work, 973 used those sizes successfully this year.
-RC
Never though about doing hex like that. Makes a lot of sense. And it saves our team kinda a lot in terms of us, if ever switching to hex (hopefully!) the we wouldn’t have to buy a broach machine.
I’ve used this method before on other non-FIRST projects that required high precision hex alignment, and it works quite well. The only downside is that you can’t go very deep with it on small hex sizes. Typically you don’t want to broach very deep anyways, so it’s not usually a problem.
That being said, in most cases it’s easier to broach. You can hex broach most wheels/hubs for FIRST with just a regular arbor press and some cutting fluid if you’re careful, so it tends to require less time than trying to mill it. If you have access to a mill, you most likely have access or room for a press that can broach.
I’m surprised there hasn’t been any action on this thread since the game was announced and we got the details on the drive parts in the KoP. Maybe it’s in another thread that I’ve missed, but I’ve searched and haven’t seen it.
The KoP contains two 39-tooth aluminum pulleys, 5mm pitch, 30mm wide. The belts are 15mm wide, so the idea (I presume) is to run two belts side by side on each pulley, going to 15mm width pulleys on separate wheels. Not sure I would have designed it that way, because I don’t like the belts rubbing where they cross, but I guess it will work.
The part number given in the Drive Base checklist is P39-5M-30 AL. Searching for “pulley” on AndyMark yields the am-2265, which gives more details such as Gates part number 39-5M25SP01. I can’t find either part number, or anything like them, on Gates (or McMaster, or anything else). I’ve found pulleys (or “sprockets”) for 5mm HTD belts, but only in 15mm widths.
We’re considering using a different size pulley on the gearbox driveshaft, to change the torque/speed characteristics. For now, we’ll try to stay close to the original design of two belts coming off the drive pulley, but we may need to change that. AndyMark doesn’t sell any other size, and I can’t find it anywhere else.
We don’t have the ability to make these parts from scratch. We could combine two smaller pulleys, machining off the flanges where needed (but maybe best to leave at least one flange). How to mount these would be a design consideration, but I think we can figure that out.
Any help on finding sources for these parts would be greatly appreciated. Links are especially helpful.