After hearing about Rush many times on this board and never having used them we thought we would give them a try. We all see after their name that they are expensive but I figured that would be just a bit higher than Small Parts since Small Parts is only restocking gears from Boston and other manufacturers.
Let me tell you was I ever wrong! We went to order an 80 tooth 20 pitch 20 pressure angle gear, needed it in about a week. Just to get a quote on the gear you needed to fill out all of the account paper work, took over a day to process, then the quote came back.
[gets up from floor after nearly having heart attack]
per gear the price was over $900, yes that is in hundreds, we thought they maybe screwed up the decimal place since they were under $100 every where else. Nope. I think that Rush shouldn’t even be listed as a source for FIRST type robots. After a bit more searching we found that Motion Industries had them all in stock at way under $100 each and they are ready for pickup in only 2 days. I think it would be beneficial if we get together a white paper or similar listing valid sources for the different materials that teams use. It could save allot of teams allot of time.
We used McMaster-Carr for gears last year, and they were pretty reasonable. They also ship very quickly, and shipping rates are low.
We’re going to try WM Berg this year, because McMaster doesn’t have exactly what we need. McMaster-Carr has a wide selection, Berg has THOUSANDS of gears.
In terms of sources, I really wish FIRST had chosen McMaster rather than MSC as the primary vendor. The MSC book has a lot of tools, not a lot of parts compared with McMaster. The McMaster web site is also much easier to use. I don’t see us ordering anything out of the MSC catalog.
Rush Gears is targeted toward industries that ask themselves: “How much money is lost PER MINUTE while my machine / assembly line is inoperative?” For these companies, $900 to have that non-standard gear machined and shipped overnight is a steal.
I agree, Rush Gears is not a good source for FIRST teams. We are simply not their target market.
In all honesty, I find that most gear companies, WM Berg included, seem short on gears made out of materials other than aluminum, stainless steel, and plastic. I spec’ed out Martin gears this year, because they were the only ones I could find that were made of “regular” steel. Their prices (through Applied Industrial Technologies seem reasonable to me as well.
I’m having trouble finding the bearings I need, however. A comprehensive, and regularly updated, list of where-to-get-things would be very cool indeed.
Here is what we have been doing for the last four years: Go to Motion Industries for ALL our stuff. What we do is look online at primarily Berg, Martin Sprockets, and Boston Gear. Sometimes Stock Drive and PIC Design (0.7 module gears). They all have the specs and part numbers online. All of our standard bearings come from SKF and our slim large cross section bearings from KAYDON. We compile our list from each vendor and fax it to our local Motion Industries rep. It took the first year to get them used to us, but now I know our rep by name and he knows what I expect. They will look at all the gear companies to find the best price and get back to us with anyone who takes longer than a week. They are definitely the way to go.
About gear selection. 32 DP Stainless steel gears work fine for most drivetrain stuff. The only gears that really need to be regular steel are the output gears. My recommendation is 20 DP from Boston or Martin (very interchangeable) for the output.
2 things reduce the life of gears: Contact Stress and tooth bending. Very rarely to FIRST gears wear from contact stress (the even wear of a gear tooth until it is a razor blade). Most failures I have seen have been tooth bending. The 2 largest factors driving that are tooth size(Tooth Size goes up as DP goes down) and gear width (face width).
We never use brass (why? it is as heavy as steel … well, very close) and use aluminum on the 1st stage of our gearbox. Stainless gears from Berg are very good for the rest of the gears except the output as I said above.
On Team 824, we experimented with cutting our own gears. The logic here is that a complete set of involute gear cutters for a specific DP would be a cheap investment over 2 or more competition seasons as opposed to buying new gears every year.
We can cut aluminum gears okay, but I made the decision to just go with store bought gears this year. The technology is new enough such that I don’t want to deploy it into the field without extensive testing. We can probably cut steel (and possibly even titanium) gears with our setup, but there would need to be some extensive modification to the machine, namely to get high torque at low RPM that these materials cut best at.
We used a Sherline CNC setup with some custom tooling that myself and some of my high school students made. We will probably put out a white paper on this after the competition.