So last year our drive train had some issues with a center chain in a WCD, so we decided this was finally going to be the year we actually made a direct drive gearbox in order to fix these problems. This is what we came up with. Its a direct drive single speed gearbox with toughbox spacing except for 12 tooth pinions instead of 14 tooth pinions. The only question I have is if the material surrounding the bearings is enough. Right now they are between .2 and .3 inches. Should I make them thicker, or is that good enough? Also do you think there is anything I can do to make it better.
It’s probably thick enough. I think the standard is .25".
This looks pretty similar to WestCoast Products’ shifting gearbox. So similar, in fact, that I question the need for you guys to fabricate your own. I doubt you can do much better than their price of $250 per gearbox, and you’ll save a lot of time. Of course, if the goal is to get experience in design and machining, by all means go ahead.
I looked at the WCP gearboxes, but we dont have the money for the dual-speeds, and I really dislike the ratios on the Single speed. The ratios this can get are much better for our needs
I’ll echo what T^2 had to say, and suggest you take a serious look at the WCP SSes. I’m not sure when you last checked, but they’ve updated their product line since the season. You can get a reasonable ratio on basically any FRC diameter wheel out there, and I’m fairly sure that you can get a similar gearing to what you’re getting with the Toughbox. They’re really awesome products for the money, and we’ve been very satisfied with out DSes.
For 6 inch wheels they jump from 7.9FPS to 16.5FPS. There is no in between with the WCP ones. That is tough, because in most games 7.9 is too slow, and 16.5 is too fast for a single speed. Plus at $150 a piece, we have bought all the gears, shafts and materials for about $100, which is much cheaper. If they could get a 10FPS option with 6 inch wheels, that would make them look better, but they would still be too expensive.
I know 6 inches are big, and we plan on using 4s, but I like contigencies. Also, can you fit an AM Kit wheel or a VexPro VersaWheel onto the 1.25 inch output shaft? Everytime I look those wheels are wider, and I don’t even know how you would mount those to a 1.25 inch long output shaft.
WCP sells theirs single speed for $150, are you saying you can make the above single speed for $50? I’d love to get your suppliers :rolleyes:
Not trying to pick on you, it’s just I’m not buying the cost argument.
Making your own box for people to learn, so it’s yours, so it’s cool, etc… are all valid reasons, but I don’t see this saving appreciable amounts of money (and it saves that money at appreciable amounts of time).
EDIT: On some more thought, $50 per gearbox isn’t implausible. It’s a little lower than what we spent, but not impossible.
Someone somewhere may have told me prices will be going down sometime.
Just don’t knock out WCP’s gearbox. I’m holding some in my hand right now and it’s a beautiful thing with perfect ratios. Like you mentioned it is for a WCD which is designed for 4" wheels. If you’re making a WCD you should have no need for anything larger than 4" wheels.
Contingencies are always a good thing, but remember ‘jack of all trades, master of none’. You often are making sacrifices to be able to account for large varieties of wheels, etc. While this time of year is absolutely the best time of year to explore those options, when its time to start spending money and cutting metal on a build-season robot, the best bang for your buck may be a very focused design.
For shaft mounting the width of the wheels is not what matters, the length of the hub is what matters. A hub does not necessarily need to span the entire width of the wheel. A 1.5" wide wheel may operate perfectly fine with a 1" long hub, and still leave space for a .25" spacer between the hub and bearing on a 1.25" output shaft.
Total cost not including the metal for the plates, is $101.8 all from Vex. Thats enough for 2 gearboxes. The only thing that doesnt include is the sprockets, which the WCP doesnt include either so its moot.
As for machining, at our school we have 9 lathes, 3 mills, a CNC, and students who know how to use all of them. During week 1, we have kids that are much more interested in machining then designing, so we can make these during down time, when we don’t have a full robot designed yet.
I’m not writing them out, and if we run into trouble that will be option 1. But I think we could do it more efficiently, cheaper and more focused to our needs by doing it manually. Plus it will keep the students occupied week 1.
Also what 4 inch wheels actually fit the 1.25 inch output shaft? I’d love to know, so we could make ours even shorter if needed.
Also if you want to use wider wheels what we did was tap the end of the shaft and put a spacer(we put hex, can be round) to get the extra length needed.
Keep in mind that the WCP product is an end all solution. It just works. If you design your own you will need to prototype(you will not get it right otherwise). Also you will have to make your own replacements if parts fail(WCP takes care of you on this). Lastly the time can just be better used elsewhere. Sure people may not like designing, but prototyping is very important. If you don’t want to buy premade bearing blocks(WCP sells COTS ones too) than those need to be amchined for a WCD. Drive rails and shafts are more things that can be machined week 1.
This has been a recurring theme of commenters in several threads: “Why would you build X when you can just buy it? It will save time, money, be more reliable, you can spend time doing more productive things, etc.” I think we can all agree that there are very good reasons for buying stuff off the shelf, and we’re all aware of the upside in doing so. Is it really necessary to first point this out before helping answer a few good questions?
The goal of all FRC teams is not to build the best robot as efficiently as possible. Many teams try to learn, do new things, and knowingly do things the hard way.
Just think if some 6th grader would have given you a calculator in 3rd grade and said “Here, use this instead of doing that long division stuff. It’s much faster and you’ll make fewer mistakes”.
That’s what the offseason is for. It’s great if you’ve tested an idea in the offseason, but very rarely will a team be able to implement a new custom design in the season and be more successful than a COTS alternative.
tl;dr: Learn in the offseason, apply in the build season.
We are actually building them right now. The plates are currently at the waterjet shop being made as I type this. We also plan on running this test robot at the offseason events this fall. We are prototyping, and if it fails we will look elsewhere. Thats why i was asking for suggestions on the actual design itself, not if we should use it.
However like everyone else says, you’re building the WCP transmissions. It would be a lot better learning experience for your students to develop something entirely new that fits your needs. All of my team’s transmissions have been COTS, and will continue to be COTS in the future, however I’ve definitely tried developing my own gearboxes in CAD that were unlike any I’d ever seen, and that has been the greatest learning experience to me.
