mating 2009 rover wheels and sprockets

[smcmahon]

Good morning. 2656 is trying to repair our Lunacy robot for an upcoming event. We had some issues with the bolts that mate the Rover Wheels and sprockets together.

According to this PDF, the wheels and sprockets both utilize a #10 mounting hole. Needing more of these machine nuts and bolts, I went to The Home Depot last night. I bought a few bags of #10 x 32 2" machine screws (with nuts).

http://usfirst.org/uploadedFiles/200...%20Rev%20B.pdf

I'm currently trying to fit these through the #10 mounting hole in the Rover Wheel. However, it just doesn't fit. It's right on the verge of fitting. If I take a screwdriver and turn, it starts to thread the inside of the hole... and strip the flat head of the screw... (wish I found phillips head instead)

Are these actually #10 holes? Is 10x32 the right size? Should I have to "thread" the holes as I put the machine screws in there?

I have another, very similar machine screw that's slightly smaller. Perhaps #9 (if that exists). It fits 99% great, with about 1% of wiggle room. What did everyone else use?

[Greg Needel]

to use #10 screws in the rover wheels you need to tap the holes. To use a through bolt with no wheel modification you need a #8 bolt. Either way is generally acceptable. Most of the sprockets from andymark are bored with #10 so that is the way I believe most teams went.

[Andy Baker]

The holes in the 2007, 2008, and 2009 FIRST Wheels (aka: Rover Wheels) have a diameter of 0.17". The intention of this diameter is to use the hole as a pilot hole for a #10-32 or #10-24 or M5x0.8 screw. Some teams drilled out this hole to 0.20" and used a long #10 screw and a nut. While this is a secure way to fasten the sprocket, it is not needed.

As Greg correctly points out, you can tap the hole for a #10 screw. Alternatively, you can simply drive a #10 screw into the hole, even without tapping the hole. If you use a cordless driver, the heat of the screw cutting through the polycarbonate will actually melt the polycarbonate a bit, right around the screw end, and act as a very secure locking method. So... you don't have to use a tap to thread the hole.

Some FRC teams used "thread cutting" or "thread forming" screws. We have found a good one, that has a 5/16" hex head for easy driving, and we offer it here on the AndyMark site. This screw requires no tapping of the hole and it is very easy to drive.

Sincerely,
Andy Baker

[smcmahon]

Wow! Thanks Greg and Andy. CD always gets me the answers I need, in crazy-short amounts of time. I was trying to twist the #10 screws in by hand, mainly because I couldn't come up with the DeWalt... I guess using the power tool will be much more efficient.

Worst case scenario, we'll hit up Lowe's after school today and get some #9 instead. Thank you so much gentlemen. That's exactly the information I was looking for.

[Tristan Lall]

Originally Posted by smcmahon

Worst case scenario, we'll hit up Lowe's after school today and get some #9 instead. Thank you so much gentlemen. That's exactly the information I was looking for.

I don't think you're going to find a #9. Greg probably meant #8. (Here's a chart.)

Originally Posted by Andy Baker

We have found a good one, that has a 5/16" hex head for easy driving, and we offer it here on the AndyMark site. This screw requires no tapping of the hole and it is very easy to drive.

Do you know how well those particular screws perform with repeated insertions? Do you get a self-locking effect as well?

[Greg Needel]

Originally Posted by Tristan Lall

I don't think you're going to find a #9. Greg probably meant #8. (Here's a chart.)
\

Yea I meant #8 that's what I get for posting on CD during 6am conference calls.

[Andy Baker]

Originally Posted by Tristan Lall

Do you know how well those particular screws perform with repeated insertions? Do you get a self-locking effect as well?

We have done life testing with only 3 screws holding the sprocket in place. This works well. As for insertion and re-insertion, I am pretty sure that these will work well. If they don't work as well, then I suggest using 6 screws.

Andy

[Jon Jack]

Originally Posted by Andy Baker

We have done life testing with only 3 screws holding the sprocket in place. This works well. As for insertion and re-insertion, I am pretty sure that these will work well. If they don't work as well, then I suggest using 6 screws.

Andy

The wheels on our practice robot only had three screws holding the hub in place. That set of wheels saw between 32-40 hours of run time this season (compared to the average competition bot which gets about an hour and a half a season).

We had zero problems with just three screws.

[sanddrag]

As a general note, McMaster Carr has a great selection of good-quality screws, at pretty fair prices. You're much better off figuring out what you need and ordering from there, than trying to piece it together with the garbage sold at Home Depot.

[ChuckDickerson]

Originally Posted by sanddrag

As a general note, McMaster Carr has a great selection of good-quality screws, at pretty fair prices. You're much better off figuring out what you need and ordering from there, than trying to piece it together with the garbage sold at Home Depot.

In addition teams may want to check out their local Fastenal store. Fastenal stores are everywhere and carry just about every type of nut and bolt imaginable along with just about everything else you could ever need in an industrial hardware type store. They can be a bit expensive if you pay what they are asking, however, over the years our team has developed a nice relationship with our local Fastenal store and they give us a large (at or close to their cost or sometimes even free) nuts and bolts and even materials including aluminum extrusions. We consider Fastenal to be a valuable team sponsor and for their generosity we, of course, are happy to plaster their name and logo on everything we have like our team shirts and the robot. I agree with sanddrag, skip the cheapo low quality nuts and bolts at Home Depot and go for the higher quality and better selection at places like McMaster Carr and Fastenal.

[smcmahon]

http://lib.store.yahoo.net/lib/yhst-.../AM09WNick.mp4

I watched the above video, which I found in a similar thread from January. I guess having this problem in mid-October is kinda funny...

I did end up just buying the #8 hardware since I couldn't find the DeWalt (turns out it's at a mentor's house). We'll keep all of this in mind though, for future mating of wheels, sprockets, and spacers.

Thanks everyone!

[artdutra04]

Enco is also a great source for fasteners, and depending on the type, can be a lot cheaper than McMaster.

[AdamHeard]

Originally Posted by Tristan Lall

Do you know how well those particular screws perform with repeated insertions? Do you get a self-locking effect as well?

We had a set of wheels that we hubbed/dehubbed a good 5+ times last year. Only issue was the screws backing out over time (the heads were rubbing on the bumper) and we had to retighten them. I don't think they got looser overtime, if anything they got tighter and retightening them was very difficult.