Drive Assembly Sprockets are Custom Bored

[Paul Copioli]

Mark,

I re-read your initial post thinking I might have responded harshly. Nowhere in that post did you ask for help. Since you are an advocate of constructive criticism, I will give you some of my own.

In your initial post, you could have just asked for the dimensions and specs. I would have been the first to respond with the answer. Instead, you took "pot shots" at the individuals who provided the parts. Now I know that sometimes words on paper don't come out quite like intended, so I will just chalk this up as a misunderstanding.

I will assume that you have good intentions and want to improve FIRST for not only your students, but all the students touched by this competition. If you have any other questions or concerns about the transmission, feel free to ask.

-Paul

[activemx]

Must say its an excellent design Paul, Props on that!

[Biff]

All heat aside, I love the transmission. I also like the information in this post, I most likely would have missed the shaft being metric with out it. Being responsible last year for getting 3/64" key ways cut by mistake in a pair of 30t #25 sprockets, (was supposed to be 5/8" bore with 3/16" key) we used the T shaped key way and adjusted. I took one look at the casting and said wow, custom die cast and low cost to make so many, somebody did a great job with the over all design. After my first read of this post, I looked at the output shaft and thought, Cool start with 3/4" hex stock and go from there if you want to get to 5/8 final out. My second read finds use a metric drill and metric broach, if you need a different final sprocket. Thanks Paul for the great work and the learning that has flowed from it. Tom Cooper

[Gdeaver]

Those gear boxes are are gold to our team. We only have hand tools and very little cash. Thanks for your time and effort.

[reventlov]

I agree with Mark, FIRST should have given us some heads-up before custom boring the sprockets and making it costly to upgrade our drive system.

[Cory]

Originally Posted by reventlov

I agree with Mark, FIRST should have given us some heads-up before custom boring the sprockets and making it costly to upgrade our drive system.

I had really hoped all the moaning about the sprockets would stop now that FIRST is selling the sprockets you need for $20 each.

Everyone who has complained seems to be forgetting that FIRST and other individuals bent over backwards to make sure that EVERY team could have a driving robot. They didn't have to. And not only did they develop the gearboxes and frame, they compiled a fantastic guide to using them, and possible upgrades.

FIRST made an option available to you. You don't have to use it. You don't have to spend the $40. Since their solution costs so much, why don't you develop your own? I can tell you right now, you won't be able to. You'll spend hundreds of dollars to make the same thing FIRST did, and who knows how reliable it will be.

Seriously guys, no matter what FIRST does, there's always something being griped about. As has been said many times in the last few weeks, if you're going to complain, do something about it. Offer your services to FIRST. Find a supplier that will donate sprockets to FIRST. This is a lot like voting. You have no right to complain about our political system if you don't vote. If you don't do anything to resolve what you're complaining about, DON'T COMPLAIN.

[Rickertsen2]

<sarcasm>

What!! The kit isn't a lego set!!!¿?¿?¿?¿? You actually have to build and design something? This is terrible!!

</sarcasm>

This is relly ghetto but i have dome something similar before and it worked. Run the gearboxes at full speed. Get a piece of coarse sandpaper, a pair of gloves and sand that sucker down.

[Steve P]

Four wheel drive is simple. Its called sprockets on the other two wheels, and one chain with a tensioner.

[cdawzrd]

Originally Posted by Steve P

Four wheel drive is simple. Its called sprockets on the other two wheels, and one chain with a tensioner.

But, if the chain breaks, you can't drive on that side. I've seen enough chains break during matches to want the extra redundancy.

[Andy A.]

My team ran into this. We opted to run with the two wheel drive, but to drop the 21 toothed sprockets for 15's (we wanted to slow down a bit, rookie driver and all). I was in charge of ordering the new sprockets, and just as I was on my way out shop one night, I asked a student to measure the shaft for me so I could order them that night. He quickly grabbed a pair of calipers, and I guess 16mm was close enough to 5/8ths that he figured he had made a mistake and assumed it was 5/8ths (all our other drive train shaft is). I probably would have done the same.

So I ordered sprockets from McMaster with a finished bore for 5/8ths. Needles to say, I was confused when the sprockets just wouldn't go on!

After a while, we figured it out. 5/8ths of an inch does not equal 16mm's it seems. The solution was to ream out the bore and 'press' the sprocket on with a hammer. It was tighter then I would have liked, and I hope we never have to take that thing off, but it works. I probably spent more time trying to figure out why things didn't fit then I did fixing anything.

Moral of the story- Sometimes, that metric system will show up in the most unlikely of places. Read your manuals!

Although, now that I think of it, I probably still would have gotten the same sprockets. I'd rather have to take a few passes with a reamer then drill/bore out a unfinished sprocket. But I'm lazy.

My only critique of the kit trannys is that ours seem to run out lubrication real fast. That may have something to do with how we (mis)assembled them, but I notice that they need periodic lube jobs. If thats my only beef with them, I'm happy enough to go back to dealing with all my real problems on the bot, like where I'm going to find room for ballast.

-Andy A.

[sanddrag]

Originally Posted by Rickertsen2

This is relly ghetto but i have dome something similar before and it worked. Run the gearboxes at full speed. Get a piece of coarse sandpaper, a pair of gloves and sand that sucker down.

Are you referring to making the sprockets fit on the shaft easier or something like that? We use a tool I call the "vertical lathe" (there actually is such a thing, but this is not it). We pop the shaft into the chuck of the drillpress, spin it up and put a nice file, sandpaper, or preferable emery cloth to it. Works every time. Slightly less ghetto.