Beware - transmission output shaft is not 5/8"!

[jskene]

You cannot just slip a standard 5/8" sprocket on the transmission output shaft. This shaft is metric, with a diameter of 16mm, or 0.63", NOT 0.625".

You will need either to turn the shaft down to a smaller diameter on a lathe, or drill out your sprocket to 16mm with a metric drill. This year and last year we turned the shaft down.

[Andy A.]

This came up last year as well. Everyone just took a quick look at the shaft with a pair of calipers and assumed it to be 5/8ths. Then we all had to figure out why we couldn't get any sprockets to go on.

I think most teams just ream out the sprockets, and call it even. It's a pain, but hopefully teams learned a lesson and took the time to look at the drawings this year.

Thanks for the reminder though, I had completely forgotten.

[Mr. Van]

All I can say is WHY?!?

Why give teams a great transmission and make a drive system easier for teams to get up and running, but then make in necessary that teams turn down a shaft (a keyed shaft for that matter!) or ream out sprocketts simply to change the output sprocket?

WHY?!?

Does anyone know of a source of various 16 mm bore 35 pitch sprocketts with a standard keyway?

Perhaps I am a bit frustrated because a great deal of our work time goes into making non-standard parts work together. For teams with limited machining ability, this is a real issue. Yes, I know. It has always been an issue, but with the Kit Chassis, Kit Transmission, etc. FIRST has moved a great deal towards making things easier, but a 16 mm output shaft on the transmission seems to be like "Two steps forward, one step back".

(This whole thing was not an issue for us last year, because we made our own shafts that fit the Kit Transmission. I'm speaking for those teams who have limited machining opportunities - like us this year - we lost our shop!)

-Mr. Van
Coach, 599

[Ken358]

Yea its a bit of a hassel. Just ream out the sprokets. I think this is the easiest approch. However, You may have to cut the keyway a bit deeper to get the key to fit after reaming.

Ken

[ChuckDickerson]

Originally Posted by Mr. Van

All I can say is WHY?!?

Consider it part of the challenge. Sure it would be easier if they were 5/8" but part of the challenge of FRC is to work with what you have in the time your given. This is just another one of those real world simulations. Consider that in the rest of the world 16mm may be more common than our 5/8". Maybe this is a hint from FIRST to start moving toward the global metric standard. It is a bit odd though to have a 16mm bore on a 3/8" (#35) chain sprocket.

[artdutra04]

Originally Posted by Mr. Van

All I can say is WHY?!?

Why give teams a great transmission and make a drive system easier for teams to get up and running, but then make in necessary that teams turn down a shaft (a keyed shaft for that matter!) or ream out sprocketts simply to change the output sprocket?

WHY?!?

Why metric? Why not?!?

There are only three countries in the world that haven't changed over to the metric system - Liberia, Burma, and the United States. Using metric is not backwards, but rather the correct way to do things nowadays. We silly backwards Americans still cannot get that through our heads.

[Andy A.]

Also, I believe that the answer given by the transmission designers was that the output shaft was 16mm because it was the most cost effective method, while still giving teams the option of using 5/8ths sprockets with relatively little effort.

Reaming out sprockets is fairly easy. If you can not do this, then consider turning down the output shaft either by cutting on lathe or by turning it and liberal use of sandpaper. None of the methods of using 5/8ths hardware is ideal, so you should consider buying sprockets from IFI through their website. You are stuck with 21 teeth from IFI. Another option is to look around and find a 16mm sprocket supply. They are out there.

-Andy A.

[sanddrag]

Here's the deal. FIRST is not a "buy it and build it robot kit" competition. If you can't be resourceful enough to at the least make do with what they give you, there is no way you will survive in coming up with your own designs. I can't believe that FIRST is so generous as to provide such a great gearbox, and some of you still complain and find every little thing wrong with it. If you don't like it, make your own. But let's not complain when we are getting magnificent items in the kit that teams just a few years ago could only wish for.

Back in the day, we never had beautifully machined pieces included in the kit of parts. Hex broached gears. Cast housings. We didn't even have CIM motors.

Be thankful for what you have, not frustrated with it because it doesn't exactly suit your needs.

[ChuckDickerson]

Originally Posted by sanddrag

Here's the deal. FIRST is not a "buy it and build it kit robot" competition. If you can't be resourceful enough to at the least make do with what they give you, there is no way you will survive in coming up with your own designs. I can't believe that FIRST is so generous as to provide such a great gearbox, and some of you still complain and find every little thing wrong with it. If you don't like it, make your own. But let's not complain when we are getting magnificent items in the kit that teams just a few years ago could only wish for.

Back in the day, we never had beautifully machined pieces included in the kit of parts. Hexed broached gears. Cast housings. We didn't even have CIM motors.

Be thankful for what you have, not frustrated with it because it doesn't exactly suit your needs.

I agree 1000%!

[Gdeaver]

A dremel tool with a sanding cylinder and 10 minutes will make a standard 21 tooth 5/8" bore sprocket fit. A 9th grade girl team member did ours last night.

[jskene]

We decided to turn down the shaft, as that then gives us the ability to change sprockets easily, should we want a different gear ratio.

[Andy A.]

Originally Posted by sanddrag

... But let's not complain when we are getting magnificent items in the kit that teams just a few years ago could only wish for.

Back in the day, we never had beautifully machined pieces included in the kit of parts. Hexed broached gears. Cast housings. We didn't even have CIM motors.

AND we had to walk uphill both ways to get to our shops!
And we likesed it that way!

trying to keep it light hearted,
-Andy A.

[Nitroxextreme]

someone should make this a sticky at least for years with the transmission....it will save a lot of people time and anguish

[Mr. Van]

I am very grateful for the increadible advances that have come along to help teams. As one who has been there (since 2000) and walked uphill both ways, I know what you are talking about.

In those days, many, many robots barely moved - so great were the challenges in getting the drill motors mounted and coupled to a drive shaft and delivering power to the drive wheels. Now, rookie teams are able to build very compettive robots even if they have limited machining capabilities. Do keep in mind that there are teams out there who are trying to be competitive with nothing more than hand tools or perhaps a wood-shop band saw and drill press.

Thank you to those who suggested practical ways for us to use standard sprocketts - we'll probably try the dremel... that sounds pretty easy - we could do that.

Thanks!

-Mr. Van
Coach, 599

[John Gutmann]

Stick it in a drill or drill press(if available) and use sand paper on that, then it is an easy 5 minute project.