Drive Assembly Sprockets are Custom Bored

[Mark Pettit]

We just took our transmission assembly (out of the kit) down to Bearing, Belt, and Chain, Inc. thinking that we could get a couple of more sprockets that would fit right onto the assembly so that we can get our machine driving by this weekend. They informed us that the sprockets for these are custom bored (as designated by the "b" in the model number). They said that we could use standard keyed sprockets but if we did that we would have to have them pressed onto the shaft.
We thought FIRST was doing us a favor by making a ready to go tranny/drive assembly, but if we want to go four-wheel-drive with a different sized sprocket, then we're pretty much out of luck. I can't figure out why they would limit us like that, but maybe you (Chief Delphi Participant) can shed some light on it?
Update: And to get the same "custom bored" sprockets from IFI will cost us an additional $80 for about $14 worth of sprockets if they weren't custom bored.
Whaaaaaaaaaaaaaaaaat?

[Doug G]

We noticed that today as well. I haven't had a chance to check it with my calipers yet, but one student suggested that it was close enough that we could heat up our standard 5/8" bored sprockets and press them on. Might be worth a shot, but check it first with some calipers to see how big the difference is, because it maybe harder to get off then it was to get on (especially if the transmission is all put together).

[LBK Rules]

Yeah, we're in the same prediciment.

[JVN]

The transmission output shaft is metric - 16mm dia with a 5mm keyway.

(as taken from the transmission manual found here: http://www.ifirobotics.com/kitbot.shtml in the output shaft drawing spec)

Paul, please correct me if I'm wrong.
Teams can buy any size sprocket they want (with a bore less than 16mm), rebore it to 16mm and rebroach to 5mm. There is probably a fancy way to broach this keyway, but the simplest way is just to buy a metric broach set.

Anyone else have advice?

[Rich Kressly]

I'm trying to be gracious and professional about this, but ... before anyone calls this a "predicament" or thinks they are "limited" please think twice. First off, how much design, engineering, and manfacturing time was spent by Paul, JVN, and IFI? What if you had to include that time in your build and/or deduct it from your allowable expenses? 80 dollars would seem pretty cheap then. And FIRST DID do you a favor. Try and build this with last year's kit. I don't remember anyone promising you 4WD right out of the box. What you were promised was a robust gearbox and ready made chassis to get you rolling quickly.

Relax. Have fun. Enjoy the improvements. Build what you want to. Thanks Paul, JVN, IFI, and FIRST.

[Cory]

Ok, according to my nifty little (well, it's like 4" thick) KBC tools catalog, a 16mm drill bit will run you approximately $16

as for the keyway, if you have a mill, mill a key, it wont be pretty, but it's a hell of a lot cheaper than a broach set.

Or, get your freshmen to start filing

[DukesAZ]

Mr. Kressly,

I don't think anybody is attacking the work Mr. Neun did on the transmission kit this year. From what I have seen, the transmission is top-notch. Mr. Neun has also been extremely helpful on these forums and I appreciate the work he has done. I also don't think Mr. Neun is responsible for what was and what was not included in the kit of parts.

However, FIRST could have informed us of the custom modifications made to the sprockets and informed of us the fact that we could not use standard sprockets unless we made modifications. I also feel FIRST was misleading on how easy it was to build the drive system. Most teams DO NOT have access to the type of machinery needed to custom bore and/or press the sprockets onto the shaft. This isn't the biggest hurdle in the world, but it is a major annoyance and it will cost us (even it is just 80 dollars, it adds up!).

[Joel Glidden]

You could also turn down the output shafts to 5/8" on your handy dandy lathe. You could also mill a 3/16" keyway on the opposite side of the shaft from the existing 5mm keyway.

-Joel

[Cory]

Originally Posted by DukesAZ

Mr. Kressly,

I don't think anybody is attacking the work Mr. Neun did on the transmission kit this year. From what I have seen, the transmission is top-notch. Mr. Neun has also been extremely helpful on these forums and I appreciate the work he has done. I also don't think Mr. Neun is responsible for what was and what was not included in the kit of parts.

However, FIRST could have informed us of the custom modifications made to the sprockets and informed of us the fact that we could not use standard sprockets unless we made modifications. I also feel FIRST was misleading on how easy it was to build the drive system. Most teams DO NOT have access to the type of machinery needed to custom bore and/or press the sprockets onto the shaft. This isn't the biggest hurdle in the world, but it is a major annoyance and it will cost us (even it is just 80 dollars, it adds up!).

How much would it have cost you to make those gearboxes?

The answer is either:

A) We couldn't, because we don't have access to a mill or lathe

-or-

B) A whole hell of a lot of money and time.

Major annoyance? How big of an annoyance would it be to make the darn things from scratch? How annoying would it be to design it?

The value of those gearboxes should be measured in the hundreds of dollars, so even a measly 80 is quite a deal.

and like I said in my previous post, buy your $14 sprockets, buy a $15 16mm drill bit, and I'm sure you have files and then you're good to go. That adds up to about $50 less than if you buy them from FIRST, so you should be happy

Originally Posted by DukesAZ

I also feel FIRST was misleading on how easy it was to build the drive system

Have you seen the FIRST drive systems of the past? They were big pains in the $@#$@#$@#. This one is incredibly easy and light years ahead of anything they've ever given us before. You could set it up in an afternoon. FIRST isn't responsible for making sure every team can have a driving robot, but they choose to by giving us this.

[Eric O]

Originally Posted by DukesAZ

Most teams DO NOT have access to the type of machinery needed to custom bore and/or press the sprockets onto the shaft. This isn't the biggest hurdle in the world, but it is a major annoyance and it will cost us (even it is just 80 dollars, it adds up!).

I don't see in any way how this is an "annoyance". A complete lightweight frame and 4 motor drive train out of the box. So FIRST only gave enough sprockets for 2 wheel drive, but you can upgrade to 4 wheel drive for $80. Thats four custom sprockets that you can attach to your kit bot and almost instantly have a 4 motor, 4 wheel drive robot base. Sounds like a pretty good deal to me.

Eric

[Rob]

OK I have 2 things to say on this subject:

If you dont like what is in the kit, then be thankful you did not do FIRST in the past. This is by far the best quality and most useful kit ever provided.

If you don't want to buy an $80 custom sprocket, then don't. just use the provided 21 tooth sprocket on the gearbox output shaft. You will have to cut some pieces of PVC or aluminum tubing to do this. If you can't cut PVC or aluminum, you can buy a bunch of large washers at your hardware store.

You can also skip the sprockets that FIRST gives you to put on the wheels. In fact this might be a good idea because the provided wheels have low traction. This does require a bit of creativity and custom designing. You will need the following items:

Some 5" long 3/8" bolts for axles.
some wheels with bearings (3/8" bore).
some sprockets of whatever size you choose to use (1/2" bore is probably good).
some 3/8" bore 1/2" OD bronze bushings.
some spacers.
some small diameter bolts long snough to go through the sprockets and the wheels.
the ability to drill some holes through the sprockets and wheels.

Press the bushings into the sprockets, and place them on the shaft with the wheel. Drill holes through the sprocket and wheel. Bolt them together. Cut your spacers to position the wheel sprocket in line with the transmission sprocket. Put another sproket on the other side of the wheel. make a simmilar wheel, but with only 1 sprocket on it. run chain from the transmission to the wheel with 2 sprockets, run chain from the 2nd sprocket to the wheel with only 1 sprocket.

for a 4 wheel drive setup, this might cost you around $80 to $100, the same as your replacement sprockets. If you were to make your own drivetrain from scratch it would cost you well over $400, and maybe not be as high quality.

Good luck with the driving!

Rob

[Andy Brockway]

This is a good example of engineering for all students. Many US industries have converted to metric, it is the US general public that does not have/use metric on a regular basis.

[Paul Copioli]

WARNING! Long Post!

I can't figure out why they would limit us like that ...

I don't think anybody is attacking the work Mr. Neun did on the transmission kit this year. From what I have seen, the transmission is top-notch. Mr. Neun has also been extremely helpful on these forums and I appreciate the work he has done. I also don't think Mr. Neun is responsible for what was and what was not included in the kit of parts.

Mark & dukesAZ,

"They" is me. Do not blame FIRST for the design decisions made on the gear box. I designed the entire thing. JVN had a lot of design input, but he spent most of his time designing the frame and interfaces. Your beef is with me. Your beef is not with FIRST, IFI, JVN, or anyone else. That being said, I have volunteered my time since July to design, test, and source the transmission gearbox, so be a little more tactful when expressing your dissatisfaction (that one was directed at Mark). The transmission manual: yep, that was me too. I did not receive one red cent from FIRST, IFI, or anyone else. I spent the equivalent of an entire six week build season making sure all the criteria were met (see the transmission manual page 1-2 for details). As for my qualifications: I have my Master's Degree in Mechanical Engineering from the University of Michigan and hve been working at FANUC Robotics for 8 years designing and engineering mechanisms for industrial robots.

Every single choice I made on that gearbox was weighed against many others. The custom die casting, for example, was chosen due to the volume of housings we needed to make and the cost (yes, cost) impact. Our criteria was to beat the cost of the drill motor solution or it was a no go. The gears are cut from a long roll formed bar and are sliced to our specs. They can be replaced with Martin equivalents. As a matter of fact, I made the prototypes from Martin gears. Martin can bore any size hole you want and they actually put the keyway in, too. Call Martin sprockets and fax them the drawing at the end of the manual and see what price you get. I bet it will be cheaper to buy the stuff from IFI, because we got a volume discount on the sprocket modifications. Better yet, take Corey's advice and modify them yourself. The standard 21 & 28 tooth sprockets have a 1/2" bore. Buy a 16mm drill and a 5mm broach set from MSC or McMaster and you are all set for the input sprocket. Bottom line is that if you do not like it, then build your own. There is no way you will get the same functionality for the same cost.

However, FIRST could have informed us of the custom modifications made to the sprockets and informed of us the fact that we could not use standard sprockets unless we made modifications. I also feel FIRST was misleading on how easy it was to build the drive system

dukesAZ,

The custom modifications are clearly spelled out in the transmission manual on pages 5-13 and 5-15. In fact, every single part drawing is shown in chapter 5. Misleading? The standard drive base can be put together in a matter of hours. My 4 year old son put together one transmission housing in 30 minutes by just looking at the pictures (yes, he knows how to use Allen wrenches). Custom modifications are essential to get cost out of high volume products (over 2400 units). If you use standard components, the cost goes way up and it would have been cost prohibitive to put them in the kit.

In closing,

I expressed my dissatisfaction with FIRST at the end of last year. I said they were not doing enough to help the rookies and lower funded teams be ready to drive on day one of their regional. I offered my services and they took me up on my offer. If you are not part of the solution, then you are part of the problem. I suggest you start being part of the solution.


Paul

[Mark Pettit]

Paul and everyone else.
Calm down people.
One of the major problems that I see with FIRST is that one cannot offer the slightest bit of criticism of FIRST without someone else getting overly worked up about it and starting a flame war.
The first couple of responses to my issue (up to and including JVN's) were what I was going for by posting this thread. I wanted to make sure that I was not the only one with this problem and I was hoping someone could offer a fix. Low and behold, JVN told me of a quick and easy fix. I would have been happy if the thread ended right there, or even if you would have chimed in with your reasoning.
What makes me and my team upset is that we cannot put our beefs with FIRST out there without someone feeling as if they need to be the defender of the almighty FIRST. Criticisms should be allowed. According to everything I've heard from the regional directors, FIRST wants to hear them.
They, and I will include YOU (Paul) in this since you developed the tranny, should be the only ones that need to answer to the criticisms. The regular team mentor, coach, or member that thinks they have the right to get upset with me for criticizing FIRST is the real problem.
Can't we all just get along?

[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