Chief Delphi - Transmissions

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Re: Transmissions

Quote:

Originally Posted by lukevanoort

However, we've never built a shifter, since we lack the money to buy AM (why do they cost $330 anyway?)

Since you asked, here is a rough estimation of what it would cost to make only 1 or 2 AM Shifters. These are not our costs, since we make large batches of these at a time.

Gear stock (broached holes not included):
12 tooth CIM: $7 each x 2 = $14
40 tooth: $19
28 tooth: $11
35 tooth: $18
48 tooth: $24
15 tooth: $10 (we make this into a shaft, but I would not do that to make 1)

Total gear stock = $96

To fabricate the 12 tooth, 28 tooth, 40 tooth and 15 tooth gears to fit keyed shafts and hex shafts, you would need to have a set of broaches ($100-200) or pay someone about $20 to do this.

To get someone to machine in the "dogs" to the 35 tooth and 48 tooth gear, that will be a good cost. More importantly is the 0.0005" diameter tolerance on the bearing press fit for these gears. Make the hole too small and the bearing is wasted upon insertion. Make the hole too big and the bearing falls out. This is the trickiest machining operation on the entire gearbox. Expect to pay $20 extra for each of these gears. We sell them separately for less than you could buy a blank gear from McMaster-Carr, by the way.

Gear fabrication = $60

Bearings:
3/8" flange bearings, shielded: $5 x 2 = $10
3/8" flange bearings, unshielded: $5 x 2 = $10
1/2" flange bearing, shielded: $9
1/2" bearing, unshielded: $6
3/16" bearing, unshielded: $3

Total bearings = $38

Side Plate fabrication:
Side plates on these gearboxes have +/- 0.001" tolerance on the shaft hole location. This is not trivial. This means they need to be made precisely. Expect to pay $30-35 per plate on the market.

2 plates = $60

Shaft fabrication:
2 hex shaped shafts are needed. One would simply be lathed down on the ends (or you turn the 15 tooth gear into a shaft as we have). The output shaft needs a keyway, a hole, and a lateral slot. Also, the shifter shaft is needed. It has a lathe operation and 2 drilled holes. The spacer shafts holding the gearbox together will cost about $3 each.

Cluster shaft: $8
Output shaft: $25
Shifter shaft: $8
Spacers: $3 x 6 = $18

Cost of shafts = $59

Dog Gear:
This is not an easy part to make either. I estimate that it would take a machine shop $40 to make this part.

Dog Gear = $40

Oh, and there is that little cylinder plate. It will be $14 to have someone make that.

Cylinder plate = $14

Also, you will need fasteners, spacers, key stock, and plating. For these things, throw in about $5.

So... adding up the costs noted in bold letters, that totals $372. This cost is unassembled and not debugged.

From my point of view, teams are getting a very good deal with $330 for a tried and true gearbox.

Do these numbers seem correct?

Andy B.

Re: Transmissions

Quote:

Originally Posted by Andy Baker

Do these numbers seem correct?

Andy B.

These transmissions are a great value. The machining and design time you save by using them can be invaluable, and most definitely worth more than the $600 odd dollars it would cost a team to use two of them.

Re: Transmissions

Quote:

Originally Posted by Andy Baker

From my point of view, teams are getting a very good deal with $330 for a tried and true gearbox.

Do these numbers seem correct?

Andy B.

The price for this gearbox is really a great deal, especially considering it is engineered and tested for you, and you will get great support by being able to deal directly with the manufacturer and designer.

One thing that many teams overlook is how precise you have to be when making systems that use gears. There is a reason that my team almost never uses gears...we just can't make parts to that precision.

Even if you took the plans and raw materials to a local shop that was donating labor, you would probably have some tolerance issues that you will not have buying the AM product.

It really is a steal.

I'm assuming that you forgot to consider cost of manufacture in your questioning the $330 price. It is a nice deal for FIRST teams that they have lots of free child labor :)

Rob

Re: Transmissions

Quote:

Originally Posted by NoodleKnight

There are two common ways of shifting found in FIRST robots, one is dog shifting -- where you move a metal dog (it looks like a metal cylinder that has been cut out to have 2, 3, or more fingers or protrusions) to transfer power from the gear to the wheel. A good example would be the AndyMark shifters.
The second common way is mesh shifting (like noted above) where instead of moving a dog, you move a cluster of gears. this is a good example, it's team 254's gearbox from 2004. The second gear cluster from the left is the one that moves to shift gears.

There are other ways like team 222's ballshifting method, or using a CVT (continously variable transmission, commonly found on today's hybrid cars), or even by physically changing the size of the wheel, like what 986 (or was it 980?) did in 2003: click

You could make a FIRST shifting transmission "automatic" by having the programming shift gears, rather than the operators.

Also, yep, you need a source of physical energy to shift the gears -- most teams use pneumatics, others use motors or even servos.

Hope this helps

Thank you very much, i'll keep these points in mind for next year ^___^

Re: Transmissions

Quote:

Originally Posted by Andy Baker

From my point of view, teams are getting a very good deal with $330 for a tried and true gearbox.

Do these numbers seem correct?

Andy B.

Couldn't have said it better. It cost us more to make our 2004 transmissions based on Andy's 2003 design than he charges for them. Plus we wasted a bit of money destroying parts debugging fit issues.

Our team has long been a fan of the buy it if you can philosophy. This limits the hassles and headaches with getting some transmissions to work on the first shot if you can't afford the time and cost to remake those slight fit issues you messed up on. The AndyMark is a simple and light as you can get for the value and 177 is proudly using them this year.

Just to give you some ideas in the past we have done the following canniblization of COTS trannys:
Adapted the KOP Bosch transmission to work with the FP motor in 2004. We parralleled the NBD but used kit material for it. Can't find the white paper on it that I posted.
2005 we used the transmission from a winch with both FPs driving it to raise and lower our arm. We could lift 3 tetras with it extended.
Edit: I designed a two speed using the 2005 KOP transmissions and some left over 20dp gears from from 2004s making of the Technokats 2-speed. This was so we could do it on the cheap when we had a budget crunch. :End edit

The jist of this is don't just think drive train or "FIRST" transmissions. There are a lot of inexpensive durable COTS transmissions that you can use with a little creativity.

Re: Transmissions

Team 716 has also posted their 2005 dual speed here. We are using it again this year. Material costs are $250 for two transmissions and this gives you enough shafting for years! The design was made so fabrication can be done on a lathe and miller without cnc. It helps to have some experience for the bearing holes but the dogs are quite easy to make and not as fussy as I have called out on the drawings.

Another option is to buy some of the AndyMark components, such as the output shaft and associated dog with gears, and build the rest yourself.

Re: Transmissions

Quote:

Originally Posted by Andy Baker

For center to center gear spacing, I use a 0.002" addition to the calculated center distance. I previously used 0.0005", but that did not allow for manufacturing tolerances.
It is better to have a slightly "looser" transmission as opposed to a "tight" transmission. I believe that this 0.002" addition for center distances is good. Also, I don't trap the gears along the length of the shaft, as I would rather let them float on the shaft as opposed to being bound tightly. Some AM customers are suprised that the gears can slide on the shaft 0.03-0.04".

That sounds good, we added .002'' to our pitch diameter center distance this year and they sound much better. Who knows how accurate our center distances were on pre 2006 transmissions, but we never added a few thousands to the calculated center distance. Do to the nature of our transmissions, we also let our output gears float around a little bit, probably 100 thousands of an inch at most.

Good post Andy.

If you have any questions about our "Ball-Lock" method of shifting as seen here:

feel free to contact me by PM, email bsr150@psu.edu, or AIM bsrtunkpa.

Re: Transmissions

Thank You all for your input...

Once we can finally decide on what we are doing, I will be sure to post pictures and possibly a white paper depending on how it comes out

Re: Transmissions

Quote:

Originally Posted by Andy Baker

What Andy says above goes without saying, we have duplicated much of the designs from the dog style shifting transmissions and I can't buy and have fabricated the individual pieces for 2 transmissions for less then $800 which makes the $330 ea. seem like a steal. I have contacted Andy more than once to question how he is selling pieces that are already machined to the proper size and tolerance for cheaper than I can get the STOCK!!!! We went with the single speed this year for simplicity but I think the evolution of Andy's gearboxes will be more options into the same base designs such as encoders, and possibly something like a servo shift. We servo shifted the dog transmissions with no issues over the past 3 years and it works well if you're not using pneumatics on your robot. We also changed to design for our use with a high engagement arc to make sure they slammed into gear at full speed. This makes the whole drive train slightly 'sloppy' (maybe an 1/20 of a rotation at the drive wheels without any rotation of the motors) but the encoders are downstream of the dog and compensate for that.

My thoughts anyways.......

Re: Transmissions

Quote:

Originally Posted by Andy Baker

It is better to have a slightly "looser" transmission as opposed to a "tight" transmission. I believe that this 0.002" addition for center distances is good. Also, I don't trap the gears along the length of the shaft, as I would rather let them float on the shaft as opposed to being bound tightly. Some AM customers are suprised that the gears can slide on the shaft 0.03-0.04".

LOL...no wonder our 2-speed gearbox makes so much noise this year. Thanks for the tip. I'll make sure to include that in our next year's gearbox draw
Also, I have question. What difference do 14.5 P.A and 20 P.A make?

Re: Transmissions

Quote:

Originally Posted by geo

What difference do 14.5 P.A and 20 P.A make?

14.5 PA runs smoother and quieter, but has more backlash and handles less of a load than a 20 PA. 14.5 PA teeth appear taller and skinnier than 20 PA.
20 PA will be noisier and not as smooth, but will have less backlash and can handle slightly more load. If anyone can back me up on these statements, I'd appreciate it because I wanna make sure I didn't post any wrong information. I know 222 switched from 20PA to 14.5PA and we haven't had any trouble with our gears and they do seem to run smoother and quieter.

Re: Transmissions

One thing I would suggest for the off season is build a chassis and design a drive and mount it. Try it out, if you don't like it try a new design or chassis or both. This way you get first hand experience and get a feeling for drivetrains.

Re: Transmissions

Quote:

Originally Posted by camtunkpa

Thanks for the info. We used 20 P.A this year and the gearboxes are quite noisy. Maybe that's the reason or the spacing between the gears are too tight...lol

Re: Transmissions

Quote:

Originally Posted by geo

Thanks for the info. We used 20 P.A this year and the gearboxes are quite noisy. Maybe that's the reason or the spacing between the gears are too tight...lol

We ran 20PA gears in our 2004 tranny and they were very noisy. They were noisy but the biggest reason wwas we had not figured in an extra couple thousandths in the center to center distance.

Re: Transmissions

I Love the andymark transmission and i suggest a raffle at your school for money to buy them they are so worth it no problems at all