what is modular pitch? is that the same thing as diametrical pitch?
English pitch works like this. Teeth divided by pitch = pitch diameter.
Metric pitch works like this: Teeth TIMES module = pitch diameter.
Thanks, sand.
I love having both metric and imperial units ;). It makes everything more fun.
So, the drill pinion is 15 teeth mod .7? what about pressure angle? Where can I get an appropriate gear to mesh with the drill pinion? Thanks.
I believe it is a 20 degree pressure angle but don’t hold me to it. You can get Mod 0.7 gears in Acetal from www.sdp-si.com and the only place for metal ones in North America is www.pic-design.com SDP is usually pretty fast with orders, PIC usually takes 4-7 WEEKS for those gears. Good luck! Let me know if you have any more questions.
EDIT: I forgot to add that team 571 used the Acetal ones with no failure, however they did not use them directly on the shaft of the Chiaphua motor like 2003 Tecknokats style. http://www.chiefdelphi.com/forums/pictures.php?&action=single&picid=6328 If you run the numbers, there is not much PSI on the gear teeth and keyway and the plastic might be able to take it, however, there’s a greater piece of mind that comes with steel. 
When you convert mod to DP of the .7 mod using the equation DP=25.4/mod you find that the gear on the drill motor is close to 36dp, which in turn is close enough to a 32dp gear. we took a 32 dp brass gear and “ran it in” it worked flawlessly, its an old technique used by SPAM. Makes it much easier to get the size gear you need quickly.
Are you serious? This is very intriguing. Tell us more.
Well, after deciphering the german white paper provided by first, it seems that the drill pinion does, in fact, have a pressure angle of 20 degrees.
It also says the modular pitch is .7, which probably anyone could have told me, but how the heck are we supposed to read the white papers if they’re in freakin german?! I started a thread a while ago about how I crapy I thought the FIRST white papers are, but no one replied. I guess most people are too cool to have use for them or something… http://www.chiefdelphi.com/forums/showthread.php?t=25374
I have heard (From no less a person than Raul the Magnificent) that 111 used to do that same thing.
Even so, I cannot recommend this practice. While you can get it to work, it is less than ideal.
If you think you need to mate to that .7 module gear, just buy a few in the off season from PIC-Design or have gears wire burned during the season. Either way, your gearboxes will thank you.
Joe J.
Whats Wire burned?
and can some explain in a as far away from german as they can what SPAM uses that so intriguing?
-Osc-
I bet Joe Johnson could explain better than I. It uses really thin wire that gets really hot and it cuts intricate shapes in metal. Look for “wire EDM” on google. I found this that tells a little more http://www.emachineshop.com/machines/fabrication/kerfing/wire-edm.htm
(http://www.emachineshop.com/machines/fabrication/kerfing/wire-edm.htm[/quote]
yes, I meant Wire EDM when I said “wire burn”
EDM stands for Electro Discharge Machining. Essentially, you use a very good conductor (carbon, copper, etc.) as a “tool” and you pass a spark from the tool to the work piece. The spark vaporizes a bit of the work piece (as well as a smaller bit of the tool). This allows for very detailed parts to be made (almost all tools for complex molded parts use some EDMed features in the tool). In the case of wire EDM, you have a copper wire that “burns” its way through the metal. The tool is constantly made new by moving new wire between the upper and lower wire guides. Wire EDM is perfect for flat parts like gears – it is even better if you have several gears to make as many plates can be bolted together allowing one pass to make N gears.
We typically pay about $50 for a custom gear made from 1/4 inch steel plates. If you don’t have a wire EDM source in your neck of the woods, I can put you in touch with some sources in the Detroit area that will take MasterCard and will give you a good price for FIRST projects.
One big advantage of EDM by the way is that it does not care if the work piece is hard or soft. Also, the parts themselves get warm but not so hat that the heat treatment of the base metal is affected – so hard parts stay hard.
This year, the only thing we used our EDM source for is to put accurate holes in the hardened pinions we used in our Dewalt transmission (yes, I know I owe folks a whitepaper on that topic – it will come, be patient). The source we used charged us $20 per pinion to put very accurate holes into the hardened pinions we bought from Dewalt so that we could press these pinions on the Fisher Price and Globe motors. We felt that $20 was not too bad for what it saved us.
Joe J.
P.S. most sources like to have an IGES file with the gear profile you want cut rather than saying “a 10 DP gear with 100 Teeth” Again, this should not be a road block if you don’t have access to CAD, but things usually go smoother if you can give them an IGES file.
But how do you get the proper involute curve? Can AutoCAD or MasterCam do it?
The reason that we went with this method is that we didnt know what size gear we would need, and didnt know that we were going to even be making gearboxes when the season started. We dont have enough money to have an assortment of gears on the shelf to make the gearbox how we need it. We never ran into any trouble with the gear boxes, they seemed to work pretty well. I would much rather use a .7 mod gear for effciencey. But then again using the run in gears makes the gearboxes have this awesome sound. Attached is a clip of the first stages of our run in procedure. Ill post the steps we took in a future post or a white paper.
Joe, how long does it normally take to get gears Wire EDM burned?
drillmotor.zip (92.5 KB)
drillmotor.zip (92.5 KB)
If you have enough money, only a few hours! Really – 3D-Services, former sponsor of Team #1, will burn you a gear by close of business if you get them the file that morning – assuming you have $200 to $300 to waste (By the way, I have NEVER done this for FIRST, only for my day job of making show cars to sell stuff to OEM’s)
For those with less than unlimited budgets, my typical wire burn sources (for example Louis Oudin at Capital Die 248.542.9200 or e-mail him CapDieTHE-AT-SYMBOLaol.com*) give parts in 3 days without breaking a sweat or charging me premium prices. Typical prices $50-$150 for an 1/8 thick aluminum sprocket depending on the size. $50-$100 for typical 1/4 thick steel or aluminum gears (webbing extra) again, depending on size.
By the way, if you don’t have a wire EDM source in your neck of the woods, Lou takes credit cards, loves FIRST, and will work you from long distance. You can do worse than work with Capital Die (no kickbacks or bribes were paid for this testimonial, though I DO have an open slot in my lunch schedule next week Lou… 
Joe J.
*sorry for the obfuscation but I didn’t want to have some e-mail snatching, web crawling slime bot getting Lou on its spam mail list.
I called a place near me and asked how much it would be for a custom spur gear about 2 inches in diameter cut out of 3/16 steel plate. They said for 4 of them is would be $40-$50 apiece and would take a day.
Now, I didn’t ask if they need a file to import but I assume they do. Now my problem is getting a proper drawing. Can MasterCam or Autocad do gear drawings good enough to cut from?
You all might want to look at this thread too: http://chiefdelphi.com/forums/showthread.php?t=27622&highlight=lasercutting+spur+gears
EDIT: One thought that crossed my mind about meshing the 32P with the Module .7 is that a 54 tooth 32P gear is about .200 larger in pitch diameter than a 54 tooth Module .7 gear. Gearing depends on the difference in diameter between the two “wheels” However, these “wheels” have teeth. The number of teeth is directly proportional to diameter of the “wheel.” So in a situation meshing gears of different pitches, what makes the ratio, teeth or diameter or a bit of both? Doing this seems like one of those things that isn’t supposed to work but it does.
some one is likely to come along with a better sounding answer, but the pitch diameter is the diameter where proper meshing should be. So when using gears that “mesh”, but doesn’t have the expected pitch diameter, the true pd is not being achieved in one, the other, or both gears. In that case, it’s hard to say what ratio they’re running at. Perhaps it’s somewhere between the ratios using the dp of the correct gear and the substitute.
This is not true. While it IS true you cannot calculate what the true operating pitch diameter you CAN calculate the ratio exactly.
Unless the mesh is so bad that the gear teeth pass each other the ratio is the [Nteeth-on-Gear1 / Nteeth-on-Gear2].
Joe J.
P.S. Knowing the ratio tells you the ratio of speeds exactly, but it does not allow you to know the ratio of the torques. Don’t forget that the ratio of the torques is [the gear ratio X efficeincy]. This efficiency is going to drop considerably when you loose “conjugate action” (by mating involute gears with different DP’s or Pressure Angles for example). Lapping or running the gears in will help in this regard, but it is no substitute for using properly matched gears to begin with. JJ
Personally, I think the 32 pitch and .7 mod meshing is awsome. In the sense that, if someone can do it well, more power to them. They have learned what few can do, defy engineering rules. We gotta get together and talk about how to send a banana back in time 
haha sorry for the randomness… onto real suffs.
I would buy .7 mod gears off PIC design, you can get them in steel with a .1875" face width up to about 128 teeth. I have bought a lot of gears off PIC, and I always get them in EXACLY 14 days. Very strange…
By the way, wire EDM shops have gotten very cheap. While I would never get gears done there, (you can always buy better ones) I always go to EDM to get precision work done. I am working on a 3 speed shifter, and I got the intricate shifter cut into the gears for VERY cheap. 12 gears total (I made a spare set) for about 200 bucks. It was really cheap because it was the same cut. The guy even offered to harden them before they were cut for 50 bucks. Of course I could not resist.