"Motors and Drive train edition" of Fresh From the Forum

[Ken Leung]

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III. Gears and Sprockets
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FIRST opened up the rules regarding gears and sprocket this year… You can get whatever gear you want, at any amount as long as you robot fit inside the dimension and weight limit. Of course, these have to be off the shelf products, meaning, they should be commercial products out there open to everyone to purchase. There have been a debate about whether custom making your own gear/sprocket is bounded by the additional hardware list and small parts catalog rule (if you can only custom make gear/sprocket with allowed material, or if you can use whatever material you want under the any gear/sprocket you want rule). But without a clarification from FIRST, your best bet is still to buy gear/sprocket from stores or online stores. Try to stay within rules and its spirit… Gracious Professionalism is KEY.

http://www.chiefdelphi.com/forums/sh...&threadid=2026
http://www.chiefdelphi.com/forums/sh...&threadid=2079

Before you decide to buy the gear/sprocket, do some calculations for what kind of gear/sprocket you would need for your component. After all, you want your gears strong enough to withstand the load, AND save weight and cost at the same time. For example, Delrin gears are probably not too good for the drive train, but steel would. Also, you might want to buy different tooth gears to try out different ratio. There are only so many calculation you can do before slapping on different gears and try out how they will work out.
“It's possible you might get by with a delrin gear early in the drive train (say the 1st gear that mates with the pinion) but this depends on the ratio. My feeling is you would certainly experience a disaster at some point early in the competition, why risk it.” -Ed Sparks
“Brass is a very good gear material. The yield stress of many brasses is higher than that of many steels. Also the wear & friction properties are often better than steels.” -Joe J.
http://www.chiefdelphi.com/forums/sh...&threadid=1957
http://www.chiefdelphi.com/forums/sh...&threadid=1812

If you want to learn about calculation of gear’s strength, check out this thread with a good approximation that’s sufficient for the usage on FIRST robot:
http://www.chiefdelphi.com/forums/sh...&threadid=1873


About sources for gears:
There are a lot of online places you where can buy gears/sprockets… Here are some suggestions from different people:
“A few good small components sources:
www.wmberg.com
www.allieddevices.com” - Keithicus
“mcmaster.com and stock drive products (sdp-si.com) are good sources. Also, motion industries is a good source.” -Joe J.
“http://www.globalspec.com
You can search across the industry for the part you want. It is particularly useful for gears and sprockets.” -ChrisH
“We found a company called Motion Industries that carried the identical part. Turns out they have about 500 outlets around the country (check their locator at http://www.motionindustries.com/ ).” -dlavery
http://www.chiefdelphi.com/forums/sh...&threadid=1975
http://www.chiefdelphi.com/forums/sh...&threadid=1882


About Buying 0.7 modulus gears…
“Go to Pic-Design.com
They are the only source I am aware of that sells metal 0.7 Module gears.” -Joe J.
http://www.chiefdelphi.com/forums/sh...&threadid=1890


About pairing up Chiaphua and Drill with a gearbox...

A little discussion about making gear box for pairing up bosch and chiaphua
http://www.chiefdelphi.com/forums/sh...&threadid=1949

Which lead to another topic, turns out not a lot of people understand how gears and ratio work. It might seem confusing at first, but actually quite easy to understand. I included a little section about understand gears and ratio in my WRRF motor selection lecture notes, which can be downloaded @ http://www.chiefdelphi.com/forums/papers.php?s=
But basically, gears and sprockets can be use to reduce speed and increase torque, or the other way if necessary. Also, they be used to change direction of rotation or motion, and transfer power from one place to another. Basically, when gears are being driven, there is a certain torque and teeth force on that gear. And if you put different size of gears together, the gears pushing each other will generate different torque on each gear. Just think about this in terms of lever arm and torque. If you understand the concept of torque, then you should understand this.

About CVT…
A really interesting about Continuous Variable Transmission… This kept me awake for a couple of nights. The discussion starts some where toward the bottom.
“Picture this ... the output from the drill motor transmission is the sun gear for another planetary stage. We use the fisher price motor to rotate the ring gear” - Paul Copioli
http://www.chiefdelphi.com/forums/sh...&threadid=1179