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View Full Version : LEGO gears for a gear box?



gammaprysem
05-07-2013, 01:25 PM
ok so im trying to create a very lightweight nerf luancher for a robot but i was just wondering has anyone tried using lego gears to create a gear box for something like this?. . . . i mean i made an RC helicopter using lego gears but thats different theres not as much torque and strain put on the teeth of the gears. in adition im tryna find some gear sets with assorted sized gears and gear types, for further experimentation. know where i could find this?

Lupulus
05-07-2013, 03:42 PM
I used Lego gears for a project awhile back, in which I needed a small motor to slowly lift a weight on a string. Worked fine for me.

Legos are made from ABS plastic which is reasonably tough, probably as good or better than similar size micro-RC plastic gears. If you need something stronger you could go to metal gears. [EDIT: Checked becasue I didn't want to give bad info--plastic RC gears are typically made from Nylon, which actually is a bit stronger (+33?) compared to ABS.]

However, snapped-together Legos do have a tendency to un-snap when you least want them to. One easy way to fuse together Legos is to apply some acetone (AKA nail polish remover). This melts the plastic, and leaves them fused when it dries. For maximum hold you can mix some ABS shavings in with the acetone to make "Lego glue", but it's not really necessary in my opinion.

There's plenty of hobby sites on google that would love to sell you some gears...I don't have experience to recommend one in particular though.

jwatte
05-07-2013, 04:49 PM
When it comes to bevel gears, the gears have to have the same "pressure angle" and the same "pitch" or "modulus" to be compatible. Additionally, the gears have to have the same basic build -- "stub" versus "standard" are not compatible.

Old-school gears typically use a pressure angle of 14.5 degrees, which leads to long, spindly teeth, and less ability to transfer a lot of torque, but the gears may run more silently. Modern gears use a pressure angle of 20 degrees, so teeth are thicker/stubbier, and they can take a lot more torque. Lego gears look like they have a very low pressure angle -- probably even lower than 14.5 degrees. Thus, you should expect them to not be very sturdy under load. Also, I'm not sure if they are "true" involute gear designs, or if they have a different tooth profile to better suit the specific experimenter use.

There are gear sets ranging from simple plastic gears from some place like Tamiya, to collections of precision metal gears you can put together from places like McMaster-Carr or sdp-si.com.