# I need a coaxial gearbox that translates reciprocating clockwise & counterclockwise rotation to unidirectional while increasing speed of rotation?

I am a noob engineering student. I want to design a coaxial gearbox that takes an input shaft that rotates reciprocally (clockwise then counterclockwise) and increases the speed of rotation unidirectionally to a coaxial output shaft.

For example, a hand-crank is turned 180 degrees clockwise then 180 degrees counterclockwise repeatedly while rotating a flywheel only clockwise. However, the torque from the hand-crank in both directions must be used to increase the speed of the flywheel in a single direction. In other words, both the clockwise and counterclockwise torque must be transmitted smoothly to the flywheel. Hopefully that makes sense. Thanks!

• Check out valve lapping tools. Commented Jan 14, 2022 at 19:59
• Very cool idea! Thanks! There was a patent on something similar in 1929, but I would still need additional spur gears to increase the speed. Great start, thanks.
– Dev1
Commented Jan 14, 2022 at 20:25
• A sprag clutch? If you're ok with wasting the reverse motion? Commented Jan 14, 2022 at 23:28
• @PeteW. Thanks, but the reverse motion cannot be wasted and needs to be equivalent to the forward.
– Dev1
Commented Jan 15, 2022 at 0:05
• @CarlWitthoft. It's not homework per se, just an idea for a project. Design idea # 1: an input shaft w/ two gears, both mounted on opposing 1-way (clutch) hubs. Gear #1 has 40 Teeth (T), gear #2 has 20T. Clockwise rotation of the input shaft will transfer force from gear #1 to gear #3 (20T) on the output shaft. Counter-clockwise rotation of the input shaft will transfer force from gear #2 to (idler) gear #4 (20T) and to gear #5 (10T) on the same output shaft as gear #3. I think this design allows reciprocating clockwise and counter-clockwise rotation in concert with a 2X speed increase. Yes?
– Dev1
Commented Jan 18, 2022 at 21:00

You're describing a mechanical rectifier. Here's one.

A pair of reverse-facing bevel gears with uni-directional clutches take the oscillations of the input shaft and rectify it so that the output rotates only one way. As far as I can see this design will work with input power on either shaft.

I found the image on a Google image search which linked to an article on Science Direct and the full article is available by purchase.

• Very cool. Thanks! But I would still need additional spur gears or a planetary set to increase the speed after the bevels. I am trying to do it with one set of gears. Thanks, definitely moved me forward!
– Dev1
Commented Jan 14, 2022 at 20:32
• To increase the speed within the bevel gear system, increase the diameter of the gears on the input shaft. Commented Jan 14, 2022 at 20:35
• @Dev1: Look at the gears in the illustration. How many teeth has each one got? If the vertical shaft is rotated once how many degrees will the horizontal shaft rotate? Commented Jan 14, 2022 at 20:36
• I may be missing something, but in my intended design, the 2 counter-rotating input shafts and 1 output shaft must be coaxial. Therefore, the horizontal bevel gear in the illustration must be an idler and changing the gearing in the bevels will not increase the output shaft speed.
– Dev1
Commented Jan 14, 2022 at 21:03
• Add a planetary gear assembly to increase speed coaxially
– jko
Commented Jan 17, 2022 at 18:33