# Is a 1:1 Worm Drive possible?

I am working on a project that requires a wing to be rotated and I need the rotation mechanism to be fail-safe -- if power fails, the wing will stay in place and not move around. My thought was to use a worm drive since they are not reversible. However, worm drives typically reduce speed.

Would there be anyway to make this reduction in speed from the motor to the gear as little as possible using a worm drive?
Should I just forget the idea of a worm drive and use a motor that can hold its position even if turned off (if so what type of motor could do this?)?

• You could always use a worm, which will reduce things, and then add a spur gear set to gear it back up? Other options include electromagnetic brakes (requires current running to release) or a spring loaded, servo retracted pin of some kind... My question is, why can't you deal with any reduction? Were you originally planning to couple the wing directly to the motor shaft? Do you need to spin the wing at a few thousand rpm, or rotate it more slowly? Jun 27, 2018 at 5:40
• I need to be able to change its angle. So it doesn't have to continuously spin but it needs to be able to move quickly. Jun 28, 2018 at 5:13
• how quickly? Why wouldn't a relatively 'fast' worm gear work for you? Jun 28, 2018 at 6:52

A worm drive presents a reduction with a ratio of one to the number of teeth on the driven gear. This means it would be necessary to have a gear with one tooth and yet remain circular. Obviously not in our universe.

Thanks to Phil Sweet, I've become aware of multi-start worm gears, also called multi-threaded worms. This would improve the mechanism by reducing friction and increasing efficiency. With the typical maximum multi-start of 4, you would still need a 4 tooth gear, also impractical.

However, it becomes easier to implement the secondary gearset. If a 12 tooth driven gear is used, the ratio become 1:3 requiring a 3:1 secondary gearset. That's easier than having to deal with larger numbers, such as 40:1 or worse.

In order to accomplish your objective, you would have to select the smallest gearing mechanism of your resources and use it to drive another set of gears to increase the gear ratio.

• 1:1 worms with no feedback are possible and can have as many teeth as you like. You don't have to have just one spiral on the worm. You can have many. Jun 27, 2018 at 19:20
• That's an interesting concept. I found a site: khkgears.net/new/worm_gear.html that indicates the typical maximum is a four-start multi-threaded worm. That leaves a four-tooth driven gear, which seems yet impractical. An advantage to a four start worm is reduced friction and increased efficiency. This would make the secondary gear set easier to manage. A 12 tooth driven gear means only 3:1 is needed for the secondary gear set. Thanks for the pointer. Jun 27, 2018 at 19:48
• The direction I was going was to try to get the OP to see that a 1:1 worm was just an ordinary pair of crossed helical gears. Jun 27, 2018 at 20:21
• And by extension, that once you get a practicable "1:1 worm", the fact that it's difficult to backdrive is no longer true. Jun 28, 2018 at 4:56

You can use a one to one worm drive, even though I don't see the advantage.

Also as has been mentioned in other answers there are many cluching- locking mechanisms that need either a mechanical or electrical switch to release.

Aviation industry commonly uses all manner of cluch and release in applications such as the hinge connection of propellers to shaft in adjustable pitch propellers. You can google Cessna 180 and Mooney, etc.

I would use a stator motor with a sliding shaft key to lock position as needed. A ratchet gear system may not be a bad idea in this case to lock final position as long as fatigue is not going to be an issue longer term.