How to rotate a combination of discs along the same axis - Page 1
Forum section: electronics / projects

author: msr
author_rank: Regular Contributor
timestamp: March 30, 2016, 08:55:42 pm
content: Hi everyone,I have an engineering background, I'm an EE, but I know almost nothing about mechanics. Also, I'm not aware of a mechanics forum and that's why I'm writing here so hopefully some could help me.This is the challenge: how to control the rotation of multiple discs along the same axis? Assume you have a sliced cylinder. The ideal scenario would be to control every slice independently, but to make things easier I think it helps to consider that you can move them in a fixed number of combinations and on the same direction (e.g. a mechanism that enables to rotate the top and bottom cylinders at the same time and same direction - combination #1 - and the inner ones in the same way - combination #2 - but not as the same time as #1).Any idea on how to accomplish this?I though I could use something like a "key" along the axis/shaft/rod. By moving it up/down it would lock different discs/slices. Not sure if this is a good idea. One issue I can see with this one, is that the slices that weren't locked by the "key" could be rotating freely and I want them to be steady.

author: ataradov
author_rank: Super Contributor
timestamp: March 30, 2016, 09:06:27 pm
content: How many slices do you need to control and how big they are?

author: msr
author_rank: Regular Contributor
timestamp: March 30, 2016, 09:18:03 pm
content: This is still a conceptual challenge so nothing really... real. But I would say 6 ~ 8 slices.Another important detail I missed: the less motors required the better (I assumed this on my original post but that may not be obvious). The disc/slices must be close to each other, i.e. almost no space to insert complex mechanisms or electronics in between them.On the solution I presented I was considering to use two stepper motors: one for up/down (threaded rod) and another one to control rotation (with a gear).

author: Marco
author_rank: Super Contributor
timestamp: March 30, 2016, 09:25:46 pm
content: You can use hollow shafts to drive the slices at different speeds (outer shaft drives the nearest slice, inner shaft drives the farthest slice).

author: ataradov
author_rank: Super Contributor
timestamp: March 30, 2016, 09:26:00 pm
content: It is really hard to tell without having any limits set. If they are big enough, then you can make them hollow and make internal surface into a rack and use pinions to bring the control rods out.Or, if discs are big enough, you can just insert small stepper motors inside the disc itself. There are very tiny stepper motors that are used in car dashboards to move hands on the speedometer and other equipment. They are pretty weak motors, but you have not specified how much friction you plan to have either.

author: SL4P
author_rank: Super Contributor
timestamp: March 30, 2016, 10:19:53 pm
content: Do the slices have to move in the same direction of rotation, or at the same time?You may be able to to something with ratcheted teeth in one direction or the other...or all are driven - with selective 'braking'?

author: amspire
author_rank: Super Contributor
timestamp: March 30, 2016, 11:48:22 pm
content: You could have a single shaft fitted to a stepping motor. All the disks are on the shaft with a friction fit (so they can slip) and each one has notched gear attached and a solenoid that locks into this gear.Only the disks with the powered solenoid will turn. Since the disk position is normally locked the friction can be a low friction. The shaft can have a groove milled along the length, and you make a whole lot of washers with a pin to fit the grove in the shaft. Then you assemble it with a disk, washer, spring, washer, disk, washer, spring,... Most of the parts can be laser/water cut with just a bit of milling.

author: jeroen79
author_rank: Frequent Contributor
timestamp: March 31, 2016, 04:12:56 am
content: What is the intended use?What exactly are these disks/slices?

author: ataradov
author_rank: Super Contributor
timestamp: March 31, 2016, 04:13:34 am
content: And if you only need small number of positions (like 10), then you can make your own small stepper motor with number of magnets equal to number of positions and 3 coils per wheel. This way by alternating current though the coils you can rotate the disc in any direction and fix it with the same coils.

author: ataradov
author_rank: Super Contributor
timestamp: March 31, 2016, 04:17:58 am
content: Quote from: jeroen79 on March 31, 2016, 04:12:56 amI would guess some sort of automated cryptex device.

author: pmbrunelle
author_rank: Regular Contributor
timestamp: March 31, 2016, 12:04:44 pm
content: For 8 slices, you can use concentric shafts to remotely drive the slices from each end.So, on each side, you could have one solid shaft, and three hollow shafts, all concentric with one another.From the remote drive ends, you could use steppers with timing belts to drive the hollow shafts. For the solid shafts, the steppers would not necessarily require timing belts; these could be direct drive.This would be similar to a clock, with hour, minute, second hands that require driving. Or like a triple-spool Rolls-Royce engine.