Electrical Rotary Joints with Stepper Motor?

[SiDawg]

Hi all, my first post, thanks for reading

Basically my question is "how do you combine a stepper motor with a 'slip ring' or 'electrical rotary joint' so something can spin through and past 360 degrees without twisting wires?


I'm in early planning stages of a small (inside 20cm) robot: I started thinking about "fully rotating" turrets and how that could be achieved: I can find for example 12 wire 'slip rings' that take care of the "twisted wire" problem, but how can i combine that with a stepper motor? Is there a product that combines the two for me? Is there a slip ring with will fit over a motor axle? Is there something obvious im missing? Or is that just impractical and/or unnecessary?

So for example, my base/chassis may be a standard-config vehicle, two wheels with motors, plus a third or fourth free-wheel... No surprises.

But I want a 360 degree scanning turret: something holding range sensors, light sensors... i.e. "some number" of directional sensors.

I imagine the standard approach is to just rotate one way through 360 degrees, then back through 360 degrees... all the wires will just twist one way then twist back the other way... a stepper motor can be housed on the base and the turret attached... But obviously if you wanted to go past 360 degrees, then all the wires going to/from those sensors would just keep twisting until they can't twist no more...

Thanks for your help

[SiDawg]

... I guess how it COULD be achieved is a circular gear on the turret (or the base!) and the stepper motor has just a small gear feeding on that that... so in effect stepper motor off-centre of turret.

Then structural question... it doesnt look like slip rings are designed to really hold and secure a turret to a base for example so if the stepper motor can't be used to attach to the base and the turret (stepper motors seem "sturdy enough" for the weight im talking about) then some other structure would be needed to hold up the turret, provide bearings, etc... hmm...

It should definatley be possible to build a stepper motor and strip-ring in one: after all a motor has slip rings built in anyway right? Just add a few more and feed wires through the middle of a hollow axis...

[mklrobo]

  Hello!
Interesting problem!
I would offer an opinion, where permissible. 
At first glance, I would check the Thomas Registry. This document holds all the
names of manufacturers in North America. If it is manufactured in the USA, then
you can find it. 
If not, you may have found a nich'e, in which invention is required. Depending on your amperage draw,
any number of answers spring to mind. Ideas are;
1> transformer on lower and upper half to transmit power.(no contact needed)
2> slip rings. (you thought of that one already)
3> laser emission. One side is emitter, and the other acts like a solar cell, to absorb power.
4> heat; one side emits heat, the other side has a thermopile, to convert heat to energy. (very unlikely to use)
5> generator around the shaft of the receiver arm. The driver arm moves the shaft in rotation; while that
is happening, a generator in the upper receiver shaft converts mechanical energy to electrical energy
to power whatever is on the receiver shaft.( ) I have to stretch to come up with that one!!! 
That is all I can think of at the moment.  Good Luck!!! 

[SiDawg]

Thanks mklrobo that's an interesting take on the problem! It would be quite a fun and interesting challenge to transmit power wirelessly... Then there's all the "information" or data lines going to all the sensors: I guess as long as there's power I could transmit via radio. Probably overkill but an interesting challenge

I'll check out the Thomas Registry! Thanks for the tip

[SiDawg]

I think i've found a solution... "hollow shaft stepper motor", for example like the one below (though this is very high voltage: surely something similiar available at lower voltage)

http://www.autonics.com/products/products_detail.php?catecode=03/01/02&db_uid=72

So you could mount that to base and turrent, and then buy a "slip ring", something like this:

http://www.moog.com/products/slip-rings/slip-rings-faq-s/

Mount that underneath the motor on the base... feed the wires through the middle of the stepper motor shaft, attach turret to outside of stepper motor shaft and attach wires coming out of shaft to whatever you like: they will free rotate as the stepper motor rotates (probably want some sort of "clutch" on turret, something fixed to turret that grips all wires together securely, so all the twisting force is limited to the gap between top of slip ring and point of that clutch rather than being transfered to where they're soldered to your parts.