Return to 12 oclock position accurately

[djdesai_98]

Hello All,
I am looking for a electrical motor or some other device which will return to zero position or 12 oclock position accurately everytime after it is clocked manually. In other words, if I grab the shaft and turn it clockwise or anti-clockwise it should return to its original position accurately when the hand pressure is removed. I know this can be done mechanically by springs etc, but that is not accurate enough, so I am looking for some sort of CNC or electromechanical device.


Thanks

[austin.mn]

pnuematic rotary actuators come to mind (i would think they would be the simplest) otherwise if you wanted to do it electronicly you could use a plc hooked to an encoder and motor drive. then when the plc senses the movement and see's that the movement has stopped (you took your hand off) then it would pulse the motor drive and get the axis back to its home position. that would be a fairly simple program to create and there are a number of small plc's on the market that are pretty inexpensive. the motor and drive could cost you, depending on how much weight you are moving around.

[Geof]

Originally Posted by djdesai_98 Hello All, I am looking for a electrical motor or some other device which will return to zero position or 12 oclock position accurately everytime after it is clocked manually. In other words, if I grab the shaft and turn it clockwise or anti-clockwise it should return to its original position accurately when the hand pressure is removed. I know this can be done mechanically by springs etc, but that is not accurate enough, so I am looking for some sort of CNC or electromechanical device. Thanks

How far are you turning it away from the zero position and what is your definition of accurate? If it is less than about 270 degrees either direction a spring return with a mechanical stop will bring you back to zero to within a small fraction of a degree.

[djdesai_98]

Thanks. I dont have much rotary movement. About 45 degrees from the 12 oclock position, but I cannot use a mechanical stop, because it is both + and - 45 ie rotation from 12 oclock to 10 oclock and from 12 oclock to 2 oclock, so I am forced to eliminate the mechanical stop am put 2 springs that pull against each other and these do not bring it back to 12 accurately.

Also please tell me what plc is, and where could I buy all this stuff, including the motor. (I am a newbie at this)

Thanks

[Geof]

You can do it with two springs, a single stop pin and two discs that are held against the pin by springs. I have uploaded a picture. This type of mechanism is used in the hinges of doors that open both ways and always return to the closed position. Not at all an original idea.

[austin.mn]

i 'PLC' is a programmable logic controller. you can find them on ebay, or other industrial suppliers on the net. you will want to find one that you can program, some brands require you to buy software to program them, so do a little homework before making a purchase. Keyence is a brand that comes to mind that has free (although time or usage limited) software available. these are programmed using 'Ladder Logic' for something basic, like what you want it to do, the programming will be fairly easy and you should be able to learn what you need to know in a weekend on fiddiling with it. as far as the motors and drive that you will need, that will depend on how strong you need it to be and how fast you need it to move.

i would start with looking into plc's, download a manual and see if you understand it. if not you will have to hire someone to visit you to do the programming and setup, and that will cost you.

what is this for anyway?

[djdesai_98]

This is for my PC based race car game. I am not satisfied with the cheap plastic sticks and wheels in the market, so I want to design my own. There is not much mass to be moved, ie I dont want too much resistance to my hand ( 5 or 10 pounds max) turning the wheel, and want the wheel to get back to its original 12 oclock position in about 3 to 5 secs. There is an IDEC PLC available on ebay. Will that do the job? what sort of motor do I search for?

Thanks

[Al_The_Man]

A PLC would work, though you will need a PLC or a card that will take encoder input as well as an Analogue output module, which could put the price up, If you are up to learning new electronic tricks there is the MicroChip way, it may take a bit more than learning PLC but the end result may be more compact and flexible.
This is two examples of what can be done, either one of these could probabally be adapted.
http://ww1.microchip.com/downloads/e...tes/00531e.pdf
or
http://ww1.microchip.com/downloads/e...tes/00532c.pdf
I think the trick is going to be if you want the motor to hold the 12 o'clock position (unless you have a detent of some kind) but release when you turn it, and then revert back to servo action when you release the shaft. Both these conditions would have to be detected.
Al.

[austin.mn]

i agree that the microchip route may be the best way to go on that application. how much electronics experience do you have? i would say that you could use a simple indexing wheel with two optical sensors and a little gear motor should do the job.

what is wrong with the available wheels out there? those companies spend quite a bucks trying to make those work properly. i don't want to discurrage you or anything, but it could be a bit of a battle making one work much better.

[djdesai_98]

I want the motor to hold at 12 oclock constantly and provide resistance to the hand movement, and then when the hand is removed, the motor should rotate the wheel back to 12 oclock

[Al_The_Man]

Would something like this work? I have used them for torsion mounts and the return pretty accurately. Look at the DR-S & DR-A type.
http://www.rostainc.com/PDFs/KAP02_EN.PDF
The only thing is the torque increases with angular movement.
Al.

[djdesai_98]

I want the torque to increase with angular deflection, so that is great. The only problem I can see is that the rubber insides may not be accurate enough on the return to the 12 oclock position. But it is definitely worth looking into. I am going to call them