Hydraulic stepper motor

wolram

Is there such a thing? i have had a search but found nothing, i can think of a way that one would work, but i need one that can (step) 90 degrees in 25 milli seconds and hold possition until the next step is called for.

anyone that can help will be rewarded with one of my fantastic chili cakes.

brewnog

As far as I'm aware, not as such. However, I've seen applications using some nifty electronically controlled valvegear to control a hydraulic motor by using a position sensor on the motor to feedback to the controller. Will have a dig around.

Is this the same application that you were querying your mutilated gears for a while ago? Chilli cakes sound good.

Danger

I gotta enter the contest just because I love chili. Never had it on a cake, but I'll try anything.
Does it have to be a stepper motor? Would a piston-actuated ratchet wheel work?

wolram

I do not think so Danger, i need to index quarter steps continuosly, i guess i could use half or even full 360 with gearing ,but i want to keep it a simple as poss, Brewy has the idea ,the way i would do it would be to have a vane motor with a valve on inlet and exhaust with a feed back sensor to vary the signal pulse lengh to the valves, or some such, the (motor) volume would have to be quite small as 25 milli secs is rather rapid.

It is the mark three Brewy.

Danger

Hmmm... not sure about response time, but maybe something like a 'Geneva wheel' attached to the motor shaft as your position sensor/valve actuator?

FredGarvin

I have never seen a stepper motor tht was hyraulic. However there is a fair amount of motion control that is hydraulic based. Check with companies like Moog.

wolram

Thanks Fred, Danger, i have gone through thousand of (product) pages with no luck, it seem pnuematic and hydraulic devices are images of one another, neither have a stepper design i can find, (why) there must be a reason, would they be so difficult to make?
May be i could make one but where to start, seals would be a major part as would fluid flow times.

Danger

It just occurred to me that perhaps the lack of hydraulic steppers has to do with the shock loads of a high-pressure system starting and stopping so rapidly and repeatedly. I would suspect that there would be a lot of stress on the components. While you stated 25ms as the needed response time, you didn't mention how often it has to step.

wolram

Approx 40 times a minute, which i think is not over the top, some manufacturers are using hydraulicaly opperated valves on ic egines at
15000 rpm and they lift 6mm.

http://www.sturmanindustries.com/mai...sActuators.htm

Danger

Well, that would apparently negate that explanation.

brewnog

Parker Rexroth?

wolram

I think the problem i have is that what i want falls between a motor and a actuator, and no one has ever had a need for hydrulic stepper, i think if i want to continue this idea i will have to make my own, (even though i have no idea how to yet)

Danger

Hey... does this thing continously step in the same direction, or is it reversible?

edit: Actually, never mind that; it doesn't matter. Just an example of things running through my head while I'm trying to come up with something. So... here goes. I have no diagrams or tech data or anything else on hand right now, so I'm just going by memory here. I'm wondering if you could use a 4-piston pump (the kind with a swash-plate) as a motor. Blasting oil into it for long enough to 'compress' one piston should result in 90 degrees of rotation, right? Obviously, this is just an off the top of my head thing, and I won't have a chance to really think it out until at least after I get home tonight.

FredGarvin

I think you are simply looking for an actuator. We have used linear hydraulic actuators and precisely controlled the position with a pulse width modulated control valve and position feedback.

By definition, a stepper motor is an elctric device.

Why do you need a stepper motor? Why not use an electric one?

Danger

I already tried that one; he didn't buy it.