Question about air motors (fast answer would be great)

Hopefully by entering this thread you know what an air motor is. :slight_smile:

I’m working on a project which requires that I rotate a lightweight assembly inside of a cabinet - there is 200degree hot air being forced into the cabinet and I need the aseembly to spin at around 30 r.p.m.

Can I acheive this with an airmotor? Maybe an airmotor and a reduction gear?

I never thought about trying to put an airmotor into such a hot environment before. I know that with increased temperature comes decreased efficiency from compressed air.

So what’s the dope? I have been googling all day and can’t find this specific esoteric bit of pneumatic trivia. Help!

It depends on the relative contribution of the hot air entering the cabinet, and the compressed air flowing through the motor, to determining its temperature. Is the air motor running constantly, or occasionally? What I’m getting at is that if you put insulation around the air motor and run cool compressed air through it continuously, it remains cool even in the hot environment.

Which do you mean, °C or °F? If it’s °F, the motor might be just fine at that temperature anyway. 200 °C probably requires special lubricants and might introduce differential expansion issues.

Is it a necessity to have the motor in the cabinet? You’ll likely need gearing, the air motors I’m familiar with (not that many) wouldn’t run as slow as 30rpm. The effect of heat on the gears and keeping them lubricated could be a problem. It would be much easier to pass a shaft through an opening in the cabinet. A Teflon bearing might be able to maintain the temperature you require and provide a fairly tight seal if that is needed. If you need to contain the reduction gear inside the cabinet, a wormgear might be the best way to obtain a large speed reduction.

200 degrees f.

I’m not concerned with efficiency here. I just need to rotate a basket of manufactured parts inside of a cabinet. The cabinet contains a platform which raises and lowers via an air operated piston, and the lid closes on top of it (preventing people burns :slight_smile: ). The hot air is forced into the cabinet to dry the parts, which have recently been immersed in water.

It’s a big fancy dryer. But i need to tumble the parts around in there, because they are so small that they just stick together and don’t get dry without temperatures over 250 degrees f, and that’s outside the bounds of what this heater will produce.

So, I’m gonna tumble the parts around on the platform via a rolly-basket holding thing that mounts to the platform. Platform goes down into cabinet, lid closes, air turns on, and baskets rotate thus agitating them and allowing hot air to completely dry them.


I hope.

But I need to do it slowly, or else the parts won’t tumble, they’ll just all fling to one side of the basket and stick together, nullifying the rotating effect.

The mechanics of the cabinet and the lid and the platform make it impossible to have anything OUTSIDE of the cabinet making the rotating. It’s gotta be self contained. My first thought was to mount a rack (from a rack and pinion setup) vertically alongside the platform and have a pinion gear mounted to the rolly-basket rotating assembly I have yet to fabricate. The when the platform goes up and down via it’s pneumatic cylinder it would roll the basket assembly along the rack and rotate it.

So this is my dilemma. I need to cost compare, and I can’t cost compare without knowing whether the air motor option is even technically feasible. If it’ll be too hot in there for the air motor to work effectively, or if I can’t get it to spin slowly enough with enough torque to rotate a 15 pound assembly, then my available options is reduced to one. I like having options.

Can you couple the piston with a swashplate to turn the up and down motion into rotary? Or use seperate piston that way. Converting reciprocal action to rotary may be a good way to run an air motor at low speed, and avoid gears and the associated heat and lubrication problem. The swash plate will need lubrication and to be heat resistant, but 200F isn’t all that hot.

Is it possible to turn the platform its side so it rotates like a hamster wheel? The tumbling issue becomes a lot less problematic.

I take it the air supply for the motor is not contained in the oven?

Cool the compressed air down first, insulate the motor itself a bit (so the heat in the oven has trouble getting to motor), and vent the exhaust from the motor outside of the oven so that doesnt cool down the oven (or heat it with an electric element as it leaves the motor if the exhaust must be in the oven).

Given how much air flows through the motor, you probably don’t need to cool the crap outa the air, just cool it down a bit (given that the temps don’t sound particularly high).

I don’t know what a swashplate is…

However, this was my intention with the rack and pinion idea. Using the existing motion of the platform up and down to rotate my baskets, even though it would be rotating back and forth. It seems like the most simple way to do it, and probably the most reliable in the long term. My boss is the one who wants to cost compare the air motor idea…probably because he came up with it. (of course, after I wrote it off as technically unfeasible…and difficult.)

I ran this one through my head first…but I decided I didn’t have enough room in the cabinet. What I would give for a few more inches! (that’s what she said!) :smiley:

This post helps me to see just how many little tiny difficulties are present with the airmotor idea. It’s really more complicated than I think I want this to become. Not that I don’t appreciate your response, it’s helpful in it’s own right.

I’m definitely leaning towards the rack and pinion idea more and more, unless anyone sees an even simpler solution. :slight_smile:

I appreciate all the responses. I can definitely see who here likes to work a problem through even though it doesn’t affect them at all. :slight_smile:

Think of it this way. If you build relatively tall walls (think sidewalls on a tire, except the material will be some kind of mesh to allow airflow) you can probably pack a whole lot more parts into it (and keep them all tumbling) than you could to a horizontal tray of the same diameter. Or, you could make s significantly smaller vertical wheel to tumble the same number of parts.

It’s the motion of the ocean, lover. :slight_smile:

How about a rotary actuator? It would tumble them one way and then the other direction. Not the rotation of the OP but that would probably do a even better job of mixing the parts. It would eliminate the exhaust and speed reduction issues. The website shows position sensing options so you could use the signal to shift the valve and rotate the basket the other way. Or just a couple of timers, that might be cheaper. With a pressure regulator and some flow controls, you would have a lot of control over the speed of rotation.

Heres the Wiki for swashplate. In your case you would want an elliptical swashplate that is connected to the basket, off tilted rotational plane of the basket. A fixed ‘follower’ would have a groove that fits onto the rim of the swashplate. The up and down motion will force the swashplate to turn to keep a the rim at the level of the ‘follower’. It’s all kind of inversed because the swashplate is moving up and down and the ‘follower’ isn’t moving. I’m not sure how to name those parts. The physical inverse of a swashplate would be a groove that follows a sin wave around a cylinder. I’ll look for some better illustrations. Similar drives using a grooved cylinder were once used to drive the backforth motion of a dot matrix printer head using a derivative action.

Here’s another example. In this case two pistons are needed because the follower is just a wheel. You can have a single fixed follower that mounts on the edge of the plate and contacts on both the top and bottom of the plate.

That sounds like a workable idea. You might be able to start with actuators for ball or butterfly valves.

Another idea is a vertical drum supported by rollers, one of which is powered and much smaller in diameter than the drum.