Ball-and-Ramp Actuator

Try, "recirculating ball drive".

I think you'll like it.

Lyn

Thanks Lyn. That's very close, although I don't need the balls to recirculate, and am hoping to find something more compact in the axial direction.

Your answer stimulated some thinking, and I searched a few patents, finding what I want under the term "ball ramp" (usually without the "-and-"). They are built into various things, but I haven't yet found the sort of standard piece I am hoping to find... something one of the bearing makers, clutch makers, sprag clutch makers, etc might sell in various sizes.

Here's a picture that shows the concept employed in a multi-disc brake. You pull on the orange linkage, which rotates the half of the unit with the thrust bearing, causing it to move to move axially relative to the other half, which is pinned to prevent rotation.

Hi Blink,

I must say, from your original post, this drawing is just what I envisioned. I looked for a while then but did not find anything. Anyway, good job of describing what you were after!

Mike

Thanks, Mike. I worked for a while as a technical writer, so I especially appreciate your kind words.

Consider checking with manufacturers who use these devices routinely. Some rotary solenoids/actuators do, e.g., see http://www.solenoids.com/, lower left item in opening picture. And how about http://mechanical-components.globalspec.com/Industrial-Directory/rotary_solenoid_micro ?

Thanks, Ron. Good suggestion and links.

You're welcome.

Are you looking for one piece, or just a few, or quantity production? Does it need to be long lived, or is it something that will see relatively few cycles? With today's multi-axis machining capability, using a ball mill to cut a spiral ramp is almost trivially easy. I actually designed a mechanism using a straight ramp-&-ball mechanism (two pairs) to clamp microfiche between glass plates held by brass frames. [Operating the mechanism actually opened a slot to permit entry of the film, and it was spring loaded to close] Although the brass wouldn't have withstood hundreds of thousands of cycles, it was perfectly capable of doing the job I needed, and could have been chrome-plated to add an order of magnitude or more to the lifespan. If you got parts made of tool steel and had them hardened, they could be hard machined, or merely refined after hardening with abrasive finishing, and you could design around available bearing balls. Very likely, the actuation means and connection would involve greater design effort than the ramps. If you're doing proof-of-concept, a decent machinist with a mill and rotary table can make such a part.

Hi Ron,

Yes, you're right that this would be pretty easy to make, and for the time being I only need two.

This goes on a proof-of-concept vehicle for which I have made countless little pieces on my lathe (with some other pieces hired out to people with bigger, better machine tools). If I count my time, I often end up with $100 bushings that "should" cost $1.00 if I could find the item mass-produced.

This project is self-funded (for the time being, but not by choice) so I am often debating "penny wise, pound foolish" sorts of things. I used to be a pretty good welder, but am now just barely competent (I'd like to think it's the equipment, but I think it is mainly my eyesight) so in the interests of economy, I weld pretty much everything myself, and everything seems to be holding, but its not pretty.

I even use my drill press (which is pretty heavy and solid) as a mill occasionally. I have an x-y vise, and a tilt-and-rotate table, and could probably knock out a couple of these things in brass -- and my local machinist could do it much better and much faster, but for more money.

Thanks again. Your comments are right on the money.

Blink,

I looked into my Mechanism and Mechanical Devices Sourcebook (McGraw-Hill second Edition)

Would the be a Overrunning Clutch

Looking at your drawing seems that its more axial movement implemnting a type of swash plate

p911

Hi phoenix911,

Yes, it is axial movement that I need. The basic ball ramp mechanism is used in many things, but usually for very small (but relative high force) movement in the axial direction. I need at least 1/2 inch axial movement, and can make something up to work, but was hoping to find a standard part.

The overrunning clutch, in fact, is a good example of a highly-precise carefully heat treated special alloy part that is cheap to buy as a standard item, but really expensive and time consuming to make as a prototype.

Fortunately, for my application (in a proof of concept), I can make the thing I need out of very standard materials, and I don't have to worry much about durability, perfect finish, etc.

Such "devices" are used in many pneumatic nutrunners as torque limiting clutch. I would think that you could adapt one for your project. The ramp-discs are made of high quality hardened steel so that the life expectancy is quite high. You may even use a piece saved from a nutrunner out of use.

Sources: Ingersolrand Atlas Copco and many other.

Hope it will help.

Thanks again to everyone -- lots of good suggestions!

But Blink [winey voice]

How's the hot rod coming

quit teasing us

Arrrrgh... just as I was finishing up this post (I thought) my connection hung, and I inadvertently closed this browser tab... Darn! the post was absolute poetry!

Things are going pretty well. Regen works great -- the brakes are stone cold after several laps of my hilly neighborhood.

I thought "How bad can the vibration be?" as I made some simple rubber mounts for the rear subframe which holds the generator and its engine. I got my answer: very bad. So I have remounted the engine on isolation mounts, and the vibration is much more tolerable now -- my back no longer feels as if I've been given forty lashes every time the engine runs.

These ball ramp gizzies will be used to make the existing CVT (attached to the electric traction motor) manual instead of automatic. Due to regen and reverse (which the CVT is not really designed for) there are certain conditions under which the belt is slack when starting out, and the motor has to be revved way up to get moving -- and then the thing takes off with quite a lurch, shudders, etc. The keyway in the rear wheel sprocket has enlarged considerably from such shenanigans, so I want to have better control over the CVT. (I may make a couple very short, fat hydraulic cylinders instead of using ball ramps... although the idea of oil leaks around a dry belt is unappealing.)

Most of my welds look crummy, but have been holding together, with the exception of one on the exhaust system, which took some fiddling to get it to stop flailing around in sympathy with the engine vibrations.

I contacted Delphi to get info on their engine management system for small engines. They said "Forgeddaboutit, you're too small to even send any details to, and we don't want to even think about treating you like potential future customer."

The conceptual stuff all seems to be working fine. Loads of little details to sort out though.

Let's see what else? It looks different. I'll post a few pictures in a new thread in a few days.

Success sounds like poetry

no matter how akward

I look forward to pics

I find the reason my welds look like chicken scratch is my hands don't go the right speed anymore