Help needed

[Eddy Matthews]

Hi all,

Hopefully one of our members with a bit more common sense than me can help....

I need to take the rotary motion of an electric motor, and have it drive a shaft (at 90 degrees to the motor output) such that the shaft will rotate back and forth over a 90 degree arc - ie. rotate 90 degrees clockwise, then rotate 90 degrees anti-clockwise, whilst the motor continues to rotate in one direction...

I hope that's clear? I'm sure it can be done, but for the life of me I cannot figure it out!

Once I have the basics, I then need to know how to tweak it to alter the output rotation to 70 degrees, or 100 degrees etc etc for fine tuning.

Anyone care to enlighten me? I've got very little hair left to pull out nowadays!!

Eddy

[Eddy Matthews]

Oh, one more thing, the method of achieving the above needs to be as compact as possible as it has to fit into a very limited space!

Regards
Eddy

[Dinosaursoupman]

Hey Eddy,

If you are talking low rpm's then a cam based idea would be possible.

On the face of a disk that mounts on the motor shaft, machine a cam. I'm trying to think of something similar to the idea, give me a minute. Until I can think of it , I'll continue. On the shaft, have an offset similar to a crankshaft that follows the cam. Spring load it so that it remains in contact with the cam.

I don't see an easy way to adjust degree of rotation especially if you want continuous smooth motion. But it is and idea to work from.

Actually, you could start with a cam that does 110 degrees of rotation and by putting a stop on the crank and adjusting the motor back or forth, that would limit your degree of rotation. It just wouldn't be smooth and continuous.

I'm sure some of the engineers have better ideas.

Randy

[bogstandard]

Hi Eddy,

Do either of these help.

The link one is very limited because of the range of movement it can give, as you will tend to get a mechanical lock if you take it to the extremes.

In all cases you should use the drive disc slot for making the throw adjustment.

John

[Eddy Matthews]

Wow, that was fast!! Thanks guys, that sorts that problem.....

Now onto the next bit which is related.... I now have a shaft rocking backwards and forwards (clockwise and anti-clockwise), and I need a rod mounted vertically which pushes up onto a linkage when the shaft is rotating clockwise, and drops back down again when the shaft moves into the anti-clockwise direction.

Again, I hope that makes sense? It's not easy trying to explain this in words!!

Regards
Eddy

[Tug--Kenny]

It's not an invention to paint the wife's kitchen is it?

To add to John's drawing, you could have a triangular block on the end of the lever, which pushes a rod up when moving right and drops the rod when returning left.

Just my two penneth.

ken

[bogstandard]

I think this is what Ken is on about.

John

[Eddy Matthews]

Thanks Ken and John,

I'm not sure that the wedge/ramp would actually do what I need...... I'm going to have to think about that for a while!

Ideally, I need the rod to push up as soon as the rotation is clockwise, and then drop down as soon as it switches to anti-clockwise rotation - If I'm thinking straight (which I'm probably not at 7:30am), the ramp would slowly raise and lower the rod, and I need more of an immediate action so that the rod is "up" throughout the clockwise stage, and "down" throughout the anti-clockwise stage.... If you see what I mean?

Regards
Eddy

P.S. No, it's not a device for painting the kitchen!

[Dinosaursoupman]

Hello Eddy,

You could do it with a cammed micro-switch and a solenoid. Instead of a ramped cam as Ken has illustrated, a split level cam that activates the micro-switch thus activating the solenoid.

Randy

[Dinosaursoupman]

Scratch that last idea; That won't give you the "up" position in one direction of travel and the "down" position in the other.

Randy

[Eddy Matthews]

I thought of the micro-switch and solenoid Randy, but I'd prefer to stick to a purely mechanical system if possible.

To clarify one point which was rasied earlier, the device will operate at a maximum of around 50rpm.

Regards
Eddy

[karl]

Eddy, Would the type of drive used on a metal shaper help make up the design? It has the forward and reverse motion in addition to a variable stroke.
Karl

[Eddy Matthews]

Eddy, Would the type of drive used on a metal shaper help make up the design? It has the forward and reverse motion in addition to a variable stroke.
Karl

To be honest I have no idea Karl, I don;t know what a metal shaper is or how it works.... Can you give more information please?

Regards
Eddy

P.S. Welcome to Paddleducks! 

[karl]

Just went downstairs and grabbed Audels machinists handy book. On the motor a drive gear that spins a bull gear in the center of the bull gear is a slot with a screw, this allows a crank pin movement from center to the edge of the gear (scotch yoke) a rocker arm with a slot in the middle and fastened at the bottom will supply a back and forth motion. I wish I could scan the page for you. The full name of the book is Audels Machinists and tool makers handy book by Frank D. Graham copyright 1941.Thank you for the welcome
Karl

[karl]

My description was as clear as mud. Please try "http://en.wikipedia.org/wiki/SHAPER if you scroll down it shows a example of the drive.
Karl