First time inventor

Basically, you only need to mount an arm on the shaft and have it hit a couple of limit switches. Make sure you use the kind that allow overtravel. The problem will be hitting 365 degrees; I suspect +/- 5 degrees would be OK, but you're gonna have significant inertia with that gearhead. If you want a little more accuracy for more $, use a optical switch and carefully calibrate it by trial and error. For a lot more effort, you could put an encoder on there with relays to reverse the motor. There are mechanical reversers you could use, and they would be pretty accurate, but that would be pretty expensive.

And, one more thought. If this is just a one-off project, you might hang around electronics markets and find an old computer tape drive. One of those servomotors and position sensors should work great.

This is a sketch of a mechanism which will allow for the extra 5° of rotation.

• A - motor shaft
• B - rod fixed to shaft
• C - lever pivoted at point D
• E and F - limit switches

The rod C can be held centrally between the switches by a spring (or two).

Use slotted optoswitches (as previously suggested) instead if mechanical limit switches if you need better accuracy/repeatability.

Do you want the motor to auto-reverse on the limits & run continuously cw/ccw between them? What kind of shaft speed? Bit more info, please!

I'm having trouble picturing 1/8 of a horse... that's about a front leg I s'pose?

I get confused by the whole horsepower thing...I'm happier talking in watts or maybe tourque on the output shaft ..(I just hate Newtons)

How quick does this need to go? What load are you rataing, how often (duty cycle)? What sort of life are you after? (Not a philosophical question...how long before it can wear out?)
Are you thinking DC motor/ gearbox? 'cos that is real easy to reverse....

Del

1 HP ≈ 746W, so we're looking at 95W (ish). Say 4A @ 24Vdc. If he's talking horses, it's more likely ac mains - so about ½A @ 230Vac. (Just to save you buggering about with calculators/slide rules etc.).

Used to hate Newtons - but I'm OK with them now (though why motor manufacturers don't get their act together & stop quoting torque in Nm/mNm/Ncm (& then oz-in) I'll never know).

If you heft a biggish apple (~3½ oz) in your hand, that's somewhere near a Newton. (I hope - if not, there's some kit out there hopelessly under- or overrated ).

May I suggest that limit switches are just not reliable enough, you need further "limit" switches just in case the first ones go wrong!!!

May I suggest that you need an encoder (as has been suggested already by others) a small PIC controller or similar to do the dirty work and what we call "crash stops" in the industry.

You start up your controller, it runs the motor slowly in both directions, monitoring motor current to see when a crash stop is encountered, these are noted by the controller and then it knows exactly where it is.

Now you can move the motor at varying speeds withing the crash stop limits to your hearts content!!!

A lot more complicated, but once the hardware is designed, you can change the control program to fulfill your wishes.

About ten years ago, I attended a lecture where a physician from another country was discussing tests where they were using a 40 ft-lb torque motor to quickly move the subject's head 90°. When I talked to him about the technical details, I noticed they were using only a resolver for travel control, with no safety limit past that. Since I've seen many a motor spin out on resolver control, I asked him how he managed to get the volunteers to agree to this. He said, "Oh, we don't use volunteers. We use soldiers."

This can be done without limit switches using a cam...arm link...driven cam by ratioing the primary (drive) cam link pivot point to the driven cam permitting the 365 degree travel in inverse ratio... (gets tricky here...three ways to solve) WILL NEED A CURVED LINK ARM TO INSURE CORRECT DIRECTIONAL REVERSE TRAVEL CHANGE ....constant one direction motor load, no limit switches, if in constant duty...one limit start/stop switch/time controlled or limit if manually start...end of cycle off mode..... if in intermittent/manually started non continuous use.

oil well pumps use this concept of turning rotary motion into linear motion. The 365 degree travel is unusual.

MR, GUY

MR. GUEST (OP),

There are a lot of folk taking the time & trouble to sort out all manner of possible solutions to your problem - and apparently you can't even be bothered to respond!

If this is due to circumstances beyond your control, I apologize for my outburst - please come and join in - give us the feedback.

_{If not, ignore my signature, bugger off and don't come back.}