Mounting a Key to a servo

william chan

Hi,

I've been talking to a few metal workshops about mounting a metal key to a servo motor.
The operation is simple, the servo is supposed to turn the key to lock or unlock.
But most of them has declined to take up the job, saying it is too difficult.
They can't mill a metal cap that fits the servo's plastic head securely ( without slipping off because the screw is not used ).
The key is supposed to be welded to this metal cap.

Any ideas out there would be greatly appreciated.

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www.fd.com.my
www.mercedes.com.my

Mike Green

How about a metal cap with a slot for the key and a hole for the mounting screw accessible through a drilled out channel in the center of the slot? Rather than being welded, you'd have some setscrews in the side of the slot that would hold the key tightly in the slot. For that matter, you could have holes through the key and run the screws through the key and the sides of the slot to hold the key in place.

william chan

Mike,

Thanks for the idea.
Another problem.
It seems that they can't easily mill out the grooves from the inside of the metal cap b'cos it is so small.

How now?

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www.fd.com.my
www.mercedes.com.my

Phil Pilgrim (PhiPi)

Instead of a slot, why not use a small piece of aluminum angle? One leg would be screwed to the servo horn; the other, to the key. You may want to use a spacer between the aluminum angle and the key to position the key on the axis of rotation. You wouldn't really need a machine shop for this if you have a hacksaw and an electric drill at your disposal.

-Phil

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'Still some PropSTICK Kit bare PCBs left!

Mike Green

Use the existing molded nylon "horn" and mount it to the bottom of a metal cap using screws. If you leave a channel in the cap for the mounting screw, you can fasten the "horn" to the bottom of the cap, then mount the whole thing to the servo. You may have to drill out the holes in the servo "horn" and use flat head screws, but this seems to be commonly done.

DosManDan

Well, let's look at the problem a little more closely....

Is this a key, as in a door key? If so, is it a house key or is it something smaller, like a cabinet key?

The reason I'm asking is since you a leaving the key in the lock, security from one sode of the door isn't a problem. Possibly this is a double keyed lock and you are going to turn the key from the inside to open it.

So, what are your thoughts behind why you selected a key as the solution? I use to do locksmithing and though I could offer some help solving the problem.

Dan

Timmoore

How about http://servocity.com/html/servo_hub.html they already have a alum hub milled for a servo with threaded holes for you to mount to.

T Chap

I would suggest you post some pics of the servo you are trying to use, plus the key, anything else related.

Phil Pilgrim (PhiPi)

Pursuant to my comment above, here's a key turner that took all of 15 minutes to construct using simple tools:



-Phil

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'Still some PropSTICK Kit bare PCBs left!

Chris Savage

Phil,

Now you just need a skeleton key for it and you’ll be all set.

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Chris Savage
Parallax Engineering

Duffer

There are those that teach, there are those that do and there are those rare few that have the skill and patience to teach by doing.

Nice job Phil and thanks.· I've copied the key geometry from your inclosed photo. I'll be at your home later tonight to steal everything you own. Remember, no good deed goes unpunished.

Duffer

Phil Pilgrim (PhiPi)

Duffer,

LOL! Good luck with that. Assuming you could even make it past my attack cat, you'd discover that the key (which came out of a junk drawer) won't fit!

¡Lo siento mucho!
-Phil

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'Still some PropSTICK Kit bare PCBs left!

william chan

Phil,

You are a genius!
I didn't quite understand what you were saying until I saw the photo.

Do you keep separate labs for electronics and mechanical?

Where you get the small round horn? (why they call it a horn?)
Parallax didn't give me any extra horns apart from the already fitted cross type which is too bulky.

But the truth is, I had hoped to minimize the mounting distance required as the casing would have to be bulky if the servo stands too tall from the door.
Nevertheless it is a good start.

Thanks again.

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www.fd.com.my
www.mercedes.com.my

Phil Pilgrim (PhiPi)

Willam,

Development, bookkeeping, and shipping are in one room; mechanical, soldering, inventory, assembly, and packaging in another.

The horn came with the servo, but it may not have come from Parallax. Any horn with a Futaba spline should work, though, if you have a Parallax servo. Your local hobby shop probably has them. You can also cut down the large cross types with a pair of nippers. I do that all the time, and they're nearly as sturdy as the disk type.

One thing to watch out for: if you unlock your lock all the way, you may have trouble locking it again with the servo. This is because the lock pins sometimes catch on the edge of the tumbler holes. It's something we, as humans, deal with all the time without thinking by jiggling the key a little. If you can retract the bolt far enough to open whatever you're opening without turning the key far enough that it could be extracted, I think you'll have a lot better luck.

-Phil

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'Still some PropSTICK Kit bare PCBs left!

SRLM

As for size, you can't really get it any smaller without using gears or the like. If you look at the photo, you'll see that you can get about 1/8" more between the key and angle iron, and thats about it. Everything else is unchangable.

I suppose you could cut off the round head part of the key, and solder it to a piece that attaches to the horn. You could also use a smaller servo like they use in model helicopters.