Hi there,
still working out the details, I bought an Arduino and looking for a suitable stepper motor with low detent torque.
One question: how do you suggest to connect the shaft of the stepper motor with the linchpin of the lock?
Thanks again

Check adafruit.com. Lots of stepper motors, drivers and instructions on how to program arduino.

 

Maybe a toothed belt, how many degree's of the knob does it take to open, 180° ?
Max.

 

Maybe a toothed belt, how many degree's of the knob does it take to open, 180° ?
Max.

Nope, it has to make 3 complete revolutions, so 3 * 360°

 

If you have calculated the torque required using a spring scale etc per Alec_t suggestion.
Is it possible to install some kind of small pulley on the face of the knob, or even replace the knob with a pulley?
I am assuming it may be better to have the motor 180° instead of the shaft in line with the knob and extending the length this way.
Max.

 

In terms of movement, you need force and distance. In the US, lbs is used. So a spring scale and some distance works. Especially if you have a peek reading spring scale. if you know what it is at 6", you configure out what it is at 1".
Torque (oz-in) = distance(in) * force(oz)

You really need a force perpendicular to the lever arm.

Before I bought a spring scale, I used a cans of food to determine the force required to move a curtain rod.

The lock I would LIKE to automate is like 1-3/4 of a turn and the in and outside position has no relationship to open or closed.
it's a 2-key deadbolt. And yea, turn the key on the inner side. Lock and unlocked on the lock isn't enough to say the door is closed, so you really need closed and locked. The key cylinder on the inside and outside doesn't know if the lock was turned.

Jam is a possibility if the door is partially closed.

I don't remember what the lock looks like inside.

it's close to this:

https://www.americankeysupply.com/p...d-boxed-ilco-535-53-41-6460?cPath=106_208_246


I did find an absolute encoder that would hold the value after a power fail except for the turns count. I think it was like $400 USD.

I think you have a European lock and I did find some system that looked really cool for those. I'd have to hunt for this info.

Lockitron had a take-apart video on youtube:

 

Hi there,
still working out the details, I bought an Arduino and looking for a suitable stepper motor with low detent torque.
One question: how do you suggest to connect the shaft of the stepper motor with the linchpin of the lock?
Thanks again

Also, check out RobotShop.com
Has many options to connect shafts.

 

Another wild idea: Assuming " the knob " can be replaced with a gear, we have 3 gears,
A - 1 cm dia. attached to a gear head motor & is pivoted to bear against B - 2 cm which is
connected to lock, C - 7 cm bears against B. A 5 band Gray code disc is attached to C which is read with 5 reflective sensors. Add a sensitive door switch & we should have enough information . Could add a Red/ Green LED visible from outside to indicate status.

 

Another wild idea: Assuming " the knob " can be replaced with a gear, we have 3 gears,
A - 1 cm dia. attached to a gear head motor & is pivoted to bear against B - 2 cm which is
connected to lock, C - 7 cm bears against B. A 5 band Gray code disc is attached to C which is read with 5 reflective sensors. Add a sensitive door switch & we should have enough information . Could add a Red/ Green LED visible from outside to indicate status.

I have 2 ideas about how to connect my contraption to the lock:
1 my favourite: manage to build something with a recess that matches the linchpin of the lock, much like the August Smart Lock solution. This way i would have something that can "cover" the lock on the internal side of the door and replace it.
2 two conic gears, one attached to the shaft of the lock and the other to the shaft of the stepper motor, which would be attached parallel to the plane of the door.

I am new to all this stuff so I don't have any real idea how to connect the contraption to the door

Question: what is the purpose of the gray code disk and reflective sensor? You want to know if the lock is already locked or not?
The diameters have a particular reduction factor?

Thanks

 

Do you have the lock in your hand ?
A short digression on an Electronic Owl. The owls head is attached to a Gray code disc & a gear head motor. Gray code data read from photo reflective sensors is converted to binary
& fed into a digital comparator. The other side of the comparator is fed from a random number generator ( or could be open or close ) . Output from comp. controls an H Bridge
which controls the motor. Every 16 minutes a new command is given & head moves to one of 8 random positions. Comparator gives a left- = - right output to H Br. so head from present position always knows which way to turn & how far to turn to reach new address .
The C gear is 3 + times the B gear so that the code disc only makes almost one revolution.
Why not an even 3 X; because we do not want Open & Close to have the same code word.

 

Do you have the lock in your hand ?
A short digression on an Electronic Owl. The owls head is attached to a Gray code disc & a gear head motor. Gray code data read from photo reflective sensors is converted to binary
& fed into a digital comparator. The other side of the comparator is fed from a random number generator ( or could be open or close ) . Output from comp. controls an H Bridge
which controls the motor. Every 16 minutes a new command is given & head moves to one of 8 random positions. Comparator gives a left- = - right output to H Br. so head from present position always knows which way to turn & how far to turn to reach new address .
The C gear is 3 + times the B gear so that the code disc only makes almost one revolution.
Why not an even 3 X; because we do not want Open & Close to have the same code word.

Oh boy... I had to read it 23 times before I could understand a thing.
Sorry but I am a real beginner, I was thinking about something like:
1 when triggered, the device tries to lock the door rotating 3 revolution clockwise
2 if the stepper motor can't rotate at all, the door is already locked, so rotate 3 revolutions counterclockwise to unlock the door
3 if the stepper motor can rotate less than 3 complete revolutions clockwise, the lock was engaged but not completeley locked, so lock the door

I read here that using servos when they can't rotate you see an increase in current, I don't know if with stepper it is the same or there is any other way, but from you I learned that Gray code disks exist and they can be one way to understand it a stepper is able to rotate in a given direction or are stuck

 

gray code: Like binary, but only one bit changes at a time between counts.

 

gray code: Like binary, but only one bit changes at a time between counts.

Now I am aware of it, thanks to Bernard and Wikipedia

 

With a stepper you can still use the 1:3+ to turn a cam giving open or closed but no inbetween.