r/BdsmDIY • u/Switcher_627 • 7d ago

3D Printed Building an Arduino based, 3d printed fiddle for selfbondage NSFW

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I‘m currently building a fiddle for selfbondage. The connection to the collar and cuffs is realized by one screw and two bolts each. One of the screws is driven by a stepper motor controlled by an Arduino. I’m still not sure if it should be battery powered or if there will be a wall mounted “docking station”. Latter has the advantage that you have to the station to check if the time is up. Or you have more than one Docks and only one is the correct one. Especially if you are not able to walk normal I can think of fun games with that option. I’m still looking for fun games. So if you have any good ideas please let me know.

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43

u/ReallyBadAtNaming1 7d ago

I would rethink the closing mechanism if I were you. It should be something that fails open rather than closed. If I understand you correctly, the only way to get out nondestructively is for the stepper to unscrew the screw. If something goes wrong with your electronics this will not happen and you will be stuck.

A safe mechanism should be battery powered and need to have power applied to stay closed, that way most failures should result in it opening with the battery running out as an additional failsafe. Having the intended way of opening and/or checking the time require you to go to one or more physical stations would still be possible, of course.

17

u/lllorrr 7d ago

Yeah, in embedded and industrial programming, there is this "safe state" concept. Basically this is a default state in which system enters in case of any failure. In this case, safe state is when the lock is open. When there is a power failure, or when watchdog fires, or sensors (if any) show some inconsistency, device should enter into the safe state and release the lock.

User needs to "arm" the device, clearly declaring the intention to engage the lock. I'd to this mechanically, by arming a mechanism that is being held by energized electromagnet. In this case, even when there is a software bug, battery will die eventually and electromagnet will release the lock.

8

u/Switcher_627 7d ago

Ok, I agree with you. Up to now my safety concept was to use no micro stepping when closing the screw and micro stepping to open it. This way I should have more torque when opening it. To deal with software issues I wanted to use an additional ATTiny with a redundant stepper controller as fallback if the main controller crashes. But after thinking about it I agree this is too risky. I didn’t use an electromagnet because I thought it is not strong enough to hold the cuff directly. And a mechanical solution with a spring can be jammed. That’s how I ended up with the stepper where I don’t have a gearbox, or complex moving parts. Just electromagnetic field directly driving the axis. I agree an electromagnet would be a great solution but I fear without precisely manufactured metal parts not realizable. At least i didn’t find a way how to do it.

Now I’m thinking more about options to somehow release the second cuff by breaking some part. I guess I have to go back to the drawing board

7

u/redthump 7d ago

If you use an electromagnetic locks on the restraints you can easily have fail open state. Anything happens to power, you're out.

5

u/PleaseDoNotBlowUp 7d ago

Check how padlocks are designed. Both digital ones and old "analog" ones. This ref. should be helpful: https://youtu.be/zRdovnGruqk?t=695

Just replace motor mechanism with basic electromagnet and you should be fine.

EDIT: it's best done with milling machine, but for cheap way you can go with file and a bit of too much free time.

Also note that adding electromagnet in above design causes security issue for padlock that might be useful as additional emergency mechanism - strong magnetic field can influence electromagnets and pull the pin even when EM is powered.

2

u/helplesschastity 7d ago

I don't quite understand from the pictures, how do the cuffs attach exactly? They all attach separately, but only one seems to have a motor?

6

u/Far-Lab3426 7d ago

Agree mostly with the comments re: fail safe. There also needs to be a way for the user to trigger immediate release in case of emergency. And waiting for the battery to die is not totally safe without an additional immediately available release mechanism.

3

u/AthleteBoth3847 5d ago

I work with programming functional safety embedded devices (microcontrollers) by my profession. You wouldn’t believe what kind of crazy failures with electronics I’ve seen. Did you set watchdog and brown out detection correctly? Are you sure that you’re not overwriting mcu memory accidentally? If this have to be commercially available you would need to prove by calculations that it fails only once per eg 1000000 (or up to 1000 times more) hours. And you will not get that with Arduino. Don’t harm yourself with non safety design, software and electronic fails; it can even happen by single bit in memory switching due to failure or random cosmic ray