Ancient lock gets smart

Description

My apartment has a very old rim lock that is not compatible with any retrofit smart key kit (Nuki et al.) The building is from the late 1920s and I assume that the lock is pretty much from that era.

I modified the inside mechanism to allow the inner cylinder cam to move the door latch and 3D-Printed an adapter plate to replace the inner side cylinder with a G2T pulley. The modification is completely reversible and invisible to anyone but a retired locksmith. This is important to me because my landlord is nice but not really my grandma; I wanna leave it as I found it the day I leave.

Details

This is door is pretty much the only reasonable way I can get into my house, so some extra precautions will be needed to avoid accidentally locking myself out. This can happen if the inner side cam is in a position that does not let the mechanism move freely.

Conversely, I also wanna be able to get out quickly if something goes wrong. The manual latch keeps working, and the pulley can be easily twisted by hand to move the bolt. I want to keep that "feature", so I hope it will still be possible once the motor box is mounted and the belt under the required tension.

Components

1 × NodeMCU ESP8866 board

1 × DRV8833 Dual MOSFET H-Bridge

1 × GY-370 DC Motor with reduction and hall effect encoder

Project Logs

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It works!
Ivan Stepaniuk • 12/19/2020 at 01:03 • 0 comments

A NodeMCU (ESP8266) paired with a DRV8833 Dual MOSFET H-Bridge comfortably drives the DC motor
This is the last iteration of the motor mount / enclosure:
Back from the shelf
Ivan Stepaniuk • 10/30/2020 at 18:51 • 0 comments

After some time abandoned, the lock had the pulley installed but no motor. I just finished the enclosure for the motor, ready to 3d-print!
3D Printed adapter
Ivan Stepaniuk • 04/04/2020 at 23:52 • 0 comments

When I was testing the idea, I thought I could use the original cylinder with the key in it, like on the retrofit kits. I got to learn the hard way that a pin tumbler lock does not operate well under the axial load of a belt. Nuki and other systems that work with the original key are mounted on top of the lock and avoid this, but I wanted to keep the contraption as flat as possible, since this is a rim lock and it's already bulky.
I then partially copied the lock in CAD, on top of which I designed a mounting plate to fit two small bearings and support the short axle for the belt pulley and actuating cam.
Got this printed this with PETG (because it turned out that's what my brother had in the printer at the moment). Feels really solid, especially when assembled. The bearings press-fit nicely, lucky me.
Latch action from the inside
Ivan Stepaniuk • 04/02/2020 at 01:01 • 0 comments

This lock does not actuate the latch from the inside, it makes no sense since it has a dedicated plunger for that. After considering actuating the plunger electrically, I decided it was easier to modify the internal latch mechanism to operate from the inside in the same way it operates from the outside.

I riveted a screw into this lever arm so it is reachable by the inner side cam. The lever is normally only operated by the front side cam, not on the picture. Both inner and outer lock cylinders are coaxial.

The rivet gets pushed by the cam on the inside side cylinder. The original pin tumbler cylinder is behind that cam wheel with the two screws on (only one visible)
Designing 3D-Printed the motor box
Ivan Stepaniuk • 04/01/2020 at 18:45 • 0 comments

I am now in the process of designing and printing a motor mount/box and associated electronics.