Locraker

Plans & Schematics

After receiving numerous email requests for the plans, I've put together this page of resources. Enjoy!

Hardware

The above CAD drawing gives a clear view of the Locraker. Some points of note:

Lock [red]

The lock is held in place by an elastic-tensioned locking bar behind it and a peg in front of it.

Stepper motor [grey]

The stepper motor can be raised or lowered on the four support beams to conform to different sized locks. My stepper motor was salvaged from an industrial fax machine.

Gripper [yellow]

It took me forever to figure out how to reliably interface with the knob on any combination lock. Then it occurred to me that the standard interface was a pair of fingers. So I built a pair of them, tensioned by an elastic band.

Solenoids [grey]

Two solenoids are needed, one to pull the clasp, the other to push it. After failing to pull the clasp open, one must push the clasp back in otherwise most combination locks will jam. These are big 24v solenoids from Active Surplus in Toronto. The noise they make while pounding away at a lock is quite memorable. Because of their coils' inertia, they cause the entire device to slowly 'walk' across the table or floor until it unplugs itself.

Cut-off switch [blue]

When the clasp finally opens, the brown solenoid shaft moves further back than if the clasp stayed shut. The brown plate on this shaft collides with the blue switch mounted below it. This switch is attached to an input pin on the controlling computer, causing the program stop and display the winning combination.

Solenoid mounting plate [blue]

The solenoids and the cut-off switch are mounted on one plate which can be slid forwards and backwards. This allows the whole subsystem to be positioned to accept locks of vastly different clasp lengths (including bicycle locks).

Interface

View the full electrical schematics for the Locraker (GIF, 26Kb, 1501x951). It connects to the parallel port of any PC. Some points of note:

• Basically the interface is just a big amplifier. There is no logic, no intelligence. One bit on the parallel port equals one coil on the stepper motor or one solenoid.
• The ten buffers are optional. I have this phobia about plugging uncertified heavy-duty equipment straight into my expensive new laptop. These buffers serve the role of a fuse: if something goes 'boom' it will be a 50 cent CMOS chip, not my computer.
• The buzzer is totally pointless. The original idea was that once the Locraker had opened the lock, the computer would sound the buzzer to attract attention. If you've ever heard those solenoids in action, and the deafening silence which follows, you'll understand why the buzzer is not required.
• The "Stepper sync reference point" is an optical sensor which allows the computer to detect when the stepper motor (and thus the knob) is passing some arbitrary point. By keeping an eye on this, the computer can detect if the stepper motor has skipped a few phases, and reset it appropriately.
• What's the point of the input to pin 13? So that the computer can detect if the Locraker's power supply has been switched on.
• There is a loopback (wired directly on the connector) from pin 9 to pin 15. This enables the computer to strobe pin 9 on each parallel port and autodetect where the Locraker has been plugged in. Plug and play.
• The only items not shown in the schematic were eight status LEDs and their driving transistors. The interface box had a large 7-segment LED mounted on one side. Instead of displaying a digit, the segments were assigned to various functions. Four segments in a square were assigned to the four stepper coils. The two remaining vertical segments represented 'push' and 'pull' respectively. The remaining horizontal segment represented the cut-off switch. And the decimal point represented the stepper sync sensor. This graphical status display was exceedingly useful for debugging, and looked neat in operation too.

Software

The software that drives the Locraker was written in QuickBasic (yes, yes, quit laughing). It provides an on-screen stats display of the current combination being probed, the number of failed combinations tried, the number remaining, the elapsed and remaining times (average and worst case), and the status of the Locraker. One of the more advanced features of the software is to smoothly accelerate and decelerate the stepper motor, thus increasing the maximum attainable speed. Another useful feature is to enter the last digit of the combination, thus shortening the time to crack a lock. This is often known since an open lock usually freezes the position of the knob on the last digit, so if you forget the combo, it is obvious what the last number is.

Despite repeated requests, I am not providing copies of the software. It is written in an obsolete language, with hard-coded busy-loops calibrated to a 25Mhz 80386, and is undocumented. Hackers wishing to build their own Locraker would be much better off writing their own software. Some day I'll get around to writing new software. In the mean time, the core loops do a good job of showing how it works.