Natalie Lambert: Act Natural

Last Friday (06/06/08) I was contacted by a friend of a friend of a friend of his girlfriends friend….. or something, in a last ditch attempt to help finish her final year’s degree show installation at the Glasgow School of Art.

The project entailed an elaborate and monolithic installation of (fake) wooden beams hanging the entire length of the GSA’s main stair well, which if you happen to have been in, you’ll know its 3 stories of original Charles Rennie Macintosh design. ooooo, swanky!

I’ll let Natalie explain the artistic intentions behind the piece later, but it involved 3 of these beams attached to a system of pulleys and cranks, each moving at different intervals. The cranks are attached to a 12v motor, kindly donated by RS components, the PSU for the motor was a regulated 13.8vdc 20A monster from Ripmax, and the cranks and support system were all hand built specially for the job by natalie and friends.

Her vision was to have the system triggered off and on by sensors picking up visitors to the exhibition walking up the main stairs.

The system is active, slowly winding away until the sensors were triggered, pausing the motor and allowing the beams to hang there, rotating under their own momentum.
After discussing what she was looking for, we settled on the use of a PIR sensor with a built in relay instead of a system of laser or IR beams and LDR’s that she had already tinkered with.

The sensor was then attached to the motors PSU via a 12vdc, 30A power relay rated to 28vdc, to de-activate the motor when the sensor was triggered by passing visitors.
She had initially experimented with timer delay circuits and the laser sensors as mentioned already, but I managed to strip back a lot of the components as the PIR already had an always on relay switch which was cut when the PIR was triggered by movement. This made it far simpler to integrate with the finished system considering the time scales involved. We had initially intended to use multiple sensors attached to an Arduino board, but I, and those rip off merchants at Maplin, were out of stock of the parts I needed to integrate 12v sensors with the 5v board, and I didn’t have my trusty orienteering map and compass handy for the trek to RS, plus it’d been a late night the evening before thanks to Phil….

After experimenting with a few different circuits on  Saturday night and Sunday, I was happy with the results from the PIR and the power relay. The power relay had to be used as the PIRs relay could only source 100mA, which was woefully inadequate to interface with the motors PSU but more than enough to trigger the coil in power relay. This resulted in a simplistic and very stable design requiring a few additional components.

We mounted the sensor on the landing between the ground and first floor, running the cable down the supporting stairwell beams to the basement where the motor and cranks were installed. A small ABS box housed the PSU for the PIR sensor, the power relay, a few other components and the wiring to interface with the motor, and I installed a switch to enable her to flick between continuous movement or the PIR sensor circuit in case there were too many visitors and the system was permanently triggered to an off state.
All in all it was a great project to be involved with and I was happy with the results despite the lack of time to research other possibilities properly. Congratulations go to Natalie and her team/slaves for such an amazing instalation, and for winning the Benno Schotz Prize on the night!

Next time, don’t leave it so late! ;O)