Me and pwf have been working with Eglė Lekevičiūtė on her art installation. It’s part of her exhibition called Ratais Kvadratais, open May 13 to June 30th at Vaikų galerija.
It consists of two sets of bicycle wheels mounted on opposing walls. One side of the set has wheels and a motor connected with a long chain, while the other side has corresponding stationary wheels connected with a tube of cloth. There is one motor on each wall and the wheels of the sets are interspersed.
Movement. The target speed of the motor changes like a sine wave with a period of about a minute, though slightly different for each motor. They start synchronously, but slowly drift apart and back, in and out of phase. Due to the lack of feedback the actual speed is also influenced by changing friction, which is essentially unpredictable due to the complex and unreliable system of wheels and chain.
pwf welded cogs directly to the wheel hubs.
The biggest challenge is making the chain work reliably. This requires mounting the wheels on a flat plane, tuning the bearings and applying just enough tension on the chain. One of the gallery walls is not completely flat so we had problems making that side turn consistently.
Electronics. We used 12V windshield wiper motors. They have an integrated transmission with a low gear ratio, therefore a slow speed, but high torque. To control the motors’ speed and direction independently, I built a driver using a pair of L298 chips. The chip has two channels each rated for 2A, while the motors require about 2-3A, so I bridged the two channels of each chip together. The driver is connected to a microcontroller which does open loop control. I used a recycled computer PSU for power.
I made a few stupid mistakes building the electronics, but eventually figured everything out, with help from mic. ioch helped me etch the circuit board.