I am working on a project with my daughter to build a bridge model. The particular bridge we are working to recreate features a center section the lifts completely veritically.
The model is being built in Knex and we are looking at setting up some motors to raise and lower the bridge controlled by an Arduino. The total travel will be less than 12 inches.
I am trying to figure out what type of motor to use and how can I ensure that the bridge stops when it is supposed to.
You could use a standard DC motor and pulleys to lift the bridge. You could use limit switches to tell when you've gone far enough. (A simple switch wherein once the bridge is moved to the proper height, it engages the switch and then the arduino reads the switch as engaged and turns the motor off). You could make such a switch easily by creating a small metal flap that when engaged connects a GND contact to an input contact. (The input goes to an arduino input pin, that input pin should have the internal pull-up resistor activated. If you read LOW off that pin, the switch is engaged.)
A decent, inexpensive pulley kit for getting started could be gotten from Tamiya.
An alternative to pulleys would be a gear rack and pinion gear - which could also be cheaply sourced. Again, you could use any cheap old DC motor for this.
I found a great resource on the DPDT and that sounds much easier than using the arduino with a motor driver IC, which is the direction I was going.
With an arduino the limit switch seemed easy enough to understand, when the switch was engaged I would simply disable the motor. How would I use the limit switch without an arduino?
Tinkerbot - the easiest way is to use the limit switches in a "normally closed" fashion - that is, they allow power to flow to your control switch to receive power, until they are engaged, at which point they break the connection (become open).
Of course, if you used an arduino, you could have it move when a boat were to appear near the bridge (proximity sensing via IR or the like), or have flashing lights and sirens, or have it raise just enough to clear the boat, etc! (Hey, I'm just trying to talk you back into it =)
