Hi! Could anyone suggest the simplest dc motor/controller combination from the Pololu line that would allow me to have a dc motor that will precisely run a movie camera at 1440 rpm? The torque requirements are about 8 ounces per inch (600 -700 gram/centimeter).
I’m not interested in anything fancy: just unidirectional will do. The movie camera has a mechanical tachometer that indjcates the frame rate visually: would a feedback arrangement be necessary to get within the error tolerance of +/- 2.5 percent? Using a potentiometer to adjust the speed seems like the best way.
Sorry if i am being ignorant and asking something hopelessly simply or hopelessly impossible. Any suggestions will be gratefully recieved!
You need a closed loop system for accurate rpm, which would be based on a motor with tachometer or encoder.
I don’t work for Pololu, but I looked through their line of motors with encoders. It appears that there is only one that matches your requirements. This one with the 4.4:1 gear ratio has 8 oz-in (600 g-cm) of torque and a maximum RPM of 2200: pololu.com/product/2270
You will need a motor driver and PID controller to establish the RPM. The JRK controller pololu.com/product/1394 might work with that motor and encoder, or you could use a microcontroller like Arduino with PID software and a simpler motor driver.
As a rule of thumb, small DC motors should only be run at about 20% of their stall torque for continuous operation. Our 4.4:1 Metal Gearmotor 25Dx48L mm HP 12V has a bit less power than that, but it still might be fine for your application. That motor is the closest one we carry to your specifications.
Our Simple Motor Controllers (like the SMC 18v7) can use a potentiometer as an input to adjust the voltage being sent to the motors, but if the load varies, the speed of the motor at that voltage will change. It is possible that using that sort of control (and visual feedback from the mechanical tachometer you mentioned) could be precise enough.
A more precise option would be to use one of our jrk motor controllers (like the jrk 12v12), which can use an electronic pulse from a tachometer as a feedback and can adjust the output power sent to the motor to more precisely match a target speed. You can use a potentiometer to adjust the target speed the controller is trying to achieve. The feedback would help reduce errors from things like varying mechanical loads or supply voltages (which occur with batteries as they discharge).
You can find more details about how those motor controllers can be configured in the jrk user’s guide and the SMC user’s guide (which are linked to on the “Resources” tab of their product pages).
Thank you all for your reponses! Looks like this is the way to go. I really appreciate it, especially as trying to figure out what’s what by looking through the other electronics websites is really a nightmare of confusion. POLOLU forever, thanks again!
