Comment by jeb | Hacker News Reader

Comment by jeb | Hacker News Reader

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Nice, that's exactly the info I want to hear. By the way, I need to also measure the position of the object being turned. That is, I was intending for my robot to have two modes - training mode and execution mode, so your DC suggestion makes it even better.

Thing is - I don't want to skimp on the positioning logic - I need it pretty accurate in space (sub millimeter) and in time. Overshooting the target is fine, I'll correct it with one of those algorithms.

What is the most arduino compatible and accurate measurement method that will handle both use-cases? I should be able to use it both to control my DC motor, and also to record the position of the wheel being turned, even when the motor is switched off?

For a similar project we used the IR sensors off a USB ball mouse along with homemade encoder wheels to provide motor feedback. This method costs next to nothing and is pretty damn accurate.

It was a ball mouse which featured two scroll wheels, meaning we could recieve feedback from 4 DC motors using a standard USB interface & mouse driver.

We used the mouse buttons as triggers to mark the rotation stop points for use in the initialization routine.

The motors we ended up using were high end electric RC car motors. They were the highest torque in the smallest package we could realistically get that still fitted our budget.

You can't. Once your device is switched-off, you can't know what position it will start up in. The easiest option is to have an initialization routine that will move the motor to a known position. For instance, move it all the way clockwise until it jams (assuming there's a limited range of motion) or until it signals a button, whatever that it has reached a position. This is known as calibration or zeroing.

What I mean is that the item it is turning is marked, so I can detect it's position. Using infrared perhaps?

You can get motors with encoders built into them that are very, very accurate. You can decode their pulses into position with a quadrature decoder like the HCTL-2020.

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