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I was thinking about building a self-assembled easy to use fraction collector controlled by raspberry.

A Fraction collector is a piece of equipment used in liquid chromatography which has some tubes or holes and moves every some time to the next tube / hole.

I was thinking about two servos one moving in X plane and one in Y plane but I don't know that piece of equipment would be the best - step motors, micro-servos or maybe even something else.

I would like to use python to program time required to gather single fraction and move one or the other servo X or Y position.

Could someone suggest me a good starting point?

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Since this is a device that needs precision, I would use a stepper motor, if a direct drive were absolutely required. In addition, I would have something that the Raspberry Pi could sense to know that the disk was in position.

If the number of positions is constant, I think a very simple mechanical device known as The Geneva Drive would be better. It was originally designed for watches. Using a motor at a constant rate of rotation, this would bring a new hole under your collector at equal and periodic intervals. You could use just an inexpensive DC motor and controller (or a servo motor) to drive the disk.

If your intervals are not strictly periodic, then you could stop the motor until the hole was ready to move again.

In any case I would use a sensor to detect when the hole was in place so that the collector could fill the test-tube or whatever you have waiting for it. This same sensor could also allow the Raspberry Pi to stop the motor until the the collector is ready with a new faction.

It would also be good to have some sort of sensor so that you don't overfill the containers.

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i would suggest to go for two stepper/servo motors depending on the rpm and rate of commands you plan to give to the motor with Ir speed controller enter image description here

TO choose motor click here Motor is completely application specific and output dependent weather precise movement or timing controlled movements

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    I will check it. Usually I would need to change the position by few mm every 0.5 - 5 min. Depends on the flow rate and fractionation volume. Thanks. – Dawid Feb 5 '18 at 9:53
  • then I would suggest stepper motor for your environment – Sampath Madala Feb 5 '18 at 9:59

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