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  1. #31
    Student
    Join Date
    Nov 2015
    Location
    Oklahoma
    Posts
    22
    Quote Originally Posted by CescoAiel View Post
    Depending on the stator/rotor confuguration (and whether it is brushless or not) you may even be able to sense the rotor rotation from the outside, without attaching any magnets... Something you could test before even attempting to open it and attach a magnet anywhere...
    From the photos, I'm pretty sure it has brushes and permanent stator magnets. I have no idea whether the rotor magnetic fields can be detected outside the motor, but I doubt it, with the steel casing and stator magnets shielding them. Maybe a hall effect sensor could be located inside the motor as close to the rotor as is practical; that might be able to count the passing rotor lobes, however many there are. That might be easier than dealing with the noise in the power circuit.

  2. #32
    Quote Originally Posted by DoulosDS View Post
    From the photos, I'm pretty sure it has brushes and permanent stator magnets. I have no idea whether the rotor magnetic fields can be detected outside the motor, but I doubt it, with the steel casing and stator magnets shielding them. Maybe a hall effect sensor could be located inside the motor as close to the rotor as is practical; that might be able to count the passing rotor lobes, however many there are. That might be easier than dealing with the noise in the power circuit.
    Agreed, but it's worth a try to save on time dealing with dis- and re-assembly...

    Since you're experimenting with peristaltic pumps, I've let that go. I'm now thinking about cheap ways to make a movable platform with sufficient resolution instead...

  3. #33
    Student
    Join Date
    Nov 2015
    Location
    Oklahoma
    Posts
    22
    I'd bet we could print everything but the tube and motor for under $1. The tube can be silicone fuel line from a RC hobby shop or site, and the motor can be salvaged from a car mirror adjuster. A project for my spare time in the future... LOL!

  4. #34
    Quote Originally Posted by DoulosDS View Post
    I'd bet we could print everything but the tube and motor for under $1. The tube can be silicone fuel line from a RC hobby shop or site, and the motor can be salvaged from a car mirror adjuster. A project for my spare time in the future... LOL!
    Heck, you could print a large chunk of the motor too, just need some wire and magnets.

  5. #35
    Technician
    Join Date
    Oct 2013
    Location
    nsw australia
    Posts
    81
    I had spotted one in ebay with a stepper moter included, BUT it is A$52 and from hong kong

  6. #36
    Student
    Join Date
    Nov 2015
    Location
    Oklahoma
    Posts
    22

    Peristaltic Pump Exploded

    OK, I received my $12 PS pump, and I am impressed with its simplicity. The motor shaft serves as the sun "gear," though it is smooth; the 3 rollers are the planetary "gears," driven by contact with the motor shaft, and press the tube against the U-shaped housing. The rollers have a circular plate with an axis for each to keep them aligned with the motor shaft and tube. I have attached photos and a sketch of the geometry:
    PS2.jpgPS3.jpgPS4.jpgPS5.jpgPSP Geom.JPG

    I made the shaft and roller (0.435 in.) measurements with a micrometer and a digital caliper, and the outer diameter is derived from them. Calculating the motor shaft turns per 1/3 rotor turn: Given C = Pi D, 1/3 Pi 0.96 = x Pi 0.09, x=0.32/0.09 =3.56 I clamped a vice grip pliers onto the motor shaft end and rotated the pump housing 4 times, resulting in approximately 1/3 rotation of the rotor. Perhaps the difference is due to the compressed tubing at the outer circumference.

    I will have to put sensors on the motor shaft and rotor to experimentally determine the precise "gear ratio" between motor turns and rotor turns. Because the smooth motor shaft has the potential to "creep" with respect to the rotor position, unlike gears, counting motor revolutions alone may eventually allow errors due to stopping the pump during a pinch transition (non-constant flow) instead of between pinches. I doubt the "creepage" would be enough to cause significant errors when counting motor turns to provide integer multiples of 1/3 rotor revolutions, but, the software should have a sensor input on the rotor as well, and have a self-correcting algorithm to ensure the rotor position is known within a turn of the motor shaft. I'm assuming the Hall effect sensor on the rotor will be accurate, but not very precise, especially when trying to stop at the same position running forward vs. reverse. Conversely, a sensor on the motor shaft would be more precise, but less accurate due to "creepage."

    An optical sensor disc could unambiguously locate the rotor within a fraction of a turn. If the disc supporting the roller axis were installed inversely, opposite the motor rather than between the motor and the rollers, the optical disc pattern could be printed on the outer face of the disc and the optical sensor array could "view" the disc through a slot in the pump housing.
    Last edited by DoulosDS; 05-06-2016 at 03:32 PM. Reason: Add drawing

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