pF: adding sensors

I skipped talking about the sensor part. Here it is:

(Lots of thanks to Shane for explaining this to me and creating the diagrams below.)

Hall effect sensors are glued in between the stator teeth and they detect the pole orientation of the rotor magnets as the rotor spins. The magnets alternate N-S-N-S etc, so each sensor should be outputting some kind of square wave. The controller wants to see the three sensor output signals with 120 deg phase shifts. So, where should we put them?

The figure below shows half the magnets and motor windings in my motor. The first 3 arrows on the left represent 3 hall sensor positions that would generate the correctly phase shifted signals. However, two of them do not represent practical places to actually put the sensors on the stator. So the other blue and red arrows to the right are where we will put them.

18 stator teeth, 20 magnet poles

For reference, this is what a 12 tooth, 14 magnet sensor layout would look like:

12 tooth, 14 poles

By flipping the hall sensor to face in instead of out, you can come up with other configurations (look at the blue arrows).

I wired up my hall sensors and then supper glued them between the stator teeth.

two of the three hall sensors are shown (marked by yellow circles). Wiring for them runs on the other side.

To actually hook the motor + sensors up to the controller takes some guess and check. I think a good way to go about it is to remember the order of the sensor wires (black – blue – red according to the picture above) and solder them in that sequence to the connector that will plug into the controller.  I think this will make it so that they are either correct or “backwards”, which is something you can just fix by changing how the motor phases connect to the controller.  After the sensors are hooked up, you just have to try all the combinations of the motor phases to see which one is right.


5 thoughts on “pF: adding sensors

  1. Pingback: Day 5: throttle, batteries, sensors « Amy Qian

  2. hello, can you help with alternator conversation to a motor?
    i have 36 slots with 12 magnets rotor and i cant figure out how many slots apart the hall need to be place in, i can place them in 60 or 120 e.deg.

    • I think your motor controller may need to have the hall sensors 120 deg out of phase with each other. So in your case, since 6 slots span 2 magnets, or a complete period in the magnetic field signal, you will want to place the sensors 2 slots apart. Because the number of magnets is a multiple of the slots, I think you may need to be careful to start spinning the motor before you give power, or it will want to lock up in a fixed position. Please post about your project when you finish, I’m curious to see!

  3. Awesome project. I figured I’d find something interesting when googling “electric penny farthing”, and once I took out the YikeBike results I saw your work 🙂

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