Hall sensor magnet pickup ring on shaft LMX?

I am using the small 30mm LMX motor. I'm having some issues with the hall sensor signal not being clean. I suspect that I am picking up flux from the windings because the sensors are so close to them.

I was considering making a small plastic ring with magnets and a stand alone hall board so I can be completely away from the windings.

So I am wondering about the optimal shape and arrangement of the magnets. I can get arc magnets that form a complete circle or small rectangular magnets to glue into slots on my ring. Its only a 4 pole motor and the rotor magnets wrap almost entirely around the rotor.

Which option is better? Is it ok to have large gaps if I am using latching sensors since they will still trigger on the change events?

• If I use rectangular magnets there will be big gaps between them

• If I use arc magnets there will not be large gaps between them

• If I don't make a ring but move the sensors from in the slots to pointing axially down at the ends of the rotor magnets, would that be an improvement?

DanGT86 said:

I am using the small 30mm LMX motor. I'm having some issues with the hall sensor signal not being clean. I suspect that I am picking up flux from the windings because the sensors are so close to them.

I was considering making a small plastic ring with magnets and a stand alone hall board so I can be completely away from the windings.

So I am wondering about the optimal shape and arrangement of the magnets. I can get arc magnets that form a complete circle or small rectangular magnets to glue into slots on my ring. Its only a 4 pole motor and the rotor magnets wrap almost entirely around the rotor.

Which option is better? Is it ok to have large gaps if I am using latching sensors since they will still trigger on the change events?

• If I use rectangular magnets there will be big gaps between them

• If I use arc magnets there will not be large gaps between them

• If I don't make a ring but move the sensors from in the slots to pointing axially down at the ends of the rotor magnets, would that be an improvement?

mag ring.PNG

Click to expand...

I’m definitely not an expert, but wouldn’t you want the magnets to mimic the spacing of the actual magnets so the hall sensor signal is created correctly? I would think you could have some issues with your controller if your hall signal duty cycles were smaller than they should be.

My understanding of the latching hall sensor is that it stays in whatever position it's in until the next magnet flips it. So it seems to me that once the North facing small magnet triggers it it would be the same as the arc magnet staying next to it. I think I would just need to align the leading edge of the small magnets to the same location as the gaps on the arc shaped ones.

For me the big unknown here is if the halls would stay latched or if the flux coming off the wires would flip during the gaps between the small magnets.

I feel like the advantage to the arc magnets is that they would overpower any errant signal coming off the windings. But they are more expensive and harder to find in the size that I want so small rectangular magnets are more appealing.

I'm also wondering if simply pulling the sensors out of the stator slots is all I really need to get the winding interference to go away.