A previous post to the EV list:
There’s been a bit of talk about the speed sensor the Hairball likes to see, and some of it has been described in a way that is particular to one situation, so I figure it’s time I lay down the core data so you all can determine what might work for you.
1) A speed sensor is not required to run the Zilla controller, but it is highly recommended. It is required in order to use the over-speed cutoff as well as the “stall detect” which protects your motor commutator from people who try to “hill hold” with the motor.
2) The 2171 Hall effect sensor that I sell works quite well, but it does not fit well for everyone. Pictures that clarify the installation requirements are here: Speed Sensor
If you mount it like that then it should work well and you can ignore the rest of this message.
3) The speed sensor input to the Hairball requires four pulses per revolution. The Hairball pulls the sensor line up to 12V with a 2.61K ohm resistor and the sensor pulls it low. It normally does this when the magnet is in front of the sensor.
4) I stock a stand alone hall effect sensor with loose magnets. This is a experimental setup that can be made to work in situations where the end of the motor shaft is not as accessible. Picture of the sensor here: Exp Speed Sensor
This is the one that Roland is using, and I’ve not heard how well it’s working and I don’t know if he has checked to insure it doesn’t drop out at very high RPM. But this is good for those who do not shy away from making a ring of magnets and testing the system. If someone else wants to try to fabricate around this system I do have sensors and magnets in stock. Be aware though that I consider it experimental since I have not checked the limits of such a system myself yet. (since this was written, many people are using it with good results).
5) For those people who are not using the 2171S stock sensor and want to make something else work this is the important timing information:
Since the signal needs to be filtered to remove noise from the wiring, it is designed to work up to 12,000 RPM at 50% duty cycle. You sharp ones have probably already figured out that you can drop either the high or low duty cycle to 25% if you only need 6000 RPM. But leave yourself at least a couple thousand RPM over your expected max RPM for security.
Kirk at Shift EV has made a video with a great example of a custom speed sensor installation using our experimental kit, have a look at it here:
Customizing Speed Sensor
Hopefully this covers most of the questions and makes it clear why normal low duty cycle CDI pickups will not drive the input at higher RPM.