Zilla FAQ20 Feb 2007 12:14 am

A previous post to the EV list:

Hello All,
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.


5 Responses to “Speed sensor requirements”

  1. on 25 Feb 2007 at 10:04 am Paul Wallace

    I’ve got a speed sensor that counts the fan blades and then creates a pulse stream suitable for a standard 4 cylinder tach display. The sensor is made by K&W, model TD-100. It also does overspeed sensing and has a contact it opens on the overspeed event. I’m using a standard VDO type 3.25″ tach display and it works fine. Will this signal be suitable for the hairball input?

  2. on 25 Feb 2007 at 10:20 am Otmar

    Hello Paul,
    I have never looked at the output of the K&W unit on a scope, so I do not know if it would meet the 50% duty cycle requirement.
    The Hairball actually needs twice as many pulses, 4 per revolution, like you would expect from a 8 cylinder engine so at a minimum the K&W would need to be adjusted for that, but if I remember correctly it may have an option to do that.

    One thing to be aware of is that optical sensors on motor fans often fail when the motor gets dirty from brush dust buildup. I am not comfortable relying on such systems to protect my motors.

  3. on 30 Jan 2008 at 3:49 pm James May

    Hi Otmar

    I just ordered a Zilla 1k and I’m very happy, have wanted one for some time!
    I have a plan to lighten my flywheel and leave a thin flange around the rim which I can cut 4 equal slots in which are 50% duty cycle. The flange would be surrounded by an gap type opto-sensor. I know you have reservations about opto but can you see any other reasons why it wouldn’t work?
    My current car is 752 on evalbum. It is beyond repair now and I’m going to build a new one based an MGF.

  4. on 30 Jan 2008 at 9:09 pm Otmar

    Hello James,
    That’s a cute car!

    I suspect your idea will work well at first, but like all opto sensors I worry that clutch dust and other dirt will inhibit it from being reliable in the long run.
    Another concern is that motors are often designed with springs to preload the bearings and if those move when you push in the clutch (as sometimes happens) then it may destroy the opto if the gap is not wide enough.
    I wonder if you could use a hall effect with a built in magnet that would sense your flywheel protrusions? Some sensors are built that way and sold as zero-speed-sensing gear teeth sensors.


  5. on 02 Feb 2008 at 2:44 am James May

    Thanks Otmar!
    Your new site is good. It must have been a lot of work.
    I really appreciate your effort to keep the entry-level Controllers at a lower price for the EV enthusiast. I expect this approach will pay you back in the long run.