Question about GMAC hub and CA speed sensor freakout

[onewheelskyward]

Hey all! Short-time lurker, first time poster. Here's the skinny:

I have a GMAC Clutchless geared rear hub motor and a Phaserunner controller, all wired in to a CA 3.1. Twist throttle, no PAS yet.

My question is, under load (starting from a stop going up a hill or when carrying cargo) the speed sensor on the CA fluxuates wildly, bouncing off the speed limiter even when I set it to 199mph. Once I get up to speed (say, 13-20mph) it settles out and works just fine.

I clearly have some kind of misconfiguration but since this is a Big Dummy, now a Big Dumb-e, I'm going to be hauling cargo with it often. Does anyone have an idea what this might be? Thanks in advance!

 

[markz]

Have you tried reading the instructions?

https://www.ebikes.ca/product-info/cycle-analyst.html

The quick start guide for the current V2.4 CA Firmware is available here.
https://www.ebikes.ca/documents/CycleAnalyst_V24_Web.pdf

The V2.3 manual contains more details on display screens and setup parameters, and is available here.
https://www.ebikes.ca/documents/CycleAnalyst_V23Web.pdf

Old versions of the user manual going right back to the Drain Brain devices are available from our documents listing.
https://www.ebikes.ca/learn/documents.html

The 2nd link
7.1 How the feedback works

 

[onewheelskyward]

In fact I have- the entire section of how feedback is interpreted has been deleted from the CA 3.1 PDF. Thanks for the pointer, I'll go tweak those settings! And if anyone finds this in the future, I suppose it would be good to read _all_ versions of the CA documentation.

 

[onewheelskyward]

Actually here's the best detail yet- a blow by blow of the settings in CA 3.1 with simple definitions:

https://www.ebikes.ca/documents/CA3-1_settings.html

 

[amberwolf]

My question is, under load (starting from a stop going up a hill or when carrying cargo) the speed sensor on the CA fluxuates wildly, bouncing off the speed limiter even when I set it to 199mph. Once I get up to speed (say, 13-20mph) it settles out and works just fine.

The most likely thing is that under load there is electrical noise induced from the phase wires into the speed sensor. If the speed sensor is a hall signal wire, it makes sense given that those wries are bundled together in the cable coming from the axle, with no shielding between them, and higher currents induce a stronger magnetic field around the phase wires that then induces a larger noise element into the other wires around it.

So...put a small ceramic capacitor (0.1uF) across the speed signal wire to ground, at the CA's connector to the controller. If that makes any difference at all, then this is the problem, and you might need more or less capacitance (or an RC filter) to get rid of the noise without degrading the speed signal itself.

 

[onewheelskyward]

Oh wow thank you!! I'm going to try this out. I dropped all my gains to 0 and got no improvement.

 

[amberwolf]

There aren't any settings to amplify or reduce the speed sensor signal.

There is only the number of poles. (and the wheel size)

All the gains/etc are for feedback on things like power / current / speed control loops, and PAS / throttle operation.

If you can't get a clean signal from the hall sensor in the motor, you can always add the external speed sensor from Grin Tech. That can be done either by cutting the (yellow?) speed sensor wire in the CA-DP connector and splicing the external sensor there on the CA side of the wire (and the other spliced into the black ground wire), or by opening the CA casing and desoldering the CA-DP cable's speed sensor wire from the pad on the board inside, and soldering one external sensor wire to that, and the other to the ground pad next to it. (not polarized, doesn't matter which external sensor wire goes where).

 

[onewheelskyward]

Just catching up/closing this one out- at some point with either upgrades or software updates, this particular problem went away. I did see a software update at some point which mentioned this particular issue. I've now had the system on the bike for about a year and it still gets better every day.

Thanks for the help!