Erratic, intermittant, jerking motor with no throttle input... SOLVED.

[Tommycat]

Just a friendly heads up if anyone experiences similar symptoms. 

Issues: Ever see a top fuel dragster after it's burn outs, jerkily move forward to the starting line? Well my Magic Pie V5 was doing just that, with out my hand on the twist throttle.    Another symptom was that it would erratically drop out of cruise. Unsettling to say the least...


Trouble shooting: Input to throttle hall sensor- 4.37 volts dc.  Throttle sensor output: no twist- .9 volts dc  full twist- 3.58 volts dc  motor start @ 1.25 volts dc.  Mechanical operation seemed sound, solid magnet in position. Hall sensor snug and secure in housing.


Getting lucky:  While pulling the hall sensor out to look it over, the grounding wire fell off!  Found inadequate solder on wire and sensor terminal. Repaired.


Lesson learned: A poor throttle hall sensor ground will result in a higher than normal and in this case some times erratic voltage sense line output. Causing unintentional jerking and occasional loss of cruise. Just as if you'd jerked the throttle back momentarily.  Which may come in handy for someone that has less than desired output, as adding a resistor in series with the ground wire may produce acceptable results.

This seems similar to Alan's posted comments about overloading the ground wire with too many electrons (Amps) and subsequent voltage drop from a light install causing problems with the small gauge wiring...



Respectfully submitted,
T.C.


Regrets: Wish I'd pulled the heat shrink off the other two wires and checked them also with the assembly apart. 

[Bikemad]

If the ground wire was disconnected completely before you turned on the power, then the motor would not run.
But if the ground wire came detached suddenly while the power was already on, then the motor would try to run at maximum power.

This is another reason why the supplied brake levers with the safety cutout switch should always be used, but having said that, if a break should occur somewhere along the single common ground wire going to the controller while the power was already on, then the motor would be stuck at maximum throttle (regardless of the brake switches) until the power was turned off. 

The bigger VEC controllers (300, 500, 700 etc.) have a throttle maximum voltage setting which should prevent this from happening, but the hubmotor controllers do not. 

A poor throttle hall sensor ground will result in a higher than normal and in this case some times erratic voltage sense line output. Causing unintentional jerking and occasional loss of cruise. Just as if you'd jerked the throttle back momentarily.  Which may come in handy for someone that has less than desired output, as adding a resistor in series with the ground wire may produce acceptable results.

This seems similar to Alan's posted comments about overloading the ground wire with too many electrons (Amps) and subsequent voltage drop from a light install causing problems with the small gauge wiring...

It should be possible to fine tune the throttle using the following modification:


Click here for more details.

But if your +5V output is already too low to achieve full throttle (3.25V output signal) the additional 5k Ohms load (2 x 10k Ohms resistors in parallel) could possibly pull the +5V supply down slightly and decrease the maximum rpm even further. 

Alan