# Curtis 1209B - Jerky low speed control



## frk2 (Jan 2, 2009)

I have a 1209b coupled with a ADC 6.7" motor. The problem is that low-end control is quite jerky (and borderline dangerous in traffic). There seems to be no way I can gradually push the car forward - its either 0 or 5kmph which is a problem. Is there some setting on the controller that I can fix? I have checked my potbox and the resistance varies more of less linearly so that doesnt SEEM to be the problem.

any Ideas? thanks!


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## frk2 (Jan 2, 2009)

Just to add to the above - I have fixed all 'lashes' in the driveline, removed the clutch even (went clutchless) but the jerky motion is definitely due to the fact that there is no way to properly control the low speed operation


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## Dave Koller (Nov 15, 2008)

frk2 said:


> Just to add to the above - I have fixed all 'lashes' in the driveline, removed the clutch even (went clutchless) but the jerky motion is definitely due to the fact that there is no way to properly control the low speed operation


How is the pedal? I mean strong spring on potbox? Weak spring can cause "foot " bounce - you sure the pot is not dirty or has a "bare" spot ? 

My tractor jerks all over using the pedal - that's why they have preset hand throttles ! Your foot can move - then the vehicle moves and it's starts up a jerky oscillation.. Could it be that simple? Just a thought


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## frk2 (Jan 2, 2009)

Pedal is very good. The problem is that even if I try pressing the pedal VERY VERY gently with my hand there is a distinct point before which there is 0 kmph and after which it is 5kmph. Hence there is a bad jerk going through that point. The pedal SEEMS to be okay with resistance increasing gradually.


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## ngrimm (Oct 19, 2007)

My Ninja acted the same way you described. A check with the Oscilloscope revealed that the throttle pot was picking up electrical noise and the controller was amplifying it and passing it thru to the mosfets. Seems I overlooked putting a capacitor on the throttle input comparator when I built the controller. So I put an .01u cap across the throttle input and that fixed it. May not be your problem but thought I would pass it along.


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## Dave Koller (Nov 15, 2008)

ngrimm said:


> My Ninja acted the same way you described. A check with the Oscilloscope revealed that the throttle pot was picking up electrical noise and the controller was amplifying it and passing it thru to the mosfets. Seems I overlooked putting a capacitor on the throttle input comparator when I built the controller. So I put an .01u cap across the throttle input and that fixed it. May not be your problem but thought I would pass it along.


That makes the most sense - I was going to say he should look at the signal if he has - or could get and Oscilloscope.. This noise problem creeps up on a lot of builds - homebrew or factory... I am used to bypassing everything I build for harsh environments ... If it is not a bad pot then harmonic noise might be the problem at low speed... Get a 5k pot from radio shack and remove the potbox wires and hook it in and see if by turning the pot by hand smoothes out that low speed....


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## frk2 (Jan 2, 2009)

Cool! So its definitely not the controller but the potbox? Will check using a simple potentiometer. On a ohm-meter it looks very, very smooth!


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## Dave Koller (Nov 15, 2008)

frk2 said:


> Cool! So its definitely not the controller but the potbox? Will check using a simple potentiometer. On a ohm-meter it looks very, very smooth!


We were just saying maybe --  I see you are in Pakistan - so do you have a Radio Shack there/  If not what would the equvilent be?


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## frk2 (Jan 2, 2009)

you would be surprised. Theres a gigantic electronics market here which is basically like digikey.com on the street


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## Dave Koller (Nov 15, 2008)

No not surprised ... Seen some large parts stores in my travels... Anyway good luck and let us know what you find


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