It sounds like you have a bad throttle potentiometer or worn/bad brake. You could also have weak batteries. Let me address each of these in turn. The most likely problem is that the throttle potentiometer spring or the potentiometer is worn out. The pot is not going to a neutral position when you release it. The electrical neutral is in the center of the pot throw, not forward, not reverse. If the spring is deformed, weak or worn the pot will not come back to center. The controller electrically senses that the brakes do not need to be applied after a period of regenerative braking (lag time to slow the motor down before the brakes are applied). The electrical slider inside the potentiometer may be worn from continuous use and not making good electrical contact, thus the electrical signal to the controller is reduced. Using a digital voltmeter you can check for electrical dead spots throughout the typical 5K ohm range in forward and reverse. Center should be 0 ohms with +5K to -5K ohms to common read from the outer terminals. A bad electromechanical brake which works like a solenoid could be your problem. When the controller sends power to work the brake the solenoid needs to grab the brake disc. There could be too much brake dust or the disc may be worn out or slipping. The solenoid coil may be open or shorted, With a digital voltmeter the resistance should be between 40 to 60 ohms. With the two preceding solutions comes a disclaimer. If the batteries are old or weak, the electronics and performance including braking will be weak or poor. Make sure you have fully charged batteries that load test good. It takes a good set of batteries to make the motor turn and to make the motor stop. A good tech will charge less than an hour labor for the above service. I usually replace the throttle potentiometer and speed potentiometer as a pair since they are electrically connected in series. Hope this helps.
Answers & Comments
Peter,
It sounds like you have a bad throttle potentiometer or worn/bad brake. You could also have weak batteries. Let me address each of these in turn.
The most likely problem is that the throttle potentiometer spring or the potentiometer is worn out. The pot is not going to a neutral position when you release it. The electrical neutral is in the center of the pot throw, not forward, not reverse. If the spring is deformed, weak or worn the pot will not come back to center. The controller electrically senses that the brakes do not need to be applied after a period of regenerative braking (lag time to slow the motor down before the brakes are applied). The electrical slider inside the potentiometer may be worn from continuous use and not making good electrical contact, thus the electrical signal to the controller is reduced. Using a digital voltmeter you can check for electrical dead spots throughout the typical 5K ohm range in forward and reverse. Center should be 0 ohms with +5K to -5K ohms to common read from the outer terminals.
A bad electromechanical brake which works like a solenoid could be your problem. When the controller sends power to work the brake the solenoid needs to grab the brake disc. There could be too much brake dust or the disc may be worn out or slipping. The solenoid coil may be open or shorted, With a digital voltmeter the resistance should be between 40 to 60 ohms.
With the two preceding solutions comes a disclaimer. If the batteries are old or weak, the electronics and performance including braking will be weak or poor. Make sure you have fully charged batteries that load test good. It takes a good set of batteries to make the motor turn and to make the motor stop.
A good tech will charge less than an hour labor for the above service. I usually replace the throttle potentiometer and speed potentiometer as a pair since they are electrically connected in series.
Hope this helps.