Better speed control required for 24v dc mobility motor

[luckydog]

Hello all, hope this is posted in the right place.
You'll probably guess after reading this post for help that i'm not an electrician!
I've built a 4-wheel buggy utilising a mobility scooter motor and wish to slow down the acceleration rate.
I am utilising the twist grip throttle from a 'stand-on' electric scooter as the speed controller to a 24V 500W Electric Bicycle E-bike Scooter Brush DC Motor Speed Controller .
However, when I select the throttle to slowly accelerate the buggy, it rears up and almost back somersaults! I need something that will give me more control over the speed/power. Any ideas?
Thanks,

 

[PEG]

Hi,are you saying that the throttle/pot is ramping acutely? that is,can achieve a slow speed,but has minimal travel,from that,to max?

Or is any input causing maximum speed?

 

[oracle]

What sort of mobility scooter are you using? Best thing is buy the motor controller for it, assuming you don't have it, then integrate your twist grip with the motor controller control panel wiring

 

[Lucien Nunes]

As per PEG's description, do I understand correctly that the controller goes from zero to full over too small a range of the throttle grip movement? If so, are you sure that the throttle potentiometer is correctly wired to the controller, with the wiper terminal in the right place? If so, then the end-end resistance of the pot may be unsuitable for the controller. Do you know what that is and what the controller expects? This could be adapted, but a basic knowledge of electronics would be needed to understand how to tackle it.

Alternatively, do you have an unsuitable reduction ratio that is causing your buggy to move too fast at too low a motor speed? If so, then changing the gearing will improve control and efficiency, but provided the torque is fully adequate as-is, the controller behaviour could be modified to use only a small part of the controller output range rescaled to cover the full travel of the grip. A preset potentiometer could be added to set the top speed at full grip rotation.

 

[Deuce]

Sounds like the system you have assembled is maybe not resetting its response to the pots signal to zero each use. Pots are analogue and not at all reliable as a direct signal. When used (as just one example) on a wireless throttle pedal, each time they enter the min or max 5% of their signal range the receiver effectively re-calibrates to whatever the pot is saying in that moment. Without that in place, you will end up with a pot giving a signal that doesn't remotely reflect it's actual position. All you can ask of a pot is to tell you how far it has been rotated since it's last rotation. The actual position it's in can only be determined by electronic calculation based upon the signal vs it's last known position (hence the reference to a known min/max).

The above doesn't apply to low current pots used in PIR's etc, but the pots used at higher current in automotive industry, it's a well known issue. The electronics have to match and compensate for the hardware's limitations.

 

[luckydog]

To elaborate on the 'fault' - The speed is controllable over the throttle range (the throttle works as it should) but it is the initial opening of the throttle that causes the motor to speed up too quickly. I require a 'soft-start' that allows me to build up the speed under the the control of the throttle until a controllable speed is attained.
It is the initial surge of power that I cannot control without very careful and considered movement of the throttle lever.
When the spring-loaded throttle is released, it returns to the closed position perfectly.
I do thank you all for your inputs.
Regards,