Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: tgibbons on July 05, 2014, 10:17:27 PM

Title: Replacing two analog POTs in mobility scooter bot
Post by: tgibbons on July 05, 2014, 10:17:27 PM

I am trying to turn a mobility scooter into a base for a robot. I would like to use the scooter's motor controller and simply replace the scooter's two analog POTs with a digital POT that I could control from a PC or Arduino.

There are two analog POTs in the circuit.

•   The max speed POT sets the maximum speed of the scooter. This is a 20 Ω POT on a simple dial.
• The throttle POT is a 4.5 Ω  POT with a spring dial.  The default value is 2.2 Ω  and pressure on the throttle makes the scooter move forward and backwards.

Here is a photo of the circuit components
(http://[url=http://duluthrobot.files.wordpress.com/2014/06/scooter-16.jpg]http://duluthrobot.files.wordpress.com/2014/06/scooter-16.jpg[/url])

As best I can determine, here is the circuit diagram
(http://[url=https://duluthrobot.files.wordpress.com/2014/07/pots-circuit1.jpg]https://duluthrobot.files.wordpress.com/2014/07/pots-circuit1.jpg[/url])

Unfortunately my grasp of analog circuits is limited by the 30 years since I last worked with them... So, two questions:

First, could someone help me understand how these two POTs work together to control the scooter's speed and direction?

Second, how would I replace these two analog POTs with a digital POT which I could control from a PC/Arduino?

Title: Re: Replacing two analog POTs in mobility scooter bot
Post by: Tommy on July 07, 2014, 08:27:35 PM

Quote

First, could someone help me understand how these two POTs work together to control the scooter's speed and direction?

Second, how would I replace these two analog POTs with a digital POT which I could control from a PC/Arduino?

tgibbons, as to your first question, it would seem you have a single axis drive(one motor), I would guess your analog voltage to be 0 to 5v with 2.5v as stop, 1v would be full reverse and 4v as full forwards,I would guess if the voltage goes over 4v or under 1v the drive will go into fault mode.

as to your second question there are a number of option for PC control.
http://www.phidgets.com/products.php?product_id=1002 (http://www.phidgets.com/products.php?product_id=1002)
http://labjack.com/u3 (http://labjack.com/u3)
http://www.usdigital.com/products/interfaces/pc/usb/USB4 (http://www.usdigital.com/products/interfaces/pc/usb/USB4)

I have used both the labjack and usdigtial unit with good results

Tommy

 

Title: Re: Replacing two analog POTs in mobility scooter bot
Post by: tgibbons on July 13, 2014, 04:24:56 PM

Thanks for the feedback on the voltages. That had not occurred to me. You were correct that 2.5v on the main control circuit was stop and 0v was full reverse and +5v was full forward.

Since this was a control voltage, I was able to control it with a PWM output from an Ardunio Uno. I was happy to find a digital PWM output would work for this, so I was able to replace both pots with the digital output from the Ardunio. 

Now on to replacing the mechanical steering...