Motor speed & pwm

[russbow]

Got a motor control working with my 28x1 and the L293D driver chip. Quite happy with the low / high direction controls and was very pleased that I could control the speed by PWMing the driver enable pin.

Question – could the pwm 1 (or 2) pin on the picaxe be connected to both the enable pins? The driver data sheet suggests minimal current requirements.

Then I met the problem – cant use a servo in the same program!

I have had a look at the HPWM commands, and to be honest I get lost.

All I want to do is drive two motors, in either direction, with speed control. Both at the same speed unless one is stopped with a low / low command. From as slow as possible, consistant with a good pulling power, to full speed.

What area hould I investigate next.

Russ

 

[jodicalhon]

PWMing both enable pins will give the same speed to both motors, but you will have independent control of the direction of the motors.

A low/low command to a motor will, as you say, stop the motor. So will a high/high for that matter.

I seem to remember that one way (high/high or low/low) consumes less current, but check the datasheet.

 

[russbow]

Thanks Jo. Seems to work well pwming the enable pins. BUT the problem is that using pwmout screws up servo commands. I need to get my head round hpwm - downward spiral at the moment.

If all else fails, just use another picaxe for the motors.

 

[Wrenow]

The simplest solution to being able to use servo with motors at the same time is to use a hobby ESC (Electronic Speed Control). These puppies use a servo signal to control a motor's speed and direction. Pretty common in radio control and in robotics. High current draw motors take a pretty hefty ($$$) ESC. Mut, if your motors draw 1A or less at stall, you can use the Vex Robotics contoroller (about USD$10).

For more information and some cautions on ESCs, there is an article entitled "ESCs Lessons Learned" on the http://ntxbg.org web site, in the How To knowledgebase.

By the way, if you are interested in the Vex ESC, it is on the Vex Robotics site under accessories/logic at the bottom of the page. Comes with a 3-pin connector that is made to plug it in to a breadboard.

Cheers,

Wreno