Thread: Reversable electronic speed control

Hi there
Just wondering if anyone have schematic for a speed controller like the one hobbiest use for their RC cars. I want one that has high frequency somewhere around 20khz is great.

http://www.bobblick.com/techref/proj...wm/sv2pwm.html

this is an example but it only runs at around 2khz

any help is appreciated.

any particular reason why you want such a high requency? cause low frequency is usually sufficient and is MUCH easier to build. my guess would be to put the motor "hummm..." out of audible range. to do this with speed control and reverse direction ability you need hardware and software.

hardware takes the form of a Full H-Bridge. look for 'all in one' packages from intersil or harris or w*w.irf.com or perhaps fairchildsemi.com

all in one packages are built for less than 2A continuous operation usually. if you need more power you'll have to custom build yoru H-Bridge. a good example can be found here:

h**p://geocities.com/DIYCombatRobots/MostelyCompletedProjects.htm

Software: generally you provide your H-Bridge's switching elements (i.e. MOSFETs or IGTB) with Pulse Width Modulation (PWM) in a "locked Anti-phase" orientation. the locked antiphase has capability to go into very high frequency (>20KHz) and would probably suit your needs.

hopefully i have provided enough buzz words that will help you in your internet search.

good luck
Mr.Cool

by the way, since you are new to the forumn i will in form you on a rule.

when you post web links please STAR out your links as i have done (see previous post). notice i wrote: h**p:// instead of http://

the same rule applys for w*w.webpage.com instead of www.webpage.com

this helps to reduce the chance that an outside web crawler will link to elektroda.

thx
Mr.Cool

Thanx Mr. Cool

You are correct about taking the humm... out of the motor and one other reason would be better resolution. I am aware of the H-bridge+microcontroller method as I have build a few robots doing just that. I am not familiar with lock-antiphase drive as I simple use the enable bits and two hardware PWMs coming from a PIC16F877 to an H-bridge(L293DNE or UDN2916) running in a differential configuration. I was hoping that there would be a pure hardware setup that I can use.

If you have instructions on how to run a lock-antiphase setup please let me know


thank you

i know only of the theory of locked-antiphase.
there are 2 common ways of controlling an H-Bridge.
1) Sign Magnitude.
2) Locked Antiphase

1) the PWM signal controls the voltage (magnitude) applied to the H-bridge, usually applied to only one quadrant, and the SIGN bit is applied to the opposite quadrant.

2) in locked antiphase the PWM is applied to both H-bridge legs simultaneously. if the PWM is the same duty cycle (percent ON) then of course the average is ZERO and your h-bridge does not produce any DC. i.e. if your h-bridge were connected to a motor, your motor would not turn. however, if the PWM duty cycle were to change, such that one h-bridge leg got 5% more ON time than the other, then the motor would rotate slowly in one direction. of that same leg received less PWM duty cycle, say -45% then the motor would spin VERY fast in the opposite direction. locked antiphase is called such because it "locks" the two PWM signals applied to the legs of a H-Bridge in complementary fashion (antiphase).

Mr.Cool

Hi,

Typically, the sign/magnitude is the most commonly used way to drive motor, because it's easy to implement it.
However, the locked antiphase control is more efficient when you want to change quickly the direction of rotation.

The datasheet of the well-known H -bridge LMD18200 from National explains how works (with text and graphs) this kind of control.
This component drive (only...) 3A but you can use the basic diagram to implement such a H-bridge with discrete Power mosfet.