Author Topic: Making a servo's internal circuit  (Read 7248 times)

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Offline bootstrapTopic starter

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Making a servo's internal circuit
« on: September 28, 2008, 10:28:36 AM »
Hi,
I want to know whether it is possible to make the internal circuit found in a servo like (futaba or hitec).I have seen Open servo through (I am looking in terms of a simpler solution )just a simpler PWM servo control but not interms of data packets as Open servo does (Open servo is much complex than a normal servo).

Offline airman00

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Re: Making a servo's internal circuit
« Reply #1 on: September 28, 2008, 11:14:04 AM »
sure its possible why not

its only a potentiometer and a microcontroller to translate pulse
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Offline kgprivate

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Re: Making a servo's internal circuit
« Reply #2 on: September 28, 2008, 08:53:09 PM »
Hey- take a look at this site: http://www.anykits.com/catalog/product_info.php?cPath=46_71&products_id=239
They sell a 19$ kit based on an IC that provides most all servo functions. Very supportive tech support helped me add an h-bridge to drive big motors.

Offline airman00

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Re: Making a servo's internal circuit
« Reply #3 on: September 28, 2008, 08:59:39 PM »
Hey- take a look at this site: http://www.anykits.com/catalog/product_info.php?cPath=46_71&products_id=239
They sell a 19$ kit based on an IC that provides most all servo functions. Very supportive tech support helped me add an h-bridge to drive big motors.


interesting but too overpriced
Check out the Roboduino, Arduino-compatible board!


Link: http://curiousinventor.com/kits/roboduino

www.Narobo.com

Offline bootstrapTopic starter

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Re: Making a servo's internal circuit
« Reply #4 on: September 29, 2008, 06:37:06 AM »
Hey- take a look at this site: http://www.anykits.com/catalog/product_info.php?cPath=46_71&products_id=239
They sell a 19$ kit based on an IC that provides most all servo functions. Very supportive tech support helped me add an h-bridge to drive big motors.


Yes it is one the lines of what I am thinking,but does it accept the same standard of signals as the Standard servo does and also is there any documentation for it (Also one of the problems is,I am looking for a solution in terms of the locally available components or if any PDIP samples for such motor drivers/controllers like MC33030 are available then I can go ahead.)

Also my first task would be to build a circuit equivalent to the one in Futaba S3003 .
« Last Edit: September 29, 2008, 06:46:26 AM by bootstrap »

Offline paulstreats

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Re: Making a servo's internal circuit
« Reply #5 on: September 29, 2008, 07:59:24 AM »
The important part is the potentiometer that the output shaft is inserted into, this is the part that gives position feedback. You can create the rest of it with any microcontroller and a cheap hbridge built out of transistors or mosfets.

When the output shaft moves then it moves the potentiometer. The resistance of the pot changes and the controller knows what position the servo is at.

Offline bootstrapTopic starter

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Re: Making a servo's internal circuit
« Reply #6 on: September 29, 2008, 10:10:57 AM »
The important part is the potentiometer that the output shaft is inserted into, this is the part that gives position feedback. You can create the rest of it with any microcontroller and a cheap hbridge built out of transistors or mosfets.

When the output shaft moves then it moves the potentiometer. The resistance of the pot changes and the controller knows what position the servo is at.

I understand the working principle and the control circuitry,I can figure out the circuitry,normally the standard servo does not have a microcontroller (i mean the circuit runs without any program),is there any such implementation ,because the implementation with a micro-controller will involve heavy code running in the micro..i cannot figure out such a complex code (the code which measures the input PWM signal as well as simultaneously measure the resistance of the POT on ADC as well simultaneously drive the MOSFET driver based on PWM and at the same time do precise postion/error control).

Is there a simpler circuit without a microcontroller and components that are easily available?

Offline kgprivate

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Re: Making a servo's internal circuit
« Reply #7 on: September 29, 2008, 11:56:30 AM »
The servo kit I mentioned does all the things you ask. It connects to the same sources a regular servo does using the same 3 prong plug. Here is a link to the datasheet for the chip it uses: http://www.digchip.com/datasheets/parts/datasheet/343/MC33030.php  Hope this helps

Offline ArcMan

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Re: Making a servo's internal circuit
« Reply #8 on: September 29, 2008, 02:31:56 PM »
Hey- take a look at this site: http://www.anykits.com/catalog/product_info.php?cPath=46_71&products_id=239
They sell a 19$ kit based on an IC that provides most all servo functions. Very supportive tech support helped me add an h-bridge to drive big motors.


Thanks for the Anykits link.  They have some good kits for cheap!

Offline paulstreats

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Offline bootstrapTopic starter

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Re: Making a servo's internal circuit
« Reply #10 on: September 29, 2008, 10:02:46 PM »
The servo kit I mentioned does all the things you ask. It connects to the same sources a regular servo does using the same 3 prong plug. Here is a link to the datasheet for the chip it uses: http://www.digchip.com/datasheets/parts/datasheet/343/MC33030.php  Hope this helps

I found the circuit diagram for the circuit here:
http://www.electronics-lab.com/projects/motor_light/046/index.html
Thing is MC330330 is not available in the local market here.What shall I do now?

Offline bootstrapTopic starter

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Re: Making a servo's internal circuit
« Reply #11 on: October 01, 2008, 01:44:18 AM »
I came to know that NE544 can be used to drive the servo (as a part of the internal circuit).
It decodes the PWM signal of 1-2 ms and drives the servo using a low power internal H-Bridge.Now thing is I cannot get the servo driver chips in the local market here.How shall I get around this problem?

Offline dunk

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Re: Making a servo's internal circuit
« Reply #12 on: October 01, 2008, 03:11:05 AM »
i'd use a cheap microcontroller (probably one of the ATtiny series) but you already said you were not keen on this solution.

the only other way i can think of is to smooth the servo PWM signal using a capacitor to get an average voltage of the signal.
(servo PWM pulse trains are not true PWM. you get a variable length pulse every 50ms.)
next build a voltage divider using the pot in the servo.
now you could use a comparator to compare the average signal voltage to the voltage across the pot.
use the output from the comparator to drive an h-bridge connected to the motor...

anyone know how it was done in old fashioned R/C equipment (ie before the invention of dedicated chips)?


dunk.

Offline Ro-Bot-X

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Re: Making a servo's internal circuit
« Reply #13 on: October 01, 2008, 05:39:58 AM »
Why not use a 555 to generate the servo pulse, with the servo pot adjusting the signal, feed that to a comparator together with the control pulse and the result will drive the motor through an H-bridge?
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Offline dunk

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Re: Making a servo's internal circuit
« Reply #14 on: October 01, 2008, 01:38:26 PM »
Quote
Why not use a 555 to generate the servo pulse, with the servo pot adjusting the signal, feed that to a comparator together with the control pulse and the result will drive the motor through an H-bridge?
not sure i follow your logic.
a comparator compares 2 voltage levels. it has no way of measuring pulse length.

dunk.

Offline bootstrapTopic starter

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Re: Making a servo's internal circuit
« Reply #15 on: October 04, 2008, 04:37:13 AM »
Will it be easier to implement with a Micro controller ?What I mean is to go for the simplest possible solution and also not restrict it in some way.
« Last Edit: October 04, 2008, 04:38:17 AM by bootstrap »

 


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