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Author Topic: car wiper motor supersized servo circuit schematic  (Read 6545 times)

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Offline owkTopic starter

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car wiper motor supersized servo circuit schematic
« on: August 11, 2011, 02:36:41 PM »
anyone out there know where i can get a schematic for turning a car wiper motor into a servo, the circuit basically needs control the motor through pwm. bi directional continuous rotation speed control

Offline Soeren

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Re: car wiper motor supersized servo circuit schematic
« Reply #1 on: August 11, 2011, 06:11:42 PM »
Hi,

anyone out there know where i can get a schematic for turning a car wiper motor into a servo,
The SoR forum should be a good place.
First you need to define your exact needs (voltage, drive current, stall current and input signal.
Then try the search at this site, I have posted circuits for various similar purposes


the circuit basically needs control the motor through pwm. bi directional continuous rotation speed control
Do you mean like an R/C servo modified for continuous rotation?
When you modify a servo, it's not a servo anymore, as the feedback circuit which makes it a servo is surgically removed and it's turned into a gear-head motor with driver.

When you say PWM, do you mean that in the real PWM sense?
I ask this because a lot of people seems to think that an R/C servo is driven by PWM, but when you're talking real PWM (where the pulse can go from near 0% to near 100%), the circuit is different from what's used for the PPM signal used for telling servos where to go to (which is standardized to vary the M/S between the narrow range of 5% to 10% and which is a communication signal, quite unlike the PWM signals used for motor speed/power control.


If you just want to be able to drive the motor CV and CCV from a microcontroller in the easiest way, you need nothing more than an H-bridge which you feed with a PWM signal from the controller.

An H-bridge can either be made with 4 Power MOSFETS, or a DPDT relay for direction and a single MOSFET for the PWM. In both scenarios, a little "glue" (i.e. lesser components)is needed.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline corrado33

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Re: car wiper motor supersized servo circuit schematic
« Reply #2 on: August 11, 2011, 06:46:21 PM »
A quick google search shows that windshield wiper motors don't actually go back and forth (I really didn't know that), they just use a worm gear and a linkage.  (Well, at least the ones explained on howstuffworks.com did ) :)

So, I'm guessing they don't have any feedback control.  So to turn it into a servo would require some sort of feedback circuit right?  

Offline Soeren

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Re: car wiper motor supersized servo circuit schematic
« Reply #3 on: August 11, 2011, 08:28:30 PM »
Hi,

So, I'm guessing they don't have any feedback control.  So to turn it into a servo would require some sort of feedback circuit right?  
Exactly.
Some older models have contact traces (usually brass/bronze) on the worm wheel, to cater for the full sweep and return with even a short actuation. In newer models, electronics dominates the return control.

None of the return contact stuff will be needed for using the motor as either a geared down regular motor or a servo motor. The latter will need feedback, but that's not hard to make and while I'd prefer either an optical or Hall position sensor (position decoder), it can be used with a simple potentiometer, if life span isn't the most pressing concern (conductive plast pots will be more resillient than the old carbon track in a tin types.

A9-bit encoder would make for a resolution of 1°

Plenty of simple ones have been made, just take a peek at YouBoob.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline owkTopic starter

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Re: car wiper motor supersized servo circuit schematic
« Reply #4 on: August 12, 2011, 06:03:48 AM »
actually i don't need any feedback for the motor as it would be a continuous rotation so maybe calling it a servo was the wrong thing to do

okay so i want to be able to spin the motor left and right at a speed that is proportional to the signal from my rc Tx (fast /slow)

hope that helps

the motor takes 12v and id probably draw a max 10 amps in a stalled condition motor draws 14amps


Offline owkTopic starter

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Re: car wiper motor supersized servo circuit schematic
« Reply #5 on: August 12, 2011, 12:24:52 PM »
An H-bridge can either be made with 4 Power MOSFETS, or a DPDT relay for direction and a single MOSFET for the PWM. In both scenarios, a little "glue" (i.e. lesser components)is needed.


this is what i am looking for simple cw ccw controled by pwm from the controler

I am a noob can you show me what this H bridge is what are MOFSETS i read around but most of it is too technical for me to understand , DPDT relay and a sigle mofset that sounds simple what would it look like?

mind drawing a small diagram to help me visualize this

Offline owkTopic starter

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Re: car wiper motor supersized servo circuit schematic
« Reply #6 on: August 12, 2011, 05:36:29 PM »
Although i still dont really understand Mofsets ( like what are each of the 3 legs for and can it "understand" a pwm) i found what i have been looking for
http://www.robot-electronics.co.uk/htm/md03tech.htm

Offline owkTopic starter

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Re: car wiper motor supersized servo circuit schematic
« Reply #7 on: August 13, 2011, 06:12:13 PM »
okay this is it the simplest brilliant solution 

also http://mcsrobotics.weebly.com/tutorials.html this is a great site

Offline Soeren

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Re: car wiper motor supersized servo circuit schematic
« Reply #8 on: August 13, 2011, 08:47:20 PM »
Hi,

this is what i am looking for simple cw ccw controled by pwm from the controler
So, you want the wiper motor to be controlled from a PWM signal out of the equipment you already own?
And how do you want to translate it?
If you have a ~0% to ~100% PWM signal (and nothing but) and you want to convert it to +/- 0..100% PWM, you have to decide on where you want to divide. It could be that from 50% down to 0% of your signal, controls the motor speed 0% to 100% CCV and 50% up to 100% of your signal controls the motor speed 0% to 100% CV.
Or... You could part at eg. 30/70, if you think that you're not gonna use the reverse that much, to get a finer control of the forward.

What frequency is the PWM signal that you wanna use?


I am a noob can you show me what this H bridge is what are MOFSETS i read around but most of it is too technical for me to understand , DPDT relay and a sigle mofset that sounds simple what would it look like?

mind drawing a small diagram to help me visualize this
For learning the basics, try Google. There are plenty of beginners tutorials and forum posts aren't meant for tutorials. You can also find very basic tutorials on MOSFETs.

The relay+MOSFET is attached.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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