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amplified motor signal

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hpcycling2010

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Hi,

Im making a modified Xbox steering wheel controller, machining some nice parts, using real bearings and hopefully upgrading the force feedback motor.

Here's what im trying to accomplish
The xbox motor turns clockwise and counter clockwise depending on the force feedback from the game.
I want to use that signal to drive a bigger motor, without burning out the xbox motor driver...

essentially what I have is a +/- 24V (0.5A stall motor) signal, and I want to turn it into +/- some voltage (maybe 24v from a different supply) with more current (20 max Amps - stalled motor )

I'm assuming I need an op amp, a voltage divider and then its all black magic from there, but I'd love to see anyone's take at this.

Thanks ahead of time!

-Hans
 
A 24v 20a motor allthough considered small in industry circles would be an animal in a force feedback appliction, you probably wouldnt be able to stop the wheel from turning against the motor.

To start you need to find how the original motor is controlled, which would involve the use of a 'scope, the chances are it'll be pwm possibly a full bridge, to soup that up you'd need to arrange a full brige setup using 4 mosfets, and drive it from the o/p's of the original xbox's controller brisge o/p's, do a google for h bridge motor controller.
 
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Thanks! I'll go straight to the source, no piggy backing!

The motor has a 20A stall current. I found many smaller motors but the stall currents were too high! ( 40-70amps stall currents)
I will have an adjustable power supply though so anyone can turn it up or down depending on what they like for the force feedback.
I'll probe around the PCB this weekend and see what I find out.
 
Something else to consider: most motors aren't designed to be kept in a stalled state for long periods (as would be the case in a force-feedback gizmo) and would overheat. So you would probably need to run your motor at way below its stall current.
 
I think you are right about limiting the current.
So, this may be a silly question but, would a standard H bridge driver limit current on its own, or do you know of any kits or pre-made H bridges that have that option? I was looking at some on eBay that had 40A peaks, but, I don't know what happens if the motor is trying to draw 60A, would it kill the driver or would the driver just output its max current.

Thanks
 
If the driver is rated 40A and you pass 60A through it you'll let the magic smoke out :(.
Some H-bridge motor driver ICs have a current-limiting function with current being sensed by use of an external resistor.
 
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Alright, so far no signs of a PWM, however, there are two OP amps on there.
Motor output is actually -11 to +11 and it is variable.

Is there any way to use the -11 to +11 to drive some power op amps? If this was the case, can a regular DC 24V power supply do the trick?
Meanwhile, I'll keep on searching for PWM's....
 
The o/p might be pwm, in fact I'm fairly sure it will be, a multimeter might well read pwm as a variable voltage.
 
If you have access to an oscilloscope you can check for PWM.
 
Off to the lab to see if I find PWM. You gave me good confidence I'll find a signal somewhere.
Part 2 to this. I have my updated motor, stall current ~12 Amps and the torque I want!. I would like to make a current limiter (not regulator) any ideas on how to do this? 0-12Amps with a power supply capable of 28V 20A.
You guys are the best.
 
Alright, good news and bad news.
Good news is I found the PWM, and it comes straight out of an H bridge, no PWM going into the H bridge, its analog in, digital out (A3950 IC)
Bad news is that its a 24V PWM and I'd love to hear ideas on how to bring this down to a 5V PWM.
49Khz PWM.
 
So, most PWM driver's I have been able to find are 25Khz top end, and my signal is actually 46.7KHz. Is there a way to use a flip flop or something alike to "half" this frequency, yet keep the duty cycle?
By the way I attached the picture of the signal.
PWM Signal.JPG
 
no PWM going into the H bridge, its analog in, digital out (A3950 IC)
:confused: According to the datasheet for the A3950 it has a PWM input on the Enable pin.
 
You are quite right. I feel dumb.
Either way... I still have a 46.7KHz frequency and most Bridge drivers out there do 25KHz, and a few do 40KHz. I'm looking out there on other forums for splitting PWM signals, but the biggest issue is that half the frequency halves your duty cycle... Thoughts?
 
So here's one option...
I found the source of the PWM, 3.3Volt Amplitude, 46.9KHz and 50% duty cycle max.
I could create a circuit with this chip (link to data sheet) and since they have a 40V 2.8A capacity, I could have several of these hooked up in "parallel" to get my desired current.

I am creating a new thread to address the issue more specifically. If you have any more notes or options... let me know. thank you
 
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