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Author Topic: Stepper motor length of cable to driver chip  (Read 2807 times)

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Offline cagesTopic starter

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Stepper motor length of cable to driver chip
« on: July 03, 2010, 05:45:36 PM »
I have got a driver chip for a stepper motor.
The only information on the datasheet about the output(to stepper motor) of the driver chip is that the max current is +/-35mA.
The stepper motor is Unipolar.
The chip will drive the motor at a frequency of about 3kHz (microsteeping).
The motor coil resistance is 300ohms inductace is 0.4H.
Driver and  motor voltage 5V

The driver chip can drive the motor(tested).
The question is the motor will be about 10feet from the driver chip (PCB with controller and driver chip).
Will the length of the cable from driver chip to motor affect the reliability of the motor operation (miss steps), or is there a way to calculate the maximum length of cable or type of cable to use giving the information from the motor and chip.
Any suggestions will really be helpfull (eg change the design).

Thanks.
« Last Edit: July 03, 2010, 05:57:39 PM by cages »

Offline Jdog

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Re: Stepper motor length of cable to driver chip
« Reply #1 on: July 03, 2010, 10:43:47 PM »
Well, it depends how strong you want the motor to be. The longer the wire, the weaker it will be because there will be more resistance in the wire, therefore the total circuit will draw less current and therefore have less power.

In short though, for your situation, the motor is drawing so little current that the length of the wire really does not matter unless you are talking about ridiculously large lengths.

Now, if you are interested, here's all the exciting math behind it :P:

To calculate the approximate resistance of the wire you can use R=(pL/A) where L is the length in meters, A is the cross-sectional area of the wire in meters and p is a constant (if it is copper wire the constant is (1.72x10^-8))

From the specs you have given, the motor draws 16.66666667 mA (I=(V/R)) of current at .0833333333 Watts (P=IV) with no other resistances.

So if you calculate the resistance of 10 ft of let's say 18 gauge copper wire, it will be about .00005 ohms, and then you double it because you have two 10 ft wires running to the motor. So the resistance of both wires will be .0001 ohms.

So with the wires the motor will have .0833333056 Watts of power. With ten feet of wire you will have a difference in power of about .00000003 Watts which is basically nothing.

Offline voyager2

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Re: Stepper motor length of cable to driver chip
« Reply #2 on: July 03, 2010, 10:46:17 PM »
My experience with electronics tells me that motors/sensors/servos don't work to well 1-2 meters from the power source.
Use low resistance wire for optimum results.
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Offline Soeren

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Re: Stepper motor length of cable to driver chip
« Reply #3 on: July 03, 2010, 11:39:59 PM »
Hi,

The driver chip can drive the motor(tested).
The question is the motor will be about 10feet from the driver chip (PCB with controller and driver chip).
Will the length of the cable from driver chip to motor affect the reliability of the motor operation (miss steps), or is there a way to calculate the maximum length of cable or type of cable to use giving the information from the motor and chip.
Any suggestions will really be helpfull (eg change the design).
You tested the driver with the motor - good.
What stopped you from continuing this line of skillfull construction?
It would take you what, 10 minutes max. to hook up this wire and you'd know for sure.
If you run into problems with erratic driving that you cannot see a solution to, then is a good time to ask for help, but don't give up on your own abilities until you at least tried :)

The most likely problem you may be facing is the inductance of the long wires, which, apart from being a noise transmitter, will slow your transitions, but it's my guess that you won't have any real problems (apart from the efficiency issues and noise mentioned).
Twist the wires to reduce these effects.

But... Why not put the driver where the motor is and then use the long wires for control signals (which will be few compared) instead - that's the pro way of doing it.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
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Offline cagesTopic starter

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Re: Stepper motor length of cable to driver chip
« Reply #4 on: July 04, 2010, 06:15:32 AM »

But... Why not put the driver where the motor is and then use the long wires for control signals (which will be few compared) instead - that's the pro way of doing it.


The control signals from the controller (PIC18) are 5V TTL; I am assuming the output pins of the controller are not designed to drive long lengths of cables (10feet) at 3KHz.
Would a TTL signal be reliable over a cable of that length (more reliable than the motor driver signal over 10ft length)?
I will test the cable length on the motor as you suggested, I am a bit worried about reliability of the design (intermittent faults)?

Thanks,
Daniel

Offline Soeren

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Re: Stepper motor length of cable to driver chip
« Reply #5 on: July 04, 2010, 10:14:46 AM »
Hi,

The control signals from the controller (PIC18) are 5V TTL; I am assuming the output pins of the controller are not designed to drive long lengths of cables (10feet) at 3KHz.
I'd place the controller there as well, but anyway - try it and see, nothing beats experience!
If it won't work, a simple current loop (i.e. low impedance) could be made with a transistor and a couple of resistors at each end of the wire.


Would a TTL signal be reliable over a cable of that length (more reliable than the motor driver signal over 10ft length)?
It's not TTL. but yes, you'd get over issues with inductance in the wires. The output from the drivers should have as sharp transients as possible to get the lowest loss and largest efficiency.
The input to the drivers are not nearly as critical.

What motor driver are you using?
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 cagesTopic starter

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Re: Stepper motor length of cable to driver chip
« Reply #6 on: July 04, 2010, 02:54:17 PM »
The link has the data sheets for the motor an driver chips(used as dial controls).
http://www.microcomponents.ch/products/switec/switec.html

The driver chip I am using is the X12.017

Offline Soeren

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Re: Stepper motor length of cable to driver chip
« Reply #7 on: July 04, 2010, 07:37:46 PM »
Hi,

The link has the data sheets for the motor an driver chips(used as dial controls).
http://www.microcomponents.ch/products/switec/switec.html

The driver chip I am using is the X12.017

A datasheet always helps :)

I'd suggest you get some ribbon cable, as used with IDC connectors (which I'd recommend as well).
Either get 20 wire or 24 wire cable and wire it up with ground connected wires between each signal wire - like this:

(00)0R0S0S0S0S0S0S0S0S0+(++)

R = Reset
S = Signal wires (i.e. clock and direction lines)
0 = Ground/0V
+ = +5v
(00) and (++) for if you go by 24 conductor wire.
Depending on the electrical environment (I get the idea that you don't want to use it in a car), you may or may not need to terminate each signal line and the reset line, at the X12.017 side of the cable with a resistor to ground.
With a PIC driving the works, you could use down to 220 Ohm if needs be, but I'd suggest 1k to 2k2 for starters (if they turn out to be needed at all) - This is the best way to drive a 10' cable from CMOS output.

And patch up the supply etc. as in Fig. 5 of the datasheet (which you should read carefully).
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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