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5746  Using Arduino / General Electronics / Re: Why did I burn my TIP120? on: June 08, 2013, 03:12:14 pm

Basically the TIP120 is the wrong thing to use here. You need a logic level FET.


Or a water cooling system for the TIP120, using a tiny little water pump switched by a 2N2222!
5747  Using Arduino / Motors, Mechanics, and Power / Re: Motor/generator control on: June 08, 2013, 06:51:01 am
Some suggestions:
 IRFZ44 isn't logic level transistor, you may need a driver if load current > 1 or 2 Amps.
 Remove serial print from the loop, make debug printing by request from the user via console.
 Look into PID library for arduino.


Yes, looking at the typical output characteristics graph its very marginal at 5V.  You certainly
don't want to reduce the gate voltage below 5V as you have done with the two resistors - place
the 10k resistor on the Arduino pin, not directly on the gate electrode.  But the basic mistake
is using a MOSFET that wants 10V drive at 5V - you need a logic level MOSFET really.

The instability problem is a symptom that your control system is not tuned.  You probably need
to research PID control theory and experiment.
5748  Using Arduino / Motors, Mechanics, and Power / Re: Servo potentiometer glue on: June 08, 2013, 06:44:50 am
In other words calibrate it.
5749  Using Arduino / General Electronics / Re: Two Arduinos hooked up to one mosfet on: June 08, 2013, 06:43:22 am
@fungus, I think I'm gonna pass on that one...

Oh, go on, I'd love to know the amps between two pins.

You've already been doing it for ages ... a few more seconds won't hurt. smiley


Output transistors on an Arduino pin are around 20--40 ohms each IIRC, two fighting each other
is thus 40 to 80 ohms across 5V, so in the ball park of 100mA (absolute max rating is 40mA).

One arduino pin shorting to ground would be twice that current, overloading the output pin
and the power pins of the Arduino I think.
5750  Using Arduino / Motors, Mechanics, and Power / Re: Harvesting steppers and power supply from old printer - stepper running hot on: June 07, 2013, 09:00:20 pm
Yes I expect you're right. I managed to burn out part of the power supply when I left it on too long so that probably wasn't designed to sustain that either.

Is it enough to set all the inputs of the motor to +24v? I'm trying to remember my physics A-level and iirc if there's no potential difference then no current will flow and no power dissipated.

Yes, correct.
5751  Using Arduino / General Electronics / Re: Avoiding High Voltage Spikes from Inductor Coils on: June 07, 2013, 08:56:35 pm
You could add protection or snubber circuit across the inductor (for instance back-to-back zener
diodes, aka TVS diodes, can limit voltage excursions).

Snubber circuits are RC networks designed to both limit the voltage spike from an inductor
and limit the "ringing" of any LC resonance (using just a capacitor would usually lead
to extensive ringing).

When dealing with relays motors etc a simple freewheel diode is used to prevent back EMF
spike on switch-off.

Most scope probes have a "x10" setting (which divides the voltage by 10) - always choose this
if high voltages may be present since there will then be 9Mohms in series with your 'scopes
input(s).
5752  Using Arduino / General Electronics / Re: Arduino Pro Mini Wiring Issues With SD Card Reader on: June 07, 2013, 08:49:03 pm
Photos might be more illuminating.

One thing you may not realize is that the side rails on some breadboards have breaks along them,
usually indicated by a break in a coloured line too.

BTW your last Fritzing image is clearly incomplete as you don't connect ground from the voltage regulator
to the rest of your circuit.
5753  Using Arduino / General Electronics / Re: no response from stepper on: June 07, 2013, 08:44:04 pm
Determine the windings with the motor disconnected from the driver board.

Once you've paired up the two windings, call them A and B and connect to the right pairs of
pads on the driver board.   I'm assuming a 4-wire stepper motor - is that the case?
5754  Topics / Science and Measurement / Re: Calculate heat transmission coeficient? on: June 06, 2013, 07:17:40 pm
Copper is much more expensive than aluminium, it doesn't make much sense to use copper anyway.

Hopefully one day they will be able to make cheap diamond heatsinks, more efficient than any
metal smiley-wink
5755  Using Arduino / Sensors / Re: Simpe torque and agnle sensor on: June 06, 2013, 07:11:11 pm
There is a world of difference between measuring stationary torque (relatively easy)
and dynamic torque (torque on a shaft that is rotating) - which usually requires remote
wireless sensing.
5756  Using Arduino / Motors, Mechanics, and Power / Re: wierd running of motors using arduino and l293d on: June 06, 2013, 07:01:56 pm
Mark, I don't know what you mean by those PP3 motors.... But all I know is that it's a basic DC geared motors, and they look exactly like this:


Whoops, typo, I meant PP3 batteries....
5757  Using Arduino / Motors, Mechanics, and Power / Re: Measuring the spec of stepper motors on: June 06, 2013, 07:00:58 pm
I do have access to the coils, what wire diameter would correspond to what ampereage?

If you disassemble a stepper motor you will irreversibly weaken it. With respect to the current capacity of a given wire size you should google for an "ampacity chart".

I believe that's no longer a problem - modern rare-earth magnet hybrid steppers are fine.
Older permanent magnet motors used magnet alloys with low permanence that were
very easy to demagnetise.  Such alloys lose magnetisation if hit with a hammer too...
5758  Using Arduino / General Electronics / Re: Old stepper motor Pinout? on: June 05, 2013, 03:49:31 pm
The typical way to drive these is with a darlington array with free-wheel diodes like the ULN2803, but any switches will do
if they can handle the voltage and currents involved and there are the relevant diodes.
5759  Using Arduino / General Electronics / Re: problem in dc motor need a push to start on: June 05, 2013, 03:46:23 pm
Any chance of some schematics?

Some things to note:

1. The motor is a 3V motor, 4 1.2V batteries is 4.8V.
And the L298 will lose 2.5V or more, its not a great choice for low voltage motors.
Quote
2. The stall current is 2.1A - that is how much current is needed to get it moving from stationary
Stall current is the current it takes when the motor is prevented from running (rotor locked in place) and
its given its nominal voltage in full.  Its equal to  nominal voltage / winding resistance.

The current needed to get it running from stationary should be about the same as the no-load current,
this is due to frictional losses mainly.
(or if under load it depends on the nature of the load).
Quote

Is there any load on the motor, or is it just free-running?
5760  Using Arduino / General Electronics / Re: Receiver's Noice Input =K*T*BWeq ? on: June 05, 2013, 03:40:03 pm
Sorry, got completely confused there, its k T bw, the ln term comes in signal to noise ratio.
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