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16  Using Arduino / Motors, Mechanics, and Power / Re: Power 1A led from arduino output on: April 18, 2014, 05:38:33 pm
Sounds like a job for a CAT4101...
17  Using Arduino / Programming Questions / Re: No output, GSM module not responding on: April 18, 2014, 01:30:26 pm
 There's no delay before the first string is sent, perhaps the GSM module takes longer to
bootup than the Arduino?
18  Products / Arduino Due / Re: Using Analog Reference on: April 18, 2014, 01:22:32 pm
Its rather tricky to get at that component as its in the shadow of a large MLCC,
I hope a revised board uses a switch or jumper.
19  Using Arduino / Programming Questions / Re: max payload ? on: April 18, 2014, 01:19:31 pm
Thank you very much all of you for you're time and you're answers .

I have read from an example this command:
// enable dynamic payloads
  radio.enableDynamicPayloads();

This still limit the max size at 32 ?

Yes, the hardware sends at most 32 bytes because that's the size of the
FIFO slots.  Dynamic payloads means you can send different length packets
rather than having to pad-out and discard extra pad bytes.
20  Using Arduino / Motors, Mechanics, and Power / Re: using analog pins on a uno to move a servo on: April 18, 2014, 01:13:45 pm
high, i'm working on a hexapod(18 servo's) it all works sweet on a mega, but i want to make it work with a uno. is there anyway i can use all the digital and analog pins at same time to run the servo's using servo.h library or is it a hardware issue.i have tried it but no matter what i do i can't get analog pins to work same time as digital.i know it says on datasheet it'll only run 12 servo's but i've seen people write their own library's and get 18, but that's a bit above my grade.

Adapting the existing Servo library to more channels isn't, I think, too tricky - it
may even be as easy as changing one constant in the source.  You will get a slower
update rate per servo as a result of course... 

If someone else has already adapted the library to 18 channels then you don't have to!
21  Using Arduino / Motors, Mechanics, and Power / Re: MIDI to Stepper motors on: April 18, 2014, 01:10:27 pm
You have first to split your task into two pieces and get those working, then
combine.  One reads MIDI messages and extracts pitch info.  The other moves a
stepper to a given position.
22  Using Arduino / Motors, Mechanics, and Power / Re: How does an AC motor work? on: April 18, 2014, 01:08:46 pm
How does a motor that runs on alternating current move?

Is the only difference between an AC and DC motor that one using alternating current and one uses direct current?

Sorry, I'm an engineer-in-training  smiley-red

There are literally dozens of kinds of motor, so we'll assume you mean an induction
motor, being the commonest AC motor type.

The stator creates a rotating magnetic field as the current(s) alternate.  This induces
current in the rotor (which is basically a set of shorted one-turn coils), and this
current acts as an electromagnet that interacts with the stator field to push the rotor
round. They are cheap and reliable (no brushes).

Induction motors have massive turn-on current spikes, so the larger ones usually have
a soft-start mechanism.

The other widespread ac motor type is the universal motor, which will work from
ac or dc, as only the relative phase of the armature and field coil current determines
the direction of rotation.  They have brushes are are commonly used in power tools as
they can spin a lot faster than an induction motor which is fixed by mains frequency.
23  Using Arduino / Motors, Mechanics, and Power / Re: PWM Control (For Stepper) on: April 18, 2014, 12:58:55 pm
I need to run a stepper at variable rpm. I have a stepper driver. I was previously using a digital output but the frequency does not go fast enough.
What frequency do you need?
24  Using Arduino / Motors, Mechanics, and Power / Re: Motor fast driver on: April 18, 2014, 12:57:46 pm
I went back and experimented based on your suggestions. The thing that made the most difference was not moving in full steps. In full step mode, I have to keep the current low (<50 mA) or I get missed steps during acceleration or deceleration. This occurs even if the ramp is low. So I suspect that's a resonance issue. If I switch to half steps, I can easily use currents of 250 mA or more and accelerate far faster and to much higher speeds.

Microstepping is almost always needed to get best performance from a stepper motor,
as it reduces the amplitude of vibration and resonances.
25  Using Arduino / Motors, Mechanics, and Power / Re: Project a solenoid on: April 18, 2014, 12:52:42 pm
Calculating the resistance of the coil is the easy part - you need to take
the resistivity of copper and the packing density of windings into account.
resistance = resistivity * length / area.

The magnetic circuit is much harder to characterise, many different ferromagnetic
materials are available to form frame and plunger.

Generally the smaller the gap and the lower the reluctance of the magnetic circuit the
larger the mechanical force for a given MMF (magneto-motive force, measured in
ampere-turns).

Go and look up "soft" v. "hard" magnetic materials - you want soft for a solenoid,
with low remanence.  Generally iron is the best cheap material, although mild steel
is more commonplace (but less soft in both senses).
26  Using Arduino / General Electronics / Re: Basic question: Arduino wires on: April 18, 2014, 12:44:08 pm
Aluminum is as magnetic as copper.


Ah ok, thanks. TBH, I rather foolishly thought until now that only Iron, copper and cobalt were magnetic. Does that mean an aluminium wire coil will have the same inductive properties as a copper one?
Iron, nickel, and cobalt.
And gadolinium...  And many alloys.
27  Using Arduino / General Electronics / Re: cable distances between sensors and arduino on: April 17, 2014, 08:22:14 am
Signals should always be paired with grounds if using twisted pair.  With a shielded
cable the wires share a grounded shield, but crosstalk can be more (matters at
higher frequencies more).
28  Using Arduino / Motors, Mechanics, and Power / Re: It's faster a motor or a solenoid? on: April 17, 2014, 08:17:09 am
Solenoids act linearly, motors act rotationally, they cannot be compared directly
since one does linear motion and the other rotation.
29  Using Arduino / Motors, Mechanics, and Power / Re: Stepper hisses all the time on: April 17, 2014, 08:14:48 am
Yes, that's hysteresis mode current feedback - it amplifies any noise in the current-
sensing components and the motor windings act a bit like a loudspeaker and produce
audible sound.  Depending on how the chip operates and what frequency its working
on it can be more or less noticeable (some keep it ultrasonic and thus inaudible).

You should find that the choice of decay mode will affect the sound.

How are the wires configured - I would suggest separately twisting together each
windings wire pair, thus reducing the current interference between A and B windings,
which may affect the noise.

Endevour to keep the wires to separate motors separate from each other and other
cables - although this may make no difference its good practice.
30  Using Arduino / Motors, Mechanics, and Power / Re: DC brushed motor angle on: April 17, 2014, 08:06:13 am
Hi!

I'm using Pololu Dual MC33926 Motor Driver Shield for Arduino, with brushed DC motor. I'm wondering (wasn't able to find out how) if I can get the position (angle) of motor. I know it's probably task for stepper, but need to do it with dc, if tere is a way.

Thanks!

There's no way from just the motor itself, so an external shaft-encoder is needed.

Even steppers don't give you position, but will hold position reliably if not overloaded,
so that once calibrated you just remember the number of steps.

Its common to use a motor with two shafts for encoders - gearing one end, encoder
on the other.
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