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5791  Using Arduino / Motors, Mechanics, and Power / Re: Need advice to control intensity in electromagnet for ferrofluid sculpture on: April 20, 2013, 09:49:21 am
PWMing soft iron core may generate too much heat due to iron-losses - esp. with high frequency PWM,
low frequency PWM may be (acoustically) noisy though.  Adding a ferrite inductor in series could cure this
(use fast PWM)....

Ideally a programmable output DC-DC converter would be used - control the voltage, no ripple at the magnet, good
efficiency.  Bit overkill though!

Can you find a laminated-core electromagnet perhaps?
5792  Using Arduino / Motors, Mechanics, and Power / Re: Multi outputs - 2 servos, and 2 linear actuators on: April 20, 2013, 09:41:26 am
Firstly you cannot run those linear actuators in parallel without good positional feedback or they
may fight each other (assuming they are moving the same load).  Also we don't know the
stall current rating for them, but at 0.8A no-load they probably take 10A or more stall.

Do you need PWM control of the actuators?
5793  Using Arduino / Motors, Mechanics, and Power / Re: Will the Arduino drive this 8-Channel Relay Module directly? on: April 20, 2013, 09:36:26 am
Googling the relays (SRD-05VDC-SL-C) suggests they need 90mA to activate, so transistors will be needed.
5794  Using Arduino / Motors, Mechanics, and Power / Re: Measuring voltage of DC motors on: April 20, 2013, 09:32:04 am
The voltage should be marked on the motor - its not easy to know the design specs of an unmarked motor. 

Running a motor at too high a voltage will shorten the life of bearings and commutator and will cause it to get
too hot in extended operation.
5795  Using Arduino / General Electronics / Re: Arduino shorterd? Circuit help please on: April 20, 2013, 09:26:59 am
So long as you only connected ground and signal pins (enables and inputs) to the Arduino there is no way to
affect the Arduino (though you might cook the L6234 if the enables were 5V while the L6234 was not powered up).

With a circuit like this I would first add protection resistors in series with all the signals (4k7 on enables, inputs) so
that if the motor controller blows it won't take out the Arduino.  Since the only other common connection is ground
I can't see how you damaged things - before allowing any significant current to flow with a motor you should test with
a current-limited power supply to make sure all is well - its startlingly easy to blow motor controllers if you are
careless.   You would at the very least need to check the bootstrap voltage was up to spec and that the outputs were
all switching cleanly with a 'scope to be confident of the thing working under real load.

Also its wise to have quite a bit of decoupling on the Vs rail since the bridge is switching lots of current.

You also haven't said what kind of motor you are using / going to use - this chip will handle perhaps 1.5A or so
with moderate heatsinking, trying to take it to the nominal 2.8A / 4A (package dependent) isn't feasible without water-cooling!
5796  Using Arduino / General Electronics / Re: Confusion with Formula for LM317 circuit on: April 20, 2013, 09:12:18 am
Your guess would have been right if the LM317 referenced the 1.25V to the ground terminal - but it doesn't
it references it to the output terminal (the technical reason for this is to provide a known closed-loop gain
throughout its range of operation).   You apply the voltage divider rule upside-down, that's all.
5797  Using Arduino / General Electronics / Re: Diod Connection understanding problem on: April 20, 2013, 09:08:58 am
The diagram is right, the diode is parallel with the relay winding.  Make sure the positive supply goes to the cathode
of the diode, and the switching transistor connects the other side to ground.  The diode only conducts briefly when the
switching device switches off.
5798  Using Arduino / Programming Questions / Re: Writing a pin for less then a second. on: April 20, 2013, 09:04:47 am
 I thought it was an output!  But then again if it is an OUTPUT then reading it will returns its last written state.


Slightly pedantic, but no, reading an output pin will actually read the physical state of the pin, not its
last written state (however unless you have a short-circuit on that pin these will be the same).  The
hardware that reads from a pin is blissfully unaware of whether its currently an output or not.

Also the read state is that from the output of a synchronizer circuit so it will be about 1 clock cycle delayed
(not that this matters for digitalRead() which takes many clock cycles to execute).
5799  Using Arduino / Motors, Mechanics, and Power / Re: Arduino Uno - GRBL - High amp motor questions on: April 19, 2013, 05:22:30 pm
There shouldn't be difficulty driving an opto-islated stepper controller - I presume the GRBL shield already
has step and direction pins for each axis?

However do check the interfacing requirements - so long as the controller does need more than 25mA
or so per signal no further interface hard needed (most opto isolators are 20mA or so)
5800  Using Arduino / General Electronics / Re: Switching LED Strips from 3.3v on battery source on: April 19, 2013, 05:15:34 pm
TPIC6B595, you may increase number of leds up to 8
But not run it on 3.3V, its a 5V only chip.
5801  Using Arduino / General Electronics / Re: Problem, IMU freeze using motors on: April 19, 2013, 05:06:40 pm
So there's a 6V battery powering the motor shield?  And how is the Arduino powered?

Are the wires from the motors kept away from the IMU?   I'd consider more decoupling on the 3V3
supply rail.
5802  Using Arduino / Programming Questions / Re: operating sine wave equation in Arduino on: April 19, 2013, 04:55:44 pm
So far my frequency range will vary from 0 up to 1.5 Hz, in increments of 0.1 Hz. I am running a robot using these sine waves and continuous update is desired, however, twice a cycle will do. Frequency controls speed of movement of my robot and ideally I want to vary it pretty quickly but smoothly within the desired range. Also, using this method would I still be able to control Amplitude and Phase difference? Thank you very much for your time!

twice a cycle?  how long i a cycle?  Also how much precision are we talking for this servo, 8 bits enough?
5803  Using Arduino / Programming Questions / Re: Incrementing a variable in a cycle, some programming advice needed on: April 19, 2013, 04:51:12 pm
or global. ditto for lastgyrostat - these values need to persist across calls to loop(), so don't declare them on
entry to loop...
5804  Using Arduino / Motors, Mechanics, and Power / Re: Winch or regular servo on: April 19, 2013, 09:15:39 am
When you say "a lot of torque" what does that mean??  Without calculating the torque you cannot choose
a servo.
5805  Using Arduino / Motors, Mechanics, and Power / Re: how to switch on a 12V motor with arduino? on: April 19, 2013, 09:12:33 am
I'm using a Lithium Ion  battery of 12V to power on Arduino.
How to use that same battery to turn on the 12 V motor ?
I want to turn on the motor by arduino when i press a switch or button.
The battery can provide 3A current whereas motor only requires a 1.5A current.
I know the programming. But I dont know how to set up the electronics needed.

I'm new to electronics..
Please help.

Please provide links to the battery and the motor...  We will just be guessing otherwise.

Is that 1.5A rating for the motor the no-load current, full-load current or stall-current?

Do you mean 11.1V lithium battery?  Does the battery have built-in protection circuitry?
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