Hello guys, I'm trying (again) to automate my roller blinds.
They are quite big; 3x2 meters, and I have measured 7kg to lift them when fully opened.
The stepper Is this one, specs below.
It's rated 2.8a, 0.64ohm so I calculated 2.8 X 0.64 = 1.8, then I doubled it to include the assumed (how is that calculated?) driver's consumtpion, so I'm going by 3.6 Watts.
The motor is rated for min. 18V so I thought of a 24V 1A PSU (?)
I have read that it is recommended in such cases to use a cacpacitor, but of which value and where should it be placed in the circuit?
Lastly, I don't quite understand where is the Arduino out on the driver?
2.8 Amp, nothing else. Set the driver to 2.8 Amp or less. Stepper motors are ran by current control of the coil current, not by any voltage. Use a power supply giving more than 2 * 2.8 Amps. The more voltage the faster response. Check the drivers maximum voltage! 50 volt it looks like but 24 volt would do fine.
I understand Dir pins are for controlling the motor's moving.
But which pins supply the arduino with power? Pul ?
Thinking about it now it does not make sense to use a psu with <2.8A, but I did read that the coil's resistance - 0.64ohm, should be calculated ?
So I need here at least a 24V 6A psu? That's some high current isn't it?
Do you have a particular reason for using a stepper? Is this just to raise and lower the blinds, it seems so from the force required. And how far do you need to pull the cord and how quickly? That will determine the power needed. For example, 7kg weight is about 70 newtons force, if you had to apply that over 2 metres it's 140 joules energy, in 2 seconds that would be 140 watts mechanical power. Also from the force and assuming the cord wrapped round a drum of given size you could calculate required torque. Would a geared dc motor be a better choice? Probably cheaper and quieter and easier to drive.
Well I actually tried doing it before with a regular DC motor but the circuit was a bit too complex for me with diodes and H bridges and limit switches and what not.
I ended up burning the motor
I thought that a Stepper Motor would be easier because the driver makes everything much simpler and I could just tell the motor where to go and where to stop with a simple Arduino code.
The Stepper Motor I intend to use is rated 1.3 N.m which is 13 kg.cm so it should be fine (?)
It's about 2 meters tall. Speed is not very important here even if takes like a minute or two it'd be ok for me as long as it works
The Arduino can be supplied its own power by;
1). 5V from the USB programming cable.
2). 5V from an external supply connected to the 5V and gnd pins on the controller PCB.
3). 7Vdc to 12Vdc in the DC power socket on the edge of the PCB.
Can you please tell us your electronics, programming, arduino, hardware experience?
So will you just arrange the stepper to drive the "pulley" around which the ball chain is wrapped? What is its diameter? If it was 2cm then at 1:1 you would have plenty of torque.
Calculating power supply current is more involved than it looks. This type of driver acts as a "switched mode power supply" and in effect steps down the supply voltage to the motor and regulates the winding current. This means that the supply current can be a lot less than the winding current that you set, and the higher the supply voltage the lower the current. The maximum current in both coils combined will be sqrt(2) * 2.8 = ~4A. But the coil voltage would then be 0.64ohms x 4A = 2.5V, and the coils would dissipate 10 watts - this represents the quiescent power the motor takes. For a 24V supply that's 10/24 = 0.4 amps, or half that for a 50v supply. Then or course the the driver is not 100% efficient and more current is needed to accelerate the motor and drive the load. But this indicates that a 6A PSU is serious overkill! I'd be inclined to use one at no more than 3A and possibly less - I have a CNC milling machine with 4 axes and it runs from less than a 6A 48v supply!
You asked about a capacitor - you may be referring to the cap that is recommended with the small driver boards often used with Arduino such as the A4988. You are proposing to used a packaged driver which is highly likely to have a capacitor inside, no need for another one.
You drive the signal inputs from Arduino outputs. The inputs are opto isolated and you can earth the "-" side of each and connect the Arduino to the "+". HOWEVER, being optos they take current and you need to be sure that the Arduino can supply this - it is typically 10mA.
You will probably need to use "microstepping" to get a smooth and quiet drive - steppers can be quite noisy! Also note that when the supply is switched off the motor doesn't have much holding torque, so if there's much weight on the chain it could slip down. Also consider acceleration and deceleration - but this is taken care of by the Arduino stepper libraries I think.
Yes it's quite high, and you don't need that much current from the PSU. Your driver works similar to a step down converter. The higher the PSU voltage, the less the current needed.
It isn't that easy to select the correct PSU only by the coil current. This must be done regarding the needed power, not the amps. And that's why the coil resistance is needed.
The power each coil consumes is I²xR - so 2.8²x0.64 = 5.02W. With two coils it's about 10W. Add at least 50% for losses and mechanical power needed. That means your PSU must provide at least 15W. That means a 24V/1A PSU would be fine.
So the 2.8A indicated is just a top limit? Isn't it related to a demanded current to reach high torque?
Could one just use higher and higher Voltage and minimize the current as long as the Watts are the same?
I did not understand what you meant here.
Anyhow my question is - which pinout on the driver supplies power to the arduino?
Well I'm a hobbyist with Arduino for the last year or so, I know the basics I believe.
I have a few working projects with servos and some sensors that I made with my 3d printer.
I have been working with that kind of blind mechanism. I think it needs quite some force even when the blind is 4 by 6 feet.
Have You made any tests showing the force needed?
You can hook a bucket to the down going part of the chain making the blind go up. Then add weight to the bucket until the blind moves. Determine the weight of the load. Then calculating gear dimensions is the next.
No, that's the COIL current, supply current is less. Stepper torque is essentially the "holding" torque when the windings are energised. As they step the "detent" position moves round and drags the shaft with it. The faster they go the lower the torque.
Coil current is what the driver maintains in the coil by switching the supply volts to it on and off at a high rate. Supply current is what is drawn from the power supply which is usually much less.
That's the moment of inertia of the rotor which determines how quickly it can accelerate if there was no additional mechanical load. You don't need to worry about this.
The thing about stepper motors is that they are always powered in operation. There are two sets of coils and current is steered from between them and the resulting magnetic field drags round a permanent magnet rotor. The amount of current in each coil is adjusted by the driver so that a given moment the rotor is held in a particular position. If you try to rotate it with more than the "holding torque" it will slip. If the currents are switched off completely then the holding torque drops to a very low value, just set by the permanent magnet. If one coil is powered, then the rotor holds at one position out of 200 at 1.8 degree intervals. As you decrease that coil's current and increase the other the rotor will move, until it's moved by half a step where you reverse the process and it carries on moving until it's in a new position one step round from where it started. By controlling the proportion of currents in each coil you can select intermediate positions which is microstepping. The driver you show can divide each full step into 128 microsteps maximum as selected by setting switches.
