Online Calculator for 3d printing

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Online Calculator for 3d printing

Postby New Passion » 2017-Jul-Sun-19-Jul

I came across this calculator tonight, and it looked like it might be a good resource.

https://nathan7.eu/stuff/RepRapCalculat ... lator.html

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Online Calculator for 3d printing

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Re: Online Calculator for 3d printing

Postby Mooselake » 2017-Jul-Mon-14-Jul

Looks good!

It doesn't include (or allow) my T8-8 (aka TR8-8) leadscrew which is (iirc) 80 steps/mm, guess Prusa doesn't sell one with that screw, but no big deal.

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Re: Online Calculator for 3d printing

Postby New Passion » 2017-Jul-Tue-09-Jul

Sorry Moose:( ... but here is the actual Formula I was looking for when I came across the calculator. I am Modding a different printer and I am tuning the stepper motors, and I needed a calculator for vref, so here is the formula I finally found VREF = Current(A) x 8 * Sense_Resistor (.1ohm RS) * 0.90

In this formula I believe, Current is the Stepper Motor amps multiplied times 8 multiplied by the sensor resistor ( In my case the resistor is R100) multiplied by .90 ( which gives you 90% of the VREF

I hope I have this right, Maybe someone could correct me if I have something wrong, and also tell me what the constant number 8 represents?

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Re: Online Calculator for 3d printing

Postby RetireeJay » 2017-Jul-Tue-11-Jul

I don't think Moose was talking about setting the current in the steppers; he was talking about the steps per millimeter using a screw that's not listed in Prusa's table. That's not hard to calculate anyway. The steppers have a native "pitch" of 200 steps per revolution and we have 16X "microstepping" enabled on the Printrboard, so we have 3200 (micro)steps per revolution. Given that information and the "pitch" of the screw in millimeters per revolution, it's easy enough to calculate the steps per millimeter.

Just FYI, the stepper controller data sheet is available online (and attached here), and it tells how the calculation of motor current works.
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Re: Online Calculator for 3d printing

Postby New Passion » 2017-Jul-Tue-15-Jul

I wasn't referring to Moose lead screws. I was just saying sorry that the calculator doesn't support his lead screws. I came across the calculator, while searching for the stepper motor formula for myself, and thought the calculator might be handy for other users on the forum. What I was asking if anyone might know what the constant number 8 represents in the formula I found for VREF.

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Re: Online Calculator for 3d printing

Postby RetireeJay » 2017-Jul-Tue-16-Jul

If you look at the document that I attached to a previous post, you will see a schematic on page 3 where it shows the current that goes through the motor passing through a sense resistor Rs. Current X Resistance = Voltage, so the motor current flowing through Rs generates a Sense Voltage proportional to the current. (That is, the current at that moment through that winding of the motor; there are two coils and two sense resistors.)

The schematic shows the Sense Voltage being compared to a reference voltage, which is created by a DAC (Digital to Analog Converter) that uses Vref as its analog reference input and a digital word as its digital input. So the DAC in this case is able to create voltages for the comparator in steps equal to 1/8 of the reference voltage. (We get the 16 microsteps by including both forward and reverse directions of the current). I think that's where the factor of 8 shows up on page 7.

But all of that has absolutely nothing to do with steps per millimeter. It has to do with how much current you send to the motor. Note that a stepper motor has just about the same total current flowing through it (the two coils combined) all the time, even when stationary. If the current is too low, the stepper will not have enough power and it will miss steps. If the current is too high, the stepper motor will run too hot. Since Vref is difficult to access on the Printrboard, most users don't try to actually measure it, but instead empirically adjust the motor current to a happy medium where the motor isn't overheating and yet has enough power to execute the moves without missing steps.

EDIT: Just re-read your post. I doubt any practical stepper motor is going to work with a sense resistor of 100 ohms; that's far too high.
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Re: Online Calculator for 3d printing

Postby New Passion » 2017-Jul-Tue-17-Jul

Now I know where the 8 comes from in the formula Thank You. The board I am referring to is not a Printrbot board it is a Melzi board, which is known to have issues, I didn't really want to discuss the Melzi here to avoid any confusion as to what I am doing, I just thought I would post the calculator I found, but if you are interested here is the best image I can find ( I know it is a little blurry, while looking at the board there are two resistors for each side of each stepper motor using the E Motor for this example R22 and R23 both have a value of 100, and I have read that the motors are usually set to high from the factory, thus running too hot and using more power than needed, and I know if I go too low they will skip steps, I just wanted to check there values and adjust if necessary. I have already had to put a Mosfet on this board for the Heated Bed. I just have been wanting to tackle another 3d printer and this looked like one that would be fun to mod. Sorry for causing any confusion for posting an online calculator.

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Re: Online Calculator for 3d printing

Postby RetireeJay » 2017-Jul-Tue-20-Jul

I think you're reading the codes on the resistors wrong. See http://www.radio-electronics.com/info/data/resistor/smd_resistor/smt-resistor-markings-systems.php If the resistor is marked "100" it actually is a 10 ohm resistor.

The larger the resistor, the SMALLER the current that will flow through the motor. 100 ohm resistors would deliver an impossibly small current, and even 10 ohm resistors will deliver extremely small currents. The resistors on the Printrboard are 0.11 ohms, so if you have 10 ohm resistors you'll be trying to run your motors on about 1% of the current delivered by the Printrboard motor controllers. It does look like your board has potentiometers for setting the motor current (but of course within limits).

HOWEVER I just looked at the documentation for your Melzi board and it seems they do use 0.11 ohm resistors just like the Printrboard. I can't read the writing on your resistors well enough to be sure of their value. The controller chips are not identical, but similar (A4988 vs A4982).
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
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Re: Online Calculator for 3d printing

Postby New Passion » 2017-Jul-Tue-20-Jul

Thanks for the clarification Jay, my mistake, I did not know about the surface mount resistor code, so when I seen the 100 I assumed it was 100 ohms, but just like the link you posted states, "However beware of resistors marked with figures such as 100. This is not 100 ohms, but it follows the scheme exactly and it is 10 x 100 or 10 x 1 = 10 Ω.", but I didn't want to come here on the Printrbot forum to ask a question about a Melzi board, but thanks again for the education.

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