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Topic: Trimpod with step motor A4988  (Read 5731 times) previous topic - next topic

batata004

Aug 30, 2016, 11:08 pm Last Edit: Aug 30, 2016, 11:09 pm by batata004
Hi, I have NEMA 16 motor and I connected it to A4988 so I can control the motor to arduino. The problem is that there is a trimpod in the drive A4988  and many people say I should first set a precise current using the trimpod to avoid damaging the module.

I saw many tutorials online and they look too complicated and I dont even have a multimeter. So my idea is this: could you please tell me which wise (clockwise or anticlockwise) the trimpod reduce and increase current?

My idea is this: I will turn the trimpod in the clockwise/anticlockwise many times so I decrease the current to a minimmum. After that I will turn on the motor and see if it spins. If it does not, I will turn the trimpod and increase the current till it starts moving so I know I am not abusing the current.

But first I need to know: do I need to turn the trimpod clockwise or anticlockwise in order to make this module A4988  have the minnimum amount of current?

raschemmel

Seriously, if you are too cheap to buy a motor you should find another hobby. A DMM is the FIRST investment you should make when you get into this hobby. Mow the neighbor's lawn or sell lemonade or something, but buy a DMM (Digital MultiMeter).

batata004

It's not about money man... if anyone could tell me which wise to spin the trimpod it would be much easier than using a multimeter... hope someone can check that to me.

MarkT

trimpot, not trimpod.  trimmer-potentiometer.

Buy a small cheap multimeter now, then take time to choose a better one later if
you want.  You cannot do electronics with no eyes!  A meter is your eyes.  Well, a
'scope is really your eyes, but for DC and sinusoidal low frequencies a meter is usually enough.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

ChrisTenone

A trimpod is an iPod that works out.

A trim pot does not regulate current, but it can be used in a circuit to do so. It is a variable resistor. You can probably look at the construction of yours and determine which two leads are the ends of the resistor, and which one is the wiper.

There is no standard, so there is not a correct direction that applies to all potentiometers.
What, I need to say something else too?

MarkT

Technically a potentiometer is a 3 terminal device, a variable resistor is a two terminal device.
The wiper is the metal bit the adjustment tool engages in, its easy to stick a multimeter
probe on it, but not while its actually being adjusted, unless you can hold the probe to the
jewellers screwdriver while you adjust it (yes, usually these trimmers are too small for anything
else).

In a high voltage or RF circuit you use a special plastic tool for adjusting trimmers.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

raschemmel

That's all well and good but I've done that A4988 current calibration several times and you need to be able to measure the current through the motor winding WHILE measuring the voltage at the test point, neither of which you can do without a multimeter. I used the power supply current display on the P.S. LCD  while measuring the voltage with a meter.

Good luck calibrating that without a meter.

jremington

Quote
if anyone could tell me which wise to spin the trimpod it would be much easier than using a multimeter... hope someone can check that to me.
NO ONE can tell you how to set it.

Buy a multimeter. You will learn something by using it. Otherwise, choose another hobby.

batata004

I HAD AN IDEA! Just please tell me this: if I turn a trimpot 100x times to one side, will I have to run it 100x times to another side so it comes back to its original value? Or if I turn it after certain point, the trimpot will not care anymore about now many turns did I make? For example: after 3 turns, if I make 10 or 1000 turns, the trimpot will not change its value anymore, and if I turn it to the other side once, it will already change the current?

Cause I am thinking about turning the trimpot 20 times to one side and pray that this side is the 0 current side (if not, I will burn my drive so at least I know now the right side) so I can turn it slowly to the other side till the motor moves. Can I do that?

raschemmel

It's a single turn trimpot so that probably won't work. (at least mine was)

Based on your reply to jremington's post you probably should choose another hobby.

batata004

Hey guys I just found this link and the guy had the same idea as me: http://rigidtalk.com/wiki/index.php?title=Stepper_Driver_Adjustment

Quote:

Method 1 - Empirical Adjustment:
The stepper drivers can be adjusted without measuring voltages, by observing motor performance. Use a nonmetal screwdriver (plastic or ceramic) to avoid short circuits. Either run a print (preferably one that's been causing motor issues) or set up manual control using an LCD Controller, or Repetier Host, or Pronterface. CAREFULLY turn the pot fully CW (minimum current) then back CCW about 1/4 turn, or enough to make the motor run smoothly. From that point, if you are able to adjust while the motor is moving (either in a print or under manual control) turn the trimpot CW until the motor starts to stall or stutter, then turn CCW until steady performance resumes. Otherwise, alternate adjusting the pot slightly and then running the motor, with the same results in mind. The general idea is to find a low current setting that results in stalling or stuttering, and then boost the current a bit to get reliable motion without going too far CCW.



BUT I need to make sure CW or CCW decreases or increase current cause in this link the guy makes reference to another driver! Any guess?




Sincerally, I think this method is the BEST ALTERNATIVE. Better than using a multemeter as many of you said. Every motor has internal firction which differs from each other. So using a multmetter is not ideal cause you will not have equal motors. I think that increasing the current little by little till you find the sweet spot is the best way to do this. You dont need to rely in resistor values, VREF, information taken from datasheets... you can do this empiraclli.

Anyway, I would like if you could reply me if the trimpot accepts 100 spins of after a certain point it stops couting the spins.

raschemmel

#11
Aug 31, 2016, 04:07 am Last Edit: Aug 31, 2016, 04:39 am by raschemmel
The fact that you persist in ignoring the recommendation to buy a meter and then have the gall to tell us you think this method is BETTER  than actually MEASURING the current ( and voltage) confirms that your future in electronics will be fraught with problems. I can only say this does does not say anything good about your judgement . The fact that the A4988 will work right out of the box without doing the calibration is not the point. Whether or not you can adjust the pot to some point that allows the motor to work is also not the point. The point is that in your inexperience and twisted logic you actually think that doing the calibration blindly is better than measuring the parameters in question is what sends a red flag about your judgement. Had you simply stated, "I need to be able to use the motor immediately so I'm going to adjust the pot to some arbitrary value where the motors will work and then buy a meter at the first opportunity" there would be nothing wrong with that. It's your outright refusal to buy a meter and insistence on calibrating it without one and at the same time saying you think it's better not to use a meter that puts your judgement in question.  

MorganS

If you are in the USA then Harbor Freight is almost everywhere and they have a DMM that is good enough for $6. Sometimes it is on sale for $3 or less.

If you are somewhere else in the world then look for a discount tool store. You should only buy the cheapest multimeter that measures volts and ohms. It does not have to be digital although those are now much cheaper than analog. That is all that is necessary for this job and many other jobs in your future.
"The problem is in the code you didn't post."

raschemmel

If at all possible you you try to get a DMM with current mode.

ChrisTenone

I think the set screw is loose on the knob on your pot.
What, I need to say something else too?

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