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1  Using Arduino / Motors, Mechanics, and Power / Re: About the rated current of stepper motors on: October 14, 2013, 06:57:52 pm
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To get high torque, use high voltages and a modern chopper motor driver, like the A4988 or DRV8825. Pololu's drivers are cheap, very well engineered and state of the art.
...

I am using a stepper drive board with A4988 on it already.  However, even with A4988, you still need to tell A4988 the current limit, which is normal the rated current.  I'm thinking of the current limit of A4988 when I said "current" in the original post.  (Sorry for being not careful enough.)
2  Using Arduino / Motors, Mechanics, and Power / About the rated current of stepper motors on: October 14, 2013, 03:59:11 pm
Hi All,

I knew it is a good idea to limit the current to the rated current of a stepper motor.  I also knew that if I provide too much current to a stepper motor, most energy will become heat instead of mechanical power.  However, I'm just wondering. What is the relationship between the rated current and the maximum torque of a stepper motor?  

Is the rated current corresponds to the maximum torque already?  Is it possible to squeeze more torque by over current a stepper motor (maybe with some heatsinks)?  Though over current a stepper motor is not a good idea in general, it can be handy if it can provide more torque quick and dirty.  Will this work?

Thanks for reading.

Gary
3  Using Arduino / Motors, Mechanics, and Power / Re: Can Aluminum Oxide be polished? on: September 21, 2013, 11:07:50 pm
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is the smooth surface Aluminium metal?
The surface of aluminum is always oxide, if you remove it, the oxide will reform in a matter of milliseconds.
This metal is very reactive, fortunately the thin layer of oxide inhibits the further oxidation, otherwise you would just end up with a heap of powder.

I suspect that you are just not getting the surface smooth enough for your mirror finish.

Then... will the smooth surface stay smooth?  One of my friends told me that Aluminium Oxide surface is rough, so the surface of Aluminium parts will have a rough surface overtime, even they start smooth.  

I'm really confused.  If Aluminium Oxide surface is a strong surface and it can resist oxidation, why would it become a rough surface overtime?  Is my friend simply wrong?  Or, is Aluminium Oxide will undergo some forms of corrosion other than oxidation?
4  Using Arduino / Motors, Mechanics, and Power / Can Aluminum Oxide be polished? on: September 21, 2013, 10:39:42 pm
First of all, sorry for asking questions a bit off the forum topic, and a bit silly.

It's a question around to me for quite a while.  I knew we can easily polished Aluminium parts to mirror shiny by removing the Aluminium Oxide on the surface. However, is it possible to just polish the Aluminium Oxide Surface to a smooth surface, instead of removing it?    What I'm doing is that I have a parts that requires a smooth surface and I want to make it with Aluminium.

I tried to polish some Aluminium bars with Autosol Metal Polish.  The polished surface did become smooth (not mirror, just smooth like axles), and it stays smooth for months now.  Here is the questions, is the smooth surface Aluminium metal? Or, is the smooth surface Aluminium Oxide?  Will the smooth surface stay smooth?

Thanks for reading.
5  Using Arduino / Motors, Mechanics, and Power / Re: Nema 17 and 4cm fan on: July 01, 2013, 02:15:53 am
I found OCD diminishes after 55. smiley-wink

You don't even know what I'm doing.  How do you know precision is important or not to my application?
If you are eager to make some comments, you can ask what I'm doing first.
If you are too busy for that, you can simply save your time all together.
Why are you doing something in between?
6  Using Arduino / Motors, Mechanics, and Power / Re: Nema 17 and 4cm fan on: June 30, 2013, 10:55:57 pm
Use a smaller diameter screw.

Arr.. off by 1mm.  It's way too big for me to do anything even in a dirty way.
7  Using Arduino / Motors, Mechanics, and Power / Re: Nema 17 and 4cm fan on: June 30, 2013, 10:37:33 pm
Are you saying... there is no fan on the market with its screw holes 31mm apart?
8  Using Arduino / Motors, Mechanics, and Power / Nema 17 and 4cm fan on: June 30, 2013, 07:15:00 pm
Hi All,

I have a stepper motor (with dimension identical to Nema 17 stepper motor), and I want to mount a 4cm fan on it.  However, when I tried to do that, I found that the screw holes of the stepper motor are 31mm apart, while that of the 4cm fan are 32mm apart.  I'm really deeply shocked by the situation.  

Is there any 4cm fan on the market with 31mm apart screw holes?  By the way, who is responsible to the decisions of stepper motor dimensions and fan dimensions?

(  smiley-sad  It is really really discouraging.  )

Yours faithfully,
Gary
9  Using Arduino / General Electronics / 12V power supply and 2.5V output on: June 30, 2013, 01:21:31 am
Hi All,

My power supply is 12V (30A), and I want to use it to power a small device which is supposed to operate at 2.5V 3A.
How should it be done?

Yours faithfully,
Gary
10  Using Arduino / Motors, Mechanics, and Power / Measuring the spec of stepper motors on: June 05, 2013, 11:25:29 pm
Hi All,

Is it possible for me to measure the spec of stepper motors without any prior information?

Here is the situation.  I brought a 3D printer a year ago, which has four cheap ordinary stepper motors.  The working temperature of the stepper motors is way too hot, at least 110 degrees C.  I suspect the reference voltage is way off from what it suppose to be.  When I check the stepper motors, there is no labels or any relevant information on it.  Then, I asked the vendor for the spec of the stepper motors.  ...

The vendor told me that the labels are deliberately removed, so that they can keep the spec of the stepper motors as a COMPANY SECRET, not a chance to tell me.  WTF!!! (sorry for being rude)  The vendor goes on and told me to do stupid things, e.g. adjusting reference voltage blindfolded, sending the machine back for maintenance at an EXCEPTIONALLY HIGH CHARGE, buying some new stepper motors from them...  They even told me that they are adjusting the reference voltage arbitrarily regardless the stepper motor spec.  Mmm... that's probably why the reference voltage is way off the chart.

Anyway, how to measure the spec of stepper motors without any prior information?  Can anyone help me out?

Thanks for your patience to read.

Yours faithfully,
Gary
11  Using Arduino / Motors, Mechanics, and Power / Re: Pushing axles into bearings on: May 26, 2013, 05:14:54 pm
In a bore of only 3 mm the thickness of the caliper blades will necessarily cause a significant underestimate.  ...

I think its the bearing quality problem.  I brought some more ball bearing afterwards, and this time, from a proper vendor (NSK to be precise).  The inner diameter is measured to be 0.03mm smaller than 3mm (the measurement is not extremely accurate, but it should still show a rough picture).  

I will only buy bearings from proper vendors from now on, crap no more.

Thanks for your help.   smiley
12  Using Arduino / Motors, Mechanics, and Power / Re: Hi, Newbie question on motors ! on: May 25, 2013, 03:24:08 pm
If the cost is a major concern, DC motors is your choose.  A stepper motor is not only more expensive on its own, but also the controller to control it.  A DC motor with switches can works just fine, e.g. .
13  Using Arduino / Motors, Mechanics, and Power / Re: Pushing axles into bearings on: May 25, 2013, 02:45:34 pm
How did you manage to measure the bore of the bearing.  Even with the proper tools, measuring small internal diameters is difficult to do accurately.  ...

I tried to measure the inner diameter at different angle with the caliper inside as many times as I can, and took the maximum reading as the inner diameter.  Though its not extremely accurate, I guess it is still useful to report.
14  Using Arduino / Motors, Mechanics, and Power / Pushing axles into bearings on: May 25, 2013, 01:44:13 pm
Hi,

I brought some 3mm diameter axles along with some ball bearings (said to be 3mm inner diameter).  When I try to push the bearing into the axle, I found that they are impossible to fit.  I tried to hammer it in, and broke some of them already.

Afterwards, I measure the dimensions with a caliper, the axle diameter is 3.00mm (damn, it's good smiley-lol) but the bearing inner diameter is only 2.80mm.  

Why's that?  Is the inner diameter of ball bearings deliberately designed to be undersized?  Or, am I just simply brought the wrong parts?  Is there a way to push a 3mm axle into a 2.8mm ID bearing without breaking it?

Thanks.

Gary
15  Using Arduino / General Electronics / Re: Bigger power supply on: May 25, 2013, 01:20:32 pm
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You should hear what this guy has to say about Volts/Amps killing you.

https://www.youtube.com/watch?v=8xONZcBJh5A


In the video at 6:00, the author actually connects himself to a car battery at 30V to measure the current flow through his body.  I guess I should be safe with 12V, provided that my hands are dry and I didn't wear anything metal.  Am I correct?  ( I swear I won't try it on purpose.  I just want to know where the bottom line is. )
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