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I have an Arduino which I am using to control this stepper motor using a breadboard with this layout. I have the Arduino connected to my Mac and it successfully runs, but the "force" of the motor seems to be extremely weak. I have tried running the motor with different speeds but if I hold on to the wheel when its running, it does not manage to run around until I let go of it.

L293D datasheet

breadboard layout

Have I missed something in the schematics or when connecting the motor, or is this kind of stepper motor just very weak when it comes to thrust? Should stepper motors that are 100% working give more thrust than just barely touching it with my hand, it does not manage to spin?

When I test the current using a multimeter from the 5V on the Arduino it shows around 640 on the multimeter screen.

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    \$\begingroup\$ Try connecting all the ground pins, 4, 5, 12 and 13. \$\endgroup\$ – Phil Frost Jan 26 '13 at 21:52
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    \$\begingroup\$ @Hakonbogen From your responses I get a feeling that you're a total beginner. FIrst about schematic: What you have provided us is a wireing diagram produced by program called Fritzing. Take a look at the article I linked. It shows the difference between the real schematic (on the right) and the "drawing" on the left. Engineers usually work with schematics and "drawings" are considered too hard to follow since they contain lots of unneeded information on one side and on the other side leave out a lot of information. \$\endgroup\$ – AndrejaKo Jan 26 '13 at 23:59
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    \$\begingroup\$ For example we don't need to know the colors of the motor's wires when constructing a circuit, but we need to know internal connections of the motor. The image you've provided us doesn't give us that information. Also schematic diagrams show real connections between pins of components so we don't need to take a look at the picture and decipher from the breadboard how everything is connected. So what you experienced with the Leon's comment is the friction that exists between the community of "real engineers" and the "makers" who tend to use Arduino, breadboards and Fritzing. \$\endgroup\$ – AndrejaKo Jan 27 '13 at 0:02
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    \$\begingroup\$ About the current measurement: If you connected the meter in current mode between the +5 V pin and GND pin, keep in mind that you MUST NEVER DO SO AGAIN! That's not a way to measure current and it usually results in combination of fried circuit, fried meter or fried meter operator depending on the source of current being measured. Proper way is to put the meter in series with the current. Take a look at the technical details of the motor and note how internally it's connected. \$\endgroup\$ – AndrejaKo Jan 27 '13 at 0:06
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    \$\begingroup\$ @AndrejaKo 4 long comments is pretty much an answer, write one. Then if you get more to write, do it. \$\endgroup\$ – Kortuk Jan 27 '13 at 6:09
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Looking at the product page, it's only a small motor with a holding torque of 150gfcm, or 2ozfin. If you compare that to this 12V 350mA stepper from the same site, which has a holding torque of 2kgfcm there is a considerable difference in power. So it sounds like it may be working fine, it's just not that powerful - 150gfcm should be quite easy to stop from turning.

Holding torque is basically how much weight, placed on a certain radius pulley/shaft is required to keep the motor from turning. Below shows a 100ozf*in motor:

Holding Torque

To test your motor, see if it can turn with up to 15g on a 10cm radius pulley (or a simple shaft with the 15g on the end) 15gf*10cm = 150gf*cm If you make the 15g able to slide along the shaft you can avoid having to change the weight.

Further reading

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