Submitted by Webbot on June 10, 2008 - 11:18pm.

First of all let me preface all of this by saying that I
pretty much bought a motor at random (very cheap on eBay) so I’m not suggesting
that this is a suitable motor for **your** project.

So here is what I purchased (at around $11 for two)

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=351-4631#header

This page gives links to the following two datasheets:-

http://docs-europe.electrocomponents.com/webdocs/0030/0900766b800305e5.pdf

http://docs-europe.electrocomponents.com/webdocs/001b/0900766b8001b258.pdf

which are less than informative. My motors arrived with no
wiring/plugs etc so the colour charts were less than useful – at which I point
I wondered if I would ever make them work!!

However:- this is what I could learn from the datasheets:-

- moves
7.5 degrees per step (ie 48 steps
per revolution on the motor shaft)
- has
6 wires
- is
a
**uni-polar** motor
- has
a 50:1 gearbox (so 50x48 or 2400 steps per revolution on the output shaft)
- holding
torque = 100 Ncm
- working
torque = 100 Ncm
- typical
working torque = 65 Ncm
- Step
rate at typical working torque=300Hz
- requires
a 5V supply
- Resistance
= 9.1 ohms per phase
- 550
mA per phase

So long as you have two of the last three parameters then
you can calculate the other using the equation Volts = Amps x Ohms

There is one potentially important statistic missing from
these datasheets that can be calculated from the data given. If we can issue a
maximum of 300 steps per second, (300Hz), and – due to the gearbox – we need to
issue 2400 steps for a full revolution then the **fastest** we can turn the
output shaft is (2400/300) ie once
every 8 seconds. This may be rather
slow for an output shaft if it is connected to wheels but could be fine if we
are rotating the turret of a tank. So this is an important fact to ascertain
before purchasing your motor.

*So what have we learned?* The gearing, steps per revolution and the maximum frequency
produce trade-offs between torque and speed. Whether the motor is uni-polar or
bi-polar can also influence the required current draw, and torque, as discussed
earlier.