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[on:]

I'm making a DIY Timelapse Slider for Canon 500D DSLR, which weighs under 2 lbs.  It involves PVC pipes with felt between them to minimize friction.  I was planning to use a small diameter pulley with a string or fishing line to pull the camera: Like a pen attached to the stepper motor shaft.  It has 64:1 reduction.  I'd like it to travel 2m.  The friction torque is 1500 gf*cm. 

Will the 28BYJ-48 be strong enough to overcome friction and pull it slowly when it's level?

Any advice on how to make the pulley?  What problems will I need to overcome?

Why does the ULN2003 have 7 drivers?  When we only need 4?  8 would make more sense then it could drive 2 motors?

[Reply #1 on:]

I'll answer the obvious one

A ULN2003 is a 16pin device.  2 pins supply VCC and ground, that leaves 14 pins for the driver amplifiers.  Each requires 1 input and 1 output pin, ie 2 pins per amplifier.  14 / 2 = 7  QED.

As to sliding pipes, felt on felt will surely increase friction.  Better to use a dry spray-on lubricant such as a PTFE spray which will dry and leave behind a non-sticky slippy surface.  However 2 metres is a long pull and friction will be non-linear due to bending and increased surface contact as the tubes collapse into each other.   You might be better to look at making a small carriage on which is mounted the camera and this carriage then rolls along a runway.

[Reply #2 on:]

It is very low friction.  The felt is small and only glued to one side.  Like this:


My friend has built it.  I have "felt" how easy it is to pull.  But I do not yet have the stepper motor to try it.  That's why I'm asking.  Before I purchase any hardware.  What do you think?

[Reply #3 on:]

They seem to be the most popular on Ebay.  What is it strong enough to move?

[Reply #4 on:]

Does anyone have this motor?

[Reply #5 on:]

Hi sbright33
I have a couple of these motors, they spin very smoothe and i would think they are strong enough for your needs due to the gearing. I think I could make a test somehow to see how much they can pull.
But because of the gearing they are very slow, maybe too slow for your pulley
Btw the ULN2803 has 8 drivers instead of the 7 on a ULN2003

[Reply #6 on:]

I understand the gearing.  I did not expect it to be fast.  But maybe speed is the issue I should be concerned about after all.  Using a pen as a pulley, how long would it take at full speed without a load?  1m/minute?

[Reply #7 on:]

It is spinning about 10 RPM , at 7,4 Volt (2 cell LiPo)

[Reply #8 on:]

Which might be roughly about 3 sec / cm with a pen as a pulley?
Perfect for timelapse!