Andy:
thanks for the response!

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Andrew Errington
> Sent: Monday, July 08, 2002 11:48 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: stepper motor in TemUR microrobot
>
>
> Problem number 1: Jerky
>
> You have your sprockets the wrong way round. It looks like your driving
> gear is 1.5" diameter, which means that each step drives the chain
> about 0.3".  The small ones look about 0.5", so if your motor uses them
> then each step is smaller (maybe 0.1").  Also, you should research the
> techniques of half-stepping, which should allow you to achieve 32
> 'steps' per revolution.  There is another technique called
> microstepping, but it is more difficult to implement.

Yes, originally the driving gear was ca. 1". The purpose of this approach
was to cover (hide) the motor.  Very early I realized, that this is not
clever since I have low-precision motor. I've changed the sprocket. It
helped but not too much. See:
http://teamur.netfirms.com/tmr002/movement_problem.htm

Half stepping is something I would like to try... I am afraid that
microstepping requires way more complicated circuit.


> Problem number 2: Power consumption
>
> Unfortunately, the coils in the stepper motor are just lengths of wire,
> with a fairly low resistance, so the current is high.  If you keep the
> current turned on you can hold the stepper motor in a fixed position,
> however, if your motor will not be subject to external forces (and the
> robot is pretty small and light weight) then you could maybe try pulsing
> the coils to make the motion, and then leaving them off when you know
> the motor has reached the next step position.  I have not tried this, it
> is only an idea.

Another yes. This was my initial idea, to put 754410' enable low after
pulsing for enough long to make a step. This way for the most of time the
motors are not powered. So far to make the robot moving I disabled H-bridge
enable pin pulsing.

> Problem n:
>
> Other small stepper motors can be found in floppy disk drives.

I tried to use stepper motors from floppies but the current constructions
require addtional support (ball bearing) at the end of the shaft. See:
http://teamur.netfirms.com/test/test_floppy_disk_drive.htm

> Vibrating pager motors are small (but they are not stepper motors)
> Increasing torque can be done with a gearbox or series of rubber bands
> and pulleys.

Yeah... I was hoping that the stepper motors can give me hardware simplicity
combined with relative precise control. There must be somewhere a mistake...
I am not going give up yet!

> Oh, did I say, neat robots!

Thanks once again!
Irek

>
> Andy
>
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