I agree with a few others that if you want to get rid of the noise you ought to consider linear stepper drivers. The difference is that instead of generating the current on the coil for a particular position by chopping, it is done using a linear regulator or amplifier. The disadvantage to linear is that a lot of energy must be dropped across the regulator/amplifier/driving elements. The disadvantage to chopping is that a lot of energy is wasted in the motor as heat and vibration. But not nearly as much as would be lost in an analog system. Since power is not a concern, and vibration is, I'd go with linear drive methods. The driver can be located on heatsinks well away from the experiment if heat is really a bad concern, but it's nowhere near the heat output of a normal computer (for small motors) so it's not really an issue in most cases. Since you've got a laser trained on a piece of reflective material already, you might be able to exploit that to 'auto' drive the stepping table - not unlike a line following robot. Camera output could also be analyzed and used to move the table. -Adam On 1/10/06, Peter Todd wrote: > On Mon, Jan 09, 2006 at 01:00:18PM -0000, Alan B. Pearce wrote: > > >To give you an idea of the stuff they do... The whole > > >setup is on a air-isolated table, they told me that heavy > > >footsteps are sometimes enough to throw their experiments > > >off unless they isolate everything from vibration. Many > > >insects "hear" through their feet. > > > > when I saw your first post I thought "they are moving the wrong thing". Now > > I am convinced. > > > > The table should be kept stable, and the camera equipment should be moved to > > follow the spider, rather like an X-Y plotter which moves the pen in two > > axis. > > They considered that too, but you see, the problem with that is the > camera equipment is heavy and bulky. There are also two cameras and one > laser inferometer, acting as a microphone. All of these are from > different angles and distances. Building a setup to move these four > elements would be very expensive and very large, I think far more than > making even a very smooth table movement. > > -- > pete@petertodd.ca http://www.petertodd.ca > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist