Moderators: Dave Moll, Andrew Davie, Steve Anderson
aussie_bloke wrote:G'day all.
I have made further progress with the NBTV camera since the last post, mainly with the motor side of things. Have got the motor now rigged up to drive the VCR head disc spindle, have put a sewing machine rotary switch as a pulley on the spindle and a pulley slightly bigger on the motor. I have fired it up and it is working but I have ran into a big problem.
The problem is the motor seems to need to draw more current to drive the spindle than it does when running on its own and on initial tests this caused the 3 ohm 20W resistor to smoke after 30 seconds!!! Then I rigged up my high current speed control circuit and within seconds the TIP31 transistor smoked up and went BOOM!!!
I also notice too that the motor struggles to rotate the spindle at the start but gradually as the spindle increases in momentum it will spin more freely which I guess the motor will run off lesser power.
So to solve this problem should I simply incorporate a super heavy duty BTJ transistor across the 317 chip instead of the heavy duty TIP31 or should I put a much bigger gear on the spindle? And is there other things I need to solve to get around this issue?
Any advice would be much appreciated.
Steve Anderson wrote:In my best Mythbusters voice..."There's your problem..." No reduction drive, both pulleys are are of (as good as dammit) equal sizes...you will need a reduction drive....
As I said before, these motors are designed to run at several thousand RPM, 750RPM is effectively a stall (locked shaft) to them. It's a bit like trying to move your manual car off from stationary in 4th gear.
Steve A.
I only just noticed the recent (changed motor) photos, sometimes photos can take ages to download by which time I've read the text and moved on...
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