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Help

Help

(OP)
Hi,
I just dont know what type of Stepper Motor to buy (cheap used).  I am hoping to use a stepper motor and driver ( advise please on type cost ect ) to drive/tune a Vaccume Variable Capacitor...all I can tell you is the VVC is 2-100pf and 5KV .  The motor will rotate very slowly ( dont exactly know how slow ) to tune the ham radio bands on the attached copper magnetic loop, so I REALLY need to know what details the Stepper store will ask for, this I do not know, Im thinking torque, step angle? Voltage? Unipolar or Bipolar???.  Im not sure but Ive read some VVC for sale adds, most say 19turns...unsure if this is 9.5 either way or 19 one way and 19 back again? Fact is I have not ordered the VVC as yet.  The run from Radio control in shack to antenna is 50feet.

All is not lost...to assist I have attached a photo of my intention.

Advise what you can.

stepper001

http://files.engineering.com/getfile.aspx?folder=12e1ec54-b5cc-4b18-9ea7-fe45d8b0785a&file=Stepper.jpg

 

RE: Help

It looks like the exemplar assembly (that you intend to copy?) includes a ten-turn pot for position feedback, driven through a 2-ish:1 timing belt, and a 0.9 degree stepper.  There does not appear to be a 'zero' sensor in the system, so I'm guessing initialization would include banging the stepper against one end stop, N times, where N needs to be slightly more than the number of steps to go from one end of the range to the other.

19 turns X 360 degrees/turn / 0.9 degrees/step = 7600 steps.

Note that the band you cover is divided into that many discrete steps, and is not continuously tunable, no matter how slow you run the stepper.

You can run a stepper with a fairly simple power driver from four bits of a microcontroller, or four bits from the printer port of an obsolete laptop computer, but the programming is a nontrivial effort.  Adding half-stepping to that result, doubling the resolution, is a relative triviality, but it may still not be what you want.

I suggest you read up on steppers some more before deciding they will do what you want.


 

Mike Halloran
Pembroke Pines, FL, USA

RE: Help

Why not go with a fully analog solution using a geared dc motor. that would make the control fairly simple. Steppers are everywhere. Find an old printer in the trash and use the paper feed gearing that is attached.  speed isn't likely an issue with this application.  Rainbow has some cheap stepper motor driver kits.  

RE: Help

(OP)
Hi,
Very greatful for the advice thank you.  I am going to wait until I locate and purchase my VVC, then I may return, why well it I just learned VVC turning range various a lot.

Regards,

stepper001

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