To continue the saga......

I fitted a variable capacitor to my 10 foot circumference 1mtr loop and am
able to tune 80 to almost 15 meters...works well..but.........

How to fit a motor drive !!!.....there seems to be nowhere to acquire cogs,
pulleys or gear sets....no model shops around that carries components, that
i`ve googled for anyway..(now when i were a lad! ).... ;-)

Can you imagine how fast that electric motor turns the capacitor, even with
reduced voltage???..you have to be quick i can tell you or you miss the
sweet spot heh,heh....

Seriously, any ideas to slow the tuning rate will be most welcome .

Thanks.

Lee......G6ZSG.....

On Sat, 08 Oct 2005 06:26:31 GMT, "Lee"
wrote:
Seriously, any ideas to slow the tuning rate will be most welcome .

Hi Lee,

Use the old stand-by of the screwdriver antennas, a screwdriver motor.

However, I expect you want two speed - then try a variable speed
battery powered drill.

For fine resolution and high speed both, look into the world of
Stepper motors. You can even design for calibrated settings instead
of hunting - or rough position indicators.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sat, 08 Oct 2005 06:26:31 GMT, "Lee"
wrote:
Seriously, any ideas to slow the tuning rate will be most welcome .

Hi Lee,

Use the old stand-by of the screwdriver antennas, a screwdriver motor.

Tried that, it has far to much torque even on low volts .... damaged the
gearing on my spare cap :-/

However, I expect you want two speed - then try a variable speed
battery powered drill.

Good idea, worth looking into!!

For fine resolution and high speed both, look into the world of
Stepper motors. You can even design for calibrated settings instead
of hunting - or rough position indicators.

I`ll do a google for steppermotors .... thanks.

Lee.....G6ZSG....


73's
Richard Clark, KB7QHC

On Sat, 08 Oct 2005 08:05:35 GMT, "Lee"
wrote:

Use the old stand-by of the screwdriver antennas, a screwdriver motor.

Tried that, it has far to much torque even on low volts .... damaged the
gearing on my spare cap :-/

Hi Lee,

One way to control that, at least speed-wise, is to turn the DC
voltage into pulse-width modulated voltage. You are always applying
the same voltage, but you turn it on for a short-to-long time, and off
for a long-to-short time over any interval. You change the speed by
changing these times. This is more properly called Dwell Time.

This offers the prospects of maintaining a constant torque over a
considerable range of speed. I'm not certain by what you mean about
"too much torque," unless you have too much resistance for the gears
to drive.... Stepper motors are also noted for high torque - it goes
with the turf.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sat, 08 Oct 2005 08:05:35 GMT, "Lee"
wrote:

Use the old stand-by of the screwdriver antennas, a screwdriver motor.

Tried that, it has far to much torque even on low volts .... damaged the
gearing on my spare cap :-/

Hi Lee,

One way to control that, at least speed-wise, is to turn the DC
voltage into pulse-width modulated voltage. You are always applying
the same voltage, but you turn it on for a short-to-long time, and off
for a long-to-short time over any interval. You change the speed by
changing these times. This is more properly called Dwell Time.

Yes, i`ve been looking into that and it seems the best way to go, a local
supplier has a panel mount version in stock £15.00 ($16.00??)......so!!.

This offers the prospects of maintaining a constant torque over a
considerable range of speed. I'm not certain by what you mean about
"too much torque," unless you have too much resistance for the gears
to drive....

Not enough resistance, the capacitor comes to the end of its travel but the
torque wants to continue..... hence the damage to my spare capacitor!!!.

Regards.

Lee...G6ZSG......

73's
Richard Clark, KB7QHC

"Lee" wrote in message
...

"Richard Clark" wrote in message
...
On Sat, 08 Oct 2005 08:05:35 GMT, "Lee"
wrote:

Use the old stand-by of the screwdriver antennas, a screwdriver
motor.

Tried that, it has far to much torque even on low volts .... damaged
the
gearing on my spare cap :-/

Hi Lee,

One way to control that, at least speed-wise, is to turn the DC
voltage into pulse-width modulated voltage. You are always applying
the same voltage, but you turn it on for a short-to-long time, and off
for a long-to-short time over any interval. You change the speed by
changing these times. This is more properly called Dwell Time.

Yes, i`ve been looking into that and it seems the best way to go, a local
supplier has a panel mount version in stock £15.00 ($16.00??)......so!!.

Typo ($26.00??)......


This offers the prospects of maintaining a constant torque over a
considerable range of speed. I'm not certain by what you mean about
"too much torque," unless you have too much resistance for the gears
to drive....

Not enough resistance, the capacitor comes to the end of its travel but
the
torque wants to continue..... hence the damage to my spare capacitor!!!.

Regards.

Lee...G6ZSG......

73's
Richard Clark, KB7QHC

On Sat, 08 Oct 2005 12:50:30 GMT, "Lee"
wrote:
torque wants to continue..... hence the damage to my spare capacitor!!!.

Hi Lee,

Then the proper design incorporates a travel limit switch.

73's
Richard Clark, KB7QHC

Hi Lee

Two thoughts

Re stepper motors. You can often find them in old junked scanners. A
nice cheap source. If you are feeling really cheap the interface can
intially be a simple TTL counter cct and some pass transistors. I once
used one off my PC parallel port for an EzAl antenna system.

Also look at the possibility of using a piston capacitor and driving
that with a threaded bar connected to your motor. This may still be a
little fast though. You might also get away with a long lever and
threaded bar arrangement if turning a standard rotary capacitor. Kind of
limits you to something less than 180 degrees tho.

A car windscreen wiper motor is another possibility also through a
threaded bar. (Overkill on the torque tho)

Cheers Bob Vk2YQA

Lee wrote:
"Richard Clark" wrote in message
...

On Sat, 08 Oct 2005 06:26:31 GMT, "Lee"
wrote:

Seriously, any ideas to slow the tuning rate will be most welcome .

For a stepper motor check
http://www.herbach.com/Merchant2/mer..._Cod e=H2-553
and for the controller check
http://www.alliedelec.com/Search/Pro...p?SKU=316-0061

"Bob Bob" wrote in message
...
Hi Lee

Two thoughts

Re stepper motors. You can often find them in old junked scanners. A nice
cheap source. If you are feeling really cheap the interface can intially
be a simple TTL counter cct and some pass transistors. I once used one off
my PC parallel port for an EzAl antenna system.

Also look at the possibility of using a piston capacitor and driving that
with a threaded bar connected to your motor. This may still be a little
fast though. You might also get away with a long lever and threaded bar
arrangement if turning a standard rotary capacitor. Kind of limits you to
something less than 180 degrees tho.

A car windscreen wiper motor is another possibility also through a
threaded bar. (Overkill on the torque tho)

Cheers Bob Vk2YQA

Lee wrote:
"Richard Clark" wrote in message
...

On Sat, 08 Oct 2005 06:26:31 GMT, "Lee"
wrote:

Seriously, any ideas to slow the tuning rate will be most welcome .

Lee wrote:
To continue the saga......

I fitted a variable capacitor to my 10 foot circumference 1mtr loop and am
able to tune 80 to almost 15 meters...works well..but.........

How to fit a motor drive !!!.....there seems to be nowhere to acquire cogs,
pulleys or gear sets....no model shops around that carries components, that
i`ve googled for anyway..(now when i were a lad! ).... ;-)

Can you imagine how fast that electric motor turns the capacitor, even with
reduced voltage???..you have to be quick i can tell you or you miss the
sweet spot heh,heh....

Seriously, any ideas to slow the tuning rate will be most welcome .

Lots of model-making and robotics suppliers in the UK have small
plastic gearboxes, plastic shafts, couplers etc. Try some of the links
from my "Components and Suppliers" page.

As a short-cut, try to find a small battery-powered barbecue spit motor
at one of the home and leisure stores (probably in the end-of-season
bargain bin). They are still a bit fast, but will run at reduced voltage
or with pulse-width control to slow them down.


--
73 from Ian G/GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek