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Author Topic: How to electrically slow a motor to power a 1:72 radar?  (Read 4001 times)

justboatonic

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How to electrically slow a motor to power a 1:72 radar?
« on: May 28, 2012, 08:32:40 PM »

Im considering fitting a miniature motor on a 1:72 scale Type 42 to power a bridge roof radar. I reckon the bridge radar probably rotates at about one and a half revolutions per second.

The motor Im considering is this one https://catalog.precisionmicrodrives.com/order-parts/product/103-100-3mm-dc-motor-8-1mm-type

Tech specs say the minimum rated speed is 22000rpm! Does this mean on 3 volts the shaft will turn 22,000 rpm!? Seems a bit fast that even at 3 volts!

Even if I use a 1.5 volt supply, that's still going to be 11,000 rpm isnt it? Or am I reading the specs wrong?

Is there any way I can get this motor down to about 90 rpm? I cant gear it down as I need to fit it direct to the bridge roof (which is already built) and there's no way to hide away the gears.

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john s 2

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #1 on: May 28, 2012, 09:12:48 PM »

You couid do worse than to buy one of Actions radar motors . Dave even supplies resistors for diffrent voltage supplies. John.
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justboatonic

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #2 on: May 28, 2012, 09:46:41 PM »

You couid do worse than to buy one of Actions radar motors . Dave even supplies resistors for diffrent voltage supplies. John.

Alas they are too big hence the small motor in the URL.
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malcolmfrary

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #3 on: May 28, 2012, 09:56:44 PM »

I don't think that there is such a thing as a motor that small that is capable of revving slowly and smoothly without using a gearbox of some kind.  
A high frequency pulse generator giving very thin pulses on a 5 volt supply might cause it to step round slowly and regularly enough.  The higher voltage is suggested to ensure reliable starting torque, the very thin on to off ratio to ensure that it doesn't get to drive far on any one pulse, and the high frequency to fool the eye.  Hopefully it won't wonk* back to its start point between pulses.  If it was easy, everybody would have one.
The torque from it is so low that it needs a given voltage to start turning - once it starts, the voltage (and resulting current), if it is unloaded, will cause the unlikely high RPM figure.
*tech talk
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john s 2

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #4 on: May 28, 2012, 10:26:02 PM »

Got that wrong . Sorry. Could a mini servo suitably modded be used? John.
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DickyD

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BrianB6

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #6 on: May 29, 2012, 12:05:41 AM »

I have used the Robbe 1:500 and 1:1000 geared motors for many years.
Available from Cornwall Model Boats http://www.cornwallmodelboats.co.uk/acatalog/motors_accessory.html
Fairly expensive but they work!
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pugwash

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #7 on: May 29, 2012, 04:43:00 AM »

I don't know what type of motor you will need ( I usually use a jotika geared motor for mine) but perhaps you should check
the r.p.m. - it is no where near 90 more like 30 for the type 1006 or 1007 navigation radar (easy to find out - on you tube there
are some good bits of film of the type 42s or 45s and with a stop watch you get a very accurate r.p.m.)

Geoff
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tassie48

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #8 on: May 29, 2012, 07:42:56 AM »

I strip a servo down remove the hard drive wired board just the red and black wires solder these to the motor can then remove the servos stops under the top of the servo then grease lightly the gears and put back together and screw together then use a 1.5 AA battery and watch the radar 1.5 volts on a old std servo gives 18 rpm correct speed for a large bar type radar then get the correct rotation for the radar to swing and then fit the shaft i use a spring or a coupling and hard wire the radar into the on off switch if the radar is swining the power is on with my models have done this to 6.5gram micro servos for radars as well cheap and works for me tassie48
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roycv

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #9 on: May 29, 2012, 08:14:59 AM »

Hi, I bought some 8 gram servos, really small, with the object of stripping down and driving a radar aerial.
regards Roy
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John W E

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #10 on: May 29, 2012, 09:07:04 AM »

Hi this may help you it was the method I used for the 1/96 scale HMS Manchester

Aye

John
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nick_75au

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #11 on: May 29, 2012, 09:26:03 AM »

Furuno Nav radars rotate at 24 RPM for seagoing, and 48 RPM for "river radar' used for faster boats in confined water.

How bout this

http://www.ebay.com.au/itm/Rectangle-Shape-Gear-Box-Micro-DC-Geared-Motor-30RPM-0-35A-6V-/180876036001?pt=AU_B_I_Electrical_Test_Equipment&hash=item2a1d0d47a1#ht_2064wt_1139

I have an identical motor sitting on my desk

I don't think you will pick the extra 6 RPM, or reduce to 5 volts

Nick
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Norseman

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #12 on: May 29, 2012, 11:26:58 AM »

Hi
Picking up on Nick's suggestion here it is on UK's flea bay
http://www.ebay.co.uk/itm/30RPM-0-35A-6V-3mm-Shaft-Dia-Mini-DC-Geared-Gear-Box-Motor-/310404307874?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item484589dba2

Here's a daft question - just out of interest has it ever been done with sort of a clockwork set up?
Here's another random thought - some movements on vessels could be water driven (tiny paddle behind a scoop)
I'll go now because Hamster power has just occurred to me - time for my tablets %%

Dave
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Netleyned

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #13 on: May 29, 2012, 05:26:36 PM »

In my time in the Andrew most nav radars ran at around 24 rpm.
The latest hi def run at 48 rpm.
24 looks right.

Ned
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Umi_Ryuzuki

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #14 on: May 29, 2012, 05:28:54 PM »

Gear motors down to 6mm diameter...

http://www.gizmoszone.com/shopping/agora.cgi?

Resistors can be used to drop voltage electrically, but most motors have a
limit to whether they will function at all below a certain voltage.
Also, a typical 1/4 watt resistor can overheat and burn out when used
to reduce voltage to a radar motor... I know this...  %)
So be sure to properly size the resistor if you are trying drop voltage in this manner.
A simple voltage regulator can be purchased, or built using transistors.

http://www.dimensionengineering.com/
http://www.queensown.org/technical-data-sheets-5.html

 :-)

john44

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #15 on: May 29, 2012, 09:24:12 PM »

Got that wrong . Sorry. Could a mini servo suitably modded be used? John.

Mini/Micro servo,s have to be modified to be used as radar motors,e.g the pot has to be removed and the wires
soldered directly to the motor terminals. They are also quite noisy even on 1.5v
Model motors direct used to do a very small motor gearbox assy.

john
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andywright

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Re: How to electrically slow a motor to power a 1:72 radar?
« Reply #16 on: June 09, 2012, 09:26:50 PM »

I bought an Action set up, and placed it low down in the accomodation in my Tug, then ran a stainless shaft through the wheelhouse roof, it was at the top of the stairs so looked like a pillar or grab rail.
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