Model Boat Mayhem

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: toot toot on October 18, 2008, 06:32:19 am

Title: 3 volt supply
Post by: toot toot on October 18, 2008, 06:32:19 am
OK, here we go. After using my bow thruster speed controller to also work my anchor winch, thanks catengineman :-)), my next little job is to make my c/r servo/radar work. currently, i have it wired to operate with a computer fan which cools the electronize speed controller, however ,now its time to do it properly, and was either thinking of dropping 1 of the 12v supply down to about 3v, for the radar. any ideas how to do this effectively .another option was ,as i have 2 speed controllers, and it sounds like you only need 1 bec supply, i wonder if i can use the 5 volt red wire i have now pulled out of the plug, as its only going to run the servo anyway, but i would still like to slow it down a bit , to 3 v as well. the way it is in my boat, i have the fan and radar switched thru 12v still, which means i would have to use a relay ::) again to switch on this 5 volt circuit via the 12v supply.  >>:-(more wires. I'm sure someone here will see a solution to my spaghetti junction i have going on below decks. will try and post a pic when i can work that out too :embarrassed:

Title: Re: 3 volt supply
Post by: Roger in France on October 18, 2008, 06:53:44 am

Rather than fiddle with lower voltage can you not just gear down your radar? That is the way most of them work.

Or am I misunderstanding you?

Roger in France
Title: Re: 3 volt supply
Post by: Rex Hunt on October 18, 2008, 07:23:59 am
Not sure how to answer this......   :embarrassed:  I don't have all the details

Maplins do a variable voltage regulator.................maybe one of the 'boffins' could enlighten us all on here as to how to use it?


Title: Re: 3 volt supply
Post by: philk on October 18, 2008, 10:17:19 am
have a look at the listing on voltage regs. you can get easily a 3.3v regulator
Title: Re: 3 volt supply
Post by: Proteus on October 18, 2008, 10:21:30 am
even simpler just use two AA cells you will prob get a season out of it the draw most small motors use that people put on radars.

Title: Re: 3 volt supply
Post by: Sandy Calder on October 18, 2008, 10:39:58 am
Forget changing the volts to the continuous rotation servo.
Servos compensate for voltage variation to a point!!!

You just need a standard servo signal like from out a receiver.
If you don't have a spare channel you run it off 4.8 or 5 volts but and you will find a vero circuit with two 555s or a 556 timer chip all over t'internet.
It also appears on a zn409 or 555 pdf data sheet.- Go look.

Something is wrong if you need to fan cool an electrosneeze speed control.

Sandy Calder
Title: Re: 3 volt supply
Post by: Sandy Calder on October 18, 2008, 12:26:32 pm
page six of (http://ttp:// shows how to simulate a receiver channel to vary the speed of the continuous rotating servo if you have not removed the drive circuit.

The white servo cable goes to right hand 555 via a resistor.
You can replace all but one of the preset resistors with a fixed one to produce a 1 to 2 ms pulse every 20 msecond.
If you use that circuit put a 1k resistor between C3 and the left hand 555 and change R3(2k7) to a 10k. Omit VR3 and VR4 and take R4 to 555( Right) pin3 directly.Make C1 100uF.

Sandy Calder
Title: Re: 3 volt supply
Post by: toot toot on October 18, 2008, 03:59:16 pm
i suppose its easier for me to explain ,but i know what i have here, maybe a bit lost in translation %%.with the fan business ,when i first ran the two motors for a bit, it would cut out and i would have to sit and wait for 5 Min's, before it would work again. now with the heat sink and fan, it works a the way ,its running two heater fan motors.

as far as the radar, its the top case with the gears and a billet bottom housing shaped like the radar base, which just houses the servo motor, no guts in this one,its all pretty compact and mounts on the mast with just two wires through the centre, as its an aluminium tube mast. so varying the volts will slow it down. :-)) the other servo i modded,which has its internals intact could be slowed down of course ,thru the pot,but was too big to hang of the mast and look OK.

the 2x AA cells Ive tried before on a tamiya gearbox, but didn't last that long, and was easier to just charge up 2 12v 7ah bats at one time.

am no green steam whiz so will need to read up more on those mods sandy, thanks for the links and input.
but keep the ideas comming, nothing like converting a mole hill into a mountain :}

cheers Chris.
Title: Re: 3 volt supply
Post by: Sandy Calder on October 18, 2008, 04:18:35 pm
I know it's going off track but which model of esc do you have?
A fan motor shouldn't be drawing more than a few amps?
The 10 amp one is "crppleware" as it uses an obselete transistor.You could solder in a newer transistor and dispense with the heatsink.
You might create a lot of heat if the BEC input is 12 volt,though. 

On the radar,I still cant visualise what you have but I would start again and bench test the c/r servo on 5volt bec with a rotary channel.
You get servos on ebay for loose change and mini servos for a fiver.

Sandy Calder
Title: Re: 3 volt supply
Post by: toot toot on October 18, 2008, 04:37:09 pm
i think I'm going to need a photo to explain. what i do have is one channel driving a servo with a "tower" spool, with 6 micro switches , 3 on one side and 3 on the a certain point in rotation or trim lever position, does
1  switch on fan and radar, the radar on the same one is because sometimes i would forget to "detrim" the channel and when i switch off , the fan would still be active, so now  the radar is more of a "switch off the trim you dummy" reminder
2  switch on smoke generater
3  operate horn
4  switch between bow thruster and anchor winch
5  turn on fire pump
6  spare at the moment.
these mostly are ON or off, but 1and  2 i can have on simultaneously and then also hit the horn for a blast,and in normal position,will have the bow thruster active

as far as the s/c model, ill have to check,but its an earlier one with the relay out the top, i think might be a 43hvr or something like that.i just have the 12v input and the bec does the rest

cheers Chris.
Title: Re: 3 volt supply
Post by: Sandy Calder on October 18, 2008, 04:52:04 pm
You need a  Pheonix F9 1/2 radio (
That and the decoder would cut out about 1/2 a mile of wire.

Bec at 12 volt can cause a lot of heat too.
Is it running anything other than speed control and rudder?
Title: Re: 3 volt supply
Post by: toot toot on October 18, 2008, 04:57:08 pm
its running speed control,rudder,spool servo,motor reverse servo,which are just 2 servos with next to no load, and now bow thruster s/c as ive taken its red wire out of use..
Title: Re: 3 volt supply
Post by: Sandy Calder on October 18, 2008, 05:15:50 pm
It takes a while to decode all these s/c and c/r references.
This decoder goes in the boat and replaces a lot of that sh#te you mention.
( (
I think they used to use your arrangement 50 years ago.I'm not that old enough to know.
R/c (oops) has come a long way since then.
Title: Re: 3 volt supply
Post by: toot toot on October 19, 2008, 01:07:20 pm
 {-) {-) {-) it may be 50 year old technology, but it works :-)). i dint need any transmitter modules with two way switches,knobs, receiver decoders that you still need to wire something into to make it happen ,and not to mention two pocketfulls of cash and a weekend of reading install manuals.been there done 7 channel computer radio keeps the typing fingers active enough. my friend now has a f 14 Navy setup, with all the switches and buttons , with a notebook in his pocket to remind him of what does what. i only have 1 transmitter stick to push up and down and trim lever to do all that,but in saying, the twin stick is handy for when we go sailing our yachts instead as Genoa trim is more user friendly.but i will take you points of info in thanks sandy, after all thats what the forum is all about. :-))looks like now i need to replace 2kg of ballast with some battery capacity some how.

cheers Chris.
Title: Re: 3 volt supply
Post by: Sandy Calder on October 19, 2008, 06:42:25 pm
two pocketfulls of cash
(or pockets full) ?
No. two pounds O0
F 9 1/2 a 2-ch system with ch3 6 way homebrew multiswitch and ch4  lever pot from S.L.M. model engineering.
About a tenth of the cost of its Futaba cousin.
Can be done to many old Futaba and Hitec sets or a pound or two.....
( ( (
Address all enquiries to "cheapskates anonymous"
Title: Re: 3 volt supply
Post by: toot toot on October 20, 2008, 01:14:56 pm
hey thats cool sandy, looks a bit like the inside of my boat {-) {-)but seriously, if you can do a lot yourself ,your miles in front.good job :-))
Title: Re: 3 volt supply
Post by: malcolmfrary on October 20, 2008, 02:40:05 pm
If I just wanted to slow down a small, lightly loaded motor I would just use an appropriate wattage resistor.  If the motor measures about 8 ohms, and you want to present it with 3 volts from a 12 volt supply, then a 22 ohm resistor will be near enough.  A 5 watt ceramic type will be adequate, cost = several pence.  An alternative to a resistor could be nav/deck lights in series or parallel.
Title: Re: 3 volt supply
Post by: Sandy Calder on October 20, 2008, 05:58:38 pm
Yes,that works for me,Malcolm.
In future I'll wait before diving in just in case servo implies the broader definition.

I have memories of serious naval modellers putting their models into comp and wanting the correct rotation and rpm.
I must have made about a dozen or so of a circuit similar to below.They didn't have to fiddle with a pot any longer.
Increase the VR1 pot value to extend the range beyond 2.5 volts.
The supply has to be 1.5 volts above the output level.
The VR1 should be a miniature type as it only needs set once as supply drop does not change rotation speed.
Sandy Calder