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Author Topic: using servos to power small models  (Read 6780 times)

John Goatcher

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using servos to power small models
« on: April 28, 2006, 03:11:45 PM »

I have heard mention of using servos stripped down to power small models and would be very iterested in any info on how to do this.
Thanks John
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Martin [Admin]

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Re: using servos to power small models
« Reply #1 on: April 28, 2006, 05:45:03 PM »

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malcolmfrary

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Re: using servos to power small models
« Reply #2 on: April 29, 2006, 10:31:44 PM »

A good link above - the only problem is getting hold of appropriate size rubber tubing these days, and then persuading it to stay put on the motor shaft.  I prefer to use the flint spring from a disposable lighter.  Even if you dont get any use out of the lighter, they are generally available at five or more for ?1 on market stalls.  At that kind of price, they are an excellent parts mine.
The springs are usually tapered, so will fit a spread of shaft diameter.

On occasion I have replaced theservo motor with a CD platter motor - electrically very compatible, free if got from a dead CD player, and having a reasonable length shaft.  I couple these with a cotton bud tube, held with a grub screw collar from the local model shop.

It is possible to modify the electronic omponents on the board to get a deadband, but lacking the required eyesight and steady hands, I have stopped worrying about never coming to a total stop.  As I cant remember when I last sailed in dead calm weather, the difference really doesn't matter.  The advantage is that the transmitter trim tab alonside the speed control makes a good engine room telegraph/cruise control.
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OMK

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Re: using servos to power small models
« Reply #3 on: April 29, 2006, 11:19:53 PM »

Nice idea about using the disposible lighter spring, malcolmfrary.
In case J.Gotcher might be interested, here's a page which shows how to convert a servo for ESC use........

http://www.seattlerobotics.org/encoder/200009/S3003C.html
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thomas

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Re: using servos to power small models
« Reply #4 on: May 08, 2006, 11:33:12 PM »

I have quite a fleet of 'plastic magic' models, and find the easiest way to connect the motors to the shaft is with a length of insulation from old electric cable.  Select electric cable of suitable size, and strip off a couple of inches of the insulation.  I prefer to use earth cable as the yellow and green strips makes it easy to see which way the shaft is turning. A meter of cable costs a few pence, and will provide couplings for a lifetime of small models!
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Shipmate60

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Re: using servos to power small models
« Reply #5 on: May 12, 2006, 10:12:22 AM »

I use the connectors from the top of jewelery boxes.
The one where it lets the ballerina lie flat when the box is closed.
These give a screw connection at both ends for positive attachment and not had one fail yet.
The only problem is getting them now.
Squires used to do them, but not now.

Bob
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warspite

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Re: using servos to power small models
« Reply #6 on: August 03, 2008, 08:04:09 PM »

I Know this topic has probably been exhausted in the past, but finding and reading relevant posts has made me spend the best part of two days, Roger in France has been very helpfull and will take his advise further if the following question makes me stumble.

I read the topic and was very interested to read about using the servo as a motor, I assume that the more 'throttle' applied will speed up the motor, so therefore the electronics for the servo become a cheap ESC and similarly also give a reverse. You just have to ensure the drive line to the prop is square on so to speak to reduce the resitance to rotating.

I assume also depending upon which SIZE of servo you use depends upon the capabilities to 'push' the vessel through the water.

My thoughts are (weight permitting) that two mini (or if possible standard) servos driving two counter rotating 10mm (give or take) brass props through 2mm aileron linkage rods and close fitting brass outer tube filled with grease, connected to a HiTec feather receiver and a 6v give or take power pack might be just enough to drive an Airfix 1/72nd Vosper MTB.

Comments please as to the folly etc, or will it just plod along like a snail on prozak, if it moves at all.

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Bunkerbarge

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Re: using servos to power small models
« Reply #7 on: August 03, 2008, 08:19:48 PM »

I take it you mean to remove the motor from the servo housing and use it at normal motor speed, otherwise it will be a bit slow?

You are correct that the motor can be used and, if you leave it attached to it's speed controller board to have a ready made ESC as well.  There was an article in Model Boats Mag about this not too long since, where exactly this was done.  You will almost certainly have to remove the gearbox though and use the motor at normal speed.

Normal servo motors come in at about 16mm diameter and two of them push  a 1.3 kg Revel u-boat at a good speed.

The problem with the Airfix Vosper is that the scale props are a lot smaller than the smallest props you can get for a 2mm shaft so you will have to decide to go for either out of scale brass props or use the kit items and try to get them spinning fast enough.

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warspite

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Re: using servos to power small models
« Reply #8 on: August 03, 2008, 08:46:18 PM »

Removing the gearing was always the intention, the motor would need to run at whatever rpm the motor is design for, although that might still mean that it still not fast enough, 1.3 kilograms !, with this boat i would probably be near to having the waterline flush with the deck at anything over 100g, hopefully find a powerpack that goes to 6v and not be any bigger than AAA batteries would be ideal, scale speed although would be nice, but flying like a bat out of hell is not practical, lasting 5-10 minutes would be preferable.

The brass prop's I have are prop shops M2 threaded about 10mm dia, I think, I was not intending to use the kit ones as they are totally impractical and would not push the water round a tee cup nevermind a bath.

From the description of the servo's i assume you mean futaba type F128's, would do, give a good turn of speed, so all I would have to do is remove the gearing, make sure the motors are free running, line up with shafts plug into receiver, attach battery pack and off we go, using servo's as forward and reverse (tank style operation) to steer, if weight too much could mini (not micro) servo's do?.

There's a new thread for mini tugs just started, would this applied to that as well?

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malcolmfrary

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Re: using servos to power small models
« Reply #9 on: August 03, 2008, 09:56:30 PM »

The close fitting tubes filled with grease would kill any performance stone dead.  Better use a larger diameter tube with bearings and lube with oil.
Without modding the electronics, the servo board gives proportional control, but with a very narrow deadband.  Rather than using the stick, pretty full control can be had using the just the trim tab as an engine room telegraph.
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catengineman

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Re: using servos to power small models
« Reply #10 on: August 03, 2008, 10:10:30 PM »

As a tip

(what I have done in the past)

once the gears are out of the way plug the servo into a system and power up then turn the dash pot until it is centered then blob some superglue or like on the shaft of the dashpot to stop it going out of center. then as malcomfrary says you can get very fine tuning with the trim tabs. (if you can set the trim tab adjustments to the lowest movements it also helps) (FX18)

R,
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warspite

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Re: using servos to power small models
« Reply #11 on: August 04, 2008, 09:30:24 PM »

From an autocad drawing of a vosper i drew for checking the fit for the motors, the prop appears to be 20mm dia with a 5mm dia central body and 5 blades - hopefully this picture will help

The Little motor on top of the grey one is a mobile phone type still complete with the overcentre weight (gives it the vibration), the prop for the driving of this boat is to be either using two standard futaba FS128 servo's stripped down as above and directly connected, i have an opposite hand prop as well, the HS55 at the back i believe would not be powerfull enough, origanal thought was to have a single prop and the hs55 to steer, the hull is supposed to be 305mm long, any comments?

Warspite
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andyn

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Re: using servos to power small models
« Reply #12 on: August 05, 2008, 12:53:20 AM »


Have a look at - http://www.boatnerd.com/model/tug/others/hyneshowto.htm


Does that work well? What about the end stop?

If that works it will be a godsend for a 9 inch model I have.
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andygh

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Re: using servos to power small models
« Reply #13 on: August 05, 2008, 05:38:51 AM »

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warspite

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Re: using servos to power small models
« Reply #14 on: August 05, 2008, 11:04:15 PM »


Does that work well? What about the end stop?

If that works it will be a godsend for a 9 inch model I have.
[/quote]

will be trying it tonight, done some water weight distribution tests, which suggests that a small JP 4.8v 180ma with the two bigger grey motors would be the maximum limit for the transmitter and the propulsion, probably about 30-180 secounds at full speed knowing my luck, i would prefer to use an overlander 4.8v 700mAh but the weight is at least double. the servo i am about to dismantle is a Futaba FP-S128, hopefully the weight will drastically reduce as i strip out the casing etc, two of them running this little boat might be more beneficial, i have a couple of Futaba S3003, whether these will be any better i do not know.

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FullLeatherJacket

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Re: using servos to power small models
« Reply #15 on: August 05, 2008, 11:15:27 PM »

Seems like a lot of trouble for a compromise end-point. There is an alternative............PM me for the link.
FLJ
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warspite

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Re: using servos to power small models
« Reply #16 on: August 05, 2008, 11:56:58 PM »

so I have had a go at stripping down the servo, the attached picture sows the hull at the top with a AA battery to the left and a AAA to the right for scale.

The two props to be used, as suggested a loose prop with a bush etc need to be made.

the white object is the JP 4.8v 180ma that might be used, depends if i can get a more up to date and powerfull battery for the same weight - size etc, oh and does not get to hot if it has to be permanently fitted.

The item to it's right is the Hitec feather and finally to it's right the servo striped down.

This weighs about the same a the small grey motor previously shown, the difference being that it also includes a speed controller, yep it works a treat, motor speed may not be brilliant but hopefully two may be fast enough to give it scale speed - which is what i want :).

if i can get the photos to resize better and be clearer i will document the build, but dont hold out any hope, i have a terrible memory, after seeing the polish gentlemans shipwright skills, i want to give up, why do you think i go for plastic kits {-)

warspite
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John W E

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Re: using servos to power small models
« Reply #17 on: August 06, 2008, 10:13:04 AM »

hi all

I am reading this topic with great interest; as I have a miniature build planned for some time in the future.

I did do a miniature build a while back and it was of a slipper-back speed boat from the Hobbies plans.  The electrics I used in this may be of interest to some of you; as they were recommended to me by the late Craig, from ACTion - by sometimes you miss people.

I was originally going to put a strip down servo motor & the electrics into the slipper-back to propel it because the model is only something like 15'' long.    Craig suggested to me to use the miniature ACTion speed controller and by gum it is small.   This speed controller runs purely from a 6volt maximum NiCad pack - the same NiCad pack which supplies your RX receiver.  So, basically it takes its motor power from your receiver pack.   It gives you a fully forward and reverse with a good decent dead-band in the middle.    As I say, it is very light.   The motors it will power are the size of the old 6volt cassette motors; but, I, in actual fact - used a motor from an early games handset controller - you know the ones for Playstation or some console.

I have attached 2 photographs - one showing (if you can make it out) the actual speed controller at the side of the boat and also you will see 2 hand controller motors alongside a 4.8 NiCad battery pack (just to give you some idea of the sizes for comparison.

I hope it gives you some food for thought; because I know my mind is busy working things out right now  ;D

If you want more information on the Speed Controller - I am sure FLJ will give you some low down and sound advice on it.

Aye
john e
bluebird
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FullLeatherJacket

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Re: using servos to power small models
« Reply #18 on: August 06, 2008, 10:31:42 AM »

Info can be found here; I did the drawings but the words and music are all Craig's. Note that there are FIVE pages to this PDF file, including the Kit Instructions (but you can purchase one ready-built and tested; most folk do). BTW the unit weighs 9gm without its case.

http://www.action-electronics.co.uk/pdfs/P68A.pdf

Suit yourselves.

...........and yes, John - some guys you do  miss.

FLJ
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barriew

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Re: using servos to power small models
« Reply #19 on: August 06, 2008, 03:16:28 PM »

You can also use the ACTion speed controller to drive a servo motor. This is from a model built from French plans - its only about 19cms long!

Barrie
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John W E

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Re: using servos to power small models
« Reply #20 on: August 06, 2008, 08:59:39 PM »

Hi there BarrieW

I am glad you put this picture on  O0  because the next time a certain Mr Riggers complains about my wiring being a bit of a mess - I will refer him to your picture - please do not take my comment wrongly - it is all meant in fun.   I do realise working with small models requires wires to be all over the place, but certain folk cannot understand this can they Riggers?  {-) O0 O0 O0

aye
john e
bluebird
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malcolmfrary

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Re: using servos to power small models
« Reply #21 on: August 06, 2008, 10:30:07 PM »

I can't see anything wrong with the wiring. ???
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warspite

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Re: using servos to power small models
« Reply #22 on: August 06, 2008, 11:38:07 PM »

so I have had a go at stripping down the servo, the attached picture shows the hull at the top with a AA battery to the left and a AAA to the right for scale.

The two props to be used, as suggested a loose prop with a bush etc need to be made.

the white object is the JP 4.8v 180ma that might be used, depends if i can get a more up to date and powerfull battery for the same weight - size etc, oh and does not get to hot if it has to be permanently fitted.

The item to it's right is the Hitec feather and finally to it's right the servo striped down.



It appears i forgot to add the picture
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warspite

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Re: using servos to power small models
« Reply #23 on: August 06, 2008, 11:43:57 PM »

Granted not a very good picture, i still have to figure how to use this camera - or at least connect the web cam.
Still debating the pro's - cons of fitting one prop and larger battery, and obviously a more powerful motor, the servo one appears not to be as fast as the grey type.

Whatever i decide, when i seal it up theres no removing anything and fitting a hatch which conceals the charging point and the on/off switch would need to be decided upon.
Warspite
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barriew

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Re: using servos to power small models
« Reply #24 on: August 07, 2008, 11:03:59 AM »

Hi there BarrieW

I am glad you put this picture on  O0  because the next time a certain Mr Riggers complains about my wiring being a bit of a mess - I will refer him to your picture - please do not take my comment wrongly - it is all meant in fun.   I do realise working with small models requires wires to be all over the place, but certain folk cannot understand this can they Riggers?  {-) O0 O0 O0

aye
john e
bluebird
John,

In fact the wiring is normally a 'little' tidier than that ;). I wanted to show all the components so had to move them around a little and disturb the wiring. As you say, in small models just getting everything in is the challenge. As you will see, I have used miniature components, but according the the article, the original was built with full size Rx and Servo, and used the electronics from the servo as ESC- still in its case!

Barrie
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