Can I connect a small motor to a servo lead?

[SoupParticipant @soup]

Musings :-

I am considering attempting to motorise/control a V small boat (a 1/72 Airfix or similar) not too bothered about speed but forward/reverse is a must (have sailed into too many situations where reverse is all important).

Initial thought :-

I have recently converted a Futaba servo (FP-514B) to continous rotation however it looks really quite slow to me. Using a gear box would negate using such small/compact gear in say a 1/72 Vosper or some such.

Secondary thought :-

Can I connect a small DC motor (no meaningfull markings on the "can": scavenged from an old CD player) to a servo lead ( need the connector to fit the reciever as I wish to power the motor from the radio battery pack). Servo lead has three wires (white, red and black), can I just cut these, terminate the white wire in some way and connect the red and black to the +- of the motor?

I assume this is a brushed DC motor as it only has two wires to the 'can', and they are very thin so I assume it is not a high current device ,no idea what voltage it is supposed to be but would imagine it would just turn v slowly if it was meant to be much more than the 4.8 I would 'feed' it.'.  My main fear is that the motor will draw so much power throught the receiver (Saturn (Planet) 2.4 GHz one) that it wll be damaged.

Edited By Soup on 26/03/2013 17:51:05

[SoupParticipant @soup]

[shipwrightParticipant @shipwright]

Not clear to me what you are trying to do – but…….. do you know the voltage of the cd player motor and the current consumption ? Unlikely that you could power the propshaft of even a very small model boat in the way that you describe.

Ian

[Dave MilbournParticipant @davemilbourn48782]

You cannot control the speed or direction of the motor without some sort of detector/amplifier circuit. Connecting the motor directly to the Rx will just result in the motor running at a constant speed while the radio is switched on. You will need a proper speed controller between the Rx and the motor – like this one **LINK**

Dave M

Edited By Dave Milbourn on 26/03/2013 18:21:02

[Paul TParticipant @pault84577]

I am one of those scavengers who gets electric motors from all sorts of places and most don't have any details on the cans, one of the best bits of kit is a cheap multi-meter which allows me to check on the motor power consumption without destroying either the motor or the power supply.

What Soup could do with is a small (cheap) radio controlled toy boat and simply transfer the guts into the airfix model

 

Edited By Paul T on 26/03/2013 19:40:24

[SoupParticipant @soup]

Thanks all.

@ shipwright I said in my OP that I have no idea what current or voltage the motor requires/will draw.

@ Dave. Shall investigate those small speed controllers. I have ones which require seperate batteries but those ones look like they power the motor from the radio battery. Saving mucho weight

@ Paul. this was more in the area of idle musing, was thinking of a toy boat being converted as well (see my other post "Adapt A Toy" 08/03/2013 20:33:12 ).

Edited By Soup on 26/03/2013 20:20:29

[shipwrightParticipant @shipwright]

Well – I have to admit that I was totally unaware of the Pico 1A and its ability to drive a small dc motor with the only connection being the standard 3 wire servo lead to the receiver. Ingenious.

Ian

[Dave MilbournParticipant @davemilbourn48782]

Well – I have to admit that I was totally unaware of the Pico 1A and its ability to drive a small dc motor with the only connection being the standard 3 wire servo lead to the receiver. Ingenious.

 

 

 

My friend and mentor, the late Craig Talbot, was a very clever chap. P68A is indeed an impressive little bit of kit – just one example of his genius for simplicity.
Dave M

Edited By Dave Milbourn on 26/03/2013 23:08:08

[Malcolm FraryParticipant @malcolmfrary95515]

Can I connect a small DC motor (no meaningfull markings on the "can": scavenged from an old CD player) to a servo lead ( need the connector to fit the reciever as I wish to power the motor from the radio battery pack). Servo lead has three wires (white, red and black), can I just cut these, terminate the white wire in some way and connect the red and black to the +- of the motor?

If you already have the servo that you are prepared to sacrifice, just remove the electronics board from the servo, and replace the servo motor with the CD player motor. Just takes nerve, a steady hand, good eyesight and the sense to note where the servo motor was connected. The position sensing pot becomes the "fine tune" to set the neutral position. The CD motor will probably run a bit slow for a fast boat, better to retain the servo motor and remove the gear train coupling direct to the motor shaft.

The big problem with such as the 1/72 Vospers is that there is virtually no payload capability – just the plastic of the kit floats at about waterline, everything added to power and control it must be as light as possible, and lightweight power is not really ever cheap. A real life problem also faced by the RN in WW2 when they couldn't get Italian motors for their MTBs any more after Mussolini decided to join in on the other side.

[TelstarParticipant @telstar]

Hi Soup I did use a Futaba servo innards to power a Graupner model "Vegesack"?

Useing the servo motor direct drive on a 25mm 3 bladed prop. the servo pot was replaced by 2 fixed resistors selected to give center "off" . The pcb was removed from the case to save weight, and the RX battery beefed up to give more mAh

It wasn't fast, but not so slow as to look silly

Cheers Tom

[ashley needhamParticipant @ashleyneedham69188]

Tomato. Come clean and tell us what boat you are contemplating… there are not that many kits large enough to motorise to likelyhood is someone has done it before.

I can see that the technical challenge of getting something like this to sail can be..a challenge, but once on the water, it is likely to dissapoint, being slow, tender and only able to sail in a dead calm.

Ashley

[SoupParticipant @soup]

@ Ashley Nothing specific Ashley I was just musing to my self "mmm wonder if I can…".

ASIDE :-Oh and it is cheese not Tomato

When I first came online I was cheesesoup (as I didn't think it existed and would be easy to remember) Some site wanted a username that was nine characters or less couldn't really get on with cheezsoup so soup I became.

The lack of scale bobbing does put me off somewht. Whilst I have great appreciation for the time/effort/skill that goes into say a four foot long USS Eisenhour to my eyes it looks ridiculous shooting along at a, scale, 150 knots and the deck heaving by a, scale, fifty feet in one second.

@Telstar Tried removing the guts of a servo but it had all been glued into place so ended up cutting the case from the innards. Pretty much made a mess of the servo PCB doing that (not the actual cutting the removal) so this half formed idea has taken a bit of a backseat

[Malcolm FraryParticipant @malcolmfrary95515]

The subject of scale speed having been raised – a scale boat, unless ridiculously over powered, is incapable of exceeding a proper scale speed. Scale speed is not full size speed divided by scale – you divide by the square root of the scale. The people who have been using test tanks have used this idea quite successfully for many years.

Bobbing is dealt with by proper weight distribution.

To use a servo as motor and ESC, it just needs the gearbox part separating off, the moulding covering the motor gear removing, and if required, the gear pulling off the motor shaft. Optionally, the mounting lugs can be sawn off.

[ashley needhamParticipant @ashleyneedham69188]

Gazpachio. (sorry) There is no doubt it can be done, loads of people have done so. A little while ago (and in wnat magazine I cant remember) someone built a Turbinia, with three shafts..and it was not a lot longer than your hand. Just decide what one you want to do and go for it. The smaller and lighter the gear has to be, the more you either pay, or be resouceful in order to succeed.

Bobbing in a model , especially that small and light will be unavoidable on anything but a very calm day. The TYPE of bobbing may well be moderated by the weight distribution, but on a plastic magic affair i think that will not be a lot of choice in the matter, as weight will likely be at a premium.

My Nelson battleship (44 inches long) was deliberately made an inch or so deeper that it should be so I could make it extra heavy and thus be more solid in the water, and it is. It is noticeably more steady than other ships on the pond, and I have not yet fitted bilge keels, which will steady things up even more.

. Scale speed…dont start this lot off !! Everyone has their own idea. Mine is.. cant have too much power installed, it is what the throttle control is for, and you need an excess of power when model boating to avoid…situations..ducks, swans, boats, unforseen logs, ice…etc etc

Ashley

[Malcolm FraryParticipant @malcolmfrary95515]

True enough, but the quote was of a 4 foot USS Enterprise. It doesn't really matter which one, with proper weight distribution, its going to ride rather than bob.

[ashley needhamParticipant @ashleyneedham69188]

Malcolm, agree, the weight distribution will certainly affect the behaviour on the water.

Ashley

[Tony Bell 2Participant @tonybell2]

When you buy electric cable for your house you are told what current it will take 5A, 13A etc. If you use the wrong size, the cable can melt and catch fire.

When buying servo extensions cables, manufacturers/suppliers tell you nothing of practical use. Will a 22AWG cable take more current than a 26AWG. What does Heavy Duty mean. Hitec/JR/Futuba?

The original question asked "Can I connect a small motor to a servo lead? Work out the motor current, then choose the cable to suit.

I wonder if suppliers actually look at their profit/loss acounts when selling cables and factor in the actual stocking cost. Why stock 4 products, 1A and 3A with either Hitec or Futuba plug and sockets when you can stock one item a 3A universal cable. The consumer then has no problem connecting up with any make of product.

Having spent 20 years in selling and marketing and lately teaching, the R/C market is one of the best businesses to use as an example on how not to run a business. I wonder if they are breaking UK trading laws ( Fitness of purpose/trade discription). Certainly the lack of information and errors defys all the principles of "Customer Service"

This comes from a years research into R/C products. It all started out by looking for a drum servo which could pull in a very large sail with a load of 5kg and did not need springs, pulleys and cord loops.

My last piece of research is to find out the importance of the antenna orientation in the transmission distance between the Transmitter and Receiver.

Has any manufacture/supplier told you. "Don't point the transmitter antenna at the plane" That's all you will find.

What is the max current of your receiver? If you burn out your receiver due to over voltage, your supplier will have to replace or repair it free of charge and there is no time limit. There is no such thing as a one year guarantee. They are incompetent by not telling you what the max current is.

I'm afraid that is how bad the R/C market. If you read my "Before Buying" you will see what I mean. Do you know what Frame Rate means?

**LINK**

Tony

 

 

 

 

Edited By Tony Bell 2 on 01/04/2013 19:18:53

[Andy HustlerParticipant @andyhustler32076]

Ashley i tend to ember i the 70's there were a motorised set of snap fit models inc racing cars and boat inc a very impresive mtb/air rescue and a minesweper i built these but cannot rember the company . They were very basic and long before i knew anything about r/c , the motior was vry smal and powrd by a single battery but you had to set the rudder in one direction otherwise you would loose it !!!

[ashley needhamParticipant @ashleyneedham69188]

I remember having non r/c motorised boats as a lad and playing with them at the seaside.. gosh. the ones I used to have never seemed to perform very well.. they were either slow, unreliable or just simply packed up very quickly.

it is just not the same being grown up.

Ashley

[Dave MilbournParticipant @davemilbourn48782]

Tony

At the risk of being controvertial or stirring up a hornet's nest, I think you may be too heavily into the technicalities of the subject to take a broad view of the trade – cynical though that view may be.

Firstly I think it's fair to say that all of the radio sets marketed today are made in the Far East. Almost without exception they are designed and manufactured ruthlessly down to a price for a very specific market i.e. ready-to-fly model aircraft and a few plastic speedboats. Granted those sets made in Japan are in all repects better than those made elsewhere but that's hardly the point. Apart from at this quality end of the market e.g. radios for "3-D" model helicopters and large-scale model aircraft – and the builders thereof – I firmly believe that the average modeller is quite ignorant of how his radio set works and wouldn't want to know even if he was invited to sit down and listen to a lecture.

He has forked out what amounts these days only to a few days' loose change and as long as his boat goes where he wants it to then the technical side is of no concern to him. It's likely he either bought it on-line or from a shop whose assistants have no idea of or interest in the items they sell. If he makes a wrong decision about installation etc then it will hardly be based on the lack of information which causes you such dismay. Cable thickness is quite probably not a factor he would consider anyway. He wouldn't dream that changing from Brand X to Brand Y might reduce the total movement of his servos because it simply wouldn't occur to him (I doubt if many would even notice). Frame rates might be relevant to those of us who have to deal with different makes of radio and match our manufactured units up to them, but they don't mean a great deal to Joe Soap.

He has a budget radio in a model which goes OK when he puts it into the water. No matter that the motor is connected to the battery with inadequate or unsafe wiring or that the battery hasn't been charged for the right time or at the right rate. He wouldn't know the difference between AWG and Amps – nor would he care. If something goes wrong there's a bloke at the club who understands these things, or another guy on an Internet forum who takes the time to explain what the problem might be – so what's the point? He "doesn't understand electronics" (or even what that statement actually means) so all is well as long as his model keeps afloat and acceptable advice is available from others.

You say that you wonder whether businesses are breaking the law by giving so little information about what they sell. My reply is also a question; why should they spend time and effort accumulating and publishing technical data which serves only to confuse and thereby turn away the average potential customer? As in most things, ignorance would still appear to be bliss – for the majority anyway.

HOWEVER a certain Mr Freshney and I have hatched a plot to bring simple model boats electrics to the masses – you heard it here first.

Dave M

[ashley needhamParticipant @ashleyneedham69188]

Dave. A very good point there, or several points i suppose.

I have no desire to know exactly how my r/c set works.

I fit servo`s and possibly some move a bit more than others, and if so i have not noticed, and nor has it made any difference to my models.

Joe.

[Tony Bell 2Participant @tonybell2]

“At the risk of being controversial or stirring up a hornet's nest, I think you may be too heavily into the technicalities of the subject to take a broad view of the trade – cynical though that view may be.”

I totally agree with you that the customer is not interested in how the electronics work (science) but that they do work (technology). But there in lies the problem. It is the manufacturers themselves that are using technical terms to sell their products because they have little else new to say.

“He wouldn't dream that changing from Brand X to Brand Y might reduce the total movement of his servos because it simply wouldn't occur to him (I doubt if many would even notice)”

My primary interest is in Sail Drum servos for sailing boats and not simple arm servos. My digital servos can be programmed to give 25mm to 400mm sheet travel with total joystick movement. Small variations between receivers make a considerable difference in sheet travel; you only have to look at my Receiver Tests. In this case your comments are incorrect.

If he makes a wrong decision about installation etc then it will hardly be based on the lack of information which causes you such dismay.

Please tell me how you would go about choosing a servo bearing in mind that stall torque is not only irrelevant but incorrect in the 50% of servos I’ve tested.

Speed at no load again is irrelevant as speed drops as soon as you put a load on the motor. These are technical facts you need to be able to choose a servo. It is quite simple to show graphically.

“Cable thickness is quite probably not a factor he would consider anyway.”

Servos are now drawing over one amp so cable capacity is relevant. I do not use the term SWG as it is not metric. I supply 3A universal servo cables because they suit every situation. Hitec male and Futaba female. I stock one product line not four.

“If something goes wrong there's a bloke at the club who understands these things, or another guy on an Internet forum who takes the time to explain what the problem might be – so what's the point?”

This forum has provided me with interesting help only because I asked the questions. But it took me many months to find out what questions to ask.

My article “Before Buying” was written as it was information I needed to be know so I could answer my customer’s questions.

“If I did not know – Many other wouldn’t either”

Let me ask you another simple question. How do you fit a 2.4Ghz antenna?

I built a test rig with six receivers and tried it out last weekend. This week I have been building a completely new one as the results were not as I or others who were watching, expected.

“You say that you wonder whether businesses are breaking the law by giving so little information about what they sell. My reply is also a question; why should they spend time and effort accumulating and publishing technical data which serves only to confuse and thereby turn away the average potential customer? As in most things, ignorance would still appear to be bliss – for the majority anyway”

I cannot comment on the above.

My experience is in Engineering, Industrial Design (Products), Sales & Marketing, teaching Design Technology, Marketing and Customer Service. This includes Consumer Law

[Dave MilbournParticipant @davemilbourn48782]

Tony

It's a pity that you seem to have taken such exception to a posting which was not intended to cause offence. It’s also a shame that you seem either to have overlooked or ignored the main point I was attempting to make, which was that the average modeller has little or no concern for the technical minutiae which seem to occupy so much of your time. Given your long list of qualifications you are clearly far from average. This being the case then offering your own experiences and attitudes as a basis for calling my remarks ‘incorrect’ is invalid. “You are not”, as they say, “singing from the same hymn sheet”.

After over 50 years since Doug Spreng invented the digital proportional feedback servo there’s been little obvious change in what they do i.e. you shove a +ve signal pulse into them approximately every 1/50^th of a second and the output disc on top rotates. So what’s new to say about them? Those of us who recognise the difference between genuine technological improvements and mere advertising bull will give both due regard. Those who don’t won’t give a fig anyway.

For the majority of average modellers choosing a servo is not a particularly difficult task. Putting model yachts aside for the moment, their needs are nothing like as stringent as yours and so the choices are pretty wide. Common sense says that a high-torque servo would be required for operating a very large or unbalanced rudder while a high-speed one would be most suitable for steering a fast-electric model. Apart from very specialised servos such as sail winches then the other choices are really only between the size, the type of gear material used and whether or not to fit servos with ball-raced bearings. I know of nobody (else?) who has the time, inclination or equipment to test the manufacturer's specifications before they part with their money. A ‘standard’ servo (40mm x 40mm x 20mm) does most jobs tolerably well for Joe Soap and costs less than a tenner; this is the reality. How I personally choose a servo isn’t material to this thread, but I would say that if you have an issue with a particular piece of equipment or advertising blurb then you should take it up with the supplier or manufacturer.

I did not say that cable thickness is irrelevant, but I would hesitate to use or sell 22AWG servo extension leads for, say, a plastic-magic conversion simply because of their weight. You say that your interest is primarily in yachts and high-power servos so you wouldn't have a requirement for lighter/thinner types. This doesn’t make those who do stock and sell them wrong-headed.

As for installing 2.4GHz antennae I would follow the manufacturer’s instructions and/or conventional wisdom until or unless they were proved to be wrong. Word about things like that gets around fairly quickly in this relatively small hobby.

I'm sure that those few of us who are interested in such matters and in such detail are grateful for the effort folk like you put into obtaining and tabulating technical data. However neither those exercises nor your CV entitle you to make – unchallenged – sweeping generalisations in an Internet forum about RC manufacturers and traders, their poor customer service, their incompetence and their allegedly dubious practices viz a viz the law. If you know of specific cases then you also know that there are set procedures to be followed.

However unless you are prepared to 'name and shame' then such comments will make you no friends within the modelling trade, of which I speak as a long-time member.

Dave Milbourn

 

Edited By Dave Milbourn on 26/04/2013 11:03:00

[TelstarParticipant @telstar]

Hi All

My twopennys worth "A little knowledge is a dangerous thing"

Most modellers don't need to read up about the technology of RC equipment, e.g. how much torque is needed to turn the rudder on 'your' boat? so what torque servo do you need.

When (if) you try to measure it what are the SYSTEMATIC errors in the test RIG

A lot of money & knowledge is used in industry plotting Antenna Radiation Patterns, and the bit of advice spun off from this for the modeller says (at least with VHF transmitters) don't point the telescopic antenna directly at the receiver IT Dosn't help! With the receiver antenna (I don't use aerial it's the nontechnical name) modellers should be aware the they should not mount the antenna below the level of the ground plane, (don't put the aerial wire below the water line) it can reduce considerably range.

I don't always agree with advice given by the "experts" on this forum, and on the odd occasion I do "get involved" I like to think that I can back up my opinions with theoretical knowledge. otherwise I say nothing, I was told "If you can't say something useful don't say anything"

For the record Duering an apprenticeship in electrical engineering I got an HNC elect eng with endorsements instrumentation, & radio communication, later a degree in physical electronics while working in medical physics, a stint with Phillips radio comms, systems eng. gives a wide technical background But my modelmaking is average at best.

Unless you are modelling at the sharp end (speed or racing) where performance matters, the average modeller does not need to know

Happy modelling

[SoupParticipant @soup]

Posted by Tony Bell 2 on 25/04/2013 22:55:33:

Let me ask you another simple question. How do you fit a 2.4Ghz antenna?

At 50 my eyesight is such that the model is out of sight before it runs out of range. So the two parts of the antennae at 90 degrees to each other (as per the Saturn's instructions), with the transmitter aerial positioned such that it is perpendicular to the water surface is good enough for me . I don't need (or want) signal propogation diagrams or such.

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