electronics

[Les Jones 1Participant @lesjones1]

Hi Gordon,
For your application you would want to aim at both motors providing equal torque. The easiest way would be to connect them in series. (Assuming identical permanent magnet motors.) I suspect this solution would not meet your requirements as it would require a higher supply voltage. You would need to design the electronics to control the PWM signal to each motor so they were both drawing the same current. I have bought an Arduino Uno but not really done much with it as it aimed at being programmed in "C" and I prefer to work in assembler. Another option similar to the Arduino is the TI MSP430 launchpad module. This can be used with "C" and assembler and is very cheap.(£7.61 +VAT from Farnell.)

Les.

[Andy AshParticipant @andyash24902]

You can use a 555 timer as a triangle wave generator.

If you compare the triangle wave with the variable output voltage from a potentiometer, using a comparator, then you have PWM without needing C or assembler.

[Neil WyattModerator @neilwyatt]

I recall from my A-level physics that, in theory, if you have two perfectly matched DC brushed motors and run them in parallel they will synchronise themselves. Load one, and counter-intuitively they both slow down.

Neil

[Billy MillsParticipant @billymills]

No Neil, not unless there is considerable source resistance or a constant current source, which is the reverse of normal conditions ( Perhaps you are thinking of Pendulum clocks mounted on a common wall, they will sync). A brushed PM motor has it's own tacho built in as the rotor back EMF. Each motor's V/rpm slope will be very slightly different but is trimmable externally so two motors can be closely matched. A very good way of doing this is to put the motor into a bridge circuit. The effect of the bridge is to drive the motor from a negative resistance which exactly matches the average internal resistance of the motor so that the motor speed is independant of motor load. This also allows very smooth very low speed running.( Many mini lathes and mills use this method to get smooth low speed running when delivering torque).

Perhaps the simplest solution would be two PWM controllers with a trimmer to match motor speeds.

If you can cope with very high motor speeds then outrunner ( or inrunner) style motors offer very high power in a very small cost and space. They are high speed three phase motors derrived from the motors long used in floppy and hard drives. Connecting two motors to one suitable controller will give virtually locked rotation and avoid other issues.

Billy.

[Neil WyattModerator @neilwyatt]

Thanks Billy,

I wasn't thinking of clocks, I wonder what it was?

Neil

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Neil ,

Two possibilities :

Motors and generators on three phase systems .

Selsyn type repeaters .

General :

Nature of drive system for two motors really depends on whether motors are mechanically commoned or not .

If both motors are driving a common shaft then no need to electrically sync them .

Somewhat similar but not quite the same if motors are driving individual wheels but both wheels running at same speed along ground . Ideally has a bit of failsafe in case one wheel loses contact .

Regards ,

Michael Williams .

[Russell EberhardtParticipant @russelleberhardt48058]

Lot's of interesting replies there but perhaps more complicated than you need. Perhaps you should tell us what voltage/power motors you are using and what the application is?

The speed of a DC motor is (more or less) proportional to the applied voltage. When you apply a load it slows down a little so that it draws more power from the supply. It is inherently self regulating so in the simplest case to control the speed you just need to control the supply voltage so a simple voltage regulator circuit will do if the speed is not too critical. This can be done with an analogue voltage regulator circuit or with a pulse circuit such as the 555.

If you want more accurate control with less slowing under load you will need a circuit with a feedback arrangement. That gets a bit more complicated.

If you want a simple circuit to play with have a look at this however these days it is often cheaper to buy ready made circuits than build them. An example is this. You couldn't but the components for ten times that price!

If the motors are identical and the relative speeds are not critical just wire the two motors in parallel.

Russell.

[_Paul_Participant @_paul_]

Have you considered building an Arduino controller? I have recently built one to control a stepper motor.

Some of the Arduino "Shields" like this one will control a DC motor or two directly.

Regards

Paul

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

There used to be component sets available for people interested in learning electronics .

Some were quite good with comprehensive range of basic components and a lot of instructive material and projects .

Some were for schools for use with C-D-T courses and science .

A more advanced one was available for OU .

Even though produced for formal education they were just as useful for people doing electronics as a hobby .

They got upgraded from time to time as technology developed .

I was quite impressed with the ones that saw a few years ago .

Anyone seen similar in more recent times ?

Michael Williams .

[Gordon WParticipant @gordonw]

Thanks for all the replies and help. I think what I really need first is some sort of simple dictionary or jargon buster. It is true that most stuff can be bought much cheaper than building them, but I would like to have at least a rough idea of whats happening. Knowing what the thing is called makes finding it much easiier. Reminds me of when we first got a computer , trying to sort problems was impossible because I did not know what to ask and the would be helpers did no know what I was talking about. Not much better now . Am looking at the speed controller with a 555 and mofset to suit power usage. See learnt something already.

[Andy AshParticipant @andyash24902]

I have a Chambers Science and technology dictionary for that. I was given it for my 21st birthday I think.

I don't use it that much, but sometimes someone will say something about biochemistry and it will get me going in the right direction to understand.

Mainly it has to be wikipedia. I'll be honest and say that it rules my life. Type the jargon into Google and follow it up with the word "wiki". So for example the word "commutator", it actually brings up a whole section on maths and conjugation. Don't be put off though because at the top of the page it says "Commutator (electrical) disambiguation", click that and you're there.

The other thing I noticed was that you were already on track with the 555 timer.

You knew you probably needed one, but wanted to know more about what it is. This is a really normal situation.

If you're close enough to an electronic part to know its number, get the data-sheet. Parts without data-sheets are rare. Some of the more mechanical components may not have part data, but all the electronic ones will. Mechanical parts include inductors, relays and connectors. Semiconductors always have them.

Some semiconductor parts, usually with hundreds or even thousands of pins will attract licence fees for use. In that small group of parts a detailed data-sheet might not be available. Usually a product summary would still be available instead.

The devilish group are parts that *used* to have a data-sheet. They're old. Everyone has forgotten. You might not be able to figure it out. Reverse engineering is your only hope.

For data-sheets, type the part number into Google and follow up with the word "datasheet".

Sometimes it can be hard to find the data. Be confident, know that it exists. This is when knowing the manufacturer begins to help.

Once upon a time parts were big enough that a manufacturer mark could be stamped on. These days manufacturers have to choose between a microdot, which can only be read by a machine, or maybe two characters that could be read by eye. Larger parts you can still work it out, but with surface mount the only time you know for sure is when the part comes out of the tape. Even then you are dependent on your supplier to put the right sticker on the tape.

It is not uncommon for the suppliers to get it wrong, and the first you know is when the product doesn't work!!!

Edited By Andy Ash on 03/03/2014 13:08:41

[frank brownParticipant @frankbrown22225]

This running the motors at the same speed is a problem. I can only think of two basic systems, one is to monitor their speeds individualy and then use electronics to sort the problem out. The other is to use a differential (its all in the name !). The output shaft would then rotate which you could detect then use to sort the problem.

Using electronics, use a ferrous gear on each motor with a pickup coil and magnet to detect the changes in magnetic field. Or use a disc with lots of holes in it and use a photo electric cell (photo detector) to look at a light source the other side. Or feed the motors each through a forward biased diode. As the brushes change over from commutator section to the next commutator section a big pulse will be produced that can be coupled through a capacitor to an amplifier, then used for speed comparison.

Once you have a speed comparison signal, say for one motor fast = 0V, when they are equal = 5V and when the other motor is fast = 10V, what then? Unless you have individual driving circuits for each motor, then there is nowhere where you can use your signal. One way would be to have a trimming circuit that , say can increase/decrease each motor voltage by 2V in 12V. But how much? and you can easily run out of headroom. say you use 12V motors A & B, if B is running slow, you slow A by decreasing the volts to 10V, If B still runs slow, what do you do?

Its better to use two electronic drive circuits, so the speed differential control is the primary control on the motor speed and the fast/slow is the secondary one.

The basic DC motor speed control is based on a system called Pulse Width Modulation, try Googling PWM

Some food for thought?

Frank

[MuzzerParticipant @muzzer]

I may have missed a post somewhere above but one option that would combine the best of several options would be to use stepper motors – but without using a micro to generate the speed signal. You could even take the opportunity to use a 555 for that purpose. No software required – no need to master Arduinos, Raspberry Pi's etc.

You could buy a couple of stepper motor drivers that simply require a speed signal (= frequency of step pulses) and a direction signal (high or low). If you common the speed inputs and set them up to have the same number of steps / microsteps, you will end up with identical speeds and positions. You can buy drivers and motors at robot shops, ready to go.

Without a position or speed sensor, you simply can't synchronise the speeds of 2 conventional (= brushed) DC motors, even if you have several PhDs. And even with that feedback signal, it's not a simple business.

Murray

[john fletcher 1Participant @johnfletcher1]

I have used for several years a home made speed controller for my battery powered 5" gauge loco. RS components sell for 50p a small printed circuit board which is pre drilled to accept a 555 timer and a few other components.It takes about half an hour to solder all the bits in place, and in one place a cut is needed.The timer is a PWM circuit which controls a pair of Mosfets. A pair of car type relays, when energised or not, determine forward or reverse. Maybe that would be all you need, cheap, easily constructed and works.Ted

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Gordon W on 03/03/2014 11:48:08:

Thanks for all the replies and help. I think what I really need first is some sort of simple dictionary or jargon buster. It is true that most stuff can be bought much cheaper than building them, but I would like to have at least a rough idea of whats happening. Knowing what the thing is called makes finding it much easiier. Reminds me of when we first got a computer , trying to sort problems was impossible because I did not know what to ask and the would be helpers did no know what I was talking about. Not much better now . Am looking at the speed controller with a 555 and mofset to suit power usage. See learnt something already.

I don't know what level you're at but if you Google "Basic electronics" you will find lots of tutorials for beginners some practical and some theoretical.

When I was eleven (1956) I followed a BBC TV series on building a one valve radio. It didn't work so I started reading and playing and thus started a lifelong career in electronics. Just playing and learning from your mistakes is a good way to learn.

Russell.

[Gordon WParticipant @gordonw]

Russell, that's about where I started. Used to build amps etc. from old tv's and general junk, even had a big book for checking out valves and finding suitable replacements. Built a one valve SW set which worked and lots of crystal sets. Then the red spot transistor came along, it was outside my price range at 7s 6d. That was the last of my electronics and am now trying to catch up.

[Andy AshParticipant @andyash24902]

I've never done any vacuum tube stuff directly myself, but I'd quite like to have a go.

I did work on a control board a few years ago which went with a travelling wave tube assembly. The TWT was about a foot long with a separate high voltage supply. That's why it needed the circuit board that I worked on. Isolation is really important with modern low voltage systems connected to powerful old tube systems.

Transistors are cheap as "chips". Get a bucketful for a couple of quid. You can do anything if you have enough of them. "3904" is NPN "3906" is PNP. expect to pay about 2p each for a hundred. Diodes are similar "4148". Although individually resistors are cheaper, you will have to buy a minimum quantity of a range of values. Getting started with resistors is more expensive.

Start off with things like Colpitts Oscillator, maybe a TTL inverter, build up to complete Op-Amp. Once you can understand and build an Op-Amp from transistors, I'd say you're pretty much there. The next thing after that is to understand the physics of the semiconductor materials.

The only reason to need that is if you want to go off in the direction of chip design. There is some in this country but it's quite rarefied. You'd probably only need or want to go that way for a job. Some people have tried making their own thin film transistors at home. You can succeed, but it is very difficult. You certainly can't make as many as you would need for a simple chip with reliable results.

You just have to have infrastructure which is impractical at home, if you want to make semiconductor chips.

The same is not true for vacuum tubes. These can be made at home with success. The only tricky part is obtaining barium for a "getter". Obviously you still need a vacuum pump, gauge and a glass lathe.

I'm thinking about trying to make some tubes at home myself.

[Neil WyattModerator @neilwyatt]

With electronics today the big choice is between making things and learning how things work.

For most things you want to make, you can get a custom chip, it's datasheet and build a reference design.

If you want to learn how things work, then the 'Art of Electronics' already mentioned is the way to go. Buy a small breadboard kit from maplins and some 'grab bags' of mixed comonents – or even one of the cheap GCSE learning packs which will entertain for a week or two. I still get pleasure from breadboarding something like a simple relaxation oscillator with a unijunction transistor and 'proving' the waveforms. I even bought a kids 'electronics' set at a boot sale for £1 and enjoyed getting the 'crystal' radio to work. – the forty foot aerial helped

The other area where you can really get drawn in is programming microcontrollers. I'll let you explore the possibilities for yourself.

Neil

[Andy AshParticipant @andyash24902]

Does anyone acutally use a unijunction transistor outside of those demo kits? I'm not sure myself.

Understanding how to use transistors in number is still extremely important. Even if you can get a part to replace them, it is often the case that the part isn't actually that complicated. There is still a high premium on ideas.

So, if you're designing a product which needs an analogue function which is a single source supplier, and your product is intended to have any kind of volume, you don't want to use the single source unless you have absolutely no choice.

The transistors on semiconductors can be smaller and closer together, electrically they can achieve performance attributes that could not be available on a circuit board. For a low volume product this can be a good reason to use a single source part. It makes a product more valuable.

Using an exotic amplifier in a battery charger is problematic. You want to make thousands of battery chargers, but you can only get hundreds of the exotic amplifier. Even so you still need the exotic amplifier because it makes charge termination more accurate and prolongs battery life. That's quite a realistic scenario.

The only way through is to understand how the performance enhancement can be had, and to develop something out of transistors which will never go out of fashion.

Until the Chinese copy what you're up to, it's the kind of edge which can build business advantage.

If you look at the mobile phone of yesteryear, it doesn't have the volume exotics that it does today. A modern mobile has a hugely exotic, nearly single chip solution inside. Equally they make it in massive quantities. The only reason an exotic chip like that can be manufactured so cheaply is because of the volume. That volume of sales had to be built.

If you can get an advantage out of a mobile phone part, it might be good. The trouble is that if you use one of those parts, the mobile phone company can lose interest overnight. If they don't need it for their product, the manufacturer just stops making it. Suddenly your product can't be made any more. That doesn't happen with transistors.

For the model engineer it makes sense only to use big powerful chips, because you'll only make one of whatever it is. On the other hand those big chips don't give you quite what you want. You end up having to learn about transistors anyway.

My only worry with the GCSE type training packs, is that they focus quite strongly on common emitter configurations of transistors. Obviously digital radio is quite complicated, but there is no reason not to build a low frequency superhet out of discretes. It's quite rare to see such a thing.

 

 

Edited By Andy Ash on 06/03/2014 18:59:14

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Gordon W on 06/03/2014 09:44:25:

Then the red spot transistor came along, it was outside my price range at 7s 6d.

Yes, I saved up three weeks pocket money for one of those. I couldn't afford a white spot though at 15s!

Russell.

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Neil Wyatt on 06/03/2014 17:56:19:

With electronics today the big choice is between making things and learning how things work.

I didn't think they were mutually exclusive. Is that where I've been going wrong all these years – trying to do both

Russell.

[Neil WyattModerator @neilwyatt]

Andy

> Does anyone actually use a unijunction transistor outside of those demo kits? I'm not sure myself.

Probably not

Transistors are great fun. I have some carefully guarded germanium ones that are destined for a replica 'Fuzz Face', but the best invention for hobby electronics in my lifetime has been the logic-level power FET – switch 30-A with no heatsink

Russell

The reason I suggested the 'choice' is you can make so many things today by just following a circuit and wiring up the bits with no theoretical knowledge at all.

I tend to 'play' with the bits, but occasionally they bond with each other and make something useful. But most of the time my electronic projects are continually evolving prototypes that never get finished.

Neil

[Ian S CParticipant @iansc]

My introduction to transistors was in 1961, when I got an OC 72, and modified my crystal set that I built about 5yrs before. Ian S C

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