can someone explain to me how the lower the turn is the faster the motor?

[littlemaf]

can someone explain how the "turn" thing works out and how its faster the lower the turn is?

[John Stones]

Turns
Turns dictate how fast a motor will run; the less turns (ie, amount of wire) the faster it will spin, but the more current it will consume. ROAR and NORCCA legal stock motors have 27 turns of wire around it's commutator, and generally applies for races in the United States, whereas stock in Japan can mean motors as low as 23 turns. Modified motors can have almost any wind down to 2 turns. For touring cars, motors in the range of 15 turns to 11 turns work best for speed, endurance, and torque.

[John Stones]

I wrote that all on my own ;D, I got plenty more motor info if you want it. just ask in a PM

[littlemaf]

cool.. *adds ur msn*

[marcoski]

Why does a lower turn motor spin faster?

Its all to do with something called back emf. This back emf opposes the voltage input to the motor and its size depends on the number of turns, the speed of the armature and the magnetic field. The motor, when a voltage is applied, will spin up until the back emf equals the supply voltage, at which point it will stop getting faster and maximum rpm is achieved.

So increasing the number of turns will produce the necessary back emf at a slower rotational speed.

Increasing the magnetic field in the can will aslo have this effect.

[littlemaf]

ok i got it now ;) thanks

[darryl]

marcus,
what do you do all day mate,do you sit in front of a pile of electronic orientated books,wow your brain must be a mine field of information lol,well impressed,i have the brain span of a gold fish about 2 seconds ;D

[LisaKeen]

It just so happens that Marcus is and very,very, good electronics engineer and thats putting it mialdly, I'm sure he will explain more, but I know he has been doing if for many, many, years.

I have had the use of his services a few time now and what he doesn't know, or cant do with electronics and such you could just about fill a postage stamp.

[John Stones]

Why does a lower turn motor spin faster?

Its all to do with something called back emf. This back emf opposes the voltage input to the motor and its size depends on the number of turns, the speed of the armature and the magnetic field. The motor, when a voltage is applied, will spin up until the back emf equals the supply voltage, at which point it will stop getting faster and maximum rpm is achieved.

So increasing the number of turns will produce the necessary back emf at a slower rotational speed.

Increasing the magnetic field in the can will aslo have this effect.




Is that the same back emf that blows up a monostable with a relay if there isnt a diode?

[marcoski]

Its the same idea, but that back emf comes from the collapse of the magnetic field in the relay core, in the motor its a dynamo effect.

[damo]

ok brain ache is now in place...

[PDW]

Neurofen Damo, neurofen. ;D

[rice98w]

LOL....

i remember a few years ago, i had a wicked argument with my physics teacher about motors.

he said the more turns, then faster it is.... which in honesty would kinda make sense, then i shows him a RC catolougue,... then i took in 2 motors, one 14 and one 10, revved them up, and promptly gave him some V's! ;D LOL

[Mark Stiles]

My physics teacher thought that 80A was a big current, until I showed him the data sheet for my mrt speed controller!

[ColinO]

80 amps still is big current, in model car terms anyway.
I believe the sometimes quoted 'amperage' of a speed controller is a theoretical calculation based on it's internal forward resistance.
Try passing 80 amps through it for any length of time and see what happens. 8)
( No, I'm not a physics teacher )
;)

[marcoski]

LOL toasty! Mind you, force a motor to accept 80 amps for more than a few seconds and watch the smoke pour out!!!

[Craig]

i remember a few years ago, i had a wicked argument with my physics teacher about motors.

he said the more turns, then faster it is.... which in honesty would kinda make sense, then i shows him a RC catolougue,... then i took in 2 motors, one 14 and one 10, revved them up, and promptly gave him some V's! LOL

The physics teacher is sort of right on that one i am sorry to say.

The more turns you have the quicker the motor will spin if you do not change the amount of current draw.

Its somthing to do with increase the something....but cant rember now.

When we use lower terms we use larger wire which then increase the speed due to an increase in amps drawn and so an increase in speed.

Hope you understand that. Marcus can you explain ill try and dig my work out for it.

[marcoski]

Craig that is true of a constant current supply, but in real life, we use constant voltage, or nearly so, so although the theory you describe is true, it does not really apply. The reason why more current is drawn initially on a low turn motor is that the back emf is smaller at low revs, most modified motors of what ever turns will draw around 5 amps at top speed off load. A fair proportion of this current is caused by comm overlap, the rest in mechanical and resistive losses.

[Craig]

I know it dont really apply but when i was doing my exam i had to keep rembering this perfect world.

But now im at A level physics where it starts to get a bit more in the real world.

[marcoski]

LOL my A level physics master's opening gambit was that physics was maths with a screwdriver!! And my rotating machines lecturer told us to throw our O level physics theories in the bin!!!!

[Craig]

LOL my A level physics master's opening gambit was that physics was maths with a screwdriver!! And my rotating machines lecturer told us to throw our O level physics theories in the bin!!!!

The opening line from my physics teacher i dont wish to repeat. Why do they teach us stuff just to forget it and learn the real physics?

[marcoski]

The problem is that at O level, we don't have the maths skills to understand the concepts properly. You need things like calculus to properly evaluate things like back emf. So they use the constant current idea and can fluff through by saying the field strength is proportional to the ampere turns on the armature, and it is true that more turns make more field and hence a faster motor on a constant current supply.

[rice98w]

O levels? what is an O-level? ROFLOL ;D ;D ;D

you must be old wise man ;)

[littlemaf]

well i know how it works now so u dont have to sya any more ;)

[marcoski]

I have asked you nicely by PM, now your last chance in public:

Please complete your profile as per rules 5 or 6, failure to do so will get you a ban

[Mark Stiles]

Yeah my physics and chemistry teachers told me on my first day back this year to forget everything that we'd learned at GCSE level, because it was almost all wrong! They said that we had learned simplified versions of thoerys and stuff, and that what we learn at A-level is simplified from degree level. So it makes you wonder how deep the rabbit hole goes! :)

[Jonny_H]

Yeah my physics and chemistry teachers told me on my first day back this year to forget everything that we'd learned at GCSE level, because it was almost all wrong! They said that we had learned simplified versions of thoerys and stuff, and that what we learn at A-level is simplified from degree level. So it makes you wonder how deep the rabbit hole goes! :)


Have you read Terry Pratchett's "Science of Discworld" books? He expounds his "lies-to-children" theory, which pretty much covers this whole effect.

Also if you're a Discworld fan with an interest in science, they're a very good read :)

Jonny

[PDW]

'Ere, you, Rice - less of the old eh?!!! ;D

When I moved to Special Physics from A level, the teacher told us to forget Newton's Laws of Motion as they don't apply to a gas! It will surprise none of you to know I falied, and took an Apprenticeship with Ford - nice mecahnical things with proper equations and stuff!! ;D

[Craig]

Have you read Terry Pratchett's "Science of Discworld" books? He expounds his "lies-to-children" theory, which pretty much covers this whole effect.

Also if you're a Discworld fan with an interest in science, they're a very good read

Jonny

The discworld books are well written and are a great read. Quite funny to. Love that libarian.

[littlemaf]

I have asked you nicely by PM, now your last chance in public:

Please complete your profile as per rules 5 or 6, failure to do so will get you a ban


i have! what else is there to do!

[marcoski]

Where on your last post does it show your full real name. Cant you read the simple rules, or are you just trying (and succeding) to wind me up?

[littlemaf]

maybe ur blind >:(

[marcoski]

Maybe you are banned - being smart and text speak. Bye.

[littlemaf]

lol. sorry

[redlinezak]

marcus could the back emf that you describe be in any way compared to impedence in a speaker cos if it can then i may understand it better as that is my field of expertise (i use the term loosely) where the lower the impedence of a speaker the louder it will theoretically be due to the fact that the amplifier will have less trouble passing more current through the coil??
I know its a totally different subject but is it similar theory?

Thanks

Nathan

[marcoski]

Er, no! A four ohm voice coil will take twice as much current as an eight ohm one for a given voltage, so demanding four times the power from the amplifier. In theory it will be four times louder if the amplifier is capable of driving it. The amplifier will do everything in its power to cancel any back emf present, because of the negative feedback ciruit in the power stage. An amplifier running within its limits can be considered as an ideal voltage source. The amplifiers ability to maintain voltage output irrespective of current and to oppose back emf is an indicator of its quality.

[redlinezak]

ok marcus it was just an idea lol i was trying to compare the windings on a motor to the windings on a voice coil but i will just have to get my head around it some other way

Thanks

Nathan

[tayracers]

quote from a great man about amplifiers

my amp goes to 11 on the dial ;D

too much info about nothing

[marcoski]

Your point....?