From: CAMINS::COMPTEC93136 "Tom" 24-JUL-1995 02:12:05.16 To: IN%"chasjesus@socketis.net" CC: COMPTEC93136 Subj: Motor questions Well, my college's news software is totally screwed again, so I was unable to reply directly to your query about motor info. However, some time ago, someone else asked a question very similar to yours, and here was my reply: From: CAMINS::COMP156W205 "Tom" To: comp156p125,comp139p125 CC: Subj: motor tech From: CAMINS::COMP112Q213 "Tom" To: comp156w205 CC: Subj: Motor tech. Newsgroups: rec.models.rc Path: suncad!camins.camosun.bc.ca!comp112q213 From: comp112q213@camins.camosun.bc.ca (Tom) Subject: Re: Motor questions Message-ID: <1994Mar15.205902.1@camins.camosun.bc.ca> Lines: 124 Sender: news@suncad.camosun.bc.ca (USENET News System) Organization: Camosun College, Victoria, B.C. References: Distribution: rec Date: Wed, 16 Mar 1994 04:59:02 GMT In article , rogue@nutrimat.gnu.ai.mit.edu (The Mystic) writes: > I have a question about RC Car eletric motors. Could someone do me > the favor of explaining about the method of classifying motors by the > number of turns they have, etc. > > What exactly does 3T Quad mean, and how do the numbers relate to > performance. > > In case that wasn't clear, what bearing does the number of turns in > the motor specifications have to do with performance, and same for the > classification "single" "double" "triple" etc... > > rogue@gnu.ai.mit.edu > -- > > > This is a question many newcomers to R/Cing have, and it is one there is a fair bit of conflicting information on, so all I am going to say is from my 6+ years of on and off road racing. I will start by explaining your example. A 3T Quad would probably mean that it is a motor that will blow up if you put more than one volt through it, since it is such a psycho motor, so let's start with a more practical example, say what you probably meant to type in, 13T Quad. That motor would be wound in the following fashion. The motor winder (boy, what an exciting job!) would take four separate pieces of wire (hence the term Quad) of the same gauge in hand. He (or she) would then proceed to wrap those four pieces of wire around the first pole (whatever one is closest at the time, there is no first pole on a blank armature) 13 times, then the second pole 13 times, then the third pole 13 times (hence the term 13 turns). Sorry about those brackets, but I just finished doing a Lisp program and I can't get them out of my head. :) But, to continue, these principles can be extrapolated for any number of turns. Common modified motors range from 10 turns to 20 turns in single to quad form, but there are many 6 and 7 wire motors, and some drag motors go down to 7 turns. In other words, if you want it, it's out there (although I have never seen more than 27 turns on a standard R/C car motor -- a slave motor for one of the dynos that came out a few years ago had I believe an 80 turn motor with it.) I believe CAM motors will custom wind a motor for you if you're willing to wait for it. Another technique for winding motors produces doublets, triplets and such. These are motors wound with several strands of wire (two for a doublet, you should get the idea) but the strands are of different gauge. I have never owned one of these, and they are not too common, so I cannot comment on their performance, although I suspect a doublet is half way between a single and a double, or something like that. Now, that's some of the stuff about winding the motors, if you look at an armature, it will all become clear. Here's the scoop on performance. To start out, lets just talk about singles for the moment. Generally, if you use less turns of wire on an armature, the motor will: a) draw more current b) produce more horsepower. This explains the craze in stock motor building to use a short stack armature -- the stacks are shorter, therefore less wire is used per revolution, therefore more horsepower. So, a 3 turn motor (to cite your example) will draw a humungous amount of current and just about blow up, while a 13 turn motor would just produce an insane amount of horsepower. The relationship between turns and performance is not linear, the difference between a 12 and 13 turn motor is more noticeable than the difference between an 18 and 19 turn motor. If you think about it, it makes sense, 'cuz the change in wire length is a larger percentage of the total length when you have less turns. So, a 13 turn motor is more than enough for just about all off roading, and it will have much more power and use much more current than a 17 turn. Now, let's get into poly - strands. Less strands will give you: a) Drastic power band at low rpm b) more current drain esp. at low rpm More strands will give you: a) smoother, more controllable power band at higher rpm b) reduced current drain esp. at low rpm This is why 1/12th scale motors are commonly quads, quints, and sometimes hex's, 'cuz 1/12th scale cars are so bloody light, it takes no torque to get them going really quick! (torque being relative to off road cars) So if you are racing on a high bite track, you might consider a single or double, and on a lower bite track you might consider a triple or a quad. Remember, though, you can change you brushes, the cut, the springs and the timing on the motor, plus all the adjustments on your car like slipper and torque control. But I don't want to talk about that right now, I probably don't have enough disk space to fit all that on! So, to sumarise. Motors are classified not by their free running rpm (a completely useless and irrelivent number, although newcomers like to boast their motor turns at a google rpm. I just tell them I'll hook up one of my old stock motors to a 24 volt power supply and THEN see who's motor turns faster) but rather, they are classified by the number of turns and how many strands of wire make up the armature. This is a much more useful figure to classify motors with, because there are no tests to fudge and boost quoted performance with. Motors with fewer turns draw more power and produce more power -- I am not too sure if the efficiency increases, decreases or stays the same with differences in the turns, however I expect since there is internal friction and such, the efficiency goes down as the turns go down. Using more strands to make an armature will decrease the current draw, prevent useless excessive slipper slipping (say that 10 times fast! :) ) and give you more useable power at higher rpm's. Of course, the battery you are going to use dictates largely what motor to use, as does the track, who you're racing against, your skill, and the car and motor setup. This is by no means a complete discussion on motors, just a general overview. If you know how a motor works (very hard to describe exactly what happens) then you can apply the information better and write this thing yourself. The best way to learn about performance of different motor types is to try them for yourself, and always remember, what works for someone else will not necessarily work for you! (but it's a good starting point! :) ) Anyway, I hope this has been of some help to you and others, if I skipped over something or have not made myself clear (I do that alot!) then just ask and ye shall receive! Ttyl, Tom. ___ TTTTT OO M M Sometimes AKA: ut075@FREENET.VICTORIA.BC.CA |~~~| T O O MM MM Be young, @o o@ T O O M M M have fun, * T OO M M and drink lots of beer!!! `-'