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Old 12-01-2005, 09:34 AM   #31
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todd P on post 18 has the torque steps and mikeD on post 22 explains how to equate torque to trck conditions. but remember, you milage may vary
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Old 12-01-2005, 03:12 PM   #32
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Mike D- You could run your same analysis with amp steps by looking at the RPM at equal amp steps. Torque is directly proportional to amps on these motors. Just thought I would throw in my 2 cents. I always go for a motor with more power at least somewhere in a broad run on the dyno. It does not really matter if you use torque steps or amp steps. Then you gear the motor on the track to take advantage of this extra power.

If you use volt steps it is also clear to see that more power at say 5 volts equates to more power at 7 Volts as power and Voltage are also a straight proportion.

burgboyz- You can use the motor checkers like the Turbodyno run feature to set up identical motors to run more or less the same on the track by adjusting the springs until you get the same no load amp draw. This assumes that you have found the first good motor by trial and error on the track. One thing you cannot do is insure that both springs have the same tension or to insure that one spring has slightly more tension. You need some kind of device to measure the spring tension to do this. It can be very simple or a cut down supported endbell that lets the brush push on the balance pan. You can also not use this feature to tune a different style of motor (different armature blank) to run the same. You have to use the track again to find the good springs to use on the first one.

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Old 12-01-2005, 03:19 PM   #33
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torque is not directly proportional to amps. that is your problem.

definition:
When a quantity gets larger or smaller, we say that it changes.

Sometimes a change in one quantity causes a change, or is linked to a change, in another quantity. If these changes are related through equal factors, then the quantities are said to be in direct proportion. Or one might say that the two quantities are directly proportional.

this means that there is a static\equal factory that you can use to multiply to amp to get torque. and there is not.

what you fail to understand is that you apply current to an electric motor, it generates a force that then is applied through the shaft of the comm. This force is measure to give you torque. but thhe force generated by an electric motor is not "directly proportional" to the current that is applied. as current is increase the resistance of the circuit is increase, even just by heat. so as this happen the power\force at the shaft is not increase the same factor as the amperage applied. there are even more factors that lower the power\force output at the shaft as current increases, but you get the picture.
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Old 12-01-2005, 03:29 PM   #34
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so what MikeD is proposing is that he is using the torque/power at the shaft as teh control parameter and adjusting the current to meet that control parameter and then reading the rpms at that control parameter.

I actually like that concept and in the last couple of week after reading his post over and over. And then applying it. It does seam that his theory give me a betterin indication weather a motor will perform as good as my control motor.
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Old 12-01-2005, 04:34 PM   #35
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theisgroup- My apologies. Direct proportion is the wrong term. I should have used torque increases linearly with amp draw. You can use a multiplier (.398) but must add a constant. Here is a plot of Yankees data as Torque vs amp draw. It is pretty straight. My motors plot even straighter as 15 amps is a little low for todays stock motors. 17.5 amps might be a better starting point. It is straight out to the limit of the turbodyno 45.

If you take a torque step and then peek over at the RPM and it is higher well then you can peek over at the power column and this will be higher as well after all that's what dynos are for, to measure power.

Hit your full screen button to get a better view of the graph.
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Old 12-01-2005, 04:43 PM   #36
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So since TQ is linear with Amp draw,we really can use the T- 35's motor run feature to compare same type motors?
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Old 12-01-2005, 04:47 PM   #37
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Hyper1- I agree with you that you can do some usefull tuning on the same type motor. I know several guys at the track that have done this. The only trouble is that you don't know the power output unless you either test it on the track or dyno it. You could be tuning all motors to some poor condition if you pick the wrong amp draw. (The dyno tells you the power) If the motor is a known good motor on the track then the motor run may be of some use after the motor springs weaken or on purchase of a new motor of the same type.
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Old 12-01-2005, 05:52 PM   #38
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Quote:
Originally Posted by John Stranahan
theisgroup- My apologies. Direct proportion is the wrong term. I should have used torque increases linearly with amp draw. You can use a multiplier (.398) but must add a constant. Here is a plot of Yankees data as Torque vs amp draw. It is pretty straight. My motors plot even straighter as 15 amps is a little low for todays stock motors. 17.5 amps might be a better starting point. It is straight out to the limit of the turbodyno 45.

If you take a torque step and then peek over at the RPM and it is higher well then you can peek over at the power column and this will be higher as well after all that's what dynos are for, to measure power.

Hit your full screen button to get a better view of the graph.
what you defined is "Directly proportinal". I understand that you see the graph and it seams to use .398 as a multiplyer. but if you were to get more points in your plot you will see that the graph is not linear, but a curve. the funtion for torque is not T=3.98A + C. for this motor, the slope of th eline is aproaching zero. so you can actually draw a curve that fit the graph more then a line.

ultimately power is not a linear result of current because we live in the real world. if that is the case, we could just apply more current to infinity and our power would aproach infinity at the same rate and that is not the case.

anyways, as long as you can find a relation to amps, volts, torque and rpm. then you have something that can tell you what motor will be fast and what is a dud.
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Old 12-01-2005, 06:16 PM   #39
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Ok. Here is yankees second motor. I am seeing a definite pattern here. It looks pretty straight. The r squared value for this second motor is about as close to 1 as you will see for a real machine taking real data. This means the straight line is a very good fit. Amps, Torque units take your pick, You will get the same result. This is not the first time that I have plotted this kind of data. I have about 200 of those little dyno sheets on about 50 different stock motors. The line stays straight to 45 amps. It is irrelevant to discuss ampere ranges at which the motor does not turn or becomes incandescent after a 4 second run.

Yankee-Here is your quote "From what I have read, I should figure out what the average amp draw is of the motor during a race and then run the motor at amp steps and then tune in that range." This is a good method. Then you are not guessing from thin air what torque values to use.
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Old 12-01-2005, 06:49 PM   #40
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what is r squared?
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Old 12-01-2005, 09:09 PM   #41
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R squared is the correlation coefficient. It describes how well a mathematical model (straight line in our case) fits the data. The closer to 1 the better the fit. This is one case where motor theory almost exactly matches the data. The line is is supposed to be straight. A similar relation is on the RPM vs amp draw graph except in this case RPM decreases linearly with amp draw. When we change the motor springs we change the slopes on these two graph which moves the power peak hopefully in our favor.
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Old 12-02-2005, 06:41 AM   #42
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This could be called the most mis-used of statistical procedures. It is able to show whether two variables are connected. It is not able to show that the variables are not connected. If one variable depends on another, i.e., there is a causal relation, then it is always possible to find some kind of correlation between the two variables. However, if both variables depend on a third, they can show a sizable correlation without any causal dependency between them. A famous example is the fact that the position of the hands of all clocks are correlated, without one clock being the cause of the position of the others. Another example is the significant correlation between human birth rates and stork population sizes.

see the probleme with using statistical analysis with small samples is that you can alwasy find a correlation that woudl either prove or disproave your theory. example plot the dyno steps of 1 through 6 on the y axis and your amp draw on the x axis for the first motor and you will see that your r^2 is 0.9968299. that does not say that the steps of the dyno are linear to the current draw by the motor and also does not correlate the 2

even if we bump the last step to a 35 amp rating, you would still see a r^2 greater the .9 does that mean the relation of amps to steps is linear?

another: plot y=2-1/x that r^2 is >.87, if you just use the first 6 samples, it says that the relationship is close to being linear. but as you extend to 14 samples you see that your r^2 is now only ~.77. what I am saying is that a motor rpm to torque relationship is more like this plot. and if you sample close to x = 1 or basically the sweet spot of the motor, you are always going to get something that looks to be linear, but in fact the correlation between torque and amps are not linear. the reason I say close to one is that if you look at both his motors, the efficiency right in the middle of the sample has very little deviation. This means the test is right around the sweet spot. You think that is a coincidence? i think not.
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Last edited by theisgroup; 12-02-2005 at 07:22 AM.
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Old 12-02-2005, 09:01 AM   #43
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guys get out and meet some girls.
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Old 12-02-2005, 10:34 AM   #44
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I agree....you guys are even starting to scare me with all the geekness:P

I personally hate all the dynos on the market today......the robi isn't bad, but still is a pain....the CE works, but the whole slave motor is a pain in the butt.....I have 7 of the things (can't find one though) and I can't get any of them to work worth a crap consistently....

For these reasons......I have gone to a company, to get a custom dyno made.....don't bother asking, the dyno is gonna be about $15,000.....and will be one of a kind.....but it will produce the most accurate results ever.....with none of the problems we see from our current units...

Later EddieO
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Old 12-02-2005, 10:40 AM   #45
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Quote:
Originally Posted by EddieO
I agree....you guys are even starting to scare me with all the geekness:P

that confirms it. if we are scaring him, there is nothing left.
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