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Old 12-15-2005, 07:16 AM   #121
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Quote:
Originally Posted by John Stranahan
Unless you use really heavy springs (unavailable really heavy springs) the power is usually peaking at 40-45 amps for motors used in stock trucks on a high grip surface. The stall torque (or starting from a dead stop torque) is predicted to happen at 114 amps. I think this is too high.
John, I just read this, and I have to clarify one thing. Stall torque is not the same as cranking torque. Yes, it takes much more current to get the motor going as a motor needs to develop torque to get the motor going (spinning), but that amount (current) depends on the actual load that the motor is pulling. Accelerate a motor with no load and read the current needed to start, add a load and read again, the current will increase due to the load.

Stall torque is the current that the motor will draw when you bring the motor down from full no load RPM to a cmplete stall. At that point you take an instantaneous current and torque reading. This will give the stall torque.

In most circumstances, MAXIMIUM POWER will take place at 0.5 stall tortque. Thus, two motors can have the same power output, different stall torques, and what you will see is the POWER BAND. The Power Curve will shift, just like Eric described above.

Isaac
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Old 12-15-2005, 03:55 PM   #122
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John, Thanks for the graphs. I am still looking them over, it's interesting to look at the numbers in different ways. I am testing at 5 volts.

Issac, It's been interesting to read and try to understand the points that you are trying to get across. I have been racing 12th scale since october of this year with the same motor, every practice, every heat. I have made small changes to the chassis, almost everytime I have run and learned some interesting things. I have made good progress, my lap times prove it. I was now thinking that it was time to work on some motors now that the car was running good. I realize that the dyno does not tell everything and practice and track time is most important. The dyno is a tool and I am just trying to get the most out of it that I can. I also enjoy playing around with motors on just to learn.


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Old 12-15-2005, 05:45 PM   #123
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Craig - It's good to hear that you are consistently improving your lap times. As long as your lap time keep getting better you know that you are doing the right thing.
Regarding your interest in motors, I think that is GREAT. I love to work with them and I understand where you are coming from. It makes a huge difference if you understand how a motor operates and how all the different components that make and define a motor relate to each other. The better you understand the relationships between the constants that define the motor and how each one can be used to improve the performance and/or understand what is happening with the motor your motor selection for a specific application will be much easier.
Once you understand all these you will see that it will be easier for you to make motor adjustments/selections based on empirical data from your dyno.

Keep working on your motors because only that way you will get better at this.

If there is anything I can help you with, or if you just want to exchange information, do not hesitate to ask. I am allways willing to help and learn.

There is never a dumb question, and only by asking can we learn more from each other.

I hope that you get to the point that you feel that you are acomplishing and seeing your motor performance go up, just as you have done with your racing.

Isaac
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Old 12-16-2005, 04:13 AM   #124
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Isaac. You didn't like my pretty colors. I'm hurt. (just kidding).

The point of Kris's post was to indicate a maximum amp draw possible. No way is it 110 amps as the armature will limit the amperage.

The starting amp draw on a Robitronic dyno seems to be a good indicator of stall torque as the flywheel is heavy. Probably only a few amps different. RC cars are heavy as well I have measured 75 amp draw on a stock truck slipping the slipper clutch. Yes you have distinguished the two.

Last edited by John Stranahan; 12-16-2005 at 12:42 PM.
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Old 12-16-2005, 08:55 AM   #125
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Hey guys! Talking about CE Dyno, where can I get an armature for my slave?
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Old 12-16-2005, 09:08 AM   #126
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3 places dc motorsports, team brood, or CE
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Old 12-16-2005, 09:18 AM   #127
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Thanx
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Old 12-16-2005, 11:32 AM   #128
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John - Your graphs are instructional (and accurate), not to say the least.
It is a GREAT way to display numbers so that people can visualize what is happening. A picture is worth a thousand words

[email protected] - Regarding the armatures for the CE dyno, I believe EA Motorsports also sells them.

On another note:

I just want to make something clear.
I have nothing against graphs, numbers, dyno data, its all GREAT, and necessary. The point I was trying to get through is that the only way to understand what happens with motors and how to best tune them is with practice, practice, practice. Hands on experience, there is no alternative.

I am sure that all your work (graphs, data, assumptions, theories, results) are not only based on numbers but also with real on track performance and backed up by experimentation (hands on work).... RIGHT?

To understand how all these equations, constants, and graphs work one must tinker and experiment with their motors and test equipment.

Hopefully most of the followers of this thread will continue with their work and get a better understanding of motors, dynos, and how to interpret and analyze the data given by their equipment.

I have received many PMs and emails, and I am doing my best to answer all of them with accurate and reliable information. If there is one thing, if I do not know something, I will not comment or give bogus answers.

Ithink on the next thread we will start something that has to do

As always, I am available and willing to help everyone.

Isaac

Last edited by BATT_MAN; 12-16-2005 at 11:06 PM.
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Old 12-16-2005, 12:08 PM   #129
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Quote:
Originally Posted by kerry
3 places dc motorsports, team brood, or CE
EA motorsports sells them also
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Old 12-17-2005, 06:38 PM   #130
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I added a third set of graphs to my post #119. The bottom graph on the third image shows the general relation of RPM to amps (with no timing change), as RPM goes down from an applied load, amp draw goes up. The second graph on the same image is Torque vs amps. Here is a link to the graph.

Torque vs Amps, RPM vs Amps
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Old 12-17-2005, 10:18 PM   #131
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Thanks for the great thread guys! Anyone want to start a thread on biology, so I can chime in
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Old 12-17-2005, 10:49 PM   #132
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Default MOTOR SPEED-TORQUE GRAPH

Quote:
Originally Posted by John Stranahan
I added a third set of graphs to my post #119. The bottom graph on the third image shows the general relation of RPM to amps (with no timing change), as RPM goes down from an applied load, amp draw goes up. The second graph on the same image is Torque vs amps. Here is a link to the graph.

Torque vs Amps, RPM vs Amps

John - In an effort to compliment the graphs that you posted, I added the sample graph from post # 88.

In this graph anyone can see the interrelation of ALL the variables that we measure in a motor. RPM, CURRENT, EFFICIENCY, POWER, and TORQUE.

NOTE: This graph uses a constant of ONE for torque (oz-in), EFF(%), POWER(W), and CURRENT(AMP) as a reference.
This material is used for instructional purposes only
This graph depicts the operation of a motor as close as possible.
This is NOT an R/C MOTOR. HOWEVER, the relatinships are THE SAME.
See NOTE #2



I am showing how RPM, CURRENT, POWER, and EFF relate to torque. (Whether you measure current or torque, the result is the same)...torque is what we are looking for at a desired current or power (watts) range or vice-versa.
The reason I decided to plot everything against TORQUE is because it is very EASY to visualize and UNDERSTAND what happens as each variable changes. THE ONLY CONSTANT HERE IS VOLTAGE. The graph depicts exactly the behavior of a motor as long as it operates within its normal operating range. As in any case, there are exceptions.

By paying close attention to this graph, it will be EASY to visualize the interrelationships between all the variables. This should make it easier to understand the behavior of a motor.

As it can be seen, CURRENT (I) is directly proportional to torque and inversely proportional to RPM (supported by John's graphs). POWER (WATTS) is always a parabola (an arch) with MAXIMUM POWER at 0.5 stall torque.
Maximum Efficiency usually happens at around 10-15% of stall torque (or max current draw), 90% of MAX RPM, 40% of MAX Power...this are +/- percentages...

So at Maximum Power, a motor usually generates close to 50% (+/-) of its MAXIMUM TORQUE and RPMs, which we calculate a few RPMs before the motors stalls.

This should make it easier understand what the numbers on a motor label depict. Please understand that most of the info that comes with the motors is expressed as MAXIMUM...(not the CE Dyno printout, these are numbers at a specific torque or current)
Once you understand these relationships, you can take those numbers and estimate the behavior of that motor.
BTW, using the numbers from the CE Dyno, you can plot a graph like the one above...or if you use sticker numbers, remember that they are at MAX ... then you can estimate some points based on what I explained and draw a graph.

I hope this will help.

Isaac

NOTE #2: This graph assumes ZERO losses due to friction and other mechanical factors. In most (all) motors the graph will be shifted towards the right as there is a torque developed by friction, thus the current will never be at ZERO (it will be HIGHER) when the motor is at MAX RPM.. I shifted the graph to makeit easier to understand.

Last edited by BATT_MAN; 12-18-2005 at 07:14 AM. Reason: Clarifications...
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Old 12-22-2005, 10:08 PM   #133
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Default Spring Thing

Someone asked me if there was a motor spring tension gauge for sale. Here is a link to the Spring Thing by Trinity. It may not read in ounces, but it will let you reproduce spring tensions.

http://www.teamtrinity.com/motors/motor_tools2.html

There is no reason you could not push this device on a postal scale and put marks on it to calibrate it in ounces. The only advantage here is the ability to compare data with someone else.

Last edited by John Stranahan; 12-23-2005 at 10:49 AM.
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Old 12-22-2005, 11:35 PM   #134
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www.teambrood.com has the orginal spring tension gauge.....the fiddlestick....its under tools.....the trinity unit is just a copy of it......


Later EddieO
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Old 12-23-2005, 01:19 AM   #135
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Quote:
Originally Posted by EddieO
www.teambrood.com has the orginal spring tension gauge.....the fiddlestick....its under tools.....the trinity unit is just a copy of it......


Later EddieO
EddieO is correct...besides the fiddlestick is much more accurate. I still use the one that BJ handed me years ago...and it still works just as good as the day I received it.

Using a postal scale is OK for a workshop, but not for the race track.

There is one issue that most ignore. At times, as the motor gets hot, the springs loose some of their compressive (or tensile) strength due to thermal issues. Then when they cool down, they return to their measured compressive strength ... Well sometimes they do loose some strength.

Isaac
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