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Old 12-12-2005, 08:12 PM   #106
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This has been a very helpful discussion, I have had a T-dyno for years and have used it off and on. I have always used amp steps. I have heard of using torque steps but had never understood it's importance.
Right now I am running 12th scale stock at Y-City in Zanesville Oh. The layout is fairly easy and free flowing with lap counts near 60. This is a jack the gripper track. I have run 1 monster stock so far this year with some success and it finally died this weekend. Now I have been going through the other motors looking for something that ran as good. Unfortunately I never dyno the good motor before it died. From what I have read here it looks like you are looking for the higher rpm motors with lower amp draw to get those higher rpms.
I have dyno'd the motor that I ran in the main and it ran decent but not quite as good as the dead motor. I know what my rollout is. After testing my motors with torque steps I have noticed a smaller difference between motors than I did with amp steps.
Does anyone have any numbers on what they considered a good monster for 12th scale? I would like to compare what I have to someone else numbers to see if I am in the ball park.

Thanks Craig
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Old 12-14-2005, 06:46 AM   #107
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Craig-The only time I would compare two motors at the same motor torque is if you gear them exactly the same on the track. Gearing is easily able to multiply torque of a low torque motor. When you compare two motors at the same torque, the higher RPM motor (higher spring tension on the same can) will always be at an advantage, although it might work better on some tracks like on high grip tracks or tight road courses it might be inferior on the oval. A test at equal amps would differentiate the motors without going to the trouble of calculating rear wheel torques. A high RPM motor would use a lower gear (smaller numerical ratio) than a lower RPM motor to multiply its torque. When the motors are geared differently it might be better to do a comparison at the same amps. For oval amps near the average amp draw and a little higher going out of the corners would be a good area to do the comparison. I don't have any Monster stock data. Maybe someone as well as yourself could post some of your best numbers. This would be enlightening for me as well as others. Voltage of the test, Power, amps (or torque)

Last edited by John Stranahan; 12-14-2005 at 08:55 AM. Reason: Had it backwards
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Old 12-14-2005, 05:37 PM   #108
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ERROR!!!
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Old 12-14-2005, 07:16 PM   #109
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ERROR!!!
You can say that again...
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Old 12-14-2005, 08:01 PM   #110
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A couple of motorsThat I just dyno'd

rpm torque watt ef amps
19208 3.0 42 56 15.1
17384 4.5 57 62 18.2
15694 6.0 69 63 21.6
14301 7.0 74 60 24.4
13178 8.0 78 57 27.0
11739 9.0 78 52 29.9

This motor was run sun and I ran the fastest lap times up front that I have run, but seemed to fall down later in the run. I was geared 1.56. a 96 and a 28 pinion and a 1.70 tire.

This next motor has not been run but I am going to try it this week.


rpm torque watt ef amps
20013 3.0 44 55 15.9
17689 4.5 59 61 19.2
15927 6.0 71 62 22.9
14602 7.0 76 58 25.8
13178 8.0 78 54 28.6
11698 9.0 78 49 31.5

This motor is a monster just like the first motor and has light springs. The first motor had 2 reds. Could this cause a car to slow down during a run?


Thanks Craig
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Old 12-14-2005, 08:06 PM   #111
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Quote:
Originally Posted by RCRacer6
From what I have read here it looks like you are looking for the higher rpm motors with lower amp draw to get those higher rpms.
Thanks Craig
Higher amp draw equals higher RPM unless there is something bound up in the motor causing drag. This is what I see on EVERY motor I build....no if's and's or butt's about it.

Look at a mod motor. Increase timing you increas 2 things....RPM and Amp draw. Despite what most say increased timing does not take torque away...it changes where it occurs in the rpm range.

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Old 12-14-2005, 08:28 PM   #112
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EA, do either one of these motors look like something you would run in 12th scale?

I understand what you are saying about rpm and amp draw, am I trying to make to many rpms and use to many amps to make a 8 min race?


Craig
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Old 12-14-2005, 09:15 PM   #113
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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.

Have been following the thread- and nice info. In doing some research, I have found some pertinent information and wanted to add it to the discussion....

"A stock motor has 27 turns of 22 AWG wire, with a length of 64 inches. 22 AWG copper wire has a resistance of .001345 Ohms per inch, so the 64 inches of wire has a total resistance of 0.086 Ohms (0.086=64*.001345). Using ohms law V=IR (V/R=I) we calculate that if you connect 7.2 Volts (6-cell pack) to this wire, you will have a current of 7.2 Volts / 0.086 Ohms = 84 Amperes. This means that although the maximum current this stock motor can pull is 84 amps this can only occur when it is stalled or restricted from rotating."
-http://www.rcboataholic.com

The 40-45 Amp peak power is real and is supported by these calcs.
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Old 12-14-2005, 09:17 PM   #114
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Quote:
Originally Posted by EAMotorsports
Higher amp draw equals higher RPM unless there is something bound up in the motor causing drag. This is what I see on EVERY motor I build....no if's and's or butt's about it.

Look at a mod motor. Increase timing you increas 2 things....RPM and Amp draw. Despite what most say increased timing does not take torque away...it changes where it occurs in the rpm range.

EA
RIGHT ON... EA !!!!! That is the POWER BAND...or is it?

The torque is defined by Kt and the current that is being drawn by the motor.

The SPEED at ANY TORQUE can be found by the BASIC MOTOR PERFORMANCE EQUATION:
SPEED (Krpm) = [V - (Ia * R)]/Kv = V/Kv - [(Torque * R)/(Kv*Kt)]
Where:
V= Voltage
Ia=armature current @ LOAD
R=Armature Resistance
Kv=Voltage constant for a given armature and winding design...in mv/Krpm
and Kt=1.3524/Kv

As the timing is advanced or retarded the Kv is changed, so can you see what happens to the motor, everything is shifting. Experiment with your motor and use this formula.
So, can you see the relationship between current draw, torque and RPM...as Kv changes due to timing changes...

Listen to what EA has to say...
NO WONDER HE IS "THE BEST"

Last edited by BATT_MAN; 12-14-2005 at 10:19 PM.
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Old 12-14-2005, 10:00 PM   #115
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Kris-Thanks for posting your data. Informative. It agrees well with all the Robitronic dyno runs I have seen on stock motors. EA motorsport-Thanks for the data on mod motor timing. Nothing like real observations to back up an opinion. Mike- I knew you would disagree on my last post as you like to compare at equal torques. The only reason you have given is non linearity of torque vs amp draw data, which is false. Please give me some more observation type data on your track and layout. I'm pretty positive on the effect of spring tension on a stock motors that use the same can arm combination (the subject of my previous post) as I have lots of dyno data on a series of measured spring tensions and I have run the different spring tensions on the track. I still have a little uncertainty on these low induction motors, tri rotor stocks, I have only a little dyno data, I never liked the motors after one run on the high grip tracks that I raced on in stock truck and stock touring car. I also have seen conflicting data from GlenW, alias dynogeek, alias ?, who used to post a lot of dyno data on stock motors. I was never confident the motors he tested had the same spring tension. The motor curves look quite different from just this change.

I am puzzled by one word posts.
Attached Thumbnails
CE Dyno Question-motor-spring-tension-guage-50%25.jpg  

Last edited by John Stranahan; 12-14-2005 at 10:10 PM.
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Old 12-14-2005, 10:09 PM   #116
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John,

It is funny how people interpret posts

THERE IS AN ERROR...and posted ... ERROR!!!

Hope that clears it

Last edited by BATT_MAN; 12-17-2005 at 09:55 PM. Reason: spelling!
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Old 12-14-2005, 10:12 PM   #117
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Isaac-Thanks.
Craig-Too light a spring will cause your brushes to burn toward the end of the run. You can not always run the fastest setup, it has to be durable too. I am plotting some of your data. I am getting a 5.34 overall ratio. Is this correct. (Spur/pinion) * car ratio. What is the voltage of your run just so I can enter that as well.

Last edited by John Stranahan; 12-16-2005 at 12:44 PM.
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Old 12-14-2005, 10:48 PM   #118
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Quote:
Originally Posted by Kris Preisinger
Have been following the thread- and nice info. In doing some research, I have found some pertinent information and wanted to add it to the discussion....

"A stock motor has 27 turns of 22 AWG wire, with a length of 64 inches. 22 AWG copper wire has a resistance of .001345 Ohms per inch, so the 64 inches of wire has a total resistance of 0.086 Ohms (0.086=64*.001345). Using ohms law V=IR (V/R=I) we calculate that if you connect 7.2 Volts (6-cell pack) to this wire, you will have a current of 7.2 Volts / 0.086 Ohms = 84 Amperes. This means that although the maximum current this stock motor can pull is 84 amps this can only occur when it is stalled or restricted from rotating."
-http://www.rcboataholic.com

The 40-45 Amp peak power is real and is supported by these calcs.

That is good data to have!!! Although it does change...soldering techniques, the quality of the copper (wire) ...there are many outside factors besides just the assumed wire resistance/length that have effects on overall armature resistance.

There is a difference between assumed armatrure resistance and REAL ARMATURE RESISTANCE (what the electrical system senses) . Brush resistance (even the resistance from the point where you solder the battery (ESC) wires to the brush contact) has to be taken into consideration, thus the difference. If you use ohms law to calclate the current through the entire motor, the brushes (and everything in between) have to be added. So the overall current will be much lower.

Also, brushes behave like a diode, they have a minimum bias voltage that most be applied to them in order to conduct. For an Si diode it is usually 0.7 volts, for brushes it is much lower, in the mv range. However, different brush compounds have different voltage bias, as well as resistance, as well as brush current density (current/sq.in) as well as friction...and all this play a role in armature current draw. This plays an interesting role in motor performance, because every time the voltage falls below the forward bias voltage, there is a lag in time (lack of voltage and current flow, back EMF kick up...Kirchoffs law)...thus the magnetic field collapses much faster, torque falls, currents get higher to get the motor back to its needed torque...it's a snowball effect...Although minimal, it does affect the performance. This forward bias voltage is different from brush compund to compound...

It is nice to know the armature resistance because it can be used to calculate many parameters of the motor, but to calculate Ia, the current flowing through the armature, the brush res. must be added, there is no way around it...ohm's law

Isaac

Last edited by BATT_MAN; 12-14-2005 at 11:02 PM.
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Old 12-14-2005, 11:42 PM   #119
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Craig- Here are a few graphs on your Monster stocks.

First some explanation a motor pulls big amps when it starts from a dead stop and develops high torque (the right side of all these graphs). On an oval the motor is running at high speed. The reverse voltage, the motor develops, reduces the amp draw. Consequently at high speed the motor draws fewer amps and develops less torque (the left side of all these graphs); the straight, the Oval. I just thought I would put this here in case its helpful to interpret the graphs.

First from Craigs data it looks like Motor II is a more RPM oriented motor. It needs to be geared lower, about 6% lower if I look at the RPM's of both motors at 20 amps. I needed an RPM vs amp draw graph to collect numbers for this calculation. You could do it at equal torques, say 4.5 oz-in with slightly different results 2% lower, but motor II is still geared lower (bigger numerical ratio). This is just a starting point and then you adjust it on the track.

If you look at the Power vs Amp draw graph it looks like Motor I has slightly more power at 20 A and would be better on the oval. The graphs don't follow the typical pattern I see with heavy vs light springs, but I don't know two things. I don't know the actual tension in ounces, I don't know if the springs are polarized (one heavier than the other on the same motor. This second factor, polarized springs, has a big effect on RPM, it can help power only a little, but can hurt as well. A heavier spring is usually run by some racers on the positive brush when the brushes are burning up, this positive brush burns faster. This combo produces slightly less power than a slightly heavier spring on the negative (.5 oz). I always geared conservatively, to save my equipment, and used a heavier brush on the negative.

If you look at Power vs Torque at the Rear Wheel with a 6% lower gear for motor II the motors look almost identical in power.

If you look at Power vs Motor Torque You get the exact opposite conclusion
Motor I looks better.

Now I have run enough stock motors to believe that motor II is better on the oval, but I could be wrong.

Note that Craig used torque steps. All the data from the motor is still easily available from a graph. It can still be plotted vs amps.

If it is easier for yout to look at graphs rather than numbers, the printout of page 1, 2, 3 or the rear wheel torque calculator spreadsheet looks like the 3 attached images.
Attached Thumbnails
CE Dyno Question-s-monster-stock-graph-power.jpg   CE Dyno Question-s-monster-stock-graph-torque.jpg   CE Dyno Question-s-monster-stock-graph-t-vs-.-jpg.jpg  

Last edited by John Stranahan; 12-17-2005 at 10:44 AM.
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Old 12-15-2005, 01:21 AM   #120
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Default THE EA EXAMPLE

This is sincere and honest observation.

This thread is instructional and interesting. However, I am starting to see some areas where it is getting out of ......

Yes, it is very nice to see motor power graphs and kind of cool graphics. But the end result is not a graph, or hypothetical gear ratios/torques based on calculations.

Motors have many variables that are not taken into consideration while using a dyno or performing the type of calculations that I see in here.

The biggest and BEST example is Eric from EA Motorsports.
He can take a motor, see how it is performing on the track, take the motor, work with it, and turn it into a winning motor.
He is not using variables, constants, and graphs. HE IS USING PLAIN COMMON SENSE AND LOTS OF HANDS ON EXPERIENCE. Not even engineering degrees can give you that. Practice and knowledge is acquired through hard and repetitive work.

Unless you know what you are doing, and what to expect from different adjustments, you can stare all day long at graphs,numbers, and all kinds of data, yet you will NOT GET THAT MOTOR TO WORK THE WAY YOU WANT.

Yes, it is nice to know how motors operate and to design them, but without experience you will never achieve anything.

My recomendation is to absorb the GOOD information that has been passed, analyze it, understand what is happening with the motors, and get your hands dirty tuning and playing with your motors.

Unless you tune and adjust hundreds of motors, you will never get profficient.

Again, the best example is Eric. He can take a motor and turn it into an INSANE MACHINE. Why, because he knows what he is doing, he has the experience, and NO ONE CAN TAKE THAT AWAY FROM HIM.

I don't think that when he is at the track, under pressure to get a motor to perform in minutes, he has the time to get a computer, start plotting theoretical torques and look at the data. ITS IN HIS HEAD, experience alone will make himn what he is, the BEST.

If anyone of you really wants to be good at tuning motors, my recomendation is JUST DO IT. Only by trial and error you will see how things work, how one factor changes another, and by either taking notes, or just having a great memory you will gain experience.

This is just my observation. I could be wrong, but I doubt it.

ERIC FROM EA is the NUMBER 1 EXAMPLE. He is not showing nice graphs and pictures, giving spring tension recomendations...etc. WHY, because he knows that for every rule there is an exception, and the only way to tune a motor is with lots of experience and know how... Because he understands what happens as he makes adjustments and changes.

I APPLAUD ERIC for what he does and the way he goes about it. Other motor winders/tuners are always giving of the head recomendations without all the facts. Eric never does that. His track record is amazing, yet he does not brag about it.

ERIC, you have all my respect. As a practicing engineer that has worked with motors for years and with some of the nations leading motor designers (outside the R/C industry), I can only say that your expertise and knowledge to get a motor to function for a specific car/track setup is second to none.

If most of you want to get your motors to work, there is nothing wrong asking questions, but unless you get to work on them and see the differences on your adjustments AT THE TRACK, you will never tune a WINNING motor. Bench testing is one thing, it gives us a reference point from where to start, but the end result is produced at the track level. EXPERIENCE AND ONLY EXPERIENCE will get you there.

Work on your motors. You will destroy a few, but that is the only way you will understand how they work. PRACTICE, PRCTICE, EXPERINCE...

JUST MY OPINION.

Isaac
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