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Old 05-26-2011, 10:15 PM   #301
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The eagle tree should work with the LCD output to determine the RPM while running the slave. I however will have to look elsewhere to calibrate the unit. I think the way to go for me will be to use a steel flywheel and the Sentry with its reliable RPM output. The problem with the Eagle tree at present is a huge amount of noise when the system is idle. Huge RPM spikes are present. At about 200 RPM the RPM reading will stailize. Unfortunately I have missed a lot of important data before 200 RPM is reached. The flywheel spreadsheet cannot be used with the Eagle tree at 4.2 v. Stay tuned.

I tried the Sentry RPM sensor on the Eagle Tree. The motor would not run.

The Eagle Tree magnetic sensor may produce smooth RPM data. This V2 sensor is full of noise problems.
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Old 05-27-2011, 10:37 AM   #302
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John, what about Eagletree's optical or magnetic RPM sensors? Have you tried those yet?
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Old 05-27-2011, 03:03 PM   #303
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I will order the magnetic RPM sensor and maybe the LCD display later on just to see if they work OK. My last test I actually started at 700 RPM as it is hard to adjust the motor to 200 RPM without an RPM readout. I only got two useful data points for the spreadsheet. I really need 12 or so. At this point I think the flywheel will work at 8.40 Volts and the slave motor will work on 4.2 V. Once calibarated it will give a useful power number.
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Old 05-29-2011, 11:16 PM   #304
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Steel Flywheel

I finished the steel flywheel. The dimensions are
Total Mass 331.0 g
Large ring 2.487 in OD x .520 in wide, .375 in ID
Small ring or shaft extension .375 OD 1.115 in long, .125 ID
Calculated Inertia 1.62 x 10^-4 kg m^2

I increased the rotor shaft support length a little to get is closer to the motor bearing and to clear motor screws.

Calvin- I was unable to download and unzip the zipped spreadsheet file. I have had this problem at RC-tech before. Please e-mail me the file to [email protected] or run those numbers through it. Thanks. Progress to come.

Notes on building the flywheel. I had put these earlier in the thread. I started this flywheel from scratch. It was a 3 " square of .75 thick steel and a piece of .375 stainless rod, a little oversize. I drilled the square 3/8 inch on the drill press. Much as I would like that hole to be straight, it was not and there was considerable wobble after pressing in the shaft. The extra thickness paid off here. I band sawed the square to more sides than an octagon. I drilled the hole in the .375 rod on the lathe with an undersized cobalt drill. I drilled half from each side, I withdrew the bit and cleared chips every .1 inch, then I reamed the hole 1/8 inch with a chucking reamer from one side. The size was good. A 1/8 shaft was a no play fit. Again you would hope the drill drills on center but it is going to wander a bit. I chucked the flywheel on the 3/8 inch shaft and could make .005 to .010 cuts to smooth the disk with a cobalt bit. Next I chucked on a long 1/8 shaft captured by the set screws. The tailstock side of the shaft was held by a precision reamed 1/8 inch aluminum bushing and oil in the tailstock chuck. I surface ground a few more thousandths of the sides and the large radius to true the part to the shaft which is what we need for vibration free performance. It was so on the motor.
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Attached Thumbnails
Dyno, Homemade, Using a Novak Sentry Data Logger, Continued, The Experimental Thread.-steel-flywheel-003.jpg  
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Old 06-06-2011, 05:24 PM   #305
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First Test with the Stanahan Steel Flywheel

I ran a first test in calibrating the slave. Attached is a copy of the output. Values past 7500 RPM are eroneous. Ouput at lesser RPM than this is good. The spreadsheet contains an equation of Power vs RPM. I can plug the RPM that this motor achieves on the slave and calculate it's power. With enough of these runs a simple formula for power vs RPM for the slave shall be obtained. This is what the end user will use. This data here on the steel flywheel is for calibration purposes or for demonstration only. Note a second double click on the graph will enlarge it.

This motor achieved 5310 RPM on the slave. That is near peak power but just after it. The slave is in a good RPM range.

Eagle Tree LCD display
I received another eagle tree order today. The LCD panel just did not work at all. I will need to return it for replacement. I have the magnet powered RPM input. I will give it a test later.
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Attached Thumbnails
Dyno, Homemade, Using a Novak Sentry Data Logger, Continued, The Experimental Thread.-lrp-x12-17-5-output.jpg  
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Old 06-07-2011, 11:34 PM   #306
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Eagle Tree LCD display
After e-mails to tech and back at Eagle tree, I am advised that the LCD does not work at high data capture rates. After resseting it to 10 points a second the display started to work. So here is the plan. 10 points a second is very suitable for slave motor work. The Eagle tree and LCD display will be a nice way to gather data for the slave dyno. It will read the Voltage, Amperage, and RPM without a full fledged computer and Excel involved. From these three values formulas from the calibration work will deliver Power, Torque, and Efficiency at that RPM. You should be able to manually calculate these with a calcultor or these days you can probably program your phone to automatically give the three outputs from the three inputs.
Another page on the Excel spreadsheet will also be provided to do the slave motor math.
John
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Old 06-08-2011, 07:46 PM   #307
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Calibration Work Continues
In a series of experiments it is often helpful to randomize the order of the experiments. This helps you pick up errors that may result from time (wear and tear for instance). With this in mind I decided to test the LRP X12 3.0 next. Here are some interesting results.

I tested the plastic tubing coupler first as this would be the less arduous test. The plastic tubing slapped me in the face. This was repeated. The motor can run at 42000 RPM on 1 cell. Any imbalance in the tubing is going to cause it to fly off (wear safety glasses). This is not a problem with stock and super stock motors. The next test was on the McPappy Aluminum flywheel. I tightened one set screw as normal, The motor spun the flywheel up and it vibrated off at about 35000 RPM. I run a wood scattershield between me and the dyno when I do these high RPM tests. Well the flywheel hit the wood and then settled on the platform still spinning at 35000 RPM, anodized surface on anodized surface. This lasted a couple of agonizing long seconds. I tilted it and the flywheel jumped on the floor ran accross it stopped on the speaker still spinning furiosly for a few more seconds. I did not want to try and grab it. Interesting burn marks on the platform. Looks like an electrical short circuit spark pattern.

I used two set screws next and ran them as tight as I could. I got a succesful flywheel run. This all with the McPappy Flywheel. the motor pulled a full 209 amps from the 1 cell Thunderpower pack. The motor developed about 211 Watts.

I plan to make a little coupling similar to the one that came on the Competition Electronics Turbodyno. It was a piece of spiral cut Aluminum rod. This will give me a data point up at high RPM for the slave motor dyno. This will allow the use of 2 cell testing on stock motors with the slave.

I am also working on the math modeling used in the flywheel spreadsheet to see if it can be improved.

Tighten those setscrews when using high power motors. Use a scattershield, were safety glasses.

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Old 06-09-2011, 09:37 PM   #308
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High RPM coupling

I built the type of coupling, that I like, so I could do my calibration runs and include some high power stuff. It consist of a 3/8 inch diameter tube, drilled and reamed to 1/8 inch. I then put a helical groove on it with the lathe. I cut this groove down to a soft steel shaft with a .010 inch thick X-acto saw. This took considerably less time than making the flywheel. Here is a pic.

LRP X12 3.0 on 1 cell
I was able to run the slave motor now with the 3.0. It developed 33,169 RPM. The run was as smooth as silk. No vibration at all. I also ran it on the McPappy aluminum flywheel. The output is attached.

(Competition Electronics provided a similar coupling on their turbo dyno so the production aspect has been solved by at least one company. I think it could be made on a setup that can make worm gears. Instead of a gear grinder head an angled slitting saw could make the cut in one pass at about 8 threads per inch. I used a .010 slit but it does not have to be so thin a cut. A courser thread can be used to compensate and add strength to the part. Or in a different setup, say a 1/16 inch carbide end mill at about 6 threads per inch on the part.)

I know that there is less interest in running the high power stuff on the dyno. The stock McPappy Coupling works very well with 1 cell and stock motors.
john
Attached Thumbnails
Dyno, Homemade, Using a Novak Sentry Data Logger, Continued, The Experimental Thread.-lrp-x12-3-0-aluminum-flywheel0001.jpg   Dyno, Homemade, Using a Novak Sentry Data Logger, Continued, The Experimental Thread.-new-motor-coupling-002.jpg  
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Old 06-15-2011, 12:14 AM   #309
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First Draft of Calibration Results
This is what has been done so far. I ran six motors and 5 winds on the slave. The winds were LRP 17.5 two 13.5s, Novak HV and Speed passion, LRP 4.5, LRP 3.5, LRP 3.0. All LRP's were X-12s. Motors higher than a 13.5 (or maybe 10.5) need the Aluminum helical cut connector to run the slave. Stock motors will work fine with the tubing. Higher powered motors needed to be run on a one cell pack. Lower powered motors (less than 10.5 wind)needed the Steel flywheel for me to determine power for this calibration.
I ran flywheel runs on each motor to determine power vs RPM. I used this output to determine power on this chart. There are five runs on the 17.5, two runs on the 13.5 with data diamonds on the graph superimposed for the most part. Note the 13.5 pulled less RPM on the slave and less peak power on the flywheel test so it shows up as the lowest motor. It has a much broader power band though that shows up in the car.

An equation similar to that shown on the bottom of the chart will be the one used to calculate power. The voltage you run at will not matter. You will just imput the slave RPM and the spreadsheet will calculate power, and efficiency and torque if you supply amps and volts, from say the Eagle tree digital display or the computer. It will be quick and easy. You can do it on a calculator. I plan to just omit the 3.0 as I had difficulties with it. It did have less power than the 3.5 on a flywheel run. RPM's were huge. On one run a small white hot plume exited the front of the capacitor for the speed control. The solid lead wire had parted in two and arced. This was at part throttle on the power supply running the slave.

This is what I need to proceed. As you can see data is rather skimpy in the middle, I could use a loaner 10.5. I should also have a data point for a 21.5. I could use a loaner 21.5. I will mail it back to you. You get dyno results. Send me a PM or e-mail to [email protected] if you are willing. I will pay your postage to and back.

Power Formula
This formula, which is the same as the one on the graph, but with more significant figures, can be used to calculate power in Watts of a motor which is run on the slave motor dyno, where x is the RPM you achieved with the slave. It will be most accurate using an LRP X12, 21.5 Slave with black rotor shaft, the Meanwell HRP-600-5, 5V 120A Power supply, set to 4.20 V. Satisfactory results are also obtained using a fully charged Thunder Power 1 cell pack which was used to run the 4.5 and 3.5 and 3.0. The formula will work with 2 cell packs as well as 1 cell.

Power = 0.4.16419E-12*x3 + 9.38044E-8*x2 + 0.005317*x +38.49502


John Stranahan
Attached Thumbnails
Dyno, Homemade, Using a Novak Sentry Data Logger, Continued, The Experimental Thread.-calibration-graph0001.jpg  
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Old 06-15-2011, 04:34 PM   #310
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Attached is an image of the spreadsheet page that will be used to calculate your test motor power when running it on the slave motor. This was my task. You put 3 measures into the green area, slave RPM, Voltage and Amperage. Power, Efficiency, and Torque are calculated and displayed in the orange area. Simple. You can obtain the data using the Eagle tree digital display or data logger and computer. The power formula is posted above and below. A considerable number of experiments were performed to develop the power formula. This work is shown further down on the spreadsheet, but need not be repeated. I could use a couple more data points to refine the formula. See the quote.

The best part about this slave motor method is the good repeatability of tests. You will be able to differentiate two motors of the same wind.


Quote:
Originally Posted by John Stranahan View Post
This is what I need to proceed. As you can see data is rather skimpy in the middle, I could use a loaner 10.5. I should also have a data point for a 21.5. I could use a loaner 21.5. I will mail it back to you. You get dyno results. Send me a PM or e-mail to [email protected] if you are willing. I will pay your postage to and back.

Power Formula

Power = 0.4.16419E-12*x3 + 9.38044E-8*x2 + 0.005317*x +38.49502

Attached Thumbnails
Dyno, Homemade, Using a Novak Sentry Data Logger, Continued, The Experimental Thread.-spreadsheet-slave-motor-power0001.jpg  
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Old 06-15-2011, 07:28 PM   #311
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high john just a quick question,im sure i am missing some thing.
the graph in post #308 shows (and i think is mentioned in #307) 209 amps @4.14 volts producing 211 watts
how can that be, wouldn't 211 watts @ 4.14v be around 50 amps
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Old 06-15-2011, 11:08 PM   #312
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Those two numbers are maximums and did not happen at the same time. At 211 W (purple power line on the graph) the motor is pulling 110 amps (green amps line) or so. Your calculated amps would be at 100% efficiency which we do not achieve. Efficiency is 60-70% at peak power (yellow efficiency line) for this motor. 209 amps is pulled in the first few tenths of a second where the motor is near stall speed.

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Originally Posted by ozzy-crawl View Post
high john just a quick question,im sure i am missing some thing.
the graph in post #308 shows (and i think is mentioned in #307) 209 amps @4.14 volts producing 211 watts
how can that be, wouldn't 211 watts @ 4.14v be around 50 amps
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Old 06-16-2011, 12:00 AM   #313
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what i am trying to say is amps x by voltage = watts
209a multiply by 4.14v = 865 watts

not saying your wrong just trying to figure out how you can get such high amps with such low wattage produced

EDIT, mite have gotten it. your saying at 209 amps the efficency is that bad its producing very little power ?
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Old 06-16-2011, 03:16 PM   #314
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You are correct in that the battery is dumping huge Input Watts into the system, but at 209 amps, the motor is turning very slow and is very inneficient. Only roughly 10 percent efficient (the yellow line on the graph starts very low on the left where the motor is pulling 209 amps and increases going to the right as the motor picks up RPM). Only 10 pecent of the 865 W is actually producing motor power at 209 amps. Rougly 75 Watts or so is the Output Watts here. The rest is heat. That 3.0 runs plenty hot.
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Old 06-16-2011, 05:59 PM   #315
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Quote:
Originally Posted by ozzy-crawl View Post
what i am trying to say is amps x by voltage = watts
209a multiply by 4.14v = 865 watts

not saying your wrong just trying to figure out how you can get such high amps with such low wattage produced

EDIT, mite have gotten it. your saying at 209 amps the efficency is that bad its producing very little power ?

Sorry to jump in here, but, when motors are running they create a reverse EMF. This EMF translates into a voltage across the motor when it is running at a RPM.

When a motor first starts, it does not create an EMF, and appears to a circuit close to a dead short. The only resistance to current flow is the resistance of the wire, and this creates a high starting current. This is the 200 Amps John is showing on the spreadsheet.

As soon as the motor starts to turn, it will create an EMF which will create a reverse voltage, and lower the current in the motor. The motor is not producing 800Watts of power when it has 200 amps of current flowing thru it, as it has very little voltage across the motor (from Reverse EMF), thus the motor is producing very little power (in watts).

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