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Old 06-16-2011, 06:33 PM   #316
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I think you guys need to take a look at this idea of a brushless dyno.

Very simple and easy to build!!!
Alot of racers in Europe are using this system.

http://www.rccartips.com/rc-car-dyno-cheap.htm
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Old 06-16-2011, 10:54 PM   #317
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I have the Dyno Calculation spreadsheet complete now. It will calculate power on a flywheel run, and now on a slave motor run. Send for a free copy to [email protected] I have forwarded it to McPappy and it may be available on his web site soon.
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Old 06-17-2011, 01:47 PM   #318
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Mr RCTech-I took a look at the dyno in your link. Acceleration seems to be computed by the two point method. (Delta V / Delta t) If you look at our spreadsheet on the second page there is an acceleration graph showing the two point method which is a big zig zag like that shown in the links screen. Our smoothed acceleration is calculated by fitting a mathematical model to the entire angular velocity vs time curve. This data is smooth and accurate. the mathematical derivative is taken to get acceleration data. Smooth results are obtained. More accurate results are obtained. Here is a quote from the link down below.
I like the direct input into the computers microphone jack. No data logger is needed. I don't like the fact the entire run goes through the drivetrain.

"For Torque and Power it is a little different. Because the "live" data for Torque and Power can be very noisy you may want to just turn both of these off. So although you can only have one on at a time, you also have the option to uncheck both."

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Old 06-17-2011, 07:23 PM   #319
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Quote:
Originally Posted by John Stranahan View Post
Mr RCTech-I took a look at the dyno in your link. Acceleration seems to be computed by the two point method. (Delta V / Delta t) If you look at our spreadsheet on the second page there is an acceleration graph showing the two point method which is a big zig zag like that shown in the links screen. Our smoothed acceleration is calculated by fitting a mathematical model to the entire angular velocity vs time curve. This data is smooth and accurate. the mathematical derivative is taken to get acceleration data. Smooth results are obtained. More accurate results are obtained. Here is a quote from the link down below.
I like the direct input into the computers microphone jack. No data logger is needed. I don't like the fact the entire run goes through the drivetrain.

"For Torque and Power it is a little different. Because the "live" data for Torque and Power can be very noisy you may want to just turn both of these off. So although you can only have one on at a time, you also have the option to uncheck both."

john
I didn't post this dyno to take away from your dyno system but to offer another
idea of a system not using a data logger.
I thought it to be very simple and easy to use.

You can run a wheel/set screw on the motor (with the magnet on the wheel) to the speaker system instead of going through the drivetain.

Just another idea.
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Old 06-17-2011, 07:27 PM   #320
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John,

The "zig zag" on the screen was simply me accelerating and decelerating the car repeatedly and does not reflect the noise in the system.
However, you are correct regarding the statement on the "live" torque and power numbers. I do not consider them reliable as slight +/- differences in the RPM will lead to wildly fluctuating torque and power numbers.

Further down on the same page you will note that the software also includes a "Power Run" function which you use to collect a true power run data set which the software automatically fits using a 4-parameter logistic curve fit. This generates the smoothed power and torque versus RPM curves.

The software is not limited to chassis dyno applications (although I feel that there are some advantages to considering the entire drivetrain in these kinds of analyses) and can easily be applied to motor testing by simply treating the rollers as a flywheel (that is entering your flywheel mass, diameter etc as if it were a roller). I have used it for motor testing (albeit low power applications) successfully. Testing using tone generators indicates that the RPM precision at 100,000 RPM is approx 2%.

I am currently working on a pulsed output wattmeter circuit, to be compatible with the software, so that you can also gather the volts / amps data alongside the rpm data in the same run.


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Old 06-18-2011, 10:10 AM   #321
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Very interesting to see how far along this concept has developed. I really like the McPappy setup
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Old 07-07-2011, 02:51 PM   #322
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DanoRC-Thanks for clarifying your dynos methods.
Matnin-good to hear from you.

I continue some work with the Eagle Tree. The LCD display will not work. an e-mail to Eagle tree suggest I reset the parameters and if this fails to mail it in.

I am also getting erroneous RPM readings fromt he brushless motor sensor. They are low by 30%. There are gaps where it reads zero. There are huge spikes at RPM in live mode. Changing the number of motor poles to 2 and then to 4 both resulted in even lower RPM readings. Here is the reply from Eagle tree.
Regarding questionable RPM readings with the Brushless RPM Sensor there may be an incompatibility between our brushless sensor and your motor/ESC combo.

"One customer who was having a similar problem found that the problem was resolved by placing a 1uF capacitor between the WHITE and BLACK wires of the brushless RPM sensor. One simple way of doing this might be to place the leads of a through-hole 1uF capacitor (from RadioShack or similar electronics supply house) into the brushless RPM sensor's servo connector, so the two leads make contact with the two pins."

Fitting those two little magnets from the magnetic RPM Sensor on the slave motor setup looks possible on one of the lockrings. Eventually, I will look into it. I have it in hand.

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Last edited by John Stranahan; 07-07-2011 at 03:06 PM.
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Old 07-08-2011, 12:26 AM   #323
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John,
A fellow by the name of Bryan Blaser (Google "Blaser's Speed Shop" for some photos) makes a really neat looking chassis dyno set up for 1 cell oval racing. I am not personally experienced with this unit, but I bring this up because he uses the Eagle Tree V4 and and display screen (I think his original units used the Novac). However, from the pictures I've seen (unless he's changed his design) I'm pretty sure he uses the magnetic RPM sensor as opposed to the Brushless Sensor (fyi those round Eagle Tree magnets fit perfectly in the holes of Kimbough spur gears - use a dab of Shoe Goo is you're scared they will come out). Can McPappy's unit handle a pinion/spur setup? Might be a consideration - it would be a way to lower the RPM of the slave motor for measuring purposes but would add some inertia effects.

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Old 07-08-2011, 06:10 AM   #324
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The McPappy could do a pinion/spur setup. Some company a while back made an adapter that allowed you to run a spur gear on a motor. I don't remember who it was though.
If anyone is interested, I have a Mcappy Dyno for sale with a slave motor and sentry unit.
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Old 07-09-2011, 02:11 PM   #325
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I fit the magnets in a milled hole on either side of the clamp rings that hold the flexible tubing. I got no RPM data. I plan to send my unit back as there are multiple problems now. There may be a problem with my unit.
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Old 06-17-2012, 03:23 AM   #326
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I am also getting spurious RPM readings in live mode from the Eagle Tree. I will try the capacitor. I assumed 2 poles. Has anyone found a better or more complete solution?

DamoRC I like your site. Thank you for sharing. Having an information overload now

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Old 07-10-2012, 12:42 PM   #327
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I recently got a MCPappy Dyno, and I am using the Optical Sensor from Eagle Tree....It seems to work quite well. keep in mind I am stricly using it as a Chassis Dyno.

Has anyone else tried it? Advantages/ Disadvantages?

Thanks,

Last edited by impson; 07-10-2012 at 12:54 PM.
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Old 07-30-2012, 01:39 PM   #328
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jon would you like to do some testing on a tekin 4600kv 4 pole
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Old 12-12-2012, 07:54 AM   #329
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Here's a picture of my home-made dyno.

Total cost so far is just 42 for the slave motor and resistors, as I already have a Novak Sentry which I use for TC racing

It completed its first two runs last night, and destroyed 4 pinions in the process. The first ones were ally so this was kind of expected, but the steel ones didn't fair much better. So I've now ordered a direct coupling to replace the pinions. At some point I'd like to get one of those spur hubs that allow a spur to be fitted to the slave motor, but I can't find anywhere that will ship these to the UK for sensible money, so the direct coupling will do for now.

Although it won't give quite the amount of information a flywheel would for comparisons of different motors/rotors, it will allow me to test motor fade, lipo fade, different cooling options, different ESCs and overall power of different motors. So plenty of use for the low cost of making it!

This all started as I wanted a way of testing different lipos under high-load, without spending a fortune on a new charger. This will do that and much more

I've also just ordered a 3 servo tester (last night it was controlled by connecting it up to one of my cars receivers, but this is a pain in the ass as I dont have a spare receiver).
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Dyno, Homemade, Using a Novak Sentry Data Logger, Continued, The Experimental Thread.-20121211_200424_small.jpg  
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Old 12-13-2012, 05:23 AM   #330
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That's a very nice dyno and at a good price too.
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