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Fantom Facts Dyno and Lipos vs Lead Acid

Fantom Facts Dyno and Lipos vs Lead Acid

Old 02-12-2015, 09:44 PM
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Originally Posted by speedpro1
B20 what mean well did you get?
Hrp-600-7.5
600 watts 80 amps adjustable 6.8-9 volts. I recommend you install a blocking diode.
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Old 02-13-2015, 09:00 AM
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For those of you new to using a Fantom. It runs the motor at 5 volts. Due to variance in their electronics very little correlation can be drawn comparing numbers between different dynos. When these were released it was recommended that you have a huge amp source at 12 volts. That is why I went with a garden tractor battery. Brushed motors could have startup draws of over 120 amps @ 5 V. And when testing multiple setups and multiple motors you needed a big power supply or a reasonable lead acid battery. Brushless don't have as big a demand but if you want to do 10+ pulls I would still want that big amp reservoir. I also equiped mine with Deans plugs just to avoid a backwards hook-up. Nothing like replacing that big cap inside after a poof.
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Old 02-13-2015, 09:24 AM
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Originally Posted by old_dude
Brushed motors could have startup draws of over 120 amps @ 5 V... Brushless don't have as big a demand...
A 17.5T brushless will pull about 113A at 5V at startup. A 13.5T will pull about 185A at 5V on startup. This is assuming the ESC can actually provide that; the better ones can, but not continuously.
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Old 02-13-2015, 10:01 AM
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Originally Posted by howardcano
A 17.5T brushless will pull about 113A at 5V at startup. A 13.5T will pull about 185A at 5V on startup. This is assuming the ESC can actually provide that; the better ones can, but not continuously.
I guess I never really noticed that as my first readings (at .1 second) don't show that high and the charted data is a little dubious before that. I do use a 120a esc. I would like to have a steel flywheel though to slow down the results.
I did ask Dave Clary about collecting the raw data since the calculations seem a little off (watts based on acceleration).
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Old 02-14-2015, 03:13 PM
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To estimate the maximum amperage of my setup I plotted my highest amperage results vs either time or rpm to estimate the amp draw at time and rpm zero. In my case that was about 43 amps.
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Old 02-14-2015, 03:20 PM
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Curious that the curves meet behind the zero time mark. The plot of Torque vs Time or RPM (for a different motor) also predicted maximum torque at a time behind the zero mark. Could be an effect of the manner in which the first interval data is collected or recorded by the software or my error of data extrapolation (though the extrapolated lines look reasonable to me).
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Old 02-15-2015, 04:44 AM
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What software are you using?
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Old 02-15-2015, 06:22 AM
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What are the units for torque?
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Old 02-15-2015, 05:41 PM
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Originally Posted by old_dude
What software are you using?
Those plots are from Microsoft Excel. I just write down the data from Facts II program and type it into Excel by hand. It would be nice if there were some other way to transfer the data to a Macintosh.
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Old 02-15-2015, 05:42 PM
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Originally Posted by kornercase
What are the units for torque?
Units for torque given by the Facts II software are gram-centimeter. The proper SI units are newton-meter and a number of related terms with various orders of magnitude, like dyne-centimeter. Gram, is of course a mass, not a force. 1000 gram-centimeters is 0.0980665 newton-meters. 1.0 gram-centimeter equal 980.665 dyne-centimeter
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Old 02-17-2015, 04:34 AM
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There is an option to change the units for the display of torque in the software.
What I would like to know is each reported value of torque based on the acceleration from zero or the last step. Anyone know?
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Old 02-19-2015, 05:48 AM
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Originally Posted by old_dude
There is an option to change the units for the display of torque in the software.
What I would like to know is each reported value of torque based on the acceleration from zero or the last step. Anyone know?
Dave Clary might respond. He just e-mailed me a key for my software yesterday.

Also, have you used RC Crew Chief software? I just downloaded that and I see it has an inertia dyno calculator. You feed it just the RPM and time numbers. It needs to know your flywheel inertia which it uses to construct the power curves.

I just just got Crew Chief running last night so I have not had a chance to feed it Facts Dyno numbers to compare its calculations with the Facts II software.

Just thinking out loud here, I need to copy by hand the RPM and AMP data for various endbell settings from the Facts II printout and type that into an Excel spread sheet, mathematically convert the numbers from 5v to operating voltage using the factors mentioned in the Facts Dyno user's manual. Then export that sheet as comma-separated file. That file can be imported to RC Crew Chief and can be used to make a mathematical model of the motor based on empiric data.

Once the motor model is in RC Crew Chief, you can use the "Acceleration" screen to simulate different gearing and motor timing combinations. I think that screen may be more useful for twisty carpet track simulation than the 'oval gearing' window of Facts II software.

What do you think?
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