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Old 03-03-2009, 02:44 PM   #1
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Default Novak Sentry as Brushless Dyno

Several dyno results









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Novak Sentry as Brushless Dyno-hacker1350-boost1.jpg   Novak Sentry as Brushless Dyno-novak1350boost1.jpg  
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Last edited by mattnin; 03-13-2009 at 02:37 PM.
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Old 03-03-2009, 04:55 PM   #2
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John Stranahan has suggested to add the moment of inertia of the rotor to the formula, and I agree. This means this will increase the power rating seen. Also I plan on calculating a 'friction factor' based upon the deceleration once the throttle has been released. This will also further increase the power rating.

If anyone has any ideas where I can find a heavier flywheel, please let me know
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Old 03-03-2009, 07:52 PM   #3
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I think a heavier flywheel would work best.

I have an EagleTree System and I may just try to duplicate what you did with it.
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Old 03-03-2009, 08:08 PM   #4
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Quote:
Originally Posted by trailranger View Post
I think a heavier flywheel would work best.

I have an EagleTree System and I may just try to duplicate what you did with it.
I used to have a spreadsheet for flywheel calculations using the eagletree set-up. I'll see if it's on an ole backup somewhere.

I have a steel flywheel from an older dyno that I used before.
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Old 03-03-2009, 08:28 PM   #5
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Is the eagle tree flywheel heavier? where can I get this flywheel? A heavier flywheel is very much needed as noticing the hacker 13.5 reached over 7000 rpm in .1s and reached max power in .2s. Part of the reason it spins up so fast too is that I am using a LIPO battery to run it. The Fantom just uses 5V.
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Old 03-03-2009, 08:49 PM   #6
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For testing my setup for velo racing, I have a home made chassis dyno that uses an old pod/tplate mounted to my scale table.

I have CAPPED tires on it, it uses a stock motor (as a slave) geared with a 4.00:1 ratio, and a resistor soldered across the motor (The gearing was tuned to pull 20 amps on a 21.5 motor at W.O.T.)

I use the eagletree to monitor Voltage/Amp Load/RPM in my car. I can divide the MOTOR RPM by the cars gear ratio and find the AXLE Speed, and calculate estimated speed (minus Aero Drag)

It's crude, but it's been pretty effective and accurate.
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Old 03-03-2009, 11:23 PM   #7
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Nice job, but I'm guessing that you either have a fantom dyno or have access to one. Why not just use the Fantom dyno instead of re-inventing your own?

I know the fantom is not "brushless ready" but I do know people are using them with brushless motors. IT's not all that difficult. I've done some testing of brushless motors on my Robitronic, the same procedure should work for the fantom or any other dyno for that matter.
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Old 03-04-2009, 07:19 AM   #8
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I can't run the RS Pro off of the Fantom power supply. I even added a receiver pack and with no voltage to the controller, it doesn't even turn on. And when the Fantom gives it juice, the controller goes through its arming procedure and by that time, the Fantom registers an error because the controller hasn't even begun spinning the motor yet.
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Old 03-04-2009, 07:46 AM   #9
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Strange... my RS powers up and finds its neutral the moment I plug a receiver pack into the receiver... whether there's any power to the RS input leads doesn't seem to matter... it comes on and initializes either way.

The motor will even creep forwards if I pull the trigger with no input power to the RS, it must be "sneaking" some power from the rx pack to creep the motor. I just wait until I hit the "run motor" button on the dyno screen and then yank the trigger at the same time...

It's interesting that your RS pro won't even boot up without input power... have you tried it leaving the RS switch in the off position? that's how I do it here. I'm using a small 2 cell LiPO from a foamy to power the receiver/RS here... maybe the higher voltage is what makes it work for me?
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Old 03-04-2009, 08:00 AM   #10
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I have the RS Pro in the on position. I actually have it hooked up to a 2S A123 and going through an HV BEC from Novak so it should be 6V at the receiver. Even when it is in the off position, it doesn't come on. Maybe I have it hooked up wrong. You have the BEC hooked up into the receiver right? And then you have your RS with an adapter with the red wire removed to the receiver?
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Old 03-04-2009, 08:07 AM   #11
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I just ran another test with the Sentry dyno with a fully charged lipo battery and I believe ideal test conditions except no current reading yet, and I finally figured out excel too! :P actually it is open office, but here it is.

This test is with 0 boost on the controller. Next test will be with 10 boost. I will be testing the Novak 13.5 next too as soon as I get my motor back from James.




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Old 03-04-2009, 08:19 AM   #12
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Quote:
Originally Posted by mattnin View Post
I have the RS Pro in the on position. I actually have it hooked up to a 2S A123 and going through an HV BEC from Novak so it should be 6V at the receiver. Even when it is in the off position, it doesn't come on. Maybe I have it hooked up wrong. You have the BEC hooked up into the receiver right? And then you have your RS with an adapter with the red wire removed to the receiver?
I have all the wires on thge RS's receiver plug in place, plugged into the throttle slot of the receiver. THen with the RS switch in the off position, as soon as I plug and rx pack into any other slot of the receiver the RS comes on and initializes (if it sees a transmitter signal, otherwise it just sits there flashing)

I don't think the RS will come on if you have the red wire removed... if you have it that way, there's no path for the power to get to the RS from the rx pack... it would then NEED to get power from the "main" pack (or dyno) to come on...

Try it with the red wire in place and the switch off... bet it'll work then. On the other hand, you seem to be doing VERY well with the Sentry method so far...
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Old 03-04-2009, 08:37 AM   #13
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If anyone wants to do this, I will show exactly the equations and how to do it (while my battery is topping off again).

First, convert RPMs to rad/s as I shown in the first post as an example.
2nd, calculate the moment of inertia (I) of your flywheel using
.5MR^2
3rd, find the angular displacement.
0 (theta) = .5(Wo +W)T, Wo is the initial angular velocity in rad/s, and W is the current angular velocity in rad/s, and T is time
4th, find the angular acceleration.
a (alpha) rad/(s^2) = (W^2 - Wo^2)/(2*(0 theta))
5th, find torque
t (N*m) =I*a
6th, find watts
power (watts) = (torque (N*m) x 2pi x RPM)/60
7th, convert torque from N*m to gm*cm if you want to
Multiply t * 10197.162

I won't go into all the math, but you can make a full equation by entering in the equation for theta into the angular acceleration formula, and then and then entering in the angular acceleration formula into the torque formula, and then simplifying.

The simplified equation for torque if the time between readings is .1s is,

t = ((RPM - RPMo)pi)/3 * I, where RPM is the current RPM reading and RPMo is the previous reading. The equation turns the data into rad/s so no worry about converting. t comes out in N*m as well.

So as an example, lets calculate some data from the previous chart @ 3.8 seconds. The moment of inertia of my flywheel is 47.59E-6 kg*m^2 or 0.00004759 kg*m^2.

t = ((11406-6282)pi)/3 * 0.00004759 = 0.2553603 N*m
convert that to gm*cm
0.2553603*10197.162 = 2603.95 gm*cm
find watts
power = 0.2558969*2pi*11406/60 = 305.01W
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Last edited by mattnin; 03-04-2009 at 01:49 PM. Reason: fixed 0 theta equation
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Old 03-04-2009, 08:38 AM   #14
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Trips, I thought the red wire was supposed to be removed? That won't blow up my speed control will it? :P This one is brand new
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Old 03-04-2009, 08:57 AM   #15
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The steel flywheel that I have is from an old old dyno that I had and tore apart for another project.

For the RS guys wanting to run on the Fantom, here's what I've done in the past.

1) Run power from a receiver pack to the receiver (turns the system on)
2) Leave the speedo/radio at neutral (and no drag brake)
3) Hit the button to start the dyno run and at the same time hit the throttle on the radio to start the run.

I've found that running like this is not very repeatable because of how the start of the run is calculated. It is very repeatable on a Turbodyno by the way.
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