gyro
GSN Contributor
12S power systems ideas and options
- Thread starter Ohio AV8TOR
- Start date
Aeroplayin
70cc twin V2
Sorry I wasn't paying attention over the last few days, but yes. I'm not going to come to any conclusions just yet, but here are some caparisons to the DM5335 with the 189Kv and the 24x10TH. Of course it is not the same sampling method, and any Castle log data, or Eagle Tree, or Jeti Profi data, would alway be welcomed if someone was able to pull the CSV files from these programs. But in the meantime, this is what we do know from the Castle data after settling in after a minute of warming up at up to 50% throttle, then taking the first 30 second at wide-open. The RPM, volt, and Watts values are a complete average of the top 30 samples, and the Amps is a Max reading, and this is all static testing.
RPMs = 6832
Volts = 44.15
Watts = 5071
Peak Amps = 117.10
Measured Thrust = 35.9 to 36.5 pounds
This is about 5.7 HP or 4252 Watts-out.
The Vess 24B also seems to be a prop worth mentioning here too:
RPMs = 6863
Volts = 44.29
Watts = 4962
Peak Amps = 114.80
Measured Thrust = 36.4 to 37.1 pounds
This is about 5.8 HP or 4311 Watts-out.
I also have data for the 24x10 PJN, the 24x12 PJN, and the Mejzlik 22x10E to see how this combo would perform on the 78 Extra and perhaps the new 78/87 MXS which should be available soon. The 12 pitch PJN seems to be produce a similar 5.74 HP but on 123.9A (peak). The volts per cell moved to lower values much quickly too, and considering the battery stress, and decrease in flight time, I would not consider it myself. JMHO.
The 24x10 PJN also did very well, and considering the price difference, it's probably a comparable option to the Mejzlik.
RPMs = 6803
Volts = 44.44
Watts = 5093
Peak Amps = 117.10
Measured Thrust = 35.5 to 36.5 pounds
This is about 5.6 HP, or 4196 Watts-out.
I also have some comparative data with these props with the Q80-8M, and one thing that stands out is the 25x10 PJN data...
RPMs = 6399
Volts = 42.52
Watts = 5144
Peak Amps = 124.40
Measured Thrust = 33.9 to 35.9 pounds
This is about 5.5 HP, or 4116 Watts-out, and the voltage was sagging to about 3.54 volts per cell when these values were recorded. Not the prop for me, but this is a lot of torque through the entire throttle curve. Interesting anyway, and guys that like a floaty, low and slow 3D routine, many want to try it as long as there are no timing issues with the added load.
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Aeroplayin
70cc twin V2
FYI -- for anyone wondering why there can be seemingly more Watts but less HP, it's just that the measured Watts is calculated using Amps and volts while HP and Watts-out are calculated using the RPMs and the physical prop specs to get a value for the amount of power required at the shaft to spin the prop that fast. The Watts includes all the other power that is used for all other aspects of the system, like heat and maintaining a magnetic field. Another problem with pure Watts calculated from Amps and volts, is that the meters we use samples them at about 10 Hertz while the switching is occurring between 8 and 12 Kilohertz.
We're obviously not using a dynamo to measure HP, but these values are relative enough to give us a decent and acceptable comparison between props and motors. It's also important to understand that most of this is reliant on your battery health.
We're obviously not using a dynamo to measure HP, but these values are relative enough to give us a decent and acceptable comparison between props and motors. It's also important to understand that most of this is reliant on your battery health.
gyro
GSN Contributor
What are your thoughts when this data is compared to my second run, (about 3 mins into the battery)
It seems I was getting a little more power through mine?
Going out tomorrow with a 23x10 PJN and a 24x10 Falcon CF gas prop.
Aeroplayin
70cc twin V2
Well, I don't really see much there to talk about because your average volts per cell does not really change... 3.56v per cell, on average, which is low to begin with. Since the Kv did not change, It would be easier to explaining the extra 90 RPMs average as a 1.5% statistical measuring error. Like I said earlier, you were sampling an 8 KHz cycle with a 10 Hz meter. I didn't do the math to see if the 1.5% RPM increase calculates to the 3% Watts and Amps increase, but that's still not enough to think that it's anything more than the battery chemistry perking up a bit with the added heat. We don't see much of that here in Florida.
gyro
GSN Contributor
Just over 18 by my calculations, will get it on a scale next time out.
Aeroplayin
70cc twin V2
18.5 pounds has always been my goal for the 8M and now for the DM5335 too. We were talking about power on another thread and I had to remind even myself, that we have a limit here. We want to keep the volts up above 3.6v per cell as often as possible, and with a 5000mAh capacity, we want to keep the Amps down below 120A or sacrifice flight time. Multiply 119A times 3.6v per cell, time 12 cells, and we end up with 5140 Watts. Add more capacity to increase flight time, and the added weight mean less power-to-weight. Add a bigger prop to gain more torque, and risk dropping under a 5 minute flight time.
For power hungry fliers like me, an 18.5 pound airplane means 275 Watts per pound at 5140 Watts, which will typically assure a full flight in the "silly" power range. Do you remember how many mAh's you put back after Brian's flight, Gyro?
For power hungry fliers like me, an 18.5 pound airplane means 275 Watts per pound at 5140 Watts, which will typically assure a full flight in the "silly" power range. Do you remember how many mAh's you put back after Brian's flight, Gyro?