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I ran some tests on my 4-cell SR 190 battery pack. Graph results shown here for tryout on this Forum’s medium. Will post the data later.
rivers
SR 190 Nicad 4-cell, twin stick pack – Full charge before each run.
Data taken 10 seconds into each run using an Emeter with 20 amp shunt.
GWS LPS RLC 4.8 v motor with 4:1 gearing. Props are GWS slowfly (orange) non-folding.Prop—- Volts— Amps— Watts—Rpm—Thrust(g)— Pitch Speed(ft/sec)
EP-6050 4.73 — 2.78— 13.0—- 5820— 85.1— —- 40.4
EP-8060 4.35 — 4.15— 18.1—- 4080– 128.7
34
EP-9047 4.22 — 4.68— 19.8—- 3480– 131.5
22.7
EP-9070 4.12 — 5.03— 20.7—- 2970– 112.7
28.9
Calculations from Mathcad:
Battery source resistance = .270 ohms (.0675 ohms/cell)
No-load battery voltage = 5.48 volts (1.37 volts/cell)
Peak power output = 27.8 watts at 10.1 amps
Notes and conclusions on next post later.From the above data it looks like the best EP prop for this motor/battery combo is the EP-8060. It gives the best combination of static thrust and pitch speed. The EP-9070 is worse because speed and motor efficiency drop off with the bigger prop and higher current.
Notes: 1. Source resistance includes: battery internal resistance, plus resistance from connectors, wires, and power switch. However, most of the source resistance comes from the batteries’ internal R.
2. Peak battery output power is a theoretical value which is not realizeable with this motor. At 10.1 amps the motor would be fried, and the battery would be cooking as well.Thanks for posting the above info. I am not sure as to the rate of charge to be used on these 190 mah battery packs. I have an Astro 112D charger. I made up a connector to charge my packs. The instructions that come with the charger recommend charging at 3 times the rating of the cell. Dumb question, but are 4 190 mah batteries in a pack considered a 190 mah pack? Or is it a combination of the 4×190 mah cells? I assume it is a 190 mah pack and 3 times the rating is .57 amps. I think. That is a slow charge according to these instructions. How would you fast charge these packs at the field without wrecking them? [ I have some literature from SR batteries that recommends slow charging at 10% rate for 10-16 hours]
This seems to be a nice charger, is it safe to leave such a charger on unattended? Or should I just wait til morning and charge the thing all day?dohrmc, Yes, four 190 mah cells connected in series is a 190 mah pack. The series connection makes the cell voltages add to a total of 4.8 volts nominal. If the cells were connected in parallel it would become a 760 mah pack at 1.2 volts.
A 3C charge rate (.57 amps) is not a slow rate. A fully discharged battery would recharge in about 1/3 of an hour. For the above tests, the battery was recharged at .30 amps which is about 1.6C. I think it’s okay to charge at 3C or even higher. Try it and see how warm the battery gets. You want the battery warm, but not hot. A warm battery performs better because it’s internal resistance goes lower. However, a battery too hot will vent and lose electrolyte.
The 10% charge rate is for the first charge only. It is called the forming charge and takes 10-16 hrs from full discharge. It’s considered a good idea to repeat the 10% charge every so often to recondition the battery.
riversThis is really great data. I have heard someplace that the 7 in prop is the best, but have not seen any data. Did you test the folder you have on the scaled down Slo Worm?
Timer guy, I tried a 7 inch EP-7060 later. The results were not that impressive:
Prop—- Volts— Amps— Watts—Rpm—Thrust(g)— Pitch Speed(ft/sec)
EP-7060 4.33 — 3.94
17.1—- 4230– 97—
35.2The EP-8060 still looks like the best non-folding prop. More static thrust.
Here is the data for the folders:
Prop
Volts— Amps— Watts—Rpm—Thrust(g)— Pitch Speed(ft/sec)
CAM 8×4.5 4.43 — 3.59
15.9—- 5130– n/a—
32.0
CAM 9×5 — 4.33—-4.13
17.9
4920—n/a
34.2It looks like the CAM 9×5 will perform about the same as a EP-8060, but will have the huge advantage of being a folder for the glide.
riversYes, but at quite a weight penalty. The CAM 9×5 weighs 21.4 grams with the spinner. Is is still a good tradeoff?
Dick, how did you get the CAM hub to work with the 3 mm GWS shaft? The hub is made for 3.2 mm and it will not tighten up on the smaller shaft. At least not for me. I tried to wrap some tape on the shaft, and that did not work.
Hank,
I do not use the CAM hub. I use a home-made hub that is held to the motor shaft with washers and nuts just like a non-folding prop. The whole assembly, with the Graupner 9 x 5 folding blades, weighs 9.25 grams. You can see it in my Slo Worm model pictures on this Forum. I’ll try to post a hub detail drawing later.Dick
Dick,
Thanks. That helps. My CAM hub alone is 9.6 grams. No blades or spinner. Yes, I would like to see your hub. I am sure others would too. This e stuff is all new to me and to most on this forum. We are all struggling to learn.
For anyone who is curious, this is the CAM Graupner hub for a folder. The parts you see here weigh 9.6 grams. And, it will not fit the GWS 2 or 3 mm shaft without some sort of change.
1. Clarification to the above data: Props labelled above as EP-xxxx are GWS Slow Fly props. These props are orange with curved blades and slight undercamber. I later found other GWS props also labelled EP-xxxx, but they are not Slow Fly props and have straight blades.
2. New Data: I ran a test to determine the no-load current of the LPS geared motor…. not easy to do, but here are the results:
Volts Amps RPM
3.80 .446 6192 (geared 4:1)Combining the above with the loaded data for the 9×5 folder we get the following LPS motor constants from Motocalc:
Kv = 1700 RPM/volt (geared)
Io = .446 amps
R = .347 ohmsThanks for the technical data, Richard. Now, if I was only smart enough to know what to do with it. Surely, someone has a better motor than the GWS LPS? I want my Sparks to climb vertical, like a hot gas job. Something that eats a battery pack every flight. Like we smoke glow plugs on high nitro and too much compression.
Hank
Hank, It is a pity, but the reality is that an E-36 is never going to climb vertical. Reason: there is not enough power available from the miserly 4-cell, 190 mah nicad pack. Look at the graph at the top of this thread. The max battery power available is only 27 watts. The LPS motor, with a 9×5 folder, uses about 18 watts on static test. So, even if you could find a better brushed motor, there is only another 9 watts available to use, and that motor is likely to be heavier.
If you want hot performance go to F1Q. My son’s F1Q FF electric model draws 220 watts. The climb is fast and near vertical.
As a point of reference check the R/C guys in class F5B. It is limited motor run competition. The electric power used is over 2000 watts! The models are a spec in the sky in just a few seconds.
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