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Old Jun 17, 2012, 05:40 PM
Gravity sucks.
Australia, QLD, Toowoomba
Joined Mar 2011
562 Posts
Quote:
Originally Posted by carl1864 View Post
Does anyone know of a good cheap motor from Hobbyking or Rctimer or similar that can give a good boost in thrust while keeping a 6" propeller, and drawing less than 40 Amps?

This might be a silly, newbie-ish question, but in all the motor upgrades I read about, people seem to gravitate highly towards the Small 4.75X4.75 props, with high KV motors.

Well, I just did some bench testing of the stock setup, vs a Turnigy 2632-3400 motor, with 40A esc, and 4.75x4.75 prop. (heard good things about that setup and was thinking about using it)

Well the stock setup I'd get around 400G of thrust, while drawing 10.4 amps.

The new setup I tested, when drawing 10.4 amps, I was getting only about 360G of thrust, so loosing some efficiency.
At full throttle on the new setup, I was getting around 760G of thrust (pretty close to double stock), but at a 35A draw (so using almost 350% as much power).

Now the stock motor is a 1800KV motor. Wouldn't a good motor choice be a motor that had a higher KV, say 3000, but can still swing a stock 6" prop? Wouldn't that give you the same level of efficiency as stock at lower throttle settings, but allow you more power if needed in the upper end, and be more efficient than the smaller prop?

If so, can anyone provide any good motor recommendations, and explain why so many people choose to use a smaller prop setup?

PS: I'm not going for real high speed, I just want a little bit extra speed, and some vertical performance when needed, without cutting my flight times too drastically.
The use of a high kv (and subsequently, speed) in this model will take more 'overhead' power to achieve, if you want to use less amps, look at lower kv with a larger prop. (in general, the drawback of this is also going to mean slower top speed)
like a 1400kv motor that can manage 25amps and an 8x5/8x4 prop
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Old Jun 20, 2012, 01:07 AM
Thailand
Joined Aug 2010
506 Posts
I am not using it on a Skyfun but the Hobbyking 2836 Ntm 3000kv motor is giving me 1098 watts on 4s with a 4.7x4.7 Graupner prop.
72 amps on 4s Zippy 2200mah lipos.
I have used an Axi prop driver and there is no vibration. Every other prop driver I tried was rubbish.
I can fly around at full throttle for 2 to 3 minutes but to give it a chance to cool off I do glide around a bit between high speed runs.
Very impressed with it and for 17 dollars it's great value.
I have installed the Winged Shadow pitot tube on board speed sensor and get around 160mph on every flight.
Jim
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Old Jun 20, 2012, 10:34 AM
ICrashRCs
United States, TN, Memphis
Joined Jun 2011
1,196 Posts
Good stuff Jim, Thank You!
Those AXI prop adapters look scarce, especially in the US.
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Old Jun 20, 2012, 10:43 PM
flying or crashing into air?
wizzard363's Avatar
Australia, VIC, Langwarrin
Joined Feb 2011
1,321 Posts
Quote:
Originally Posted by Fox-composites View Post
I am not using it on a Skyfun but the Hobbyking 2836 Ntm 3000kv motor is giving me 1098 watts on 4s with a 4.7x4.7 Graupner prop.
72 amps on 4s Zippy 2200mah lipos.
I have used an Axi prop driver and there is no vibration. Every other prop driver I tried was rubbish.
I can fly around at full throttle for 2 to 3 minutes but to give it a chance to cool off I do glide around a bit between high speed runs.
Very impressed with it and for 17 dollars it's great value.
I have installed the Winged Shadow pitot tube on board speed sensor and get around 160mph on every flight.
Jim
I am using that motor on a Skyfun with a APC style 4.75x4.75 prop and 4S 2200mah 35-70C Nanotech lipo .
The best I get is 815W and 200kmh(127Mph).Speed measured with the new Hobbyking GPS data logger (wind assisted , light breeze)
I have ordered the Graupner prop you use and will seee what the result is with that.
When bench testing I let the motor run for 20 seconds at WOT before taking the readings from my watt meter.
The initial burst readings may be higher.
I have also ordered the Turnigy 2836 3200kv motor to compare results
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Last edited by wizzard363; Jun 21, 2012 at 01:37 AM.
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Old Jun 21, 2012, 01:49 AM
Thailand
Joined Aug 2010
506 Posts
The lipos are new. I was only getting 1000 watts from my older lipos.
I take the initial reading and I must admit I don't let it run for 20 seconds.
The larger the prop the more watts it reads so maybe the APC is a smaller load than the Graupner?
My friend used a 6x5 and got nearly 1600 watts from the same motor. It lasted 2 circuits before catching fire and crashing. Not sure what burned first as everything was gone. 120 amps as well and all on an 80 amp esc so a bit stupid.
I am using the Winged Shadow pitot system for the speed. Who knows if it's accurate? It is consistent though.
My model is not a Skyfun. My friend has a Skyfun which is slower than my model with the similar set up but we don't know by how much.
My model with a 650 watt AXI motor got around 135mph so it is 25mph faster with double the power, which also seems about right.
Just taken a reading from my motor to make sure I was right and a bit shocked.
84 amps
1255 watts
14.84 volts
To verify this a you can check, 14.84v x 84.4a =1252 watts, which is almost spot on.
This proves the meter is accurate.
This lipo is 16.67v off load and 14.84 when loaded.
Prop drivers have been a nightmare and trying to get straight ones has been difficult.
Moving the prop round about 90 degrees can get rid of the vibration but getting that sweet spot is difficult.
I will try to get a photo of the watt meter to prove what I say but my telephone camera was rubbish.
Jim
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Old Jun 21, 2012, 02:13 AM
flying or crashing into air?
wizzard363's Avatar
Australia, VIC, Langwarrin
Joined Feb 2011
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A few pages back I posted a vid of my test using a 1800mah 4s nanotech.
http://www.rcgroups.com/forums/showp...&postcount=775
The initial burst was well over 900W but as it is so short lived I do not consider that the true reading.You will see it settles to about 750W
The 1800mah pack I used in that vid could not keep up with the motor , the voltage saged down to 12V so I bought a couple of 2200mah packs and that is the reading I posted above.
The initial burst would have been over 1000W with these 2200 mah packs
The 2200mah ones sag to about 13.7 volts after a few seconds but are good enough for what I need and I do not want the extra weight of a higher capacity pack
All packs were brand new and fully charged
If you do another test could you take readings after about 15 - 20 seconds ? Thanks
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Old Jun 21, 2012, 03:40 AM
Thailand
Joined Aug 2010
506 Posts
Hello Wizard, I will do that longer test but the noise is fairly severe and the neighbours may complain. I will have to go to the field and test it there.
I looked at your run and the voltage is quite low.
Plus the capacity is only 1800mah and lets be kind to the Nanotecs and say they are 35c.
35x1.8 is only 63 amp that the lipos can deliver.
I have 2200 40c so they can deliver 2.2 x 40 =88 amps.
I am consuming 84 amp so they are only just capable of delivering what the motor is asking.
Your lipos are not big enough so this is maybe why the power is down?
I have had some Nanotecs and they were awful. Not exactly what was advertised on the label. I would never buy them again.
Ok I just ran mine for 20 seconds, disconnected the watt meter and then reconnected and checked again. Readings were,
80.71 amps
1164 watts
14.27 volts 80.71x 14.27v = 1151watts so again it's fairly accurate.
I would say your batteries are not very good because they cannot supply the volts at full power.
After 20 seconds running my lipos are resting at 15.83 volts but drop to 14.27 under load. Quite warm.
I hope this makes sense.??
Jim
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Old Jun 21, 2012, 03:47 AM
Thailand
Joined Aug 2010
506 Posts
Hello again, just looked at your video and the volts drop to 12. This is way down on what you should be getting.
75 amps x 12volts = 900 watts.
I couldn't really see what amps you were getting but I think it was 75?
Maybe you could confirm that?
Batteries for sure?
With 2200 mah you need 40c as a minimum to get 88 amps. A 20c 2200 will only give 44amps. 35c 2200 =77amps
Jim
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Old Jun 21, 2012, 04:46 AM
flying or crashing into air?
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Australia, VIC, Langwarrin
Joined Feb 2011
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The ones I use are 35C and after doing some research in the last few days and getting some info from others , I have learnt that they are a bit light .
However ,based on the advice I have been given , if I am going to get new packs I will go for larger capacity more than higher C rating eg 2650mah or 3000mah 35C I think this will give better results with a lot less voltage sag
As I said above , my 2200's are not perfect but will do for now
Also if I change my prop to the slightly smaller Graupner I should get different results
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Last edited by wizzard363; Jun 21, 2012 at 09:09 AM.
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Old Jun 21, 2012, 03:10 PM
Wats the worst that can happen
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Canada, BC, Surrey
Joined Jan 2009
510 Posts
I tried my turnigy 2832 3200kv the other day with 4s. i have a 5x5e prop.
I do believe it was faster than the 3s by eye. I didnt have any measurement devices at my disposal at the time.
I did a handful of high speed passes, and brought it down quickly.
the 60A esc was quite hot, motor was too hot to touch for more than a second, and the sticky HK velcro was peeling off the battery.
Probably nothing revolutionary here - just confirms to me a larger motor (2836) as others are using, a higher C 4s battery, and placing the ESC in better airflow will be the next steps.
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Old Jun 21, 2012, 05:32 PM
flying or crashing into air?
wizzard363's Avatar
Australia, VIC, Langwarrin
Joined Feb 2011
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Quote:
Originally Posted by juice555 View Post
I tried my turnigy 2832 3200kv the other day with 4s. i have a 5x5e prop.
I do believe it was faster than the 3s by eye. I didnt have any measurement devices at my disposal at the time.
I did a handful of high speed passes, and brought it down quickly.
the 60A esc was quite hot, motor was too hot to touch for more than a second, and the sticky HK velcro was peeling off the battery.
Probably nothing revolutionary here - just confirms to me a larger motor (2836) as others are using, a higher C 4s battery, and placing the ESC in better airflow will be the next steps.
5x5 will be drawing too many amps , try a smaller prop like 4.75x4.75
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Old Jun 21, 2012, 05:47 PM
Wats the worst that can happen
TheCure's Avatar
Canada, BC, Surrey
Joined Jan 2009
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Quote:
Originally Posted by wizzard363 View Post
5x5 will be drawing too many amps , try a smaller prop like 4.75x4.75
it most certainly is. i expected that going into my flight. i was too lazy to check before hand on my wattmeter.

just wanted to see a few high speed runs to get an idea if the increased speed really does it for me (and the jet remained stable). if my impression was good, I was going to invest putting a 100A ESC w/2836 motor with 4s. if i still have headroom, then use the stock 6x4 prop instead of the 5x5.

still not sure if i will go ahead. maybe when i am bored one day.
i already have a parkjetII running the stock motor which seems significantly faster than my skyfun w/ 2832 3200kv motor - both on the same 3s battery.

i might put some fps equipment inside instead of adding the extra weight from speed parts.
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Old Jun 21, 2012, 10:24 PM
Thailand
Joined Aug 2010
506 Posts
Wizard, just do the maths and multiply the capacity by the C rating, this gives the theoretical maximum amps draw ability.
2650 mah 35c is 2.65 x 35c = 92.75 amps This should be fine for your set up.
Mine was drawing 84 amps so you are only just ahead at 92.
If you saw my voltage was 14.27 even after 20 seconds but the lipos are newish and they will not deliver that in say 3 months?
Just remember the bigger the c rating and the larger the capacity the better and the more amps you can draw without damaging the lipo.
Jim
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Old Jun 22, 2012, 02:42 PM
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Im running 2836 3700kv on 2250mah 4s 65-130c and 2700mah 4s 65-130c on 4.5x4.5 tgs with a plush 80a on my one skyfun I get 2 min flying which is okay for me and even after hard flying everything comes down cool. I get 136mph out of a dive.
Does anyone know if it will be safe to try a 5.2 x 5.2 cam speed if my setup always remains cool?

I also have a skyfun running HK 1600kv 3126 on a speed 6.5 x 6.5 on a 2700mah 6s 65-130c on a 200a HK SS but am only getting 143mph and also everyhting comes down cool. Does anyone know if I can then also run a bigger prop? I want to try a speed 7x7 or 7x8...?

I see there is a hacker 1600kv setup on youtube running 176mph on 6s with a 7x6, but I cannot see how this is possible given my attempts above...
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Old Jun 22, 2012, 08:17 PM
Thailand
Joined Aug 2010
506 Posts
Smack, you really need a watt/amp/volt meter to see what prop you can use.
If you are using an 80amp esc then you need to keep the amps below that figure or you could/will fry it.
A 1600kv motor on 6s is a bit the same as a 3200kv on 3s but you cannot tell how many watts it is drawing by reading those figures.
KV does not indicate power but only tells you the motor rpm when used with a certain voltage. i:e 3000kv x11.1 volts (3s) =33300 rpm with no propellor.
The motor should be propped for around 85% of that figure so on the above it should be propped for 28300 rpm and checked with a tacho.
Watts equals power so it's important to know that by using a meter. 746 watts is 1HP.
Sorry to get technical.
As for the 176 mph, a lot of the data collected is not always correct. Was it done downwind, a radar gun, GPS, on board telemetry, on board airspeed monitoring?
We used to fly Ducted fans at a big meeting in the UK. It was always windy and we regularly got 200 mph downwind using a ground based radar gun.
One year it was flat calm and we only got around 160mph, sooo disapopinting but so accurate. lol
Jim
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Last edited by Fox-composites; Jun 22, 2012 at 08:22 PM.
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