Thoughts on running 4s? - HeliFreak
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Old 11-23-2007, 01:02 AM   #1
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Default Thoughts on running 4s?

I'm thinking about switching to a 4s setup on my trex.

I'd end up ditching the JGF motor and going with something like one of the scorpion motors at the 4500ish kv.


How bad is the weight penalty? Does it cause any major CG issues?

What esc would be recommended(amperage)? It has to be a CC esc, because I'm spoiled by the Castle Link. I'm running a Phoenix 35 right now, would a 45 cut the mustard? Or would I want larger than that for a safety margain?

I'm assuming the woodies aren't safe at real high headspeeds. I've been running 2800 on mine for many flights now with no issues, but I'm unaware of their maximum rated rpm. Will v-blades be safe up to(or exceeding) 3300?
Bill - RWMAA #1009, AMA #805853

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Old 11-23-2007, 01:41 AM   #2
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4500KV is the wrong type of motor for 4S. A cc p35 is overkill, remember higher voltage will mean a lower current.
Spreading capibara awareness since 2006
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Old 11-23-2007, 05:28 AM   #3
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HFG how does a higher voltage give you a lower current? Is it not I=V/R (ohm's law), so if you increase the volts (r stays the same) you will increase the Amps?
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Old 11-23-2007, 06:09 AM   #4
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The brushless motor will always try to spin at its nominal speed for the applied volts. What varies is the power required for it to attain that speed. The power required to spin the blades at a given RPM and pitch is almost constant (other than parasitic I^2R losses). Thus at a higher voltage, for any given headspeed, less current will be drawn to provide the necessary power.

Going to 4s you want a lower KV motor since you have 33% higher voltage. Even if you want a higher headspeed, that will be achieved with a combination of voltage, KV and pinion.

3300rpm is really much higher than needed, even for wild 3D. Around 3000rpm is all you really need. The woodies are only rated to 2400rpm but many people fly them at 3000rpm with very rarely reported problems. It is a safety issue and good quality CF blades are certainly recommended. Metal blade grips are a must have item at those headspeeds.

So a reasonable 4s setup is probably something around 3000KV with an 11t pinion. However if you do a search you will find many recommendations for 4s setups with specific motor/pinion combinations.

As for weight, a 4s 1800 weighs about the same as a 3s 2200 with about 9% more energy so will give longer flights at the same headspeed.
* MSH Protos Stock motor/15t/Align75/Align DS510/GL730+DS520/7s A123 2300
* TRex450CF/430L/12t/CC45/HS65mg/L2100T/KP 3s 2200 25C or 4S LiFe
Previous rides: HX242, W5-4, TRex450(HDE), TRex450(SE), QJ-EP8v2, BCX2 ,Logo10, Hurricane550
SIM: Phoenix (previously also Reflex/XTR, ClearView, RF, FMS)
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Old 11-23-2007, 07:08 AM   #5
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Jazz 40 6 18
Thunder Power 4S2100 Prolites (180g) or Flight power 2100 EVOLITE (210 grams)

Go check out Trextuning 4S supertest.
Most of the winning motors are still the ones to get, maybe another Neu has slipped in as well. Just watch the weight of the motor ,this is where some good setups come unstuck (the weight issue).

I can thoroughly recommend the Medusa 28 32 2800, with an 11 tooth pinion 3200HS at full noise for the full flight of 7 minutes, 2900 HS for 9 minutes or 2600 for 11 minutes.



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Old 11-23-2007, 07:43 AM   #6
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I have Jazz 40 6 18 / Medusa 28 40 2500 100g / 12 tooth and run 30sec to a 1 minute less than Aussiemicks set-up but with 4S TP2070 217g / 4S Hyperion Litestorm 195g / 4SFP 2100 Evolites 210g.

They say there is no turning back on a 4S set-up and I agree.
8S Trex 500 3026-1000KV, Jazz 55 10 32, Sportbec, 3 9650mg's, Vistabi V Bar V4 / JR8900.
8S Trex 600esp 4025-890KV, Jazz 55 10 32 with heatsink, Herc HC/HV bec, 3 JR8915's, Vistabi V Bar V4 / JR8900.
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