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ESC for HK 250 GT

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Bigal1951 View Drop Down
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  Quote Bigal1951 Quote  Post ReplyReply Direct Link To This Post Topic: ESC for HK 250 GT
    Posted: 01/Apr/2012 at 3:58am
Can I use a Detrum 12A ESC with an Exceed 3500kv motor in an HK 250?
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chris3002 View Drop Down
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  Quote chris3002 Quote  Post ReplyReply Direct Link To This Post Posted: 05/Apr/2012 at 3:21am
Hi,
a 12A ESC is imho to small. I recommend a 25-30A ESC
In my case I use a 40A HK blue in my HK 250 GT which is of course oversized, but it was available in my spare parts box..

Best regards
Chris
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  Quote jamespal Quote  Post ReplyReply Direct Link To This Post Posted: 04/Jun/2012 at 8:48am
The speed control AMP rating depends on the voltage being run. Motor Kv rating describes 1000 RPM per volt. A 3500 Kv motor on 11.1 v (3 cell) will equal 38,850 RPM. This is theoretic in a free state. Mechanical drag will reduce this. Assuming a 10% loss, the motor RPM should be around 35,000. The stock 15T pinion equates to a 1:8 main gear ratio or a head speed at 4400 RPM.
Most of the 250 sized motors are rated at 200 watts. This does not mean the helicopter will hit 200 watts; most likely it will be less unless extreme 3D flying is expected.
Ohms law says Amps x Volts equal Watts. A 12 AMP speed control will max out at 133 Watts. Has anyone recorded the 250GT amp load at full power?
This should be a acceptable setup; at least for hover & training.
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  Quote steverb Quote  Post ReplyReply Direct Link To This Post Posted: 09/Jun/2012 at 9:15am
What about inbuilt BEC
2A or 3A ??
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  Quote WTWUK Quote  Post ReplyReply Direct Link To This Post Posted: 09/Jun/2012 at 10:18am
20-25A speed controller will be ideal and will give a good margin of safety - would you be happy to lose your heli for the want of a few £ saving on an ESC?
3A will be fine for the BEC, but if you are using Analogue servos for cyclic (you really should use a fast digital for the tail) 2A will suffice.
I will run up one of the 250's I have here today and see what readings I get.
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  Quote sean33 Quote  Post ReplyReply Direct Link To This Post Posted: 14/Jun/2012 at 11:38pm
Hi all,

I just got my HK250 kits yesterday and I began to assemble different parts together. To my amazement, there is no instruction of how to put together. So don't be surprise. It is going to take you a long time to figure it out unless you have experience building heli before. My complaints is that when I went to check each nut and bolt to lock tide them, two of the screws to main gear holder were sheared off and skids are too flimsy one bended when I tried to straighten it out it broke. I am in the process of ordering some parts for replacement without even getting in to the air yet....
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  Quote Turbobeaver Quote  Post ReplyReply Direct Link To This Post Posted: 19/Jun/2012 at 10:50am
Most all 20-25 amp esc's are running a max of 2A on the bec.For that matter,most of the 30A esc's are running 2A on the bec as well.There are only a very limited few that are rated at 3A here at HK and the reviews for those ESC's I would say leave one feeling a little less than warm and fuzzy after you've scrolled through them.I chose a Turnigy Plush 30A esc after much debate as it turned out to be cheaper than the 25A Plush and only a few grams difference between the two.Size wise they are identical as well as they share the same circuit board(minus a few fets on the 25A esc).I have used the Turnigy Plush ESC's for many years now and I trust the quality of the construction and the onboard components.They are very easy to set up with the Turnigy programming card as well.With the onslaught of digital servo's being so prevalent now in the market place,it seems to be creating some confusion amongst users with regards to BEC requirements.Can anyone elaborate on how to properly calculate a BEC amp rating requirement?On a HK-250 running 4 digital servo's and a gyro,would this warrant the use of an external UBEC?There's got to be a better way of calculating ones requirements than playing ESC Russian roulette.
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  Quote thesavage Quote  Post ReplyReply Direct Link To This Post Posted: 19/Jul/2012 at 9:06am
From "The Electric Helicopter Beginners Guide" Page 203:

BEC
Battery Eliminator Circuit.
On a nitro helicopter, there is a 4.8 volt "receiver pack" that powers the receiver,gyro,and servos. On an electric helicopter, we already have a very large battery which powers the main motor. However, the voltage of this main motor battery pack is typically more than 4.8 volts. So, the BEC will take the voltage of the main battery pack and regulate it down to 4.8 volts to power the receiver, gyro, and servos, This eliminates the need for a separate 4.8 volt receiver pack. There are two types of BECs: linear BECs and switching BECs. A linear BEC reduces the main battery voltage to about 4.8 volts by applying a resistive load and wasting the excess power as heat. This has two important implications: First, the current capacity of a linear BEC drops quickly as the input voltage rises. A typical 1 amp linear BEC can dissipate about 3 watts, so it can handle a load of 1 amp at 8 volts, but can only handle half this current, or 0.5 amps, at 11 volts. Second, a linear BEC is usually only about 50% efficient (or less) since it discards excess power as
heat. If a linear BEC becomes too hot, it will thermal shutdown and you will lose control of the model.

A switching BEC functions by rapidly pulsing the main battery voltage to create an average filtered output of 4.8 volts. This method of regulating voltage is more efficient than a linear BEC, so a typical switching BEC is 80 to 90% efficient. Also, it can handle much higher input voltages than a linear BEC (up to 35 volts or more), and the current capacity does not drop at higher voltages.

Note: Most BECs are rated for 5 volts of output. The extra 0.2 volts will not harm the electronics equipment. From an electronics point of view, a 5 volt regulator is easier to build than a 4.8 volt regulator since the parts are more easily available, so most BECs output 5 volts instead."

As an example:
- 4 off Corona 919MG Metal Gear Servo 1.7kg/ 12.5g/ 0.06sec @ an operating Voltage and Current of 4.8/6.0V & 200/240mA each, respectively for a total of 960mA
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=11854
- 1 off HobbyKing GA-250 MINI-MEMS Gyro @ an operating Voltage and Current of 3.0/9.0V & 20mA (@5V)
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=15318
- 1 off OrangeRx R610 Spektrum DSM2 6Ch 2.4Ghz Receiver @ 3.7/9.6 V (doesn't actually specify an operating current but it would be less than 200mA)
http://www.hobbyking.com/hobbyking/store/__25048__OrangeRx_R610_Spektrum_DSM2_6Ch_2_4Ghz_Receiver_w_Sat_Port_AUS_Warehouse_.html

Total Current draw (max) = 960 + 20 + 200
=1180mA (1.18A) < 2A (2,000ma)

It shouldn't matter whether the servos are either digital or analogue, just the current draw. Having said that a Digital servo tends to draw my current and may require an external switching BEC. So, from the above example the BEC in the ESC (@2amp) should be more than enough.

Edited by thesavage - 19/Jul/2012 at 3:01pm
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kanga View Drop Down
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  Quote kanga Quote  Post ReplyReply Direct Link To This Post Posted: 11/Nov/2012 at 2:45pm
I found on a 25 and 30 esc I had low power. I strapped a turnigy trust 45 amp under the bottom and what a difference it made. Bit of an overkill but not really , it works well and is still light.
I also cut of the original 250 skids, and retro fitted 450 skids under the 250. Makes it way easier to land for a learner and really does not look out of place .
Helicopters Don't fly,
they just beat the air
into submission :)
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