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Electric newbie - ESC BEC question

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MikeQ18/09/2020 22:22:40
122 forum posts
97 photos

Hello

been flying for years but have just taken the plunge into electric with an F3A Sebart Wind E 50. The ESC/Motor/battery I've plumbed for is a Hacker X-70-SB-Pro 2.6 with Hacker A50-16S V4 and a 4500mAh 6S Top Fuel Lipo.

Question is, I can't see anywhere in the ESC specs where it says what the output voltage is for running the Rx and servos. Given that some of the servos are fairly beefy HV (6v to 8v) I'm wondering If I need a separate 2S lipo for Rx and Servos or if the ESC will handle it? Receiver will be a Spektrum AR8000.

Any help appreciated.

Cheers

Mike

Dad_flyer18/09/2020 22:37:29
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318 forum posts
317 photos

The BEC output is usually 5 to 6V. I put in the part number and the Hacker website gives 5.5V. I could not immediately see the current specification, which might matter if you have big servos or digitals.

With high voltage servos a separate battery would use that extra capability and give more torque. I have not got experience there.

MattyB18/09/2020 22:39:12
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2320 forum posts
43 photos

Unless it specifically states it’s an HV ESC it will probably put out 5.5V or so. HV ESCs do exist though - the Frsky Neurons for instance have a programmable BEC output all the way to 8.4V that can be done from any FrSky TX. At the end of the day though your ESC will still run those servos, you just won’t get the best performance out of them. Having said that on a 50 sized Sebart you really don’t need super high torque servos as F3A models don’t travel that fast and are very lightly built.

Ps - Take a close look at the undercarriage and reinforce it from the outset; on Sebart models that is the big weak point. My Miss Wind is awesome to fly but the gear are perennially putting it out service. 

Edited By MattyB on 18/09/2020 22:48:23

MikeQ18/09/2020 23:03:59
122 forum posts
97 photos

Hi

thanks for getting back. I bought the servos etc based on the suppliers recommendations so will give him a bell and query that. The servos seem pretty highly specked so a reduction in performance might not be an issue. My flying style isn't extreme ... more 90s turnaround pattern type flying.

Couple more questions, I'm looking at using XT90S antispark connectors for the flight pack to ESC connection, does that sound right. Plus gold 4mm bullet connectors for the 3 motor wires. And I take it these electric models don't have on/off Rx switches per se, just disconnect the battery to kill everything? Does that sound right?

Any recommendation should on Wattmeters and are there such things as inflight wattmeter type loggers?

Cheers

Mike

perttime19/09/2020 04:33:21
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200 forum posts
11 photos

XT90S and 4 mm connectors should be just right.

You are approaching size and power levels whare SOME like to use a thing called "arming plug" to turn everything On and Off. That way, they can close the hatches and whatever else is needed, and switch on from the outside when everything is ready.

I know that some use radio telemetry features to keep track of Voltage levels, at least.

Steve J19/09/2020 06:42:30
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2077 forum posts
60 photos
Posted by MikeQ on 18/09/2020 22:22:40:

I'm wondering If I need a separate 2S lipo for Rx and Servos or if the ESC will handle it?

I would suggest using a UBEC or separate battery on a model of this size. The BEC circuits on ESCs tend to be a bit basic and it allows you to power up the receiver without the fan being live.

MikeQ19/09/2020 09:58:41
122 forum posts
97 photos

Hi

thanks ... will look into that. Out of interest the servos are:

Aileron: 2 x QZ401 Digital Coreless HV ~ 9kg 4.8v to 6v

Rudder: 1 x MG5921 HV ~ 19kg 6v to 8.4v

Elevator: 2 x MG2810HV ~ 6kg to 10kg 5v to 8.4v

Any recommendations on the capacity of a separate 2S for powering Rx and servos in this range. Would be separate 2S be too much for the Aileron servos (4.8 to 6v)

Cheers

Mike

John Lee19/09/2020 10:02:50
804 forum posts
93 photos

I'm with Steve on this one. I have an Angel 50 with the same setup but I don't use the inbuilt BEC (disconnect the red wire), rather I have a separate Jeti SBEC & a small 2S LiPo.

The problem with XT90 anti-spark connectors is that they are only available for the battery (female) end. So you will need to fit one to every battery pack. I used a Jeti anti-spark connector fitted to the side of the fuselage into which I insert the male plug. This makes arming & disarming on the flight line very quick whilst the separate power supply to the Rx enables all the checks to be done before arming.

a2bc9dc8-df80-4747-821e-180da8dc8d3e_1_105_c.jpeg

John Lee19/09/2020 10:05:22
804 forum posts
93 photos

I use these 1300Mah 2S Lipo Mike

Steve J19/09/2020 10:08:45
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2077 forum posts
60 photos
Posted by MikeQ on 19/09/2020 09:58:41:

Would be separate 2S be too much for the Aileron servos (4.8 to 6v)

The problem is that sometimes when manufacturers say 6V they mean 6V and sometimes they mean 5S NiHM which is actually 7V. If it's the latter, 2S LiFePO4 would be a good choice. If it's the former, you would need a UBEC.

MikeQ19/09/2020 10:17:44
122 forum posts
97 photos

Hi

thanks for the advice ... I'll call the supplier as I've had good service so far and need other bits and bobs I hadn't thought of ... lol ... like Velcro straps and all that.

cheers

Mike

Dickw19/09/2020 10:31:50
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760 forum posts
102 photos
Posted by MikeQ on 19/09/2020 09:58:41:

Hi

thanks ... will look into that. Out of interest the servos are:

Aileron: 2 x QZ401 Digital Coreless HV ~ 9kg 4.8v to 6v

.............................

Any recommendations on the capacity of a separate 2S for powering Rx and servos in this range. Would be separate 2S be too much for the Aileron servos (4.8 to 6v)

Cheers

Mike

While a 2s Lipo would be fine for the 8.4v servos, you are asking for trouble using one with the 6v servos - a 2s LiFe pack might be OK as Steve says.

Like John Lee, I have been using a Jeti SBEC in my Sebart 50E Pitts, but have been running it direct from the 6s 5000 motor power Lipo rather than using a separate Rx battery. It has been fine over the last few years and a recorded total of over 46 hours in the air (280 x 10 minute flights). As an added refinement, I have an isolator between the battery and the ESC with the SBEC on the battery side so I can power up the RX and check controls etc. before powering up the ESC and motor.

Earlier you asked about an "airborne wattmeter", and yes most radio systems with telemetry offer sensors which can do this. My choice was to use a third party sensor, the SM UniSens E (use Google to translate), which works well with the telemetry from many brands of radio, and gives volts. amps, watts, rpm, altitude, and more. An example of telemetry data from my Sebart Pitts is attached.

Dick

v-w 1 minute into flight.jpg

Edited By Dickw on 19/09/2020 10:32:28

Steve J19/09/2020 12:18:36
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2077 forum posts
60 photos
Posted by MikeQ on 18/09/2020 23:03:59:

Any recommendation should on Wattmeters and are there such things as inflight wattmeter type loggers?

Does your Spektrum transmitter have telemetry? If so, you would need a TM1000 (available secondhand at reasonable prices) and either Spektrum's (overpriced) current unit or an aftermarket one such as the UniSens that dickw uses. A 'T' receiver would be an alternative to an AR8000 & TM1000.

Spektrum do ESCs that talk to their latest receivers.

Eagle Tree used to do a standalone airborne logger, I don't know if they still do,

MattyB21/09/2020 10:15:00
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2320 forum posts
43 photos
Posted by MikeQ on 19/09/2020 09:58:41:

Hi

thanks ... will look into that. Out of interest the servos are:

Aileron: 2 x QZ401 Digital Coreless HV ~ 9kg 4.8v to 6v

Rudder: 1 x MG5921 HV ~ 19kg 6v to 8.4v

Elevator: 2 x MG2810HV ~ 6kg to 10kg 5v to 8.4v

Any recommendations on the capacity of a separate 2S for powering Rx and servos in this range. Would be separate 2S be too much for the Aileron servos (4.8 to 6v)

I'm sorry to tell you your "friendly" local supplier has upsold you on the elevator and rudder servos there. Here's what Sebart recommend in the manual...

As you can see that rudder servo in particular is hugely over-specced. If you haven't fitted it yet I would be taking it back for a refund, and probably the elevator too. I suppose the saving grace is that you could run them on std 5V supply with no worries if you want and dispense with the second pack, but that seems a bit of a waste.

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