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To bec or not to bec.


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Hi guys

Apologies to the Bard for taking liberties with his words.

Here's the deal:

Looking for an esc, around 60-70a, but for an 8s set up, which, I believe, means opto. Trouble is I can't find anything below 120-150a and a similar price tag in pounds.

Any suggestions?

Other than that, my current (ahem) understanding is that anything above 6s, the bec can't cope with higher voltage. So, what would happen if I used a 6s esc but disconnected the bec. Would this let the magic smoke out?

Your thoughts?

Jeff

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No experience with that particular model but, like you, I have always found HobbyWing ESCs to be very reliable. I only have one 8s installation though and that uses a HobbyWing Platinum (opto) ESC. I wouldn't recommend using a 6s rated ESC on 8s, BEC or no BEC.

 

Sorry not to be of more help.

 

Trevor

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Hi Guys, thanks for your thoughts

Trevor
Happy to use Hobbywing, if I can find one that meets my needs.

Cuban8
Selecting a bec is not the problem. I will be using 6 digital servos, so would be using a separate receiver battery, or possibly a stand-alone 20a bec.
My question was , since I only need 80a is there a way I can avoid the 120a ones costing north of £100.
Seems there is.

Gary
Turnigy Plush (the old type) are re-badged Hobbywing anyway. Used them before with success. Not sure about the newer Plush 32's. Have a couple in use and they're fine, even got the prog card, however can't say for sure whether they are also Hobbywing derived.
Your link to HK only goes to the general product page, but a google search comes up with this which is the one you meant, I think.

Ron
Thanks for that, but I'm not sure what you're advising. As I read it, you bought an opto esc from 4-Max, but the opto bit means you would need a separate power source anyway.

 

In general I'm rather surprised that anyone should produce an esc for 8s. After all, that's only 2 cells more than a regular 6s one. Especially one with a built in bec.
Looking to find a esc close to the specs I need without going for an overrated one with a price tag to match. (cheapskate moi?)
Looks like I'm spoiled for choice.

Out of interest, this is what I'm playing with. Currently got a 120 pumper on the front. Looking at ways to get the same power output with an electric powertrain. Please ignore the scruffy oik standing next to it!
If I go that way, the glo motor will be sold on to offset the cost. So far, using e-Calc, I'm looking at £150 or so for electric, definitely in the ball park.

Cheers

Jeff

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When using a separate flight battery my preferred option is LiFe, the 4-Max ESC can’t be run like that so I’ve had to use a BEC. Not a major issue but not how I wanted to have it. George has now got big red lettering notifying purchasers about this!

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In effect that’s what I’ve got but the governing factor, for the flight system power, is what the ESC needs, hence why I have the separate BEC in place. Like I said, not ideal but it does the job, in fact I now hook it up to the balance lead on one of the 2 5s packs in the ‘plane as I wanted to move the Cof G back!

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Geoff

 

One of the problems with going from IC to electric is that you lose the braking effect of the prop unless you have an ESC that provides you will adjustable braking.  The Jeti line of Spin Pro ESCs provides you with infinite braking options to keep the downline speed in check for precision aerobatics rather than the simple soft/hard options with many other ESCs.  You will need to get a Jeti Box as well so that you can set up the ESC - that adds to the price by about £30 I think.  That having been said, I've used many Spin Pro 99s and they have given faultless service even though all were bought second hand.  You might find the additional cost will more than repay itself just for having full control over braking.  This is the 80a version.

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53 minutes ago, Peter Jenkins said:

One of the problems with going from IC to electric is that you lose the braking effect of the prop

Peter,

Please enlighten me on why this is so?

Surely if the brake is set on the ESC and you select a lower throttle setting, then the prop will have the same if not a better effect than IC as IC can over-run.

Even if the brake is not set, the wind milling effect of a propeller with no power does have a marked braking effect.

Just asking as a general flyer rather than a precision aerobatic one.

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Hi Guys, thanks

Peter
Thanks for the thought, but you're looking it it from the point of view of an experienced F3A pilot.
Bear in mind that this will be my first real aerobatic plane, albeit an old fashioned one. I am hoping it will enable me to polish up my flying, but I'm a long way from being an accomplished F3A one, therefore a long way from needing to consider things like braking on the down lines.
One for the future I think.
Having said that, if I go electric I am leaning towards the Plush 32 esc. This does have adjustable brake strength in 4 stages, if that's what you're thinking of.
Also, not entirely set on going electric anyway.
Got one of my clubmates coming down today to see if we can get the glo motor started. If it does, and runs properly might be tempted to re-join the 'oily hand' society.
Everything still to be decided.

Geoff S
Looks like a good esc, but it's only 6s capable.
Contacted George at 4-Max for some power train suggestions. He said a 500Kv motor running on 6s for the Smart Move, which seemed pretty good to me.
However, for the Excelsior he suggested something very similar. 420Kv rather than 500 and a bigger battery, but still on 6s.
Given the difference in the model size and weight, that didn't seem right to me, so I kicked around a few ideas on eCalc, and came up with a 270Kv motor on 8s.
The glo motor came with a 16 x 12 prop. Using this electric set up, a 16 x 10 prop produces 6900rpm and  some 11 lb thrust. Theoretical flight speed is 64 mph. Sounds good enough as a first step.
Mixed flight time with this is some 8 minutes.
Bear in mind I haven't decided yet whether to go electric or not, but if I did the Glo motor would be sold on to help with the electric. At current prices, the electric set up I have got comes in at around £160.
Certainly not out or reach.

Still work in progress.

Jeff

Edited by Jeffrey Cottrell 2
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4 hours ago, Andy Gates said:

Peter,

Please enlighten me on why this is so?

Surely if the brake is set on the ESC and you select a lower throttle setting, then the prop will have the same if not a better effect than IC as IC can over-run.

Even if the brake is not set, the wind milling effect of a propeller with no power does have a marked braking effect.

Just asking as a general flyer rather than a precision aerobatic one.

Hi Andy

 

The braking function on the majority of ESCs only comes into play with the throttle fully closed.  The one exception is when the rpm is governed.  I am aware of only one such ESC - the Adam Debowski D3 but there may be others.  In this case, maintaining the selected power setting gives a fixed rpm regardless of whether you are going vertically up or down or flying level

 

So, with part throttle on an electric you have less braking than on an IC.  

 

I have experienced inadequate braking on a vertical down line even with 80% brake selected.  As I was flying a biplane, I made use of modified crow braking (top wing both ailerons up and bottom wing both down) but that reduced the roll rate so I changed to a 3 blade prop and that worked better by providing more drag than the 2 blader.

 

The Jeti, and some other ESCs, allow you to change braking by by either 1 or 2 percentage points so provides very finely adjustable braking but only when the throttle is fully closed.

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Hi Peter

On a downline with an electric model, what throttle setting would you use?

Reason I ask is that the Hobbywing Flyfun V5 has a new option called 'Proportional Braking'.

As I understand it, from 20% to 100% on the tx gives you 0% to 10% on the throttle. Below 20% gives braking on the prop proportional to the throttle stick position. I would guess with no throttle the prop would be windmilling. This new set up restricts the speed at which the prop can turn, so giving braking effect (I think).

Any use?

Jeff

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Hi Jeff

I took a look at the Hobbywing Flyfun V5 and based on the information they give in the Specification it's impossible to know exactly what they mean.  I had a look at the description on Electricwingman and again it isn't clear how this braking is achieved.

 

Within the F3A world, leaving aside the ESCs that govern rpm, you get braking when the throttle is fully closed.  You normally set the brake amount to get a downline speed that matches your preferred level speed and which can be maintained on a vertical upline to be the same.  In other words, you are looking for a constant speed up, down or level or all the way round a loop for example.

 

I think your best bet would be to call Electricwingman and ask them what the specification means and whether you are getting some form of rpm governor or just variable braking using reverse emf as the way of achieving it.  For the price though, it seems pretty attractive.

 

You didn't mention what type of motor you were thinking of using.  Hobby King have this one for £103 but from their EU warehouse.  

 

If you are new to F3A, you might also like to take a look at this book wot I writ.  It has received excellent reviews.  You can either buy it from Amazon or from me at the reduced price of £15.50 including p&p in the UK.  There is a "Look Inside" feature on the Amazon page that shows you the table of contents and the first 2 chapters for free.

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Hi again Jeff

 

I forgot to answer your direct question!  On a vertical downline, I have a fully closed throttle.  I use a Jeti Spin Pro 99.

 

The other point I should make is that checking the current draw on the ground is a waste of time.  That is an unnatural case as when you release the aircraft the current draw will drop as the load on the prop drops.  As an example, I recorded 3,600 watts on wide open throttle for a motor rated at 2800 watts when the aircraft was restrained on the ground - not for long I might add!  Once the aircraft was airborne, having pulled to the vertical at a slow speed and applied full power on a number of occasions, the highest wattage I recorded was 2840 watts once with all the others being around 2750 watts.  So, worth having some sort of telemetry to record current draw/ power.  I use a 3rd party telemetry device made by SM Modelbau that gives real time display on your Tx of: V, A, Watts, Height, rate of change of height, rpm.  The device is easily setup to speak a variety of radio brands using a USB lead attached to your computer.  I have found it excellent.

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Hi Peter

 

Agreed, the specs never seem to tell you what you need to know, especially for such a useful gadget.

I got my info from the FlyFun manual, here.

Look on page 2 under 'Programmable Items'.

Seems to me on a lot of esc's you can programme the brake strength, but only to one setting, which may not be appropriate to what you need on a particular flight. The advantage of proportional braking is that you can adjust the brake strength in real time as required, using

0% to 20% on the stick.

Might or might not be an advantage, your call.

Nice motor you linked me to, but this is the one that caught my eye. UK warehouse too.

I know that static current measurements are not that indicative. I do not have telemetry, but I normally fly a mixed flight, but for a specified time, then measure what the charger puts back in.

Then I can work out an average current draw, which relates much better to the real world.

Added bonus is that over a period of time, if a pack starts to take more charge than usual, that's a sure sign it's coming to the end of its life and needs to be retired to less arduous duties.

As regards your book 'how quickly they forget'. I bought it when it first came out, and that's what started this journey down the rocky road.

Having said that, if it all ends in tears you know who I'm going to blame, don't you?

 

Jeff

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Hi Guys, quick footnote

 

Decisions, decisions.

Had a clubmate come down this afternoon to try to get the glo engine started. Lo and behold, once we found the appropriate needle settings, it ran and pretty well too. He did say the bearings were a bit 'grumbly' but no biggy.

Apart from a couple of issues with the pipe coming off, successful try.

So, jury still out on whether to go electric at all.

Need to get some support bits. Going to have a root through my shed see if I still have anything, but my main issue is going to be fuel.

Seems I can get it shipped down here, but only in large quantities (4 gallons or so).

Anybody know where I can get smaller quantities?

 

Jeff

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9 hours ago, Jeffrey Cottrell 2 said:

Seems I can get it shipped down here, but only in large quantities

 

A bit of thread divergence, but, I wouldn't view 4 gallons as "large" quantities when you're playing with a 20cc size glow. Even with an economical four stroke instead of a thirsty two stroke, I'd imagine you'll burn 12oz a flight.

 

IIRC there is ~150oz in an imperial gallon.

 

4x gallon is thus 600 fl oz.

 

600 / 12 = 50 flights.

 

 

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