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Post by ginginho on Dec 4, 2008 15:15:07 GMT 1
I'm pretty new to this hobby, getting used to the SC and modding it a bit but have started thinking along the lines of going brushless.
I know I need to swap out electrics which is also being budgeted for.
This leads me to a question: I've read plenty of times that the ESC should be a certain % more amperage rating than the B/L motor to cover for errors in manufacturer's data, but is there any reason other than financial to go MUCH larger rating, say 50% or more?
i.e. 25amp peak motor should have say a 30-35amp ESC. Will a 50-60amp ESC work any better or worse with it?
Thanks for any insight!
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Post by flydiver on Dec 4, 2008 18:06:15 GMT 1
The only concerns for going with a larger ESC are $$, weight, and the built in BEC. In some models the BEC will have more Amp capability (like the Turnigy 40A with 3A BEC) which is good if you aren't going to do a separate BEC (recommended with 3S and 4 servos). Learn to read your equipment specs and do it. Lots more info in this thread on that subject: supercubclub.proboards78.com/index.cgi?action=display&board=rg&thread=1858&page=1#11898ESC larger than that often do NOT EVEN HAVE A BEC, assuming you will be putting in a separate one since you are working with a larger system. |
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Post by ginginho on Dec 5, 2008 18:36:33 GMT 1
Aah right, thanks for that. Probably a 40A is about as big as will ever be needed.
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Post by mrmugen on Dec 5, 2008 23:43:34 GMT 1
If you plan to get a bigger plane down the road a 40 might not be a bad idea. I know the SC will have no problem toting around a few more ozs, in this case a few more grams.
Kevin
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Post by ginginho on Dec 8, 2008 18:25:16 GMT 1
Thanks Kevin for the reply. It was a bit of that, but also after reading Fly's excellent post about "brown-outs" I was getting a bit concerned on the BEC front with 4 servos. The make I'm considering do a 30Amp with a 2A BEC, but the 40Amp one has a switched mode BEC (god knows what that means, but it's listed as being better than linear) rated at 3A. For and extra fiver (about 8 USD) it seems worth getting the 40A. I like the make because it also has programmable Lipo protection, up to 3.3V under load, which I think is just about acceptable from reading other Lipo threads. The weight difference between the 30 and 40 amp versions is a whapping 4grams!! After flying on Lipo's for the first time last weekend, I feel confident that the cub can handle this  Linky to the supplier in the UK below, if anyone is interested in it. Dunno if this is available in the US. www.giantcod.co.uk/hobbywing-guard-brushless-speed-controller-p-402592.html?osCsid=43d621d4e45c4b869d8684d17e03736d |
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Post by flydiver on Dec 8, 2008 19:07:29 GMT 1
A linear BEC uses resistors to bring the voltage to the accessories down > makes heat to do this.
Linear BEC uses a different method making far less heat. Most 'add on' UBEC's are switching.
fly
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Post by mrmugen on Dec 9, 2008 2:10:45 GMT 1
Just a side note. The servos you will use in the cub will not matter to the bec much. The bec's are able to handle 3 standard digital servos most of the time . 4 of these servo's do not draw the power one digi will. I run all my small servo'd planes off the esc's bec and most have 5 servo's in them. Never had a issue to date and I have many planes that I do this in. Now if you were planning to run 4 or more standard servo's I would not say this.
Kevin
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Post by ginginho on Dec 9, 2008 12:02:35 GMT 1
Just a side note. The servos you will use in the cub will not matter to the bec much. The bec's are able to handle 3 standard digital servos most of the time . 4 of these servo's do not draw the power one digi will. I run all my small servo'd planes off the esc's bec and most have 5 servo's in them. Never had a issue to date and I have many planes that I do this in. Now if you were planning to run 4 or more standard servo's I would not say this. Kevin I bit the bullet and got the 40A ESC. I'm planning on using 4 9gram servos so ordered some of them too. I read that they are clones of the Towerpro SG90's but have struggled to find any stats on what they (or the SG90's) draw. I think I should be OK with the 3A switched BEC on the ESC, guess I'll have to give it all a good test on the bench. BTW, the motor in the order is a 220W 1050Kv brushless. Seems to be about the same as the park480, without the price tag. We'll see....... |
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Post by mrmugen on Dec 9, 2008 13:25:38 GMT 1
In my current 450 powered SC I use the 40a Elfite esc. I use 2 hs-55 servo's for ailerons, 2 HS-81's for elev and rudd, and a futaba 3108 for my drop door. Thats 4 that are constantly used and one that is seldom used......
Hope it goes well for you too.
Kevin
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Post by ginginho on Dec 12, 2008 16:10:35 GMT 1
In my current 450 powered SC I use the 40a Elfite esc. I use 2 hs-55 servo's for ailerons, 2 HS-81's for elev and rudd, and a futaba 3108 for my drop door. Thats 4 that are constantly used and one that is seldom used...... Hope it goes well for you too. Kevin Thanks for the info Kev, that confirms that I will be safe with the ESC ordered. Just out of curiosity, any reason other than weight/physical size as to why you use the smaller servo's for the ailerons?? |
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Post by mrmugen on Dec 12, 2008 20:59:01 GMT 1
I always beef up the tail servo's more than the aileron servo's. The tail servo's make contact with the ground the most so I like them to be overkill. In my bigger planes all the rudder servo's are metal geared....same with elevator. Seldom do the aileron surfaces take a pounding. They are plenty of torque for the ailerons.
Kevin
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Post by retiredbri on Dec 13, 2008 22:53:19 GMT 1
Hi all
I measured the current from the battery to supply the dual AR6200 receivers and two HS-55 servos.
Without any servo action the Rx current and the "idle" current of 5.4mA for each servos was 85mA at 4.97V from the BEC (part of Castle Creations Pixie 20A brushed ESC/BEC). There was no prop motor load.
This meant that the dual Rx and LED on the ESC was consuming about 74mA.
When I operated the two servos with fast and full stick deflections, the current peaked at 350mA. This makes sense since the working current of a single HS-55 is spec'd at 150mA.
The BEC is spec'd at 1.5A and 5V, suitable for 4 servos with 7 cells and 3 servos for 8 cells.
When I add the extra 2 HS-55 servos for the ailerons, the peak (all 4 servos working at the same time) current should be 650mA.
This gives me some confidence (well under the 1500mA capacity of the BEC) against brown-outs, even with 4 servos and 8 cells.
BUT when I stalled just one servo, the current drawn shot up to a whopping 490mA. I need to make sure therefore that my servos cannot ever stall by making sure that I do not overdrive them through the Spektrum Tx set-up. Equally, to make sure that the servo arm and horn holes combination can never drive them to their end stops.
I read somewhere that you should disconnect the control wire at the horn and move the elevator (then rudder then ailerons) to the end stops and then operate the Tx to see that the control rods are always inboard of this position (even with 125% travel set on the Tx).
Sorry if I'm this has all been covered before - I'm learning so much that I thought I'd pass it on the other new-bees.
Regards
retirerbri
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Post by mrmugen on Dec 14, 2008 0:03:25 GMT 1
Good post! Lots of good info in there. Thanks for posting!
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Post by mythotical on Jun 15, 2009 8:12:40 GMT 1
I do not mean to hijack but I have a question. I have ordered the turnigy 30A brushed esc to use on an old futaba RX with my Old futaba attack 4
I plan to use four servos two HTX 9g for the ailerons and two old futaba standard servos for the tail and rudder, should I have any concerns?
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