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ESCs...for beginners - please keep it simple

The Electronic Speed Control

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Tim Mackey23/08/2009 12:32:00
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 The ESC ( Electronic Speed Control ) is exactly that - it controls the speed of the motor.
As seen in the main intro section, it connects between the battery and the motor, and also has a lead which goes off to the receiver throttle port and this usually supplies power to the whole onboard radio system, as well as receiving commands back from the receiver as to the throttle position.   Two other main features of most ESCs are
1) The BEC ( Battery Eliminator Circuit ). This eliminates the need for a separate radio system battery, and cleverly "drops" the high voltage from your main flight battery down to around 5V which is what your radio needs. It is carried along the same wire as the one that plugged into the throttle port, so nothing is normally plugged into the main battery port of the Rx. This is great for saving weight - and dont worry, this radio voltage will be maintained long after the battery has dropped so low as to not power the motor any longer, so although you may experience a "dead stick" if the battery does drop this low, the radio will still allow you to guide the model back to the strip.
2) The LVC ( Low Voltage Cutoff ). This little circuit within the ESC cuts the power to the motor when it detects that the flight battery has run down too low.
Batteries especially LiPo batteries will be ruined if they are allowed to discharge too far, so this clever gizmo prevents this from happening. Note that on some ESCs you have to "program" the type of battery you are using into the ESC, and this is much easier to do with the ESCs which can deploy a "programming card "
Other ESCs can automatically detect the battery cell count when first detected, and will automatically adjust this cut off point. However,  other features of the ESC can usually be programmed also, such as an electronic brake ( useful for folding props back on gliders ) motor timings, and so on.....and here the programming card really comes into its own.
Check when purchasing an ESC that....
 
1) It is a brushless ESC for brushless motors... brushed ESCs do still exist, but will NOT work on your brushless motor, The opposite is also true.
 
2) The maximum current capacity of the device. Before you purchase the ESC, you should have already worked out the maximum current that will be flowing in your setup. Choose an ESC which is "rated" for at least this amount, and little bit more for headroom. I often go as high as 50%  more , so for example, if I know my motor and prop will be "pulling" say 20 Amps at WOT ( Wide Open Throttle ) then I will likely buy an ESC rated for 30A. There is absolutely no reason at all that you could not use a huge 100A ESC on this, except for the weight penalty...so for the few extra pounds difference in price, play safe and "go large "
 
3)  That it will work with the planned number of cells you intend using in your battery.
 Many of the smaller ESC will be limited to just 3 or 4 LiPo cells as a battery maximum,   so if your rig is going to be using more cells than this, get the appropriate ESC.
Incidentally....regarding "twins" -in almost every "multi-motored" model  its best to use a separate ESC for each motor. If you still wish to supply the radio using the BEC, then its best to disconnect the BEC power ( red lead ) from one of the ESC BEC units that are connected to the Rx throttle channel ( usually with a Y lead ).
It is not uncommon for two BECS to "fight" one another if both connected .
There are many more clever features in ESCs, and also some models dont have the BEC we mentioned earlier. These often also deploy something called OPTO Isolation, where the actual commands beteween the ESC and the Receiver are communicated optically - as in fibre optic technology - and this can help eliminate any electrical noise and interference created by the ESC from actually affecting the operation of your radio.
Where an ESC does not have a BEC unit, then obviously you will need to arrange for an alternative supply for the radio sytem. This thread here, has a lot more on this aspect.
However, as a beginner with electric flight, you are likely starting off with a more simple rig, and in most cases, the ESC with a built in BEC will do just fine.
Connecting it all together.
The motor has 3 wires to connect with the 3 wires from the ESC output. These can be connected in any configuration you like, with no ill effects. If the motor, during testing runs the "wrong way" then simply swap over any two of these wires. The ESC also has another two large gauge wires - usually red and black, and these are for connection to the battery - in the right polarity!

Edited By Tim Mackey - Administrator on 15/06/2010 22:32:56

Stratocruiser29/08/2009 09:16:32
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Timbo , my ESC has 3 wires coming from it, red, orange and brown. I wanted to connect it to the Futaba supplied on/off switch, but this has only 2 wires, red and black. Does this mean I have to avoid the switch and plug it straight into the receiver? If I can use the switch, which colour aligns with which? If I have to plug it into the receiver, all the servos have white, red and black wires, so which way round do I plug the ESC in, as it fits both ways round?
Tim Mackey29/08/2009 10:19:17
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You dont use a switch between the ESC and Rx Strato....check the diagram I put up on the parent thread . The ESC becomes "live" when the main flight battery is plugged in, and then completely isolated when the battery is removed, so no switch is necessary.
 
The color codes of your cables is
White = signal                 Orange  on your ESC
Red    = battery +ve         Red        on your ESC
Black =  battery -ve          Brown    on your ESC
 
Its quite normal to find different manufacturers using different colors for their cables, and the two versions above are normally used by ( amongst others ) Futaba and JR /Spektrum.
 
Stratocruiser29/08/2009 11:08:09
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Timbo, you are a gent. Thanks very much, a sticky bun in the post for you.
Tim Mackey29/08/2009 15:00:23
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===
Bill Tillick21/09/2009 23:27:20
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Timbo, re your reply to Strato about a switch, I have a couple of planes  where the battery goes in before the wing is attached. I would prefer to use a switch so that the system is not live until I am ready to fly.
 
Presumably one could safely put a switch in the +ve line between battery and ESC?
 
Thanks,
Bill
Tim Mackey22/09/2009 09:27:54
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The switch referred to above is not a main power cut switch...ts just designed to isolate the recever signalling. I dont advise fitting a switch in the main power lines - especialy for heavy current applications - use an isolater "plug" - see my Hangar 9 camel thread for details.
Myron Beaumont22/09/2009 09:36:26
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Timbo
Going on from what you've mentioned -Does that mean that a switch rated at 1 Amp / 240 V  is not suitable for carrying 240 watts (A X V )  ?
.I'm guilty of using one like that ! It's the current rating that matters is it -regardless of the voltage written on the switch ??
Myron
Tim Mackey22/09/2009 11:17:00
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Dont want to drift off topic here guys.... Your right in many respects Myrn, but I simply wouldnt trust a switch /springs / contacts etc in a flight critical scenario where large currents are used - thats why  radio radio switches are slide rather than toggle.
Right back on topic please.
ericrw08/10/2009 15:56:29
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What is "burst current" in relation to an ESC ?
Tim Mackey08/10/2009 17:43:32
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Very short duration ( often 30 secs or even less )
ericrw08/10/2009 18:47:01
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Hi Timbo, I'm wanting to know, what it means and is a short duration better than a longer one or  the other way round ?.  It's the diffrence between two ESC I'm considering buying.  Eric.
Tim Mackey08/10/2009 19:27:46
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It means that the ESC can handle a much higher current than normal for short "bursts"
The longer these bursts are specified for, the better the ESC....generally

Edited By Timbo - Moderator on 23/10/2009 17:05:31

Alan Hall17/12/2009 13:28:17
56 forum posts
Hello Timbo
 
I'm just embarking into electric flight and have a had a few misshaps. Nothing too serious except to the pocket! I have two esc's and am unsure which to fit to a powered glider. I have a 40amp esc with BEC and a 70 amp esc that is designated OPTO and it has a switch fitted to it.
 
As the motor is drawing more than 40 amps at full power (about 47-48 amps). Up to about 7/8 throttle it stays within the 40 amp bracket.  I've considered fitting the 70 amp ESC but don't know what OPTO is or what the switch is for. Is it an on/off switch or does it isolate the power lead or what? From your thread dated 27/08 I think this esc does not have a BEC so will go into the throttle socket of the RX. Does this mean I require a separate power supply for the RX and do I need to isolate the red lead from the ESC to the RX? Can you advise me please?
 
Confused or what!
 
 
Tim Mackey17/12/2009 19:12:46
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Hi Bodger...sorry for the delay - PC woes
You need to use the 70A one as the other will cook at 48A possibly - even though he figures will be lower when actually airborne.You could of course prop down a little which would get the figures down.
The switch is meant to isolate the radio from the speed controller, NOT the main power leads from the battery. If its an OPTO unit, then yes you need another way to power the Rx.
No, the red lead will be actually "dead" if the ESC is an opto, but you still of course plug the plug into the throttle channel so the rx can send the throttle positions to the ESC.
Alan Hall17/12/2009 20:01:31
56 forum posts
Many, many thanks for that Timbo. You're a gent. The 70 amp ESC will be in the model this weekend and at least I now have a good idea of where I'm headed and hopefully so will the glider! Unfortunately I can't prop down as it is a folding prop assembly that I bought at the Nats and without traveling or taking a chance on ordereing over the net I'm a bit stuck as Lincoln is devoid of a good RC Model Aircraft shop.
 
Still, thanks for the advice. I hope Santa brings you something nice.
Hamish27/12/2009 21:15:46
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Timbo
 
Reading your very good information but is this correct
 
"The main things you need to check when purchasing an ESC are...
 
1) That it is a brushless ESC for brushless motors... brushed ESCs do still exist, but will NOT work on your brushed motor, The opposite is also true."
 
 
 

Tim Mackey27/12/2009 22:50:36
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Well spotted Hamish!
It should ( and now does ), of course , read
Brushed ESCs do still exist, but will NOT work on your brushless motor, The opposite is also true."

Edited By Timbo - Administrator on 27/12/2009 22:52:56

Sam Thomas06/02/2010 00:01:49
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So if  use a 25a motor from GC ( I would link but it just locks me out when I click on the bar) with a hobby wing 25a esc, will I be ok?
Pete B - Moderator06/02/2010 01:16:42
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You might be OK, Sam, but it is usually better to use an ESC rated a bit above the motor rating. It doesn't have to work so hard, then, and reduces the risk of you burning out the ESC. Suggest you use a 30A ESC, or even a 40A - it's not much more weight and will probably be used for something else in the future!
 
Pete
 
ps I'm sure you'll get a more technical answer from Timbo - I'm no expert!

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