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EPA, ESC and throttle

Old 02-17-2012, 06:40 PM
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solentlife
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Default EPA, ESC and throttle

Maybe like me you overpower your models ? How to limit that power and still have full stick ?

I needed to cut back the immense power of a motor for my parkjet and experimented with EPA.
I found that it worked but you have to follow a routine to make sure you don't upset initial set-up of the ESC.

a) Set-up ESC throttle stick range as normal with 100% 100% EPA ie default full range. Disconnect model.
b) If you have display function on your Tx - watch the throttle display while moving stick. This will tell you if it's reversed or not. Note which half of display bar is high speed half.
c) Go to EPA and select Throttle. Remembering which half of display is high speed ... select same here and reduce to 0%.
d) Bring stick back to zero. Connect up Wattmeter to model.
e) Now while slowly advancing throttle watch meter to see that you have selected correct % EPA to adjust. If you 0'd the wrong one - then motor won't start ... ESC in fact will tell you somethings wrong !
f) Assuming you 0'd the correct EPA ... you can see what full stick now gives you on the meter ...
g) If you need more throttle ... select EPA and throttle .. adjust that 0 up till meter reads the desired amps / watts you want ...

It actually takes more to write than to do ... and was a revelation to me when I realised the throttle would adjust on EPA same as a servo. But once adjusted - setting ESC throttle range is not advised.
I now have a tamed wild motor !!
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Old 02-17-2012, 08:02 PM
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JetPlaneFlyer
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Or you could fit a smaller prop?

Steve
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Old 02-17-2012, 09:45 PM
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solentlife
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The only question that remains ............

If a 1800kv motor is given free headroom to rpm's ...
Let's say a 3700kv on same prop but higher power ... what rpm when limited back to just under half amps ? (54 back to 25)

OK - tests run ...

1800kv on a 3S 1800mAh 25C good pack : 16,670 rpm full range WOT

3700kv on same 3S pack, with upper throttle EPA at 30% : 21,060 rpm full stick throttle.

I'm not sure how the % works and if it relates directly to motor speed ... but lets assume it does ...

I have EPA 100 - 30 instead of 100-100 ....

rpm of 21,060 = 100-30 ... so maybe 21,060/130 x 200 ? is max WOT full range ? .... 32,400rpm

At least I know that the limiting of amps has still given me worthwhile rpm and on a 5x5 prop - that is well worth it.
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Old 02-17-2012, 09:47 PM
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Originally Posted by JetPlaneFlyer View Post
Or you could fit a smaller prop?

Steve
The wait in post would kill me !! I don't have a LHS as you guys !!

Anyway - being a cheapskate and hate spending money ........... this was a freebie way to solve it !

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Old 02-18-2012, 01:24 PM
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All very true, but keep in mind that the AMPS the motor sees never changes. The esc is really just a high speed switch. The amps the motor sees during any one "one cycle" never changes with throttle setting. You are just limiting the minimum spacing between the thousands of "on" cycles that happen per second.

So make sure your esc is sized for the maximum amps your setup pulls at unlimited full throttle.

Hope that makes sense.

You are okay if you are doing this just to limit the power so you don't rip your model apart with an over powered set up.

Cliff
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Old 02-18-2012, 03:21 PM
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+1 on Cliff's comment.. End point adjust is ok if your hardware is all rated for full power and all you want to do is reduce the power you have available. Its not a safe way to limit the amps if your motor and especially your ESC is not adequately rated.

Steve
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Old 02-18-2012, 08:06 PM
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CrimzonRider
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part Cheapskate here too..lol

So even if your therotical setup is producing 54 amps and using the throttle to cut your amps down to 25, is your esc is still seeing 54 amps??...probably wrong..... or maybe my question should be why is it not safe to limit amps this way? ......just interesting..

cr
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Old 02-18-2012, 09:25 PM
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JetPlaneFlyer
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Originally Posted by CrimzonRider View Post
part Cheapskate here too..lol

So even if your therotical setup is producing 54 amps and using the throttle to cut your amps down to 25, is your esc is still seeing 54 amps??...probably wrong..... or maybe my question should be why is it not safe to limit amps this way? ......just interesting..

cr
Yes, your ESC is still having to deal with 54 amps (in pulses).. In fact the load on the ESC is highest when the throttle is about 70% open, WOT puts less stress on the ESC.

So 'no' it's not safe to limit the Amps that way.
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Old 02-18-2012, 09:55 PM
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solentlife
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Jetplane is correct in most ....but the fact is - it works and the proof of the pudding is that after 3 mins - the model came down with only a warm ESC, LiPo and cold motor.

Sorry to be a pain and go against the grain .... but the pulses are longer between and that gives a nett 25A as shown by the Wattmeter when set-up.
Yes the ESC is working harder ... but it's similar to a switching power supply you have for many items in domestic use ....

If I set the model to have full throttle range on the ESC - then I would have about 1 min flight ............. AND the ESC would fry ............ LiPO would be cooked ............ My way I get 3 min flight and still something left in LiPo, ESC is only warm, Motor is giving me 222 km/hr, something must be working in my favour ..............

Anyway - by time I get home after this next assignment - there will be the parts for a 5000kv motor to fit ... plus a lower amp draw 3800kv airmotor ............. so a world of choices for this baby ....
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Old 02-18-2012, 10:15 PM
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No worries solent, just for armchair rc engineers like me, it would be easier just to prop down to see lower amps, less heat and all other variables.

Everybody, I assume, likes to overpower their a/c and I understand what your saying. Kinda in the same boat right now, put a 700watt motor in a a/c design barely for 300...lol

Just interesting and figuring out my own opinon on the matter.

Nothing wrong with going against the grain....just makes for good debatin' and yakin' !!

have a good one guys
cr
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Old 02-18-2012, 10:19 PM
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cliffh
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Originally Posted by CrimzonRider View Post
part Cheapskate here too..lol

So even if your therotical setup is producing 54 amps and using the throttle to cut your amps down to 25, is your esc is still seeing 54 amps??...probably wrong..... or maybe my question should be why is it not safe to limit amps this way? ......just interesting..

cr
If your setup is requiring 54 amps at WOT, yes, your esc is sending 54 amp pulses to the motor.

The esc is a very high speed switch that also happens to apply the pulses at precisely the proper time, but that is another discussion.

The narrower the pulses are, the slower your motor will run AND the wider the pulses are, the faster your motor will run. This is because your motor cannot respond instantly to the power applied and instead, sort of averages out the power applied. Middle width pulses might AVERAGE out to 25 amps, but it is actually a series of many 54 amp pulses in your example.

This is a simplified version of how an esc/motor works, but the important thing is that EACH pulse from the esc (maybe 8,000 per second!) will be at FULL power.

For such simple looking devices, they are actually quite complicated in their operation

Cliff
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Old 02-18-2012, 10:35 PM
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..or.....you could just learn that the left stick has more than two positions
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Old 02-18-2012, 10:42 PM
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Originally Posted by cliffh View Post

For such simple looking devices, they are actually quite complicated in their operation

Cliff
Thanks JPF and Cliff.....It is pretty cool! My interest in this matter is keeping a lipo within its threshold of amps or at least close to its upper limits ....not really wanting to smoke a $65 45c battery but that is another topic.

cr

LOL @ oldfart.....there is??
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Old 02-19-2012, 01:13 AM
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Way to go, Nigel! Can't wait to see a video of this rocket!
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