FT Saab Viggen 70 mm EDF.

And put a 100 amp ESC in there! Running an 80 flat out isn't going to do much for it's longevity!
A few extra grams of weight is less problematic than a dead esc at 100 feet agl!
I overloaded an esc once, in a pre-bult plug n play - it blew a hole in the fibreglass fuz! (and it stunk!!!)

Klipkopwildlife wrote: I would question limiting the throttle travel, that's what your left hand's for![badass]

Normally I would agree with you Klippy, but in this case there is a solid reason for it. As Eric pointed out running the ESC at max capacity is asking for trouble. As it is buried in the duct behind the battery box, to change it & the wiring would require a lot of surgery! Seeing as there is no way I am going to need 440 w/p if I use a 4s, the simplest solution is to restrict the throttle so the ESC can only draw around 60 amps. That would still give in excess of 300 w/p at full chat ! :woohoo: Anyway my left hand is reserved for lifting pint's of beer !
STF. Apologies, I have just seen your comment. Something consider when I build the next one !

crash
Do be careful.
An ESC pulses the power so restricting the throttle does not physically reduce the amps but just the length of the pulse. It is the peak amps driven by the full battery voltage (4s in your case) that troubles the mosfets. What works once may not over a longer period.
The ESC pulses are fast and there is some reluctance in the circuit so it does take a measurable length of time for the amps to build up thus reducing the throttle will reduce the peak amps per pulse but not in direct proportion to the throttle setting.

It would be nice to think every ESC is quality tested to determine its capability for both amps and volts, but there are not, so they fall in to a range of capability.
The guide for reliability is to have the full power amps at no more than 80% of the ESC amps rating particularly if the battery voltage is also at the ESC's upper cell limit.

Well that's interesting. My plan was to set the max throttle at 60 amps using a meter, regardless of the percentage on the TX. As it happens this is about 65 % throttle travel. Are you saying that will still stress the ESC ?

What has Mr Admin done wrong?

crash
What you propose would certainly stress the ESC a bit more than a set up that took 60 A at 100% throttle.
I am not suggesting it will cause a problem but more stress increases the risk of a failure.

Eric wrote: What has Mr Admin done wrong?

OF hasn't done anything wrong, he started a post and then decided not to complete.

Modern electronics are very clever, the output circuit of the ESC (they're MOSFETS but don't worry) have very tiny forward resistances and it's resistance that causes heat. When you switch (pulse) the output circuit on it delivers ALL the battery voltage to the motor, the current in the circuit is then a function of the battery voltage, the battery resistance, the output circuit resistance and the motor resistance. If your required current was 60amps and the amps during the pulse were 600 then the required pulse length would need to be 1/10 of the possible length to give an average of 60amps.
Oh dear, I've tried to keep this simple and failed!
The bottom line, it's better to use an ESC that's rated up to 6s if you want to run a 4s, regardless of the current required. The caveat of extra current headroom on the current is to cover events sometimes beyond your control, ambient temperature, cooling air etc.
Now I'm going to do your head in, when long supply runs are required in an ESC setup, the weight of the electrons rushing down the wire becomes a problem when the output circuit shuts off![badass]

Tony, you missed the joke. OF asked - Please remove Mr Admin. I queried what Mr Admin had done wrong!
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Oh never mind! [badass]

Klippy. Good explanation & I think I get what you are saying. If you really want to do my head in try explaining the theory of light or electron probability ! The ESC is 2 > 6s rated at 80 amps with a 3 amp BEC & is positioned in the duct where it should get plenty of cooling. I used 10 gauge wire to the motor at approximately 500mm in length to keep the resistance as low as possible. Bearing in mind that a copper wire under one meter in length will handle double it's rated capacity, plus the load spread across three phases, that should be more than sufficient. In short, if it goes bang, it goes bang, I will just make the next one better !
P.S. I got the joke Eric :lol:

Klipkopwildlife wrote:

Eric wrote: What has Mr Admin done wrong?

OF hasn't done anything wrong, he started a post and then decided not to complete.

It would be nice if I (we) could delete our own accidental posts.

old fart wrote:

Klipkopwildlife wrote:

Eric wrote: What has Mr Admin done wrong?

OF hasn't done anything wrong, he started a post and then decided not to complete.

It would be nice if I (we) could delete our own accidental posts.

Err, I think you can, but you have a limited amount of time to do it, perhaps we need to ask Admin to lengthen the time window?
Sorry Eric, the Shingles affects my sense of humour, my story and I'm sticking to it![badass]

I tried to delete it as soon as I posted it and found that it wasn't where I wanted it.

Finally finished it, well as finished as it's going to get ! I couldn't decide on a colour scheme, so the bottom is matt black, & the top just got a light dusting to break up the white. I really must invest in an air-brush ! Happy Christmas.

My models look like that when they've been in the loft for a while! [badass]