Motor Size

[Tosh McCaber]

I have built a power version of my Pibros 800mm wingspan Depron delta.  It weighs, c/w with motor, 20a ESC, and 3S battery, 260g- 9 oz. 

On web advice from another builders' previous experience, I have installed a 24 gram 1700KV brushless motor outrunner, with a 7x4 thin electric prop.  I have found that this combo, on my wattmeter, with the 3S battery produces 130w on full power, with 13a current.

Two questions-

Is this going to give me an exciting first flight?

and

Presumably, if necessary, can I tone down the full motor speed by adjusting the travel on my Spektrum DX9?

Any advice appreciated!

[Geoff S]

I guess it will be quite exciting but if you want to tone it down a bit you could try (say) a 6x3 prop.  But aren't these all about speed, anyway 🤩.

[PatMc]

1 hour ago, Tosh McCaber said:

Presumably, if necessary, can I tone down the full motor speed by adjusting the travel on my Spektrum DX9?

 

Any advice appreciated!

 

No, at some point the ESC will recognise the limited stick travel as full 0 - 100%. Do as Geoff suggests, try a smaller prop. 

[Tosh McCaber]

Or try not to fly above half throttle for a start??

[leccyflyer]

That's well over 200w/lb Tosh - as Pat & Geoff said, a 6x3" prop might be an option and the model will still be pretty speedy, but with much lower current draw..

 

My somewhat similar e-Mugi was a little bit bigger -900mm, nearly twice the weight and was pretty rapid with much lower power than that - 6v sp400, Gunther 5x4.5" prop, 7xSR500 nicds. 

 

[PatMc]

Or you could ues a 2s lipo. 

[Tosh McCaber]

Thanks for the replies guys. I've just sourced from my prop box a 6x3, to start off with.  I'll to mount it on the plane and try full throttle- I suspect that all will be well thereafter!

 

I like that eMugi Leccy!  Yet another in your squadron- oops-more than a squadron- wing!!

[gangster]

On 02/05/2023 at 20:29, PatMc said:

No, at some point the ESC will recognise the limited stick travel as full 0 - 100%. Do as Geoff suggests, try a smaller prop. 

So if you have calibrated the esc to the 0 to 100 range then reset the travel to , say 50%. Surely the esc will see it as the stick being pushed only half way up , but in reality you will have the full throw of the stick. Worked on my super 60 and I had 120 watts max out of the 450 watt motor no issues at all. Must be calibrated to 100% first.  

[Simon Chaddock]

You don't have to use full throttle all the time or even at all in a normal flight.

 

With electric the throttle is an infinitely variable control just like the control surfaces. Anywhere between 0 to 100% and as many times as you like during the flight.

Get used to using it to find out how the plane behaves over its full flight envelope. Knowing what the plane can or cannot do may save you the odd an unexpected crash. 😉   

Also remember reduced throttle equals longer flight times.  

[leccyflyer]

13 hours ago, Tosh McCaber said:

Thanks for the replies guys. I've just sourced from my prop box a 6x3, to start off with.  I'll to mount it on the plane and try full throttle- I suspect that all will be well thereafter!

 

I like that eMugi Leccy!  Yet another in your squadron- oops-more than a squadron- wing!!

The e-Mugi was, I believe, the first electrified Mugi, which the designer Morgan Wood had been flying as a slope wing, before launching his website with the plans. I really should put her back in commission as a slope Mugi, but at the time - 2001 - I hadn't tried slope soaring at all, it was all flat field flying. The Correx that the e-Mugi is made from is transluscent and she's equipped with a three colour LED mount. Morgan caused quite a stir when flying his Mugis in the slopes above some of the towns in West Yorkshire. Night flying is pretty commonplace now, but it was a bit of a rarity back then.

[MattyB]

9 hours ago, gangster said:

So if you have calibrated the esc to the 0 to 100 range then reset the travel to , say 50%. Surely the esc will see it as the stick being pushed only half way up , but in reality you will have the full throw of the stick. Worked on my super 60 and I had 120 watts max out of the 450 watt motor no issues at all. Must be calibrated to 100% first.  

 

Yes that will work, but in the long term it's not good for the life of the ESC. It's always best to select the motor, prop and battery combo so that it can be run at full power safely - you will probably get away with it most of the time, but you are introducing some additional potnetial points of failure with that kind of setup. 

[gangster]

3 hours ago, MattyB said:

 

Yes that will work, but in the long term it's not good for the life of the ESC. It's always best to select the motor, prop and battery combo so that it can be run at full power safely - you will probably get away with it most of the time, but you are introducing some additional potnetial points of failure with that kind of setup. 

Thanks for that MattyB . Have you any more info as to why this is not good for the ESC. I cannot see any difference than flying most of the time at half throttle. It is not like the ESC is acting as a regulator as it is a switching device rather than a voltage dropper. What am I overlooking?

[Philip Lewis 3]

Nothing, you are quite right, I think the point being made is that an ESC is doing most of it's work at half throttle but this just means it will spens a bit more tiime there.

 

On all of my planes the throttle upper limit is +75 on a -100 to +100 scale as I simply never need the power the motor could supply, hasn't done any harm yet.

[MattyB]

1 hour ago, gangster said:

Thanks for that MattyB . Have you any more info as to why this is not good for the ESC. I cannot see any difference than flying most of the time at half throttle. It is not like the ESC is acting as a regulator as it is a switching device rather than a voltage dropper. What am I overlooking?

The links below should help you understand the issue. In most cases it won’t cause issues in the short term, but reducing current on an over-amped ESC (even a switching one) is not a good idea in the long run…

 

https://www.rcgroups.com/forums/showpost.php?p=21523350&postcount=13

https://www.rcgroups.com/forums/showthread.php?1504410-ESC-efficiency-questions

 

To be fair though I had understood initially the endpoint was being reduced to keep amps below the max rating of the esc, but a retread off post 1 that does not appear that be the case - apologies.

 

Edited May 4, 2023 by MattyB

[PatMc]

14 hours ago, gangster said:

So if you have calibrated the esc to the 0 to 100 range then reset the travel to , say 50%. Surely the esc will see it as the stick being pushed only half way up , but in reality you will have the full throw of the stick. Worked on my super 60 and I had 120 watts max out of the 450 watt motor no issues at all. Must be calibrated to 100% first.  

I assumed the end point was to be reduced, same as Matty.

Also I should have said "ESC may recognise" not "ESC will recognise" .

 

 

[gangster]

7 hours ago, MattyB said:

The links below should help you understand the issue. In most cases it won’t cause issues in the short term, but reducing current on an over-amped ESC (even a switching one) is not a good idea in the long run…

 

https://www.rcgroups.com/forums/showpost.php?p=21523350&postcount=13

https://www.rcgroups.com/forums/showthread.php?1504410-ESC-efficiency-questions

 

To be fair though I had understood initially the endpoint was being reduced to keep amps below the max rating of the esc, but a retread off post 1 that does not appear that be the case - apologies.

 

Yes, two separate issues here between reducing the power of the motor and trying to use an esc too small for the job. I have always been wary of ESC quoted ratings. I always give at least 20% headroom when choosing an esc. Having said that I have seen dozens of artf models all appearing to be fitted  with the cheapest esc possible and clearly not flown at full throttle all the time and I rarely see an esc die. Maybe the manufacturers of the esc were not exaggerating the rating of their products after all