Max amps

[Frank Day]

Having returned to find electric power wizardry I've been tinkering with a aesthetic enhancement to an "old" foamie and could use some advice.

 

I've replaced some terrible looking 2 blade props on a  Parkzone Mosquito 49" for some period/scale looking 3 bladers.

 

Having tried a few motors that fit, i've found a reasonable combo. The issue or non issue is on 3s its 40W under the max amps for the motor whereas on 4s its the same amount over. It will probably go well on 3s but!

 

So could I simply reduce the max throttle setting on the TX if using 4S to keep it at or under max Watts.

 

Thanks

[Shaun Walsh]

19 minutes ago, Frank Day said:

Having returned to find electric power wizardry I've been tinkering with a aesthetic enhancement to an "old" foamie and could use some advice.

 

I've replaced some terrible looking 2 blade props on a  Parkzone Mosquito 49" for some period/scale looking 3 bladers.

 

Having tried a few motors that fit, i've found a reasonable combo. The issue or non issue is on 3s its 40W under the max amps for the motor whereas on 4s its the same amount over. It will probably go well on 3s but!

 

So could I simply reduce the max throttle setting on the TX if using 4S to keep it at or under max Watts.

 

Thanks

If you have to limit the throttle to reduce the current to the motors, what's the point in using 4s instead of 3s?

Also, what is the maximum current rating of the ESC?

[Frank Day]

That should be max watts.

 

 I've just tried a new prop and got an extra 30W and still under max rating. But thats still a combined 360 -380 Watts on a 1.2kg 2.5lb model.

 

So may be 3S will be more than needed.

Although the throttle setting may still be a vaild question if anyone knows more about this subject.

Thanks

[Philip Lewis 3]

Yes you can reduce the throttle end point back to limit the current draw, I do this on all my planes because they simply have too much power at full throttle,also don't forget the current draw will be less in the air than during a static ground test as the props will unload a bit in the air, you'll also likely get slightly higher RPM as well. 

[Frank Day]

Hi Shaun,

 

The plan was 4S because it suits other models, batteries etc,etc.  Motors are 2 - 4S.  Durafly MK24 Spitfire and Freewing Lippisch also on 4S.

 

ESC's are 40A, full thottle the Watt meter on 4s is showing 24A. on 3S about 17A  I replaced the original 18A items as the previous owner said one failed causing a crash though I suspect he actually ran out of juice as they worked perfectly when tried.

[Frank Day]

1 minute ago, Frank Day said:

Hi Shaun,

 

The plan was 4S because it suits other models, batteries etc,etc.  Motors are 2 - 4S.  Durafly MK24 Spitfire and Freewing Lippisch also on 4S.

 

ESC's are 40A, full thottle the Watt meter on 4s is showing 24A. on 3S about 17A  I replaced the original 18A items as the previous owner said one failed causing a crash though I suspect he actually ran out of juice as they worked perfectly when tried.

Thanks Philip, I wasnt sure if the reduction was a valid way of doing this but it seemed logical that reducing the thottle limit bought the setup back with limits

[Shaun Walsh]

OK, that makes sense, which motors and props are you using?

 

[Frank Day]

Motors are 2836, 880kV.  Current  props are MAS 10x7 3 blade and 10x5 (Banggood for a B17) counter rotating. I could possibly go to a 10x8 MAS on 3S which will probably get me nearer to the motors max of 243W.

Max reading on 3s with fresh battery was 190W (10x7 prop) and 17A

[Shaun Walsh]

11 minutes ago, Frank Day said:

Motors are 2836, 880kV.  Current  props are MAS 10x7 3 blade and 10x5 (Banggood for a B17) counter rotating. I could possibly go to a 10x8 MAS on 3S which will probably get me nearer to the motors max of 243W.

Max reading on 3s with fresh battery was 190W (10x7 prop) and 17A

According to the information I have found online the original model used E-Flite Park 370 motors rated to about 12Amp continuous with a 3s battery so about 120 watts each and well within the capability of the 18 Amp ESC originally fitted. Equivalent motors would be around the 2826 size so 2836 seems like overkill to say the least. What brand of motor are they and have you changed the ESCs?

[Denis Watkins]

With this idea of " Limiting the Throttle "

An ESC does the least work at Full Throttle as it virtually joins the battery leads to the motor direct.

Point being, that with a lower end point travel on the throttle will result in All the flight

Warming up the ESC, All of the time

So, consider cooling the ESC more thouroughly, or

Just fit the correct motor, with the right prop, using the correct battery, and fly full power when needed.

 

Edited May 27, 2022 by Denis Watkins

[Frank Day]

I did try a pair of the 2826, but they didnt like the props i wanted to use.(smaller diameter shafts etc) so i opted for the 2836 with a slight remodel of the nacelles to cover the longer motor and a pair of 40A esc's I had kicking around and a pair of Wot4 prop adapters.

 

The esc's live quite nicely in the Mossie radiator intakes in the LE, they are functional so plenty of cooling.

 

Prop,motor, esc, battery choice was a bit tricky especially for me finding my way around electrickery. The added complication is restrictive space for the motors that match BL370 fitment and the props I wanted to use to make it look a little more scale. Not quite the same as my Brian Taylor Mossie but the square two bladers were horrible. Not looking to go fast generally, too scared still!

[Shaun Walsh]

OK here goes:

Just taking a generic 2836 880KV motor and plugging the numbers into eCalc I get the following

3S battery MAS 10x5 3 blade

3s MAS 10x7 3 blade

4s MAS 10x5 3 blade

4s MAS 10x7 3 blade

 

Ignore the warning about exceeding the motor current capacity as the motor is generic. Also the aircraft weight is halved as these calculations are for one of a pair of motors.

You can see running a 4s battery on a 10x7 3 bladed prop gives you a thrust to weigh ratio of approx 3:1. Using a 10x5 gives about 2.5:1 thrust to weight. Even dropping to 3s with a 10x5 prop gives 1.5:1 which is in 3D aerobatic territory, it will just go up and not stop.

The original props were 8.25x5.5 twin bladed, have you got room for clearance with the fuselage on a 10 inch prop?

You said the 2826 motor shafts were the wrong size, was it not possible to use correctly sized prop adapters, you're going to have to fit new 3 blade spinners after all?

 

[Frank Day]

30 minutes ago, Shaun Walsh said:

OK here goes:

Just taking a generic 2836 880KV motor and plugging the numbers into eCalc I get the following

3S battery MAS 10x5 3 blade

3s MAS 10x7 3 blade

4s MAS 10x5 3 blade

4s MAS 10x7 3 blade

 

Ignore the warning about exceeding the motor current capacity as the motor is generic. Also the aircraft weight is halved as these calculations are for one of a pair of motors.

You can see running a 4s battery on a 10x7 3 bladed prop gives you a thrust to weigh ratio of approx 3:1. Using a 10x5 gives about 2.5:1 thrust to weight. Even dropping to 3s with a 10x5 prop gives 1.5:1 which is in 3D aerobatic territory, it will just go up and not stop.

The original props were 8.25x5.5 twin bladed, have you got room for clearance with the fuselage on a 10 inch prop?

You said the 2826 motor shafts were the wrong size, was it not possible to use correctly sized prop adapters, you're going to have to fit new 3 blade spinners after all?

 

Thanks Shaun,

 

I have heard of eCalc but havent looked at it yet, I will do so in future. The 10" props fit perfectly. It took a fair bit of searching to find adapters, most of the issue was the length, the smaller motors also had thinner shafts as well. The Wot4's are about 10mm longer which suits the hub of the prop. I have the 3 blade spinners and squared the holes off as Horizon Hobby did for the 2 blade offering.

 

It looks like either of the 3S options would give pretty good performance, 1.5/1 and 1.9/1 for the 10x5 and 10x7 respectively.

 

I probably made it more difficult for myself as I started with the props I wanted, when tried to match that to a motor that would fit in the mount,  as it is the mounting screws are a tight fit on the way in as the motor is somewhat bigger than the BL370

 

I appreciate the time you have taken to help with this.

[Shaun Walsh]

Glad to be of service, I enjoy doing stuff like this?

[Andy48]

7 hours ago, Frank Day said:

That should be max watts.

 

 I've just tried a new prop and got an extra 30W and still under max rating. But thats still a combined 360 -380 Watts on a 1.2kg 2.5lb model.

 

So may be 3S will be more than needed.

Although the throttle setting may still be a vaild question if anyone knows more about this subject.

Thanks

 

It is best to never run an electric system flat out. Above about 2/3 throttle there is a dramatic rise in the current used compared to the static thrust.  ESC heating is not a big issue in reality, I've found. As for props unloading in the air, they do but the effect is really quite small, about 5% at 40-50mph  as I found by experimenting. Its good to have the extra power though, firstly for take-off, but also as the battery is being used, you don't feel any loss of power.

Telemetry is a wonderful thing. ?

Edited May 27, 2022 by Andy48

[Frank Day]

I think the 3S options will give enough, probably the 10x7's. 4S will require throttle end point tinkering.

 

I have a couple Spektrum AR637T RX but still having a nightmare with the setup, basic functions all good but safe etc etc  etc is taxing.

 

I have a couple of E Flite BNF models I may have to look at the TX for some clues

[Lima Hotel Foxtrot]

It seems like the root cause of your problems are the propellers, and I really don't understand changing the 2 blade props for 3 blade, unless the larger radius causes a potential tip/ground interface issue.

 

If you have to land wheels-up then 3 blade props are more likely to break themselves or maybe bend a motor shaft and IIRC 3 bladers are less efficient.

 

If this is a purely aesthetic thing, then you cant see them in flight and the sound won't be dramatically different so perhaps fly with two blade props and leave three blade for looking pretty on the ground, they're not that onerous to swap over if you need to.

 

FWIW... I really don't like three blade props! ?

[Shaun Walsh]

The only time I had to resort to 3 blade props was on a Hobbyking Skipper XL where i swapped a motor to be able to use a 3s battery and didn't get enough thrust so went to 3 blade even though less efficient.

[Martin McIntosh]

I used HK three bladers on my o/d 81" Lanc. with 28-30 800kv TGY motors. Great until one of the weak props threw a blade. Tried some tougher ones which were useless so I changed to AliExpress 10x7 two bladers which are APC copies. No need even to balance them which was a real pain with the three blade props. Loads more thrust for no greater power input due to the higher efficiency and has been said you cannot see them in the air. About 18A max draw at full power for each motor.

It is a very bad idea to reduce the high end travel on the Tx. Tried it, the ESC does not like it so don`t do it.

[Frank Day]

I don't get a warbird with a two stumpy modern looking  square two blade props. Perhaps a couple of EDF's might do!  Oddly the Micro model version has 3 blade props. I always keep any removed parts. I also have a second one of these.

 

The 3s setup will give more than enough go at 1.5:1 (10x5x3)  or 1.9:1 (10x7x3) according to Shaun's  eCalc graph. There is still a whole bunch of ground clearance and 30mm to the fuss. If it noses over then its going anyway. Props are from Banggood and fairly cheap from a B17 model.

 

 My Brian Taylor 81" Mossie is on 16x10 MAS counter rotating 3 blades as recommended for the electric setup.

 

Its all a matter of preference in the end I guess.

[Frank Day]

sorry message sent twice so edited it out

Edited May 28, 2022 by Frank Day
sent twice

[leccyflyer]

Those two bladed props fly the Mossie superbly to be fair -and you don't really see them in the air.

 

[Frank Day]

Good to see another one of these babies.