First wattmeter results and subsequent changes

[Mitchell Howard]

I've just used a wattmeter for the first time on my trainer setup; APCE12x8 prop, Ripmax Quantum ii .40 motor, ZTW Beatles 60A ESC, Zeee 4S 60C 3700mAh. The numbers it pulled seem close to the knuckle; peak power and amps at 790W, 57.9A. I think there's a few things to do to address it, but this forum always comes up with solid suggestions, so please review my approach!

1) Reduce prop diameter and/or pitch.
Not sure by how much to move away from 12x8. I'm thinking I'll get and test a 12x6 and 12x7. I'm don't think I'm pushing the envelope of thrust or speed with current setup (possibly why it hasn't died!).
4-max has the model at 50A with APCE12x6 and an 800KV 3547 motor. Difficult to read across and compare, everything's different to mine.
I've not yet figured out the best way to weigh models, so I'll assume it's the advertised 2.5kg/5.5lbs. Output power as measured puts it at 143W/lb which I understand as being 'fairly meaty'.
Surprised the Ripmax Quantum .40 box says use a 12x9 and 60A ESC. I can't find a max current for the motor but a very similar Overlander Thumper 4250 says 63A maximum, so the Quantum must be struggling too.
How far beneath 60A should I be aiming for?

2) Ventilation improvement
I'm definitely going to get some ventilation into the airframe. A clubmate had a square pocket about 60x60mm in the base of one of his models to let air out heated by the motor, ESC and LiPo. The ESC has been getting hotter that I recall it ever getting, but my confidence has been growing and I've been getting more liberal with the throttle.

3) Vibration and prop spinner
I feel like the nose of the plastic prop spinner is running slightly eccentric and above 50-60% throttle I think it's responsible for vibration.
I'm going to take it off and run it without to see if the current and vibration reduce. If it does drop, I don't think the plastic nose is going to lend itself to being pushed and pulled into a centre position.
Is this what aluminium backplate spinners are better at? I think the self-tapping threads in the plastic backplate are likely responsible for pulling the cone off centre.
I've just seen on 4-max, a recommendation to lose the stock 'IC' spinner and to use an electric one that has an alumnium backplate. What's the difference? The site just says runs truer - that must be a benefit for IC also?

[Frank Skilbeck]

Depends what the model is, if you want high thrust then reduce the pitch, this will reduce the models top speed but keep the static thrust, so take off and climb out will be similar, if you want top retain the speed drop the diameter.

 

Also while you maybe close to the knuckle on the ground, once in the air the propeller will unload and the power (and amps) drop off

[Mitchell Howard]

I'm glad you've said that, I'd got it around the wrong way.

More pitch = more speed

More diameter = more thrust.

 

It's a Seagull Boomerang v2

 

Is there a way to get a good reading without taking the wattmeter up in the air? Lift it off the deck I suppose? Two man job.

 

Do you think it's a good balance then Frank, no change?

 

What's the feeling on fully plastic spinners? I do want to resolve the vibration.

Edited June 3, 2021 by Mitchell Howard

[Simon Chaddock]

Mitchell

The important factor is the amps will drop as the plane speeds up so as long as you are within the motor & ESC specs at full power static on the ground any failure is much more likely to be through heat rather than an electrical over load.

The only way you can find out exactly how much the amps drop in flight is by using real time telemetry which is now quite possible with the right kit.

Electric power maintains a high overall efficiency over quite a wide range of throttle settings so there is nothing wrong with using the throttle to limit the electrical load and as a by product increase the flight time. ? 

 

 

[Mitchell Howard]

25 minutes ago, Simon Chaddock said:

Mitchell

The important factor is the amps will drop as the plane speeds up so as long as you are within the motor & ESC specs at full power static on the ground any failure is much more likely to be through heat rather than an electrical over load.

The only way you can find out exactly how much the amps drop in flight is by using real time telemetry which is now quite possible with the right kit.

Electric power maintains a high overall efficiency over quite a wide range of throttle settings so there is nothing wrong with using the throttle to limit the electrical load and as a by product increase the flight time. ? 

 

 

 

Do you have a feel for how much amp draw might drop by Simon? are we talking 10%? Less?

 

I think I'll hold off on adjusting prop and just get the spinner and ventilation sorted. Heat must be wasting mAh too.

 

My Radiolink AT10ii has a voltage sender module attached to the receiver which I'm about to start using, but nothing for amps. I'm quite happy with this ground pulls more amps theory, so will be interested to see spinner-less current draw later this evening!

Edited June 3, 2021 by Mitchell Howard

[Don Fry]

Are you happy with the performance? Are you happy with the flight times?

[J D 8]

    I have just got some of those Zeee battery's and they sure put out the power.

[SIMON CRAGG]

Mitchell, having been down the same road as you are now, I would recommend that you have a look at a programme called "e.calc". I have found this an absolutely essential aid to selecting motor / prop / esc / lipo combinations.

 

The free version is ok, but I pay in the region of $6 for the full version.

 

Like most of these things, it looks a bit intimidating at first, but I have used countless times for myself and club mates.

 

It will answer virtually all of the questions you posed, without the expense of purchasing a load of different props etc.

 

Brilliant bit of kit!.

 

[Mitchell Howard]

10 minutes ago, Don Fry said:

Are you happy with the performance? Are you happy with the flight times?

 

I am, I get a good 6-7mins. Another 2-3mins would be great. I'm less concerned about in-air performance, i.e. not fussed about making it climb vertically or all-out horizontal speed, but am fussed about having what I can most closely relate to as 'torque' in a car - the ability to get off the ground with ease and climb steeply, perhaps 45-60deg without any fear of stalling. It certainly has that characteristic at present.

 

 

 

It doesn't sound like the model is ?overpropped?, what with this concept of in-air amps being lower than on-ground amps.

[Mitchell Howard]

Just now, SIMON CRAGG said:

Mitchell, having been down the same road as you are now, I would recommend that you have a look at a programme called "e.calc". I have found this an absolutely essential aid to selecting motor / prop / esc / lipo combinations.

 

The free version is ok, but I pay in the region of $6 for the full version.

 

Like most of these things, it looks a bit intimidating at first, but I have used countless times for myself and club mates.

 

It will answer virtually all of the questions you posed, without the expense of purchasing a load of different props etc.

 

Brilliant bit of kit!.

 

 

Now I know the actual amp draw I should think this will be a good comparison to ecalc. I wonder if it assumes in-air amps or on-ground amps.

[Mitchell Howard]

3 minutes ago, J D 8 said:

    I have just got some of those Zeee battery's and they sure put out the power.

 

I don't have a reference point to be honest, but the ZTW 60A is hot and the Zeee LiPo barely warm! I use the EC5 connectors, and I think Amazon UK have stopped selling the 3700s. I think Zeee have stopped making them too, they're not on the website. Shame, I'll have to try something else or re-plug another Zeee pack!

 

[SIMON CRAGG]

2 minutes ago, Mitchell Howard said:

 

Now I know the actual amp draw I should think this will be a good comparison to ecalc. I wonder if it assumes in-air amps or on-ground amps.

Best bet is to install the full version, and have a good play with it. There are lots of parameters that can be tweaked!.

 

[Peter Beeney]

Hi Mitchell,

 

If it were mine think I would be wanting to just simply put a 10 x 6 ACP i/c prop on and give it check out. I’m not a big fan of E props but I’m probably far too much of a hooligan…

 

My first check is with a tacho, if it’s running at something like about 15% down from the unloaded rpm (which I’ve already checked by the way) and that might be somewhere in the ball park figure of 10,000rpm then I might like to think I’d got a topping trainer. Training models of this nature have flown for many years now using the ubiquitous 10 - 6 or something very similar driven by a good 40 i/c motor with great success and aplomb by many aspiring aviators. The propeller is not going to be the least bit concerned about what is turning it round, it will just get on with it.

 

Then I’d check the current flow which at this level I’m sure is not going to cause any sleepless nights at all, sort the spinner out, probably with a gentle screwdriver adjustment and definitely provide some adequate ventilation. Now I’m soon be going to think a possible test flight. If I’m a beginner this would start with with a proper check on control throws and motor run, ALWAYS but ALWAYS standing BEHIND my well restrained model and then invariably followed by a walk to the strip and hence into the bluey.

 

Very good luck with your model!

 

PB 

         

 

[leccyflyer]

2 hours ago, Mitchell Howard said:

I'm glad you've said that, I'd got it around the wrong way.

More pitch = more speed

More diameter = more thrust.

 

It's a Seagull Boomerang v2

 

Is there a way to get a good reading without taking the wattmeter up in the air? Lift it off the deck I suppose? Two man job.

 

Do you think it's a good balance then Frank, no change?

 

What's the feeling on fully plastic spinners? I do want to resolve the vibration.

Many fully plastic spinners are rubbish -poorly balanced and, like you said, the backplate can deform when you tighten the screws. The spinners with the ventilated aluminum backplate -like the Irvine spinners - are much better all round for electric flight. Better balanced, better contact between the spinner and the prop adaptor and they run true. You notice vibration and spinners running out of true much more with an electric set up than with IC, because the rotating motor tends to have a lot less vibration itself than a reciprocating piston engine.

[SIMON CRAGG]

1 hour ago, Cassandra said:

 

Bin it. Get a either an alloy one or one with an alloy backplate. Do you know somebody with a lathe in case you need the backplate adjusting?

 

You could also consider using a dome nut rather than a spinner.

I like domed nuts!  Less of the motor is "shielded" by a conventional spinner allowing more cool air to flow over the motor and subsequently the esc.

[Mitchell Howard]

I got rid of the spinner yesterday evening and the vibration did disappear. I've managed to adjust well enough for now to leave it in place, but will get it changed out for a better one. I charged a LiPo and ran it up again for it to show 67A and 1001W...

 

 

[MattyB]

What Kv is the motor - 800? Looks like you definitely need to prop down at least 1" on the pitch...

[Dickw]

17 minutes ago, Mitchell Howard said:

 got rid of the spinner yesterday evening and the vibration did disappear. I've managed to adjust well enough for now to leave it in place, but will get it changed out for a better one. I charged a LiPo and ran it up again for it to show 67A and 1001W...

...........................

 

That 67 amps is peak amps ("Ap" on the wattmeter) and could just be a brief peak as the motor accelerates up to running speed. It is the steady state current once running you need to consider and the video doesn't show us what that is. Did you take a note of the normal running current?

 

Dick

[Mitchell Howard]

3 hours ago, MattyB said:

What Kv is the motor - 800? Looks like you definitely need to prop down at least 1" on the pitch...

 

[Simon Chaddock]

Mitchell

This might help.

Any motor is designed to a maximum amp limit. In simple terms it is set by the maximum magnetism that can be generated in the iron parts but there are other factors that have to be taken into account as well.

A motor is not self regulating. Put too much load on and it will simply draw more amps, however above the rated maximum the extra amps are being used rather inefficiently so create more heat. The compact design of brushless motors means they can only dissipate so much heat. Work a motor too hard for any length of time and heat breaks down the insulation coating on the wires. The motor is then wrecked.

Ripmax specify 60A as the motors continuous limit. At 67 A you are moving into dangerous territory for both the motor and the ESC.?

   

  

[Don Fry]

21 hours ago, Mitchell Howard said:

 

I am, I get a good 6-7mins. Another 2-3mins would be great. I'm less concerned about in-air performance, i.e. not fussed about making it climb vertically or all-out horizontal speed, but am fussed about having what I can most closely relate to as 'torque' in a car - the ability to get off the ground with ease and climb steeply, perhaps 45-60deg without any fear of stalling. It certainly has that characteristic at present.

 

 

 

It doesn't sound like the model is ?overpropped?, what with this concept of in-air amps being lower than on-ground amps.

All in all, if you stick a 12 by  6 prop on it, it will accelerate well, climb well, use less amps, giving you a longer flight time.

Also, very steep climbs can be problematic. I know the ground can break aircraft, but first you have to arrange the contact. It’s often safer to have it close to the ground under control than busting a gut in a climb.
What do you do, in that 60° climb if it hits a gust, suggest it goes nose further up, looses speed, needs fast reactions, one chance to sort it out. Part of the B test, if memory serves, is a low circuit, a couple of double decker buses high, and near constant height. Great practice.

[Matt Carlton]

I'm not sure I understand why you need to run 1000W in a 6lb trainer? 600-700W would be perfect, cooler and put a lot less stress on your power train. Especially when your current draw is so high compared to the motor spec. 

There is no need to aim for a 60 degree climb with a trainer really, it isn't any safer, it just puts a big load on the drive train. The practical solution if that is what you really need, would be to change the motor and ESC to one which can give you more of a safety margin rather than driving all the components to 120% of their recommended performance in order to acheive something that the model isn't designed to do. Prop down to 650W with 5 or 6" pitch and the model, motor, esc and battery will be happier I would d suggest. 

Edited June 7, 2021 by Matt Carlton

[Mitchell Howard]

2 minutes ago, Matt Carlton said:

I'm not sure I understand why you need to run 1000W in a 6lb trainer? 600-700W would be perfect, cooler and put a lot less stress on your power train. Especially when your current draw is so high compared to the motor spec. 

There is no need to aim for a 60 degree climb with a trainer really, it isn't any safer, it just puts a big load on the drive train. The practical solution if that is what you really need, would be to change the motor and ESC to one which can give you more of a safety margin rather than driving all the components to 120% of their recommended performance in order to acheive something that the model isn't designed to do. 

 

Hi Matt - the current hardware I'm using is only what was recommended by the model shop. I'm still green, but I was even greener at the point I bought everything! I've got an 11x8 and 12x6 prop in the post which hopefully will be much lower in peak values.

[Mitchell Howard]

57 minutes ago, Mitchell Howard said:

 

Hi Matt - the current hardware I'm using is only what was recommended by the model shop. I'm still green, but I was even greener at the point I bought everything! I've got an 11x8 and 12x6 prop in the post which hopefully will be much lower in peak values.

 

Matt do you think I should run a smaller prop still?

 

It's recommended above to use ecalc, but I'm an engineer by training and I learnt a long time ago not to trust theoretical values too much. There's no harm in adding to the arsenal of props anyway!

[Don Fry]

Those two props will give you a good practical lesson in the difference between pitch and diameter. My beloved says a lady can’t have to many diamonds. Props are my weakness.  Most aircraft need a tweak or three to get it in the grove.

One day, if one of the good flyers in the club offers a go on one of their aircraft, take it. You will be surprised how easy it is to fly. Tweaked