Alot of it has to do with centrifugal force. Yes, once the MAS props get to full cruise RPM, then you might save some amps, thus increased flight time. BUT, getting them up to speed takes more inertial force than the stock props for exactly the reasons you mention. The stiffer the blade, the higher the pitch, the more force it takes to get it spinning up to speed. Same as trying to start a car off in 2nd gear. In a car you can do it, but in the short term you will hear your bearings clanking if you let the clutch out too fast, and in the long term your clutch might wear out while you are riding it while the clutch engages, and the car gets up enough movement to unburden the engine of the added resistance of a higher gear. If you try to leave rubber in 2nd gear, all you are going to do is stall the engine. Same as when you give the drone full power at takeoff with the higher pitched MAS props. So what do you have to do, you turn down the gains, which you need to do with the higher torque props.
I cant quite agree that the motors are working less hard at low RPM with the MAS props. If the OEM props are more "feathered" as you say, and softer, it's impossible that the MAS could be easier to turn at low RPM.
Yes acceleration might be better at low RPM with the MAS, BUT, at what cost? What you are essentially doing by asking a higher pitched prop to accelerate as fast or faster than a lower pitched prop is adding additional burden to the motor. Again, trying to turn a higher pitched, bigger prop with the same motor that was designed for a lower pitched, softer prop, is beyond the design specs for the motor. Yes, it can work, but MAS doesnt tell you that when you buy the props. When they get to cruise RPM, yes they might save on some amps, but Im totally satisfied with the OEM props, and Im not really interested in 1 minute more flight time at the risk of possible long term damage to my motors. Im not saying that this could happen, but the MAS were not designed to optimize motor lifespan, they are designed to extend flight time, and make the drone quiter to the ear. Ive got a few pairs of the MAS in different colors, but I like the OEM better. It just makes me feel better to use OEM equipment since using the MAS props makes such a negligible difference in flight time, and definitely has an effect on low speed handling and motor reaction time.
What does this mean to the average pilot? If you want your motors to last as long as they were designed to, stick with the OEM props. If you are looking for slightly improved flight times, slightly higher top speed, MAS might be an option for you, but not for me. I never fly at full speed, and like my low speed handling the way the Mavic was designed to do.
First things first Rob - You know I respect you like crazy - and I'd never want you to use product you have objections to, and therefore our debate here is without any thoughts of - 'you're wrong, I'm right' - or anything stupid like that ... So with that in mind, I'd like to continue to debate the points you have raised without any predjudice please ...
When you look at the force needed to overcome inertia in accelerating the prop's up to e.g. hover rpm, then what's more influential there is the 'weight' [Mass] of the prop's ... Force = Mass x Acceleration [F=
MA] ... I've not got the best kitchen scales at my disposal, but my DJI 8331 prop' weighs in at 8 grams (0.28 oz), while my MAS prop' weighs 10 grams (0.35 oz). There is very little in it ... Now if you observe the rpm numbers on your RC controller while you have the Mavic sitting in the hover, you'll see that number continually changing, and usually by around 500rpm (50 on the controller). So the first point is that the motors don't really come up to speed and stay there - they are keeping the Mavic stable, and therefore can be changing +/- in rpm all the time. Again - I say that if the motor was having to draw more current to push the MAS prop's harder - then I'd expect to see shorter flight durations (as every feedback input that increased motor rpm would draw more current than compared to stock DJI). Your theory also makes me ask if there are 'types' of flights where the MAS prop's are more efficient??? I've not seen any evidence of that so far ... People have reported improved flight durations with MAS prop's during all types of flights - not just a restricted envelope ...
I know there is a lot of discussion regarding reducing 'Gain' to get the 'Mavic Air'
Master Airscrew prop's under control, but I've not had to make any Gain changes in flying my Mavic Pro Platinum with MAS prop's ... What that's telling me is that the motors pretty much 'think' they are running DJI stock prop's - in that the rpm may be lower overall, but the change in rpm to get the corrective action is about the same ...
To focus on your automobile comparison, changing the prop's on a Mavic, is like changing the tyres on a car. If you asked 10 people if they still had the same brand of tyres on their car after the first set were changed, you'd probably get a majority saying - no, they changed the tyre brand - because; the rubber was too soft / rubber was too hard / original tyres were too expensive etc. As has been pointed out, there are cases for different types of tyres on cars / prop's on Mavic's depending on what you want from it ...
It's not theory, it's actual observed difference that the Mavic's motors are doing lower rpm's when spinning MAS prop's, when compared to the same with DJI 8331's. You'll still see the rpm variation as the Mavic pushes and pulls on each motor to keep steady-state hover, but while the rpm range from max. to min. is about the same for the two types of prop' - the starting point is lower for the MAS prop's. Due to the lower degree of stiffness in the DJI prop's, what actually happens is that the motor has to spin faster, and actually work a little harder to make the DJI prop's as effective as the MAS prop's - because the prop 'feathering' into the airflow effectively reduces the lift on that part of the blade to zero (note that this effect would not be seen along the whole blade length, but would be apparent nearest the tips). I can see your logic, in that you seem to be thinking ... "If the prop's are a courser pitch, and they are being spun at a lower rpm than DJI stock prop's, then the prop's are producing more drag, and the motors are working harder to spin them ..." Again - I'd agree - IF - the batteries were draining faster - which would show as a shortened flight duration ... but we don't see that. The interesting thing here is however, that if you do a comparison between a set of stock DJI 8331 prop's and a 3rd party carbon-fibre copy of the 8331 prop's - you do see it happen exactly as you describe. The rpm's are lower with the c-f prop's, BUT - the flight duration is cut dramatically!
I'd propose that both of us are right, in that the MAS prop's are making the motor work to get the required lift, but due to the stiffness and design of the blade, the required lift comes at lower rpm ... While the DJI prop's are feathering due to torsional stress (twisting along the blade length), which means the motor has to work harder and spin the prop's at a higher rpm to get the required lift.
Strangely enough. for the reasons I've proposed above, the acceleration required in the Mavic's motors to spin-up the stock DJI prop's is more than is needed for the MAS prop's i.e. the DJI prop's need to hit higher rpm to get equivalent lift/movement. I'm pretty sure that the max. ascent speed of the Mavic in its various modes, is set in software. With this being the case, I'd not be at all suprised to see that the rpm in a max rate ascent with MAS prop's on, would be lower than for DJI stock prop's ... Something I need to try one day.
Bottom line for me - and where my logic is coming from - is that if you have lower rpm's, and longer flight duration, you must be drawing less battery current. Lower current = lower Watts = less work being done by the motors. I don't know of any application where running an electric motor at higher rpm's will extend its life? ... So I'd question the assumption that you would actually get longer motor life [with higher average rpm's] using stock DJI prop's over MAS [with lower average rpm's] ...
Now - the positives for the DJI stock prop's:
1) Due to the higher rpm's, the Mavic will actually fly faster when it has the DJI stock prop's fitted. A Mavic Pro will fly faster with stock 8330 prop's then it will with 'quiet' 8331 prop's. In short, you have to be able to spin a prop faster to go faster!
2) Due to the torsional & longtitudinal flex on the DJI prop's, they act a bit like a shock-absorber, in that reacting to changes by e.g. wind gusts, should be smoothed out a bit more, giving the gimbal more time to react. In theory, this should mean that DJI prop's make the Mavic the better camera platform - but - personally, I've not noticed any detrimental effects in camera stability when using MAS prop's. The only instances of camera instability I've seen in the Mavic Pro, are when people put the DJI stock 8331 prop's on the Mavic Pro!
