The good folks at Master Airscrew sent me a few of their MR-series props to try and I thought this would be a good opportunity to do a follow-on of my ‘Jello Killer’ video.
If you watched the original video you’ll know it started out as a motor mount review and evolved into a vibration test of several dissimilar props for camera drones. This time I’m focusing on three 10-inch props of similar pitch and materials to see how they compare in both vibration and noise.
|Watch the complete video|
I would have included thrust tests but the Rotorcraft Systems Engineering and Simulation Center at the University of Alabama in Huntsville has already done extensive comparative thrust tests between the Master Airscrew, APC and Graupner E props. Also I don’t own a thrust stand.
What the Simulation Center found was that the Master Airscrew prop outperformed the others in both thrust and efficiency and for those that are interested I’ve included links to those results in the description.
To balance the blades I added weight to the light side using striping tape. And if a hub was out of balance I used a Dremel tool to remove excess material from the heavy side.
The props I tested are the Master Airscrew MR 10×4.5, the APC MR 10×4.5 and the Graupner C 10×4. All three props were picked at random from sets of four and all three required at least minimal balancing with the Graupner requiring the most amount of additional weight and the Master Airscrew requiring the least. Only the APC and Graupner required hub balancing.
But before I get into the tests I want to touch on presentation because Master Airscrew seriously has their game on.
Their products are priced similarly to the competition (actually a bit less than APC and a LOT less than Graupner) but just look at the differences in packaging compared to those guys. The Master Airscrew props come in heavy resealable bags with slick graphics and an included printed safety guide. Even their accessories and swag are tight and I really like the battery straps and badges they included. APC and Graupner on the other hand are packaged in plain, old school bags with stapled cardboard tags.
The finish of these props is just better too. The edges and surfaces are smooth and free of burrs and defects with nicely applied logos. The matte finish of the Graupners is also nice but their silkscreening is less than consistent. Both brands are available in several colors.
Then there are the props from APC. They only come in gray and the quality control seems less than stellar. I’ve actually cut myself more than once just taking a prop out of its bag because APC hadn’t properly removed mold flashings and as a consequence I now take 400 grit sandpaper to the leading and trailing edges before handling them.
How I Tested
My test jig is basically the same modified Tarot 650 quadcopter frame I used in the previous tests. An all carbon fiber frame with a rigid iPhone mount screwed to the center plate. The motor used for this test is a new 700KV T-Motor (MN3110-17 700KV) that required a surprising amount of effort to bring into balance. (The black tape over the logo just happens to be where additional weight was needed.)
The ESC is a Little Bee 30 amp flashed with BLHeli 14.8 and is connected to a Seriously Pro Racing F3 flight controller running Beta Flight. Power is provided by a 12-volt 30 amp switching supply to keep the tests as consistent as possible.
In my first video I used a simple servo tester to control motor speed but this time around I wanted more precision and the Beta Flight’s UI offers the granular control needed to set motor RPM exactly. Each test run was made at 5,000 RPM and was measured using a contact tachometer at the prop nut.
Noise and vibration were measured using smart phone apps with the goal being to measure the differences between each prop with repeatability rather than try to collect precise data against a calibrated reference. Raw data is available here.
- iPhone seismometer app : VibSensor 2.0.0
- Android sound pressure app : Sound Meter Pro 2.5.4
For balancing larger props I prefer my Du-Bro balancer. I love the smooth precision of the thing but for props under about 11 to 12 inches it just doesn’t feel sensitive enough and for those smaller props I use a modified Top Flite magnetic balancer. These rigs are okay except the balance shaft is overly long and prone to bending and once that happens it’s useless. My solution is to use a much shorter shaft from a smaller balancer and modify the Top Flite’s chassis to accommodate it.
So the APC prop actually did better against the Master Airscrew than I expected as did the Graupner C prop but those results come with caveats. The APC prop required more additional weight to balance it than the Master Airscrew plus I had to grind away some of the APC’s hub before the entire prop came into balance.
In contrast, none of the Master Airscrew props I’ve tried required hub balancing and most required no balancing at all. And of the three props in this test the Master Airscrew prop I selected required the least amount additional weight to bring it into balance.
C Is For Craptacular
That brings me to the Graupner C prop. While it was the quietest of the three and offered the least vibration its pitch is also shallower than either the Master Airscrew or the APC and it’s made from a softer plastic. It was also the most unbalanced, requiring more weight to be added than the others as well as the removal of material from its hub. Unfortunately this was one of the “good” C props.
The first Graupner C prop I tried to balance required 3 pieces of tape along one blade. And while that might have been acceptable, nothing I tried could bring the hub into balance.
Eventually I removed so much material that the prop just looks scary unsafe and is still out of balance. And at more than double the cost of either the Master Airscrew or the APC I consider that kind of loss as unacceptable disqualified it from the test.
So to sum up, the measured vibration and noise differences between the APC and Master Airscrew props I tested are negligible. However, the APC is several grams heavier, can require extensive balancing, has a less sophisticated finish, is slightly more expensive, and [according to the University of Alabama in Huntsville] produces less thrust and is less efficient than a similar Master Airscrew prop in this size range and category. Bottom line: I have a new favorite. =)