DJI s900 with 3DR PixHawk - Mounting the Pixhawk

So Sebastian here again with the second part of my build log for a DJI s900 with a 3DR Pixhawk as flight controller. In the first part I gave some tips for building the standalone frame of the Spreading Wings multirotor. This time I want to show you all my solution for mounting the flight controller to the frame with added anti vibration silicone mounts.

But before we come to the hard work, I want to answer the question why I chose 3DR components instead of DJI's?
(Of course you can skip the next passages if you don't want to hear religious jibber jabber about different system architectures again and again ;) )

As you may have already found out, DJI is selling some capable and astonishingly expensive flight controllers for this frame. The Wookong series (maybe a little bit outdated?), the Naza flavored controllers (ment for smaller crafts as far as I learned) and last the state of the art, professional A2 flight controllers. I definitely did not want to start with Wookong or Naza controllers for several reasons. The only possible choice from DJI would have been the A2. It seems to be very capable and all the DJI add-on equipment seems very thought through. Cables with already fitted connectors and meassured lengths. Prepared mount locations for everything. Available tuning values for PID stabilization algorithm. And many things more. The only thing you have to do is buy, mount and fly.
Buy a lot. Buy expensive. Buy the golden Apple-style bird cage.
No open documentation about protocols and hardware. No open software for flight controller. DJI in control about where you fly if they want. And so on.
For my taste, I do not appreciate dongled systems. I do not like somebody to tell me what I can or can not do with the stuff I bought from my hard earned money. As mechatronics/electronics engineer I like to know what parts of my systems do things how they do them. How they communicate. How they work. And DJI does simply not offer this kind of information and openness. So not my cup of tea. And definitely not my cup of tea when the flight controller plus GPS is as expensive as the main frame itself. If components were competitively priced to similar parts or even if DJI would be more open minded, I would be tempted to buy DJI. But with all the negative points I was nagging about, 3DR and their (or better ETH Zürich's flight controller), the PixHawk, seems a lot more sexy for a tinkering guy like me.

So let's start discussing about mounting the controller to the frame.

First decision: vibration damping or not?
I don't know if one can get away with plain double sided sticky tape or anything like that for vibration damping with this copter. The propulsion systems are prebalanced in factory, so there should be less vibration from the start on, compared to a complete DIY copter. But with a 1300€ frame ment to carry the same money in camera systems some day, you should not rely on a exhausted factory worker having balanced your frame/motors/props after a 10 hour shift. So additional dampening is a must have. But what dampening system is the one to choose? Well that depends on where you want to mount your controller to.

So the really first decision: where to mount the Pixhawk to the frame?
DJI is mounting their A2 in an upward position with the upper case side facing in forward flight direction to an easy to reach plate at the front left of the frame. Quite special. But there is a second DJI-box called the "IMU". It is responsible for meassureing acceleration and rotation rates. But even this box is not mounted to any point near the center of the frame. Not in the center of gravity nor near the turning axis of roll, pitch or yaw. If it works for DJI then so be it. But in general not the most advisable positions for a Pixhawk, as far as I know. Although I think it would be possible to follow DJI's solution for a mounting position (Pixhawk supports 26 plus mounting directions).
I chose a more common position which also shelters the flight controller a little better. The flat plastic dome mounted on the lower frame plate, which is isolating and housing the power connectors.
Sadly I have no good picture to show you the virgin state of my mounting position, but you can see it in this assembly video from DJI.

Benefits of this mounting position:

• It is nearly in center of all turning axis. 
• Nearer to the center of gravity. 
• In the event of a crash, which will of course never happen, the controller is located at the safest position there is. So you can at least rescue the Pixhawk and the logs to investigate why there was (of course not) a crash.

Disadvantages:

• not much space above the Pixhawk where a lot of connectors and cables must be (and that gets even worse if you plan vibration damping). 
• Not very accessible. 
• Quite some work to fit Pixhawk in there.

So how to mount the Pixhawk in this location?
This question leads us back to "mounting with vibration protection?" discussion. And I think I have made it clear enough that you should never mount a flight controller without at least a little bit of dampening.
So what option to use with Pixhawk and s900 frame? Well if you buy a genuine flight controller from 3DR there are some double sided sticky foam pads included in the package. They are ment to be mounted at the four corners on the bottom of the flight controller. The only problem is: they are way to fat.
Second option: I had bought one of the anti vibration mounts for APM and Pixhawk controllers. The ones with the two carbon fiber plates and four silicone vibration cylinders connecting the plates in the corners (quite similar to these ones). Problem: the mount is also way to high for the limited space within the s900 frame.

 
Third solution: using one of the O-Ring-style or ear-plug vibration mounts. Problem: I don't want to trust some thin silicone rings only secured in a small slot between a screw and some spacing standoffs. Or some plates with ear-plugs. So just some plates with holes and memory foam. Too much money flying around with this specific build.
Fourth solution: after searching the web and looking for some finished product, I came to the conclusion that there is no "ready to use" solution for mounting a pixhawk to a s900. So I thought: "if there is none, just build one".
Mounting the anti vibration mount from option two completly into the frame was no option as already stated. But as it was already bought and available, I wanted to use at least the silicone dampeners and maybe the carbon fiber boards. After some thinking and even asking my wife for ideas, I settled for a mix of solutions from my (our) brain storming sessions:

This design offers some advantages in my opinion:

• dampening via the silicone cyclinders
• very flat setup because pixhawk is sitting low between the dampeners (height is even adjustable via washers/screws)
• Steal screws, washers and nuts give a bit more mass for better dampening (what does a mechanical engineer do if there are too many vibrations? -> Adding more mass)

I started the construction of the mount with "machining" the small carbon fiber arms connecting the silicone dampeners with steal screws. For this I repurpesed the upper (smaller) plate of the not usable APM mount. I cut off the edge arms of the smaller plate and grinded them to the same shape with my Proxxon drill tool. It turned out that it was a good idea to fasten two of the cut mounting pieces with a 3mm screw and a nut together for grinding. So at the end you get two identical shaped pieces for the front and two identical pieces for the back of the mount:

Afterwards I drilled some 3mm holes for the connecting screws between mount pieces and bigger CF plate of the former APM mount.
With the mounting arms finished, they could be connected to the bigger, lower CF plate via the screws and washers to form the inner part of the new dampening mount.
Next step was drilling the mounting holes for the silicone dampeners into the s900's dome cover. For this I added some millimeters in direction to the outer rims of the dome so the silicone dampeners have a bit of pretension in all directions. I used a 3,2mm drill from a Proxxon drill set I bought some time ago. But I think a standard 3mm drill will also finish the job.
The silicone dampeneres are a bit tricky to install at the end, but with a small screw driver or flattened tooth pick and a bit of caution you can stuff them in there.

The final result looks like this:

And in the end there is enough space between the Pixhawk and the s900's top carbon fiber plate left for connecting all the cables.

I can't offer any meassurements for the dampening characteristics of the mount, yet. But I will extend the blog post as soon as I have some graphs and results from flying.

Please be aware I have mounted the Pixhawk facing in backwards direction so the outputs for ESCs and servos are facing in forward direction of the frame. With this it is much more easier to connect the ESCs (6 servo cables) and you can use the servo cables already delivered with the s900 package. These are very decent quality and very soft.
For mounting the Pixhawk facing backwards you will have to adjust the mounting parameters within the parameters list of the flight controller to 'YAW = 180°' (using Mission Planner or whatever configuration tool you like). The correct parameter setting is:

AHRS_ORIENTATION = '4'

What I also did to improve the charateristics of my Pixhawk regarding the barometer: add some more foam material to the inner housing of the Pixhawk.
When you open the case and unscrew the Pixhawk PCB you will find a small mounting compartment for foam in the lower case. This is directly underneath the barometer chip. With adding an additional chunk of foam prior to mounting the flight controller into the frame you can make sure to block gusts of air from the props reaching the barometer. My additional chunk was about 2cm thick. Normal barometric changes due to rise or fall of the copter during flight should have no trouble reaching the barometer. Even through you now have a much denser packed foam compartment.

A last tip for reducing possible vibrations because of the thin plastic of the s900's dome cover:
The dome is reinforced with some thin support beams on the lower side. But in general it is still a bit weak and wobbly for my taste. So what I did to reduce vibrations furthermore is adding a block of 'moon gel' right in the middle between dome and the cover of the battery terminals at the lower frame plate.

 If somebody does not know 'moon gel' yet: It is a gelly like material with very good vibration dampening properties. It is very soft and originally used by drummers (music band) to dampen high frequencies at their drums. It influences the sound by absorbing harmonics of the drum skins. My moon gel blocks are from a music instrument store around the corner and my pads are called 'Black Mamba Damper Pads'.  Just ask some employee for gelly damper pads for drums. He will most likely know what you are looking for :)

This stuff is also very good for dampening your GoPro or wahtever action camera during flight.

So this is it. My solution for a Pixhawk dampening mount in a DJI s900 SpreadingWings hexacopter.
Hope this may be helpful for you all, even if you try this mount style with another copter, plane or what ever vehicle :)

All the best, Sebastian

DJI s900 with 3DR PixHawk - frame assembly hints

Hi everybody. Sebastian again here on Peter's multicolor blog.

It is time for my next blog entry. This time I want to let you take part in quite big project: building up a DJI spreading wings s900 helicopter for professional usage with a 3DR Pixhawk flight controller.

DJI is delivering no printed documentation with its s900. You have to download it from the web or you can have a look at one of the build videos. I will only give some tips here for the first part of my build log.

First: I was not very sure what has to be in the package prior to delivery. DJI is delivering more parts than you need for assembly. And this is not only true for some spare prop blades. So don't be to curious when you have some screws left over, when the frame is assembled. What was left after my build is:

• Spare bumpers for motor mounts 

• Spare pairs of prop blades with plastic washers, regular velcro tape and velcro battery straps

• Spare battery connectors and rubber rings for landing gear

• Spare red plastik fasteners for locking motor arms in place 

Second: even when DJI is delivering more than you need, the opposite is also true for things you should have at hand when you start the build. What I did find handy and useful is the following:

• Loctite (blue one is sufficient)
• Allan keys in several sizes

So on to the main tips for the assembly:
Assembly is quite straight forward. There is a high degree of preassembly in your delivered box. I.e. the mechanics and servos for the retractable landing gear are already mounted at the center frame plates.
Before you are too enthusiastic when starting the assembly and you directly trying to puzzle your way through sticking the landing gear into the frame's mounts, make sure to slide on the thick black rubber rings onto the main carbon gear beams. I missed that in the first excitement and now my gear has gone through one disassemble and reassemble more of the ones of most owners during the first build day.
For mounting the landing gear to the foldable landing gear mounts, you need to use the screws with the very flat heads. After mounting the gear, you will some screws left over as spare parts (see fotograph)

Also don't forget to add some loctite to all screws you mount to the gear and frame. DJI has prebalanced the propulsion systems to minimize vibrations from the start on, but safety first! And I read about some owners who had to sent their frames back to DJI for recalibration because of massive vibrations.

With the gear mounted to the frame, the next (and last) parts waiting for attention are the motor arms. Arms are numbers from M1 to M6. Starting from M1 with counter clockwise motor rotation and red color as the forward right arm. Next is the second red arm with clockwise prop rotation on the front left. And then following the black ones with alternating motor rotation (ccw, cw, ...) in ccw direction around the frame.
What was very important here at my frame: checking that the upstanding plates between the upper deck and lower you mount the arms to are aligned correctly (see photograph).

There plates are only mounted with one screw and therefore can pivot around their vertical axis. One plate at my frame was slightly out of correct alignment and therefore the thread of the arm mounting screw grabbed in a wrong way into the thread. I might have screwed up one of my threads if I hadn't checked again when the screw was only very hard to drive in.

If you have a bad feeling about something during any build, always double check what you are doing. It's always very upsetting when you damage your expensive equipment because of too hasty decisions or laziness for not a wanting to read some instructions again.

So with the arms mounted correctly, it is time to connect the power and control cables. The connectors for that are located under a flat covering dome on the lower frame plate. This cover is loosened with 4 screws on the bottom of the lower frame plate.

When you have removed the dome cover first, you can connect the power cables of the rotor arms. For that DJI added a special L-shaped tool to tighten the cable lugs into the power mounts. DJI gives the advice to only tighten the screws as far as aligning the edge of the screws to the edge of the mounting brackets. At my frame the clamping force reached with that screw tightness didn't feel very reassuring at some of the power bracktes. With some vibrations always left during regular copter operations, I am not very excited to find out about an easy loosening power connection for two or more of my motors during mid flight. I rather buy a new power bracket or even a new lower frame plate than loosing a complete frame with camera because of a weak power connection (See next picture at the copper brackets. Black screws not in line with edge of brackets).

Second to last step is connecting the esc control cables. That is straight forward as DJI uses poke yoke style (can not only be mounted in correct direction) servo connectors for the ESC  control cables.

Last advise is to double check the fitting of the power cables into the precut holes of the cover dome. There is a chance to damage the silicone isolations of the power cables if you remount the cover and don't double check the power cables fitting. The following picture shows one of the black ground power cables with is exactly positioned WRONG. It would be sqeuzed and pinched if not corrected before retightening the cover dome.

If you have finished mounting the copter's  arms there isn't really much left to do. Mounting the GPS holder (if you use the one delivered from DJI). Mounting the inner part of the upper carbon fibre plate again. And that's it. You have finished the basic build up of your s900 frame.

The next steps like mounting an Atto-Pilot 180A current sensor and building an antivibration mount for the pixhawk flight controller into the s900 will follow in some next posts.

Have fun flying!

Hobbyking X650F Glass weight reduction idea.

Hobbyking X650F Glass Fiber Quadcopter Frame - Weight reduction idea.

My hobbyking X650F has under gone several modifications since purchase, so there is not really much that suggests that this  is the initial purchased frame. The center plate and landing legs are what is left. The motor booms were fractured and have since been changed to these lighter A835 13 x 13 alu tubes and the motor mounts were changed to a more stabil alu mount. The original frame was quite heavy and flight time was approx 8 minutes with a 3s 4000 mah battery. With the newest modifications flight time was up on approx. 13 minutes. The two carbon tubes that carry the battery and the gimbal broke and rather than waiting 3 weeks for replacement 10mm carbon tubes i decided to buy two 100mm alu. tubes from the local hardware store. They are more reliable for carring FPV equipment, but noticed that the video feedback has som Jello, i dampened the motors, the gimbal but there is still some Jello present, maybe the carbon tube are better at absorbing vibrations, will have to order som new 10mm tubes and test that. The Alu tubes weigh in at about double the carbon fibre tubes, i have been using them for some time getting roughly 11 minutes of flight time on a 3s 400mah battery.

Home made alu. tubes from the local harware store, very stiff and reliable, don´t break or bend under crashes, but give you an addition 30 grams weight compared to carbon fiber tubes of the same length.

I then thought of a small idea to save alot of weight when not using my FPV/gimbal equipment.

I grabbed some excess 10mm carbon fibre tube and made 4 pieces of 40mm studs 

They weigh 8 grams in total.

I removed the alu. tube that supports the landing gear.

I used the four studs in place of the alu. tube

Mounted the landing gear again.

I guess that this will not take heavy crashes but we just saved 52 grams and got myself an additional 2 minutes on the same 3s 4000maH batteries.

Hobbyking H4 - Tuning for better flight & videos

Hi

My name is Sebastian and this is not my own blog. But I asked Peter if he would like to publish a guest entry. Kindly he agreed and on the following lines I want to support quad flying enthusiasts who own a Hobbyking H4 quad. I wan't to show you all some tweeks to tune your own flying H4 a little bit. Just like Peter does so continuously in a great way since more than a year (Thanks Peter!). Most of the tips can be transferred to other multirotor frames I guess. So maybe it is also interesting for different frames.

I have divided the article in two sections. The direct following section is a little bit of my personal history, trying to explain why I can tell you all a little bit about the things I learned and why I'm writing these tuning tips. If you don't like to readd about (my) history, just skip the next passage and got directly to the tuning tips below.

My experience with the H4 frame origins from one year with flying, upgrading, servicing and of course crashing my HK H4. I used my quad at the beginning for gathering experience with just flying. I entered the quad tribe from flying a Blade450 3D helicopter. So I had some 2.2Ah 3s batteries in my inventory. This resulted in initially equipping my H4 frame with 4 NTM2826s 1200kV motors, impressively soft 10"x4.5" 'plastic spoons' from HK, 30A blue seriesESCs and an HK Red MultWii Pro flight controller. Existing batteries slapped together with freshly bought components and voila:

Picture one: Testing the motors on the first version of my new H4

And the best of all: the H was flying!

Of course I was proud like having taught an ostrich how to fly.

But guess which of these components bought at the beginning are left after one year flying and learning:

• The Frame (in most parts)
• The batteries (still flying my heli)
• The ESCs (now with new firmware).

But none of these components are near to the original state they were at the first flight. Further modifications until now include:

• Added two axis gimbal
• Exchanged landing gear
• New motors & props (best decision!),
• New flight controller (second best decision)
• And added/modified many other parts.

But now let's start with the interesting stuff.

After the "Sebastian's history" class , it's time to talk about the main improvements for the quad I did until today.

This specifically means the following topics:

• Getting the quite heavy flying aluminium clump a little lighter without losing too much frame stability
• Reducing EMC (= Electro Magnetic Compatibility) for components mounted on the main frame (i.e. for flight controller, gimbals, sensors, telemtry, radio, …
• Upgrading and tuning propulsion components for squeezing out a little more flight time

So let's start with the first topic. Getting the flying metal hog a little lighter.

I started to slim down my H4, because it felt too heavy when carrying it around. I began to ask myself: where can I  save some weight without weakening the frame integrity too much?

The frame consists of some aluminium bars, sheets of fiberglass, screws and nuts.

Obviously we need the screws and the nuts. OK, we could exchange the steal screws against some made of nylon, but until now I feel a bit safer with the metal ones. I would further use self-locking metal nuts with new nylon if I exchange the screws some time so the nuts still sit safe on top of the screws.

Next option for saving weight would be exchanging the fiberglass decks against some made from carbon fibre. This would be great because CF (carbon fibre) is much lighter and more rigid. But CF is price and I don't have the tools at home to craft this material properly. So this is something to save for a later project.

Last option: the aluminium bars. So how to process these? Easiest option at hand: drill press!

Picture two: drill press vs. aluminium bar

So I first drilled a row of smaller holes, because you don't start with a 14mm drill at metal works. Even when it is only aluminium. When drilling new wholes, take care of the existing ones for the screws keeping the frame together. I have marked the original holes and the positions for the new ones with a scriber. So at the end there are 4 existing holes and 18 new ones.

Picture three: finished with drilling all the small new holes

Sadly I have missed to take a picture from the finished bar with the big holes, but I hope the following picture with the rebuilt frame gives an impression of the finished component. 

Picture four: Drilled bars built into the frame

Picture five: Drilled bars built into the frame

It's a good advise to deburr the sharp rims and chips of the drilled wholes before you mount them back into the frame.

I haven't calculated the weight savings, but I can tell you one thing: my frame feels (with the other savings) quite a bit lighter and it still survived a crash from 13 meter over ground with this aluminium bars just slightly bent in "u" shape. OK there were some other damages, but the frame didn't suffer much.

So after the frame components are discussed what other options are viable to save some weight?

Simple answer: get rid of all stuff you can.

For me this meant moving the ESCs from within the frame to the outer arms of the H. What's the benefit? Removing the heaviest stuff in weight to volume ratio you are flying through the sky: copper!

When you move the ESCs to the outer arms:

Picture six: Escs within the Frame

Pictures seven: Mooving the ESCs to the outer arms

What's the benefit of this modification?

1. Moving a source from very bad EMC interferences which were present along the long 3 phased motor wires through the whole frame to the outer arms of the multirotor.
2. Achieving a way better cooling for the ESCs. This improves the lifespan of the electronics.
3. Saving quite an amount of weight in copper! You don't have to run 3 wires from the frame to the motors, but only 2 from the power distribution board to the ESCs. This means 4 very long copper wires less flying around. Additionally in my case: Saving many many connectors! Because I had every "high power" connection in my H4 equipped with small banana plugs. Simply unnecessary!

And in the end only the wires and the plugs are saving my 73 Gramm. That's the complete weight of my GoPro clone action camera!

Picture nine: saving a lot of weight in copper

So summed up I estimate that I have saved about 100 Gramm in weight. This may not sound very much, but for don't spending any money for new parts I think it is quite OK. And considering that the H4 now has a total weight of 1,6 Kg all sums up to a saving of about 7 percent. That sounds a little bit better than 'only about 100 Gramm'.

So enough weight saved for the moment. Let's talk shortly about the topic EMC.

With removing one of the 3 phased wires running from the centre of the main part of the frame to the outer arms and instead running the 2 permanent DC current wire from the inner frame to the ESCs at the arms, I managed to get rid of some massive twitching at my camera gimbal. You can see some of the twitching in one of my videos (i.e. during the first 20 seconds). And this twitching is a very mild example. I have some videos were the gimbal nearly all the time is twitching around pitch and aileron axis. As the gimbal was influenced that massively I am surprised that the RC receiver and flight controller were working without any hiccups. Maybe I'm a bit too anxious, but it feels saver to fly now that the gimbal is not twitching permanently any more. At the current state of my setup, the gimbal is only twitching during the more extreme manoeuvres (like full stop from fast forward or hard right to left aileron movements). Also for this I have an example video. Twitching can be watched during the last minute of the play time were I tested manoeuvrability in pitch and aileron axis of the H4. So this was the second benefit from slimming down my multirotor.

Now let's get to the last topic of improving the HK H4. Upgrading the propulsion system to get some more flight time with the same batteries. As already mentioned I am using my 2.2Ah 3s 35C helicopter batteries. This is definitely not the best choice for this quad. 3s is OK, but I think 4s batteries may be a better choice. The more worse attribute of my current flight batteries are the 2.2Ah and 35C per battery. This is definitely a too low capacity and too high C-rate. Three batteries get me in sum 6.6Ah and about 600g total weight of batteries. The C-rate should in theory also sum up to 3 times 35, so in total 105C. Even with being conservative with calculating current needs 105C * 2.2Ah are about 200 Ampere which are in theory available from 3 * 3s batteries in parallel. So with 4 motors that leaves about 50A for every motor. Way too much backup with assuming every motor will draw about 20A to 25A max.

For later improvement I plan to get some new batteries. I would cut the number of batteries down to 2, because you will always save weight in cutting down the total number of batteries (cables, plastic housing). And of course you should go up with the capacity per battery. I would probably get some 5Ah, starting at 10C, better 15 to 20C. This would give 10Ah in total instead of the 6.6Ah I am flying now and a total drawable current per motor of about 25A or more. More than enough current and about 50% more capacity at the moment.

The DC current from the batteries will be transformed to 3 phased rotating current for the motors by my ESCs. Originally these were stock 30A blue series ESCs from HK. 30A rating is more than enough for this quad, but I quickly upgraded the firmware of the ESCs to SimonK for better throttle response. Haven't regret that decision until now.

Now we get to the more interesting parts for the thrust. Motors and propellers. You always need to consider both parts together. A too small motor with a lot of KV and a big prop simple would work (too less torque for thrust). Also a big motor, low KV and small prop don't work (too less RPM for thrust). For getting an impression of what motor to prop combination gives you what flight times and performance there are some online calculators available. As mentioned in the history lessons above I started the H4 with Hobbyking NTM2826 1200KV and 10x4.5 slowfly props. Fast RPMs, good torque, props quite matching. But here come the disadvantages: massive power consume and props with a softness like pudding. Flight times even with 3 batteries were about 6 to 7 minutes. Motors were vibrating awfully quite fast over time (bad bearings). The soft props amplified that vibrations due to their softness. The result are videos with a lot of yellow effect (wobble in the video). Couldn't get rid of the yellow for half a year because of the cheap motors and props. The exchange for the bad equipment were SunnySky X2212 980KV motors with 12x5 Aeronaut CAM Carbon light props. The motors were already discussed by Peter some time ago. You have to be careful to get genuine parts. I ordered mine from a vendor in Germany over the big bay. They came in a box for A2212 motors instead of X2212 motors (A version are less durable and capable than X version), but bearings and windings seem to be genuine and they perform very well. So I guess I got genuine ones. In combination with the new props the power is more than sufficient and my flight times went up from 6 minutes to about 8 or even 9 minutes! So plus 30 to 50 percent just with different propulsion! And with a bit balancing of the props, I nearly got rid of the yellow effect in my videos.  That was worth the money I guess :)

Here are some photographs of the actual state of my multirotor:

Picture ten: lightened and upgraded quad

Picture eleven: Closeup of rear with BT telemetry, UBEC and APM power sensing module

Picture twelve: Closeup of camera gimbal at the front of quad

Picture thirteen: H4 on the bench at the flight field

Picture fifteen: Quad on bench at flight flied

So it seems I have finished my guest entry for improving weight, EMC and motor/prop-combination of the H4 HK quadrocopter. Hope it was a bit entertaining for you all and at the end I want to thank Peter again for the opportunity to publish a guest entry on his great and informative blog.

10x4.5 SF Props For DJI Motor CCW Rotation

I bought a stack of these off a seller on Ebay, and initially thought they were the usual props I always purchased. Upon receiving i noticed that they looked very familiar with Hobbykings Slowfly props. The Ebay version has a slightly different hub designThey both have the same designed hub and design, are the same. I must say i was very very disappointed with this product both the hobbyking and the Ebay version. 90% of the props that I have used have broken in exactly the same spot. As you can see in the pictures, all the props have a weak link where the hub and propeller shaft meet.

The Hobbyking version (green) has a slightly different hub.

The prop design and pitch seem identical.

The light green prop is the Hobbyking version and it shares the same characteristics as the Ebay version though they do fare a bit better, but they are not impressive. 

These props break very easily often just small twigs and light crashes will cause the prop to break, just in a single 30 minute session, i have had to change three of these props.

The Hobbyking version has the same weak spot.

This is the version I thought i was buying, 10x4.5" 1045 Nylon CW CCW Propeller Prop Multicopter QuadCopter Black&Red these props i notice are more expensive, but I have always enjoyed using them, they coup much better than the recent ones i purchased. Despite them being much thinner and flexing more, they can take a bigger beating. They get tacky on the edges or the nylon rips on the prop arm. If you hit something hard a small peice will break off, but never had one break at the hub.

The no name prop is much thinner, causing it to flex more.

I hear alot of people talking positive about the Slowfly props from Hobbyking but for me that was the last time i purchused these, i would prefer to stay with the no name Chinese version of props.