Pixhawk with DJI E800 with APM Software

Here is a short video showing my quad just after using the APM Autotune mode to automatically set the PID feedback values for the autopilot. I must say it did a wonderful job, albeit a it resulted in a fairly aggressive tuning. This is in contrast to the initial tuning with Qground control, the PX4 branch, which does not yet have an auto tune feature. Instead it uses an iterative process starting with holding the actual copter in your hand while PID tuning. Mind you, I wore my leather jacket and chaps along with my full face helmet while spinning the copter up to hovering power while holding it in my hand. I do hope that you realize that that these copters are little more than Cuisinarts with carbon fiber blades. ūüėģ

Towards the end of the video you will notice that the low battery warning occurred and the autopilot entered into the RTL Return To Land mode. I tried to bring the beast down by manually overriding the RTL with the throttle but it would not respond to my commands. That is until I switched back to Stabilized (manual) mode and awe shite! The throttle was near minimum and the damn thing dropped like a rock. I had the default settings with the left most switch controlling the flight modes which means that my thumb was off of the throttle – HUGE F-ING MISTAKE! As you can see just how quickly things can turn to shite, especially when so close to the ground.

Here are the results, one broken prop, one broken landing gear dowel, and one broken quick release prop adapter, which actually saved the prop it was attached to. I’m looking into using fiberglass rods, with pads at the ground contact area, positioned at about a 60 degree cant for shock absorption rather than the 90 degree positioning in this prototype set up.

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This is sooooooo freaking much fun I can’t possibly tell you. I love engineering and product testing. I don’t mind spending resources on learning experiences but I do take exception with being taken for a rube by nefarious marketing and sales practices. On the other hand DJI does actually have some decent concepts that it is putting into practice, mixed emotions.

DJI E800 Tuned Propulsion System Upgrade

It seems as if DJI is in the process of updating the E800 3510/350KV motor and is designating the new motor as 3511/350KV. I have to wonder if this was due to my experience with the faulty ESC and subsequently burned up motor, as well as my posts documenting the DJI failure. If so I commend DJI, if this is just a marketing ploy to redirect my posts critiquing the failure of the 3510 series then, well then DJI are simply douchebags attempting to distance themselves from their F-UP. Time will tell, I canceled my order for additional 3510’s for my hex-copter build and will wait until the new motors become available.

Stand by for an extensive review and testing of their “upgraded” 3511 motor….

DJI E800 Tuned Propulsion System Fails to Reach Rated Thrust

While I am still waiting for DJI parts to continue flying, (have I mention DJI customer service sucks?) I don’t think that I have mentioned that their parts supply chain is also extremely poor. I thought that I would do some testing on the 620 ESC and 3510/350kV motor combination. I used the FrSky X8S receiver and their Taranus Plus transmitter to supply the servo Pulse Width signal directly to the ESC.

The motor responds to servo signals from 1145 micro-seconds to 2025 micro-seconds, which translates into motor RPM’s from 658 to 8670. At a Voltage of 24.87 this translates into 349.05 RPM/Volts which is approximately the rated value of 350kV, this was tested with the motor lightly loaded using a stubby prop that I fabricated from one of my broken DJI props that was destroyed by one of my brand new ESC’s that was defective from DJI ;-(

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I measured the RPM’s using a photodiode beneath the prop and a light source above it and measured the signal with my oscilloscope.

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Here is the signal at the max speed of 8760 RPM’s, note that the dips occur when the propeller shades the photodiode from the light source above it. Every other dip represents one full revolution:TEK00002However, when I redid the test with the full size DJI 13.5 inch prop the ESC motor combination only produced an RPM of 7500 and failed to reach its maximum RPM by over 1100 RPM’s. This translates into an RPM/Volt rating of only 307 kV. I used a fully charged battery with a capacity of 10,000 mAh. I took the measurements within one minute of operation.

By this time the battery voltage had dropped from its initial charge of 25.17 Volts to 24.43 Volts. This means that in the real world the motor specifications as advertised by DJI are worthless. DJI rates the RPM/Volt at 25 Volts rather than the half 15% capacity of 22.2 Volts, the point when warnings are sounded and the pilot should be thinking of landing very soon or risk an uncontrolled crash landing.  Now I am not sure of the standards in the RC community, if there are any, I can assure you that these are very deceptive and misleading marketing tactics.

I also measured the thrust by placing the motors on another rig with the motor weighted down on a scale and placed high enough that it was above any ground effects. I was only able to achieve just less than 1600 grams of thrust, well shy of the rated 2100g of thrust as advertised by DJI. This is most likely due to the fact that the motor fails to reach it’s maximum RPM by over 1100 RPM’s and it’s RPM/Volt rating when actually loaded down with the DJI propeller. I used a fully recharged battery and did the thrust test within ten seconds of operation.

This is also very shy of the 200% recommended maximum thrust rating  for its rated take off weight. I was deceived that its maximum thrust was well over the 200% rule of thumb. Actually there are several people who recommend 120% above this rating. Now with only a 1600g thrust I suppose that the 800 gram take off weight per motor barely fails to meet this minimum, and ONLY when the battery is fully charged :-(

I also used this to test and calibrate the Attopilot current and Voltage sensor board. I found the board’s outputs actually comes extremely close to its rated values of 63.69 mV/Volt and 36.6 mV/A, the measured values were actually 63.66 mV/v and 36.22 mV/A. Remember that I overheated my board which may explain the extremely small discrepancy of the measured current.

Also if you look at the data, supplied in the spreadsheet link below, that the current compensation factor value has a much larger error in currents below three Amps but seems to level off at values above this. I did not test values greater than about fifteen amps so I would not expect laboratory grade signal from a current sense board that is rated for currents of 90A. And, like I’ve already said, this may be due to my ham handed soldering and repeated heatings of this board.

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Update, I received a new Attopilot current/sense board and the current factor is indeed much closer for currents above about 1/2 Amp. It seems that my previous board was indeed affected by excess heat but still remains fully functional.

Pixhawk with DJI E800 tuned Propulsion System 2nd Flight

Well I did the PID tuning procedure for the PX4 side of the Pixhawk Flight controller and I must say I should have done this before my first flight. Actually the parameters were not that far off from the default parameters. I had to increase the Proportional values for the roll and pitch while lowering the values for the yaw channels. When I get the PID values nailed down I will post them.

I found something interesting that I did not experience with the Phantom controller. While adjusting the Proportional portion I had no problems but when introducing the Differential parameters for either pitch or roll my PVC landing gear vibrated violently, like a monkey’s arms flailing it’s own poop. So I had to add a cross brace to the gear, I suppose I could have put the brace higher up but this should do for now. It seems as if the Differential feedback occurs at the vibrational frequency of my landing gear.

I flew for about eight minutes using about 2500 mAh from my 10,000 mAh battery so flying time, with very conservative reserves, should easily give me 25+ minutes of flight time, probably more with a hex. My Attopilot current and voltage sensing board, necessary for batteries grater than 4s, seems to be very twitchy. When I adjust the battery parameter to indicate the proper voltage it changes considerably from one power-up to the next. I must take the blame for this since I changed the setup twice, meaning I soldered three times and desoldered twice, I think that the onboard chips must not have liked the heat so I guess I need to order another Attopilot board.

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I am already working on my next project, a hex-copter, using what I have learned so far. My dilemma is deciding whether to buy additional DJI motors and ESC’s. DJI basically is screwing around with me and won’t even consider replacing the motor that was fried by their faulty ESC unless I go through another seven week customer service hostage scenario by sending them the failed motor, good grief. ¬†They did sent me a new ESC, by the way, at least I hope it’s new since it was not even properly packaged in their own sealed package???? They used the ESD safe envelope that I sent them the original faulty ESC, F***-DJI !!!!!! Their customer service sucks monkey arse !!!! Plus they don’t even have Battery Eliminator Circuits (BEC’s) with their ESC’s.

My Hex frame in progress:

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PixHawk Quad With DJI E800 Tuned Propulsion System First Flight

Well I didn’t wait for DJI to finish my customer service order to finish their process and purchased a new motor and ESC. The PixHawk open source project has turned out to be ultimately successful, but a very fragmented and frustrating path since the documentation is weak and scattered across several web pages. It actually does not help that the PixHawk has two separate competing branches. I think it would actually be beneficial if both branches worked together to produce a reliable and bug free platform from which to program the PixHawk autopilot.

Instead we have two very buggy and unreliable software paths, called flight stacks, that are necessary in order to properly program the PixHawk hardware. WARNING going the open source route is plagued with numerous updates that may, or may not, be steps forward. This is especially true since the two sides are competing for additional features instead of competing for reliability and robustness.

Well that being said, my first flight using the PixHawk and QGoundControl default settings using the DJI 350 model as a starting point was successful. The default settings use very conservative low values for the PID feedback settings and this shows in the video. The aircraft controls were very sluggish and slow to respond from error input such as the effects from strong wind gusts. Obviously more tuning is in order.

One of the things that I noticed with the PixHawk’s GPS is that it is much more sensitive. While I could get a GPS lock with my DJI Phantom placed near a window or patio door the PixHawk can lock on to five satellites a full twenty feet from any window inside of my apartment! I’m very impressed! Also note that while I had some trouble reliably controlling the aircraft, due to weak default PID input values, the aircraft still acted in a positive manner, even at the end of the video when the battery became detached and ultimately unplugged it still landed upright and unscathed! The first flight for the PixHawk were decidedly superior to my first flights using the Phantom autopilot, which all ended up with uncontrollable crashes and in the destruction of several propellers:-(

Here is an image showing My new creation with the DJI Phantom. Note the huge 10AH 6S battery that obviously needs a more robust mount than velcro and a single bungee strap to secure can provide.

_DSC2220 _DSC2219I’m actually thinking that I will use this prototypes acquired knowledge into making a hex-copter, since the extra weight of the battery eats up most of the extra power supplied by the motor-ESC combination. It was obvious from this first flight test that the hover power was actually at about 50% when adding additional weight of a camera/gimbal system will probably overload this setup, especially when used with this huge 10AH battery. DJI is actually sending me a new ESC, I’m still not sure if they are sending me a new motor and props, but I will find out Monday when the shipment should arrive.

Oh ya, I also have been spending a lot of time learning how to use and program my new radio transmitter and receiver, the FrSky Taranis Plus sixteen channel transmitter and the X8R SBUS receiver. Also an open source steep learning curve quagmire of fragmented sources of software ind information. Ultimately I am very happy with my choice, just be forewarned a lot of time surfing the web for weak and fragmented documentation should be expected.

Sounds like to me another trip to Home depot…

 

DJI E800 3510 350KV BLDC Motor Failure

Well I now looked more into the motor failure of my DJI 3510 motor and found some strange happenings inside.

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If you will notice in the above image that the wire failed about 3mm from the solder joint, wait, WHAT? A solder joint on a high current motor lead? Now I think that this is piss poor engineering! And also notice that the wires are not even twisted around each other to help make a low resistance joint. Instead the lead in wire was simply laid upon the other two coil wires (appears to be delta wound) and as such the current must travel directly through a large portion of relatively high resistance solder, and no this is not silver solder since it melts at a relatively low temperature. I also noticed that the other two windings solder joints were also obviously over heated since the heat shrink tubing was also very well cooked. Obviously this is the weak point in this motor.

Good grief, I don’t know what the standards are in the Radio Control (RC) world are but crimp connectors should have been the obvious choice here. Silver solder may be acceptable but only if the joint can be annealed after soldering. (This is why using solder joints in modern aircraft is highly frowned upon) There is also a complete lack of any strain relief making highly susceptible to failure from vibrations in these wires so be damn careful when handling the lead in wires to this motor folks. I now don’t know if the motor connections failed causing the ESC to become smoked or did the failure mode of the ESC overloaded the motor causing it to fail, chicken and egg conundrum. The motor was operating fine before I removed it and the bad ESC, so it must have broke while handling the leads during removal.
_DSC6396Now I will be able to repair the connection and slop some new Gliptol on the burned windings to create a workable motor but this one will not ever be supporting anything valuable like a heli or a camera. I’m sure that portions of the windings have to be hardened and brittle to the point that it will most likely fail again quite prematurely.

I also don’t know why the wires failed where they did, perhaps the wires were nicked causing a high resistance choke point, I just can’t say for sure.

Update, 2015-03-22:

Well, I reattached the lead in wire and with the exception of one of the leads being shorter it functions perfectly. I even did a “Identify” from the ESC Assistant software and it passed all tests, even with the crispy overheated wires. Again this motor will never be used as a heli motor, perhaps I will use it to do some development as a position control motor for something like a gimbal motor, we’ll have to see…

WARNING DJI 620S ESC May Also Destroy Your Motors!

After sending in the faulty ESC to DJI I also found out that the ESC destroyed the motor it was attached to. Here’re some pics showing the overheated lead-in wire to the windings as well as the video demonstrating the failure mode once again:

Humor allert: Six weeks turn around time? I think that the people who say the DJI customer service is actually RTC whereas the normal failure mode of a DJI drone is RTH (Return To Home) It actually takes six weeks to to enable the real failure DJI mode of Return To China (RTC). HA!

When the sh*t hits the fan ya gotta relay on humor, after all.

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DJI on the Outs

Well, its been over a week since I sent my defective DJI 620S ESC back to DJI customer service technicians and have not heard one word back, even after unanswered inquiries asking for the status of my order. DJI seems to have forced my hand and I now have a PixHawk flight controller with GPS and telemetry radios on order :-) My only regret is buying the DJI “tuned propulsion system” in the first place.

Now I am in a dilemma, do I wait for DJI to replace the ESC or will they reject my request to replace it and the six f’d-up propellers. Actually I think instead of buying a replacement DJI ESC, when an individual ESC actually becomes available anywhere in the USA, I will replace all four ESC’s with another brand. (I’m not sure why Atlanta Hobby, a DJI recommended supplier, can’t break open one of their kits and then have DJI replenish the ESC.)

Like I said in a previous post: In the drone world, drone flyers seem to fall into two camps, DJI fans and DJI haters. Reluctantly I seem to be gravitating towards the DJI haters crowd, for very good and realistic reasons.

I have given up on my DJI Frankendrone and am currently putting back together the Phantom 2 Vision with its prop guards for the sole purpose of practicing and polishing my manual flying skills. While my newest creation will be used for actual photography work, at least after extensive testing and optimizations. The DJI will be set up with current software and their  spyware programs will then be permanently deleted from both my mac and Windoze partitions.

I’m looking forward to learning a new Real Time Operating System used by the 3DRobotics people who have developed the open source code for the PixHawk. While DJI has introduced a Software Development path they only make available the highest level layers to the developers, the major portions of the code are still unavailable to the public, whereas, with the Pixhawk there are two separate open source branches with every single bit of source code made available to anyone interested.

Sorry, but I simply can’t get myself to trust any communist based Chinese state run corporation, no matter how popular they have become here in the West.

Update 2015-03-19:

Well I just received an email from DJI support saying that they have no information a for me at this time and that their turn around time will be six weeks! GOOD GRIEF! Does anyone out there want to buy a cute little one owner DJI E800 Tuned propulsion system less one ESC and two good  props? Will sell for cheap!

DJI Software IS Spyware

I thought that I would install the most recent versions of the DJI software on my windows partition and then do a virus scan on this partition so as to demonstrate the ClamXav anti-virus software warnings of the trojan horses that are reported. I did some research on the web as to what these actually are and they are quite disturbingly potentially very dangerous. They potentially disable any installed anti-virus software. (this is why they are detected from my macbook scanning my windows partition but NOT from within windows) and allow any system settings to be changed without user validation as well as allowing ANY hardware (including DJI hardware) to be updated in the background without any user knowledge.

I also read many people who adamantly defend DJI claiming that this is necessary because any software that accesses or updates hardware firmware will also trigger the same alarms. THIS IS A FALSE CLAIM!!!!! I have numerous programming software packages that are used to program various hardware and microcontrollers and NONE of them trigger any trojan horse or virus warnings.

The anti-virus was updated to the latest versions, here is a screenshot of the results:

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Both installer and program executables trigger two different trojan horse warnings so BEWARE!!!