Well the gimbal controller finally showed up, it spent a week in New York, presumably making its way through customs, it was shipped from Latvia. It seems to be working pretty good, The one thing that I would definitely recommend are gimbal motors with hollow axel shafts, this would make wiring the gimbals and IMU much easier and clean. I’m now ready to mount it on the hex copter and see what happens, stay tuned…
I haven’t been doing much with my drones or my photography lately, but with more time on my hands that will soon be changing. Here is another incarnation of a DIY three axis gimbal using Turnigy 5208 BLDC motors. The rest of the parts were fabricated from $5 worth of 1.5″ x 1/8″ aluminum stock. A Basecam controller is on it’s way. Total cost of about $300, it should easily perform at least as well as one costing more than a grand, and probably more durable than a carbon fiber gimbal as well, depending, of course, on the quality of the Chinese motor bearings.
This is actually just a prototype for an ultimate build intending to cary my Nikon D800. Unfortunately my DJI “Tuned Propulsion” motor/prop combo’s don’t produce their advertised rated thrust, therefore, they can’t cary my D800. Im designing an new larger hex with higher quality motors, ESC’s, and props and it is also in the works. Stay tuned…
Well here it is, my first incarnation prototype for a HexCopter. I have to say that a hex handles so much nicer than a quad, much more stable and predictable. This version weighs about 11 lb. (5 kg) or about 830 g/motor or just 30 g above DJI’s recommended 800 g/motor. The total maximum flight time, with an 10,000 mAh battery, was just under 20 min. with the final battery voltage of 21.35 Volts. The DJI ESC’s started giving yellow LED signals with a rapid loss of altitude afterwords. Using a Return To Launch (RTL) voltage of 22.2V should give ample reserve RTL time for a useful flight time of about fifteen minutes. Update: My battery charger reported that it took 10,325 mAh to recharge the battery.
There are several areas where weight can be shaved to allow for the additional weight for my Nikon D800. I am still fine tuning the vibration isolators for my Nikon J1 camera, there is no gimbal motors used at this time. If you look closely at the video the Nikon J1 is having severe problems with the autofocus, I’m probably going to have to give up and simply set the focus manually to infinity, as well as resort to using manual or aperture exposure modes, and forget about 360 degree pano shots, especially near sunrise or sunsets.
I’m not yet sure if I need to reduce the number of isolators, I’m currently using six DJI phantom isolators. I bought isolators for DJI larger gimbals but I found that these were way too stiff for the Nikon J1, although those are probably the ones I will need to use for my D800.
For all of those paranoid morons who are chomping at the bit to shoot down a drone I added an example of just how close a typical drone used by an amateur photographer would have to be to get any meaningful images. All of you dipsticks should realize that only a multi-million dollar military grade drone will be able to count the pimples on your nude sunbathing girlfriend/wives butt-cheeks, and from an altitude higher than you will ever be able to see or hear it from, let alone, shoot it down from 😉
Here is a quick video with my first prototype two axis gimbal with my Nikon D800 with a 10mm DX fisheye lens attached. Note the heavily overloaded vibration dampers were actually being supported by zip ties, obviously not very effective. But you can see exactly when one of the motors hit maximum thrust, the ESC LED turned yellow, the drone started shaking and within a few seconds it no longer could maintain altitude. By about 30 seconds three of the four motors were maxed out and it became uncontrollable and flipped on crash landing at about 38 seconds, Nothing broke 🙂
The aircraft weighed exactly 12.0 lbs. or 5443 g. This means about 1360 g of thrust was needed per motor in order for it to hover. The DJI E800 could not supply this much thrust for more than twelve seconds, the motors were very, very warm after this 40 second flight. There was little or no control possible once the aircraft started loosing altitude. Post flight battery voltage was 24.91 V. So much for their 2100 g of thrust rating. Proof positive DJI does not live up to its own specifications.
By the way this copter worked spectacular with my lighter Nikon J1 weighing in at at only eight pounds or about 900 g thrust required per motor.
Well I finally attached my Nikon J1 onto my quad, actually I first attached it a few weeks back but the jello effect prevented decent video. Actually the jello effect was not that bad but it still was there. I used the vibration isolation platform from my Phantom Vision 2 so it is a bit overloaded. I must shop around for some heavier duty isolators.
You will notice that when pointed into the wind everything is fine, however, when pointing away from the wind the copter had to point nose high in order to offset the wind. This caused the isolator platform to rest on the battery causing a slight jello effect which then caused the camera difficulties auto focusing. Also note the tilt of the horizon when pointing perpendicular to the wind.
The battery tested well, with out any wind, the battery flight time for simply hovering was 30 minutes from full charge to 22.2 Volts, where I have programmed the PixHawk to Return To Launch (RTL) mode, providing ample reserves. But in todays wind the flight time was limited to about eighteen minutes, Remember while stationary hovering in one position it was actually fighting the wind and actually flying at an airspeed of 15-20 MPH+.
I am now ready to design and build a two axis gimbal for it as well. Here is a short video, note that I was testing this beast in a 15-20 MPH wind that was gusting to well over 30 MPH. While the video may cause air sickness I think the PixHawk handled it quite well, at least after it decided on a point on which to hold its position. I had to provide some inputs initially to prevent it from blowing into a tree.
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. 😮
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.
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.
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….
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 ;-(
I measured the RPM’s using a photodiode beneath the prop and a light source above it and measured the signal with my oscilloscope.
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:However, 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.
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.
Update 2015 06 7:
I tested four other motors that I have and found one of them made thrust, actually 2150 grams of thrust. The remaining three made between 1800 and 1950 grams of thrust.
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.
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:
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.
I’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…