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Old Apr 26, 2012, 12:44 AM
manual flying apologist
Adidas4275's Avatar
United States, CA, Fresno
Joined Mar 2011
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if you like your savox servos just buy the gimbal without servos from gary....

although i cannot recommend savoxes since my 1 that I tried had way too much slop around center!
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Old Apr 26, 2012, 12:45 AM
John
United States, WA, Mason
Joined Apr 2011
765 Posts
Quote:
Originally Posted by Blucross View Post
...... I have been talking to Gary about adapting his landing gear and gimbal for the same RC-Carbon Y6 you have there......
Do you currently have a gimbal hooked up to WKM stabilization? -- JOHN
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Old Apr 26, 2012, 12:53 AM
John
United States, WA, Mason
Joined Apr 2011
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Quote:
Originally Posted by Adidas4275 View Post
if you like your savox servos just buy the gimbal without servos from gary....

although i cannot recommend savoxes since my 1 that I tried had way too much slop around center!
Yea, I bought the Savox a couple of months back when Gary thought they were the hot ticket. He has since moved on. -- When you say "slop around center" do you mean they had "play" in them? If I try to wiggle the control arm, there is no movement ( play) in mine. Maybe I got lucky. -- JOHN
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Old Apr 26, 2012, 01:00 AM
manual flying apologist
Adidas4275's Avatar
United States, CA, Fresno
Joined Mar 2011
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Yeah i think it is a QC thing more than the actual specs of the servo.

I would try their gimbal with your servos. You can always swap them.

The savox are fast and powerful.
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Old Apr 26, 2012, 01:06 AM
John
United States, WA, Mason
Joined Apr 2011
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Adidas, what are you using as a controller for your gimbal? I assume that like Gary you are not using WKM. Where do you have it mounted, on the gimbal or on the machine? -- thanks, JOHN
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Old Apr 26, 2012, 01:15 AM
manual flying apologist
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United States, CA, Fresno
Joined Mar 2011
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I am currently using my HoverFly Pro gimbal outputs.

So it's on the frame.

When I add 3 axis soon I'll need to get either the new HF gimbal controller or a picloc
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Old Apr 26, 2012, 01:30 AM
John
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Thanks
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Old Apr 26, 2012, 08:25 AM
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Joined Apr 2012
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Why using diffrent gimbal controller is the WKM not working good? What about futaba 401 gyros?
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Old Apr 26, 2012, 08:42 AM
Gravity is a cruel mistress...
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United States, FL, Orlando
Joined Mar 2011
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Quote:
Originally Posted by digitalCAM View Post
Do you currently have a gimbal hooked up to WKM stabilization? -- JOHN
I'll be honest, I have had a couple other gimbals but never used them or connected them to the WKM. Now that I have a need, I sold off the ones I had because I was looking for a better quality product. I've read about Gary's trials and tribulations with getting a good output from the WKM, I am figuring I'll need to use a CC or Naze32 as my gimbal controller if the WKM footage looks bad.

We shall see. Hopefully the gimbal outputs are fixed in a future firmware update but I am not holding my breath.
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Old Apr 26, 2012, 10:45 AM
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South Orange County, CA
Joined Mar 2003
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Look, you can use other servos, but the smoothness of small movements is going to be affected. If you have servos that aren't as smooth as the BLS950s, the movements will be rougher, which causes small, but detectable "micro bounces" of the camera. This is particularly noticeable in the roll axis. You can eliminate these by increasing the belt drive reduction ratio, but doing that means the gimbal won't react as quickly to large/fast platform movements. This then decouples you from true platform independence and forces you to fly smoothly, or worry about how smooth the WK-M position hold function is with the GPS mode on.

We have managed to find a "happy medium" where we can have this platform independence and still have silky smooth movements for small corrections, but it takes a "perfect storm" combination of the right servos, the right reduction and the right gimbal control outputs. With the BLS950 and a 2.5:1 reduction, we get the smoothness without sacrificing the quick reactions necessary, but it also needs to have the right gimbal output characteristics.

The problem with the WK-M and Naza gimbal outputs is that the output update rate is limited, like around 50-100Hz. They did this so that it would work with analog servos. With the high-end servos we are using, this update rate needs to be much higher, like 500Hz, in order to take advantage of the higher resolution and more precise control characteristics. Not having this faster rate limits the smoothness you can achieve. With the XA FC/AHRS setup I've been using as a dedicated gimbal controller, you can set the output period from 20ms down to 2ms. This translates to 50Hz to 500Hz, respectively. The Naze32 as a gimbal controller also allows you to set this output PWM rate to 500Hz.

Another problem with the DJI gimbal outputs is that they for some idiotic reason have decided that 90 degrees of servo travel is enough, and have limited the WK-M and Naza outputs to no more than +/-45 degrees range of movement. After a 2.5:1 reduction, this ends up as +/- 18 degrees. That's not enough to counter aggressive platform corrections. Both the FC/AHRS and Naze32 firmware allow you to open up the endpoints to get the full range of travel that the servo will allow.

Finally, the WK-M has one other issue which is a real showstopper for me, at least, and that is the GPS-based wander/drift problem that they never have addressed. When the GPS mode is active, the gimbal outputs wander around the neutral point, which causes sharp twitches in the video. This is caused by noise that gets introduced between the GPS and IMU. DJI claims it will take an IMU firmware change to fix this, which means sending the IMU back to the factory in China. The problem is worse with some combination of GPS and IMU combinations, and with a replacement GPS module, the amplitude of the twitches were greatly reduced, but not eliminated. In the v5.02 update, DJI attempted to mask the problem by introducing an artificial deadband in the gimbal outputs. Unfortunately, this in essence cuts the resolution of these outputs which again, affects the smoothness level you can achieve for small corrections.

DJI is reportedly about to release a firmware update for the WK-M, but I have no idea if these gimbal issues will be addressed. I have sent detailed PMs and emails to DJI about these issues, but they have never even acknowledged one of these messages. I guess I'm on their "ignore" list. They have other priorities in this area (read Zenmuse...), so I'm guessing nothing will change.

Not wanting to rely on DJI to fix these issues is what started us on our current efforts to make the Naze32 work as a dedicated gimbal controlller. We are very close on this. Functionally, it does exactly what is needed, but we need to do something about filtering the raw accelerometer data, as we are getting some weird sharp twitching, during a hover. Yesterday I tested another firmware version that added a 2nd order filter function, but it didn't yet fix the problem Timecop is back from vacation now, and before he left two weeks ago, he outlined a couple of other ideas he had to fix this, so I'm hopeful one of these will do the trick. Once this final issue is sorted, what we will end up with is pretty much the equivalent of the heralded PH Skyline "RSGC" unit, but at about 1/3rd the cost. I think TC sells these boards for around $65 and the firmware is all open source.

-- Gary
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Old Apr 26, 2012, 10:57 AM
manual flying apologist
Adidas4275's Avatar
United States, CA, Fresno
Joined Mar 2011
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It seems that Gary is one of the only people around who will actually criticize the WKM...

HoverFly changed their gimbal controls about a year ago to increase output rate and allow you to adjust endpoints past 90*..... this eliminated the use of analog servos and pissed some people off. They explained it was necessary to get the correct output rates for high end gimbals to work well. Now no one complains about it

I am excited to see what the HF Gimbal looks like and I hope to have one.... I am not pre-ordering (i dont think so at least, but I also would like to have it in june... so I might need to.)

I really want to try the 3 axis camera lock function on your mount!


I will patiently wait for external pot assembly for tilt as well, really it is the only thing missing from this mount to make it compete with the Cinestar mount....... I really love the look of those tilt shots that go from straight down to level in one solid movement......

But I always want more
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Old Apr 26, 2012, 11:11 AM
Destroyer of G-10
askman's Avatar
Joined Jul 2004
10,036 Posts
tilt pot has been discussed and being studied. we are also looking at alternatives. if there are enough sales, we are also possibly looking at custom servo solutions as well. (it does take big investment for custom servo though. )

3axis cam lock would be cool. as is heading lock. with naze, it should be possible to add heading lock on pan servo when used as dedicated as gimbal control. point lock is different story without a gps. we always wont more.
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Old Apr 26, 2012, 11:39 AM
manual flying apologist
Adidas4275's Avatar
United States, CA, Fresno
Joined Mar 2011
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yeah...... point lock would be like military grade, with out a sensor on the point... like the MK follow me type stuff....

I saw a controller the other day (cannot remember which chinese one it was) that had a android app and used wifi for it connect to and would do follow mode and point lock with the camera.
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Old Apr 26, 2012, 11:43 AM
manual flying apologist
Adidas4275's Avatar
United States, CA, Fresno
Joined Mar 2011
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not sure where DJ sources his but the old MKTR used one .... I am thinking of modifying my MKTR for external pot.... but i dont really know anything about it so.... we wil see


here is the one he uses
http://photoshipone.com/shop/index.p...roducts_id=215
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Old Apr 26, 2012, 11:54 AM
Destroyer of G-10
askman's Avatar
Joined Jul 2004
10,036 Posts
there are lot of 5k pots. I want a certain short shaft one. preferrably from bourne. (good quality pot with 100k cycle life). they have certain minimum order as well lol. sigh.
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