Neills DIY Gimbal Design


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BIGTACO

Member
Progress update:

I recieved in my new pulleys/belts/pot gears. My objective was to increase drive ratio while keeping with my current structure, and desired range of angular travel per axis. For the tilt axis I was able to get 3.75:1 with angular travel of 120 degrees (camera pointing straight down / 30 degrees up). For roll axis I ended up at 4.583:1 with angular travel of 90 degrees (45 each side).


The gimbal is now complete. My hoverflygimbal controller will be arriving by UPS today sometime. I designed into this gimbal a specific spot to mount the controller. After I get it all mounted and setup testing will begin.

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B

BIGTACO

Member
Well I designed it around the Nex-5n and similar sized cameras. I had planned to use the Nex-5n but at this point I am considering using the Sony DSC-HX9V. Looks to have really nice performance for the cost. This build turned out a bit more expensive than I thought. Isn't that always the case??

Tomstoy2 said:
Me also, BT. What camrea are you going to use? If you mentioned it before, sorry, I just don't remember.
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jcmonty

jcmonty

Member
Very nice build! I really like the simplicity of the design and how clean it looks. Do you mind posting the weight of the setup?

I am considering getting one of Askman's new AG700 gimbals when they come out, and you guys share a lot of design features. I must say though that the CF really looks a lot stiffer than the G10 they use. Can you talk a bit to why you decided to go with the higher gear ratios? From the testing I have seen for the AG550, it really likes the 2.5:1 to 2.8:1 ratios with the fast MKS servos they use. You gain smoothness with higher gear ratios but loose a bit of speed for reactions, which makes smooth flying more necessary. They are realliy trying for platform independence, where you don't need to fly smoothly to get smooth results. I am still in debate about what's better.

Also, I have heard and seen video of the Sony DSC-HX9V. It can do decent video if you absolutely have no vibe issues. It's a jello machine otherwise. Again, third hand info, but I thought that i would pass it along :) Great work again! Looking forward to flight video.
 

B

BIGTACO

Member
Thanks for the kind words! In regards to the Sony DSC-HX9V info I appreciate the input. I am still in the research phase and won't purchase it unless it will function well in this application. I would rather just wait for a proper camera instead of buying a camera I will be dissappointed with. I will do more looking into the vibration sensitivity issue. If thats true, the Sony probably won't cut it.

The reason I went with higher ratios is the same reason the Cinestar gimbal uses 5:1 on each axis... If you run very high speed servos (ie; Savox TG1258) you can have the best of both worlds. Enough speed as required for rapid reactions plus smoothness by way of higher drive ratio. Additionally a higher ratio enables the servo to have a better mechanical advantage on the load. This means it can get to its max angular speed, with higher acceleration. Alot of people forget that point. Also, the higher speed of my servos when compared to the BL950's helps to counteract the negative effect to speed my higher ratios impart. The BL950 servos have a speed of .12 sec/60 degrees while the servos I am using have a speed .08 sec/60 degrees. This is a speed increase of 33%. My tilt drive ratio is 3.75:1. When you compare this to 2.5:1, thats an increase of 50%. So this ratio increase is slowing down the servo by 50%, but since my servo speed is 33% higher than the BL950's I am only slowing it by 17%. And in actuallity since the servos now have a much higher mechanical advantage on the load this 17% loss in (MAX) speed isn't a problem because my servo can get to that speed is a shorter amount of time.

You will notice that all the high end gimbals (that I have seen) have high ratios on tilt and roll. There is a reason for this...



jcmonty said:
Very nice build! I really like the simplicity of the design and how clean it looks. Do you mind posting the weight of the setup?

I am considering getting one of Askman's new AG700 gimbals when they come out, and you guys share a lot of design features. I must say though that the CF really looks a lot stiffer than the G10 they use. Can you talk a bit to why you decided to go with the higher gear ratios? From the testing I have seen for the AG550, it really likes the 2.5:1 to 2.8:1 ratios with the fast MKS servos they use. You gain smoothness with higher gear ratios but loose a bit of speed for reactions, which makes smooth flying more necessary. They are realliy trying for platform independence, where you don't need to fly smoothly to get smooth results. I am still in debate about what's better.

Also, I have heard and seen video of the Sony DSC-HX9V. It can do decent video if you absolutely have no vibe issues. It's a jello machine otherwise. Again, third hand info, but I thought that i would pass it along :) Great work again! Looking forward to flight video.
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jcmonty

jcmonty

Member
Thanks for the explanation. I am actually in your camp about this one - higher gear ratios. I was just curious about your decision. Have you checked out any even faster servos: http://www.amainhobbies.com/product...ushless-Metal-Gear-Digital-Servo-High-Voltage I would worry about the torque on that one, but with an even higher gear ratio it may compensate. Seems like there is a lot of options!

Also, how did you modify your servos for ext. pots? Is there a guide out there?
 

B

BIGTACO

Member
That servo you posted up is insane. I would love to use two of those actually. With my higher ratio and small lightweight camera I think torque would be fine. They are just too pricy for me right now though, but eventually I would love to try them. Man those are fast. Wow.

Go look on photohigher's site for a procedure on how to mod servos for external pots. Thats what I used. A quick google search should pull it up...

jcmonty said:
Thanks for the explanation. I am actually in your camp about this one - higher gear ratios. I was just curious about your decision. Have you checked out any even faster servos: http://www.amainhobbies.com/product...ushless-Metal-Gear-Digital-Servo-High-Voltage I would worry about the torque on that one, but with an even higher gear ratio it may compensate. Seems like there is a lot of options!

Also, how did you modify your servos for ext. pots? Is there a guide out there?
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J

jes1111

Active Member
The new Savox brushless servos (including the 2271 you linked to) can't be modified for 360º rotation. Like the Hitec 7990, they use a magnetic encoder - a magnet on the bottom of the output shaft sits directly above the encoder chip on the PCB. Besides, the backlash in the gearhead exceeds the resolution of the encoder, making this type of servo very "nervous" for this application.
 

R

R_Lefebvre

Arducopter Developer
BIGTACO said:
That servo you posted up is insane. I would love to use two of those actually. With my higher ratio and small lightweight camera I think torque would be fine. They are just too pricy for me right now though, but eventually I would love to try them. Man those are fast. Wow.

Go look on photohigher's site for a procedure on how to mod servos for external pots. Thats what I used. A quick google search should pull it up...
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You might consider giving these a shot:

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=18399

I know some people thing HK servos are crap, but given it's not a flight control.... Failure won't be so bad. I'm actually using the .10 sec version of these on my swash, and .06 on the tail of my 600 Heli. They are pretty nice. I also got one of the .03's, but I found that it had a problem when running on a full 8.4V. It didn't center well, often buzzed badly at center. It's fine at 6V. Anyway, I put it in a drawer, but I'll use it eventually. These servos are smooth, and don't have pots to wear out.

Oops... duh, yeah, the encoder means it can't be used.

http://www.hobbyking.com/hobbyking/store/__23154__Turnigy_1209HP_ultra_Fast_Coreless_Digital_Servo_50g_5kg_0_05.html

$20?
 

jcmonty

jcmonty

Member
jes1111 said:
The new Savox brushless servos (including the 2271 you linked to) can't be modified for 360º rotation. Like the Hitec 7990, they use a magnetic encoder - a magnet on the bottom of the output shaft sits directly above the encoder chip on the PCB. Besides, the backlash in the gearhead exceeds the resolution of the encoder, making this type of servo very "nervous" for this application.
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Ah.. learn something new everyday! Thanks for the info
 


J

jes1111

Active Member
Now that I think about it, I "mispoke" ;) - not all "magnetic encoder" servos will be unmodifiable - I was thinking of one that's on my desk in front of me that has the encoder chip on the board (I could tell you the brand/model but then I'd have to kill you ;)). The Hitec 7990's actually use a separate "magnetic pot" connected to the PCB with a short ribbon cable so you could actually mod it, as long lengthening that cable didn't interfere with the signal. Probably not worth the time/trouble/expense though because you're still up against backlash issues and the Hitec's very "punchy" behaviour.

On the other hand, if you fancy giving it a try, I have 3 Hitec 7990's for sale :)
 

J

jes1111

Active Member
View attachment 5955Sorry about the fuzzy photo :)

Of course, the encoder is also "absolute", i.e. it will only ever give you a position between 0 and 360º - even though it will turn continuously. So to use it you'd have to gear it, which would kinda defeat the object :)
 

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B

BIGTACO

Member
Progress report: Video Test #1

I completed the calibration of my hoverflygimbal controller tonight. I have also begun setup of the controller to my gimbal. I am currently learning all the settings and what they all do...

I am very happy with the results so far. I have the servo acceleration settings on both roll and tilt maxed out and still the smoothness of movements is better than I expected. I am noticing some slight delay when I transition from one roll direction to the opposite direction. I am sure this is caused by the backlash of the gears inside the servo. As jes1111 pointed out this would be a limiting factor in my design if all other elements were in line. Looks like you were right Jes! I am using a NIMH 6 volt battery that is probably not fully charged so perhaps if I run a proper 7.4 volt lipo + UBEC I can reduce this delay a bit by keeping my servo voltage right at 6 volts instead of slowly tapering down like this crappy pack I am using. I picked up a nice lipo and ubec today at the hobby shop so we will see.

The real test will come once this gimbal is under my bird. I am sure real flight testing will result in more tuning and tinkering. But, for now I am super happy!

Sorry ya'll have to look at my ugly mug in this video :)

http://www.youtube.com/watch?v=6zuSZBdxpDE
 


jcmonty

jcmonty

Member
Awesome! It looks really good. I see the roll tick that you are talking about, but honestly, it's not that bad. Really really good without any tuning.
 


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