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Old Jun 28, 2008, 03:44 PM
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United Kingdom, Bath
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Accelerometer -> uC -> Tx -> Pan servo (Poor man's HT?)

The problem:

- Can't afford a proper goggles+tracking setup
- Full house glider needs both hands to fly
- No intuitive way of controlling camera pan/tilt

Proposed solution:

- Mount accelerometer on RC TX to sense tilt
- Microcontroller converts G force -> tilt angle -> analogue voltage -> replace RC TX pot

Implimentation:

- Accelerometer: MMA1260D, +/- 1.5G
- Microcontroller: Arduino
- Output: PWM+low pass filter

Obligatory video demo:

Tesing my new accelerometer based camera paning system (1 min 12 sec)


Conclusions:

- Need to turn TX very gently to avoid getting movement/vibration being interpreted as tilt
- It works but it's not very intuitive, maybe able to get used to it...

Final Verdict: Meh... Not too impressed with my design.
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Old Jun 28, 2008, 03:55 PM
albertocvr
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Its not a bad idea ! , for sure if you keep on working on it it will do the job ....
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Old Jun 29, 2008, 03:14 AM
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The problem is tilting the tx doesn't seem like a natural way of controlling the camera. Maybe it is easy for Wii players, but I need to pause and think about what I'm doing before panning the camera.

I think I'm going to try mounting the accelerometer to my head and see if tilting my head is easier...
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Old Jun 29, 2008, 03:29 AM
Cameras are EVERYWHERE...
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Quote:
Originally Posted by zitron
The problem is tilting the tx doesn't seem like a natural way of controlling the camera. Maybe it is easy for Wii players, but I need to pause and think about what I'm doing before panning the camera.

I think I'm going to try mounting the accelerometer to my head and see if tilting my head is easier...
That was going to be my next suggestion. Will it suffer from drift? And if so, can you recenter it easily?
I hope it works out for you, it's a great accomplishment so far!
Keep after it!
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Old Jun 29, 2008, 12:26 PM
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Thanks!

No it won't drift because it senses the gravity vector, which should always point downward unless you are sitting in a centrifuge, or something fundamental in the universe goes wrong .

I've tested mounting it on my hat, works amazingly well ! The annoying thing is you must tilt you head down by 20-30 degrees if you want it to work like a regular head tracker. Other wise it wont sense any change in panning.

It's too windy for flight tests today, I made a video from my stupid robot thing:

Driving in the back yard with new head tracking system (3 min 28 sec)


Right now it's a bit twitchy because I limited the head turning angle so when I turn my head I can still see the screen. Should be even better if I had goggles!

Accelerometers are much cheaper than gyros, no drift and require less processing, perhaps this can be made into a much cheaper HT solution!

Cheers,
-Z-
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Old Jun 29, 2008, 12:46 PM
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Perth, Western Australia
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I was working on my own head tracker largely based of this project that used a the accelerometers from a wii nunchuck and and arduino clone.
I paused it's development while i had exams and will probably resume in the near future.
Nick
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Old Jun 29, 2008, 12:48 PM
Cameras are EVERYWHERE...
tvdude310's Avatar
Los Angeles
Joined Jan 2008
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Quote:
Originally Posted by zitron
Thanks!

No it won't drift because it senses the gravity vector, which should always point downward unless you are sitting in a centrifuge, or something fundamental in the universe goes wrong .

I've tested mounting it on my hat, works amazingly well ! The annoying thing is you must tilt you head down by 20-30 degrees if you want it to work like a regular head tracker. Other wise it wont sense any change in panning.

It's too windy for flight tests today, I made a video from my stupid robot thing:

Accelerometers are much cheaper than gyros, no drift and require less processing, perhaps this can be made into a much cheaper HT solution!

Cheers,
-Z-
Hey Zitron-
First off, your robot isn't stupid! I have stacks of organizers full of Lego Mindstorms and other Lego kits. I know, it may SOUND stupid for a 44 year old man to be playing with Legos, but I've learned a lot from several interesting experiments. I made a vehicle that moves around the house picking up dog toys...but I could never get it to recognize the difference between toys and shoes. Not a big problem, if you're missing a shoe just look where the toys are!
So, back to the head tracker...
I have a sneaking suspicion that a new (top secret) head tracker being developed by one of our favorite RC companies is exactly what you are working on. I promised not to let the cat out of the bag, so all I can tell you is that accelerometers are definitely the way to go! Keep at it, you may be able to get yours fine tuned before theirs hits the market. Not that you would want to mass produce them, but if your solution is reasonably cheap, then they will have to price theirs accordingly to capture the business of us do-it-yourselfers.
I had an idea for a head tracker that might work well and be cheap. I feel that a head tracker should track POSITION instead of MOVEMENT. And position relative to what? Well, your Tx is always in front of you, no matter what you're doing. So why not track position relative to the Tx?
How? A Nintendo Wii tracker. The sensor bar goes on the Tx, the emitters go on your head.
It's just an idea at this point, and I'm not going to run out and buy a Wii just to hack it up, but I think the idea is a solid one, and it should be cheap and easy to implement.
BY THE WAY: Anyone who is reading this and thinks they can pull it off, please feel free to use the idea. I don't have the time or money to make it happen, but I would love to see it.
Good job Zitron (can I call you "Zit"? )
Rob
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Old Jun 29, 2008, 12:55 PM
Cameras are EVERYWHERE...
tvdude310's Avatar
Los Angeles
Joined Jan 2008
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Quote:
Originally Posted by nick.sargeant
I was working on my own head tracker largely based of this project that used a the accelerometers from a wii nunchuck and and arduino clone.
I paused it's development while i had exams and will probably resume in the near future.
Nick
Hey Nick-
I just read your post, you must have posted while I was typing...
NICE!!! See, I knew it was a good idea! RUN WITH IT!!!
Ok guys, there are several new trackers about to hit the market. Your efforts will help keep the costs down for all of us. So, FULL SPEED AHEAD!
And you never know, lots of us may just follow in your footsteps and make our own instead of buying one. It's way more fun this way anyway...
Nice job guys!
Rob
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Old Jun 29, 2008, 02:59 PM
Just trying to get a nut.
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United States, VA, McLean
Joined Oct 2006
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What about implementing it this way:

All you need is some bungy choord, or one of those retractable key ring thingies...

Attach the bungy choord to the back of the ballcap on one end, and the other end to your shirt.

Attach the accelerometer to the bungy choord.

When you look either side, it causes the bungy choord to tilt.

What do you think?
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Old Jun 29, 2008, 06:27 PM
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Nick:

Nice to see someone else using the arduino! I was also thinking about using a 2 or more axis sensing accelerometer, since elevation (up-down) is trivial to sense compared to azimuth (left-right), but I only have a 5 and 1/2 channel radio, and the single axis accelerometer is all I have at hand. If you want, I can give you my arduino code. Good luck with your project, I'd love to see your solution!


Rob:

Thanks for the encouragement, but don't put your hopes up too much yet, there's a couple of problems with my approach:
  • Because it is impossible to distinguish between acceleration from gravity and acceleration from movement, you must sit pretty still and not walk around
  • How much you need to turn you head in azimuth to reach full pan angle changes depending on your head's elevation angle, the more you tilt your head up or down the less you have to turn. So unless you lock your head in the same elevation, you won't get the same pan angle at the same head azimuth angle. Although this can be somewhat corrected using another accelerometer axis, the system will always be more sensitive the more you look up or down, kind of not ideal
  • The system can be used in two modes: 1. leaning your head side to side, and 2. turning your head in azimuth while tilted up or down, but it is impossible to tell which mode you are operating in. I realised that while it is easier on my neck to look down, in this position leaning to the left and turning to the left produced the opposite panning ! So the solution is to look up, so that leaning and turning left both produce a "pan left" command, but ideally you'd want to be completely laid back looking straight up (see above)

Because of these problems, I wouldn't call an accelerometer only system a real head tracking solution. If I was to design a proper system, I would use both gyros and accels, using a Kalman filter to use the accel data to correct gyro drift. That's the proper way of doing it, 'cause you can jump around and do whatever the system will always work. I'm guessing that's what the companies are working on. I highly doubt anyone is trying to bring a pure accel HT to market, because drift is a small problem compared to what I listed above. But of course, unless they have the cheap skates like me as their target customers !

Talking about cheap, if you get a low G single channel accelerometer with 5V input and analogue output (like this one, although this is two axis: you can get a single axis one on ebay for less than $10), you can plug it directly into the TX instead of a pot with 3 wires !! (Assuming your tx works like mine) Sure you don't get the full servo range, or linear movement that the micro controller gives you, but look at the price!

I also thought about the Wii remote photogrammetry based sensing you mentioned, that can easily be done using a computer with a webcam, some IR LEDs and some way of passing the data to the TX. Or alternatively, get the data out of the Wiimote directly using the Wii interface. It's a bit more complicated (especially when "camera" and "outside" are involved), and I just happened to have an accelerometer, so I did it my way .


scrtsqrl:

That is a GREAT idea, I wish I thought of it! I would test it tomorrow but I'm moving to a different house next week!!

There are some problems I foresee though:
  • How to prevent the accelerometer twisting around the string?
  • Need a formula to convert string tilt into head azimuth angle for linear movement

I will definitely test it out when I get the chance!

*****************************************

Phew.. got to be me longest. post. ever.

Cheers,
-Z-
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Old Jun 29, 2008, 06:35 PM
Just trying to get a nut.
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United States, VA, McLean
Joined Oct 2006
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Quote:
Originally Posted by zitron
scrtsqrl:

That is a GREAT idea, I wish I thought of it! I would test it tomorrow but I'm moving to a different house next week!!

There are some problems I foresee though:
  • How to prevent the accelerometer twisting around the string?
  • Need a formula to convert string tilt into head azimuth angle for linear movement

I will definitely test it out when I get the chance!
-Z-
Easy. mount the accelerometer on a flat pice of 1/8 inch thick balsa, maybe 3 X 3 inches close or where the choord is atached to the ball cap. Your head will get in the way and prevent it from twisting...

No need to do whacky math. Just vary the length of the chord.

I went through this drill a while back...Here's what I came up with instead...Admitedly, only single axis HT...However, it is REALLY cheap and simple...

Scrtsqrl's Poor Man's Head Tracker (3 min 40 sec)
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Last edited by scrtsqrl; Jun 29, 2008 at 06:44 PM.
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