Author Topic: Angle Advice Please  (Read 1913 times)

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Offline ChrisYardTopic starter

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Angle Advice Please
« on: October 05, 2009, 10:00:03 AM »
Hi all,
I have a R/C Heli here, I have written a program to control the Motors and servos which is working fine, what I need some advice on is how to/ what can I use to mesure the angle the heli is leaning.  I have a couple of tilt switches so that when they are activated the servos will correct it, so that it doesn't flip over and crash !! which it has done many a time !!!!!

I was just wondering if there is something out there that would send back either an analog or digital signal (via I2C) to tell my PIC what angle it is at so that my PIC could work out how to correct the angle correctly.  and not just wait until one on the tilt switches was activated and then move the servo until the other tilt switch was activated, creates a horrible rocking motion !!

Thanks
Chris

Offline chelmi

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Re: Angle Advice Please
« Reply #1 on: October 05, 2009, 10:14:22 AM »
yes, they are called gyros. Sparkfun has a nice selection:

http://www.sparkfun.com/commerce/categories.php?c=85

Chelmi

Offline waltr

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Re: Angle Advice Please
« Reply #2 on: October 05, 2009, 10:19:31 AM »
A 3-axis Accelerometer could give you the signals to determine tilt angle if the Heli is not accelerating in any horizontal direction but in a stationary hover.

Here is a link to another forum discussing this:
http://forum.sparkfun.com/viewtopic.php?t=17146&highlight=tilt+angle

Offline ArcMan

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Re: Angle Advice Please
« Reply #3 on: October 05, 2009, 02:15:11 PM »
Right.  Accelerometers measure acceleration (which, thanks to the acceleration of gravity, can measure tilt).  Gyros measure angular velocity.

Offline ChrisYardTopic starter

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Re: Angle Advice Please
« Reply #4 on: October 06, 2009, 12:59:10 AM »
Thank you every one I will look into getting a Gyro and strapping it to my heli.

Offline walkercreations

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Re: Angle Advice Please
« Reply #5 on: October 06, 2009, 10:43:51 AM »
For the most part a Gyro only helps with the tail and yaw control. For roll control which if I understand what your looking for is something totally different. I know there are a number of systems out there that can handle this. If you will do a web search for "Flybarless Heli Setup" I know you will come across what you are looking for. There are gyros for that setup that can handle everything but they are quite pricey.
Peter Walker
Fruitland, MD USA

Offline ChrisYardTopic starter

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Re: Angle Advice Please
« Reply #6 on: October 28, 2009, 01:28:16 PM »
Hi all Sorry of the delay in this response, been a bit busy designing another circuit for work......

What would be the best type of gyro would you recommend ???
300o/s
1500o/s

By the way as this is the first time I have looked into Gyros, does that mean that they take 300/1500 readings a second or is that something to do with the angles it can mesure ??

thanks for the help
Chris

Offline ChrisYardTopic starter

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Re: Angle Advice Please
« Reply #7 on: October 30, 2009, 02:24:23 PM »
Hi all,
Can any one help me on this as I would like to place the order for a gyro today.

Offline Webbot

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Re: Angle Advice Please
« Reply #8 on: October 31, 2009, 11:22:16 AM »
That will be the maximum rotation speed (degrees per second) they can measure - its NOT how long it takes to read the sensor
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Offline ChrisYardTopic starter

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Re: Angle Advice Please
« Reply #9 on: October 31, 2009, 02:25:48 PM »
Thanks for the reply, so I would be better getting the 1500o/s for my Heli then ????

Offline Webbot

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Re: Angle Advice Please
« Reply #10 on: October 31, 2009, 02:32:07 PM »
Thanks for the reply, so I would be better getting the 1500o/s for my Heli then ????

The trade off is accuracy vs range. A gyro that can measure say 300 deg/sec will provide better accuracy within that range. Whereas a 1500 deg/sec sensor will measure a larger range - but with less accuracy throughout that range. You dont get something for nothing?

Of course the ideal situation is: use 'both' !!! Ie read the 1500 deg/sec sensor and if less than 300 then read the 300 deg/sec sensor to get more detailed info. But thats probably a 'luxury' !

So you need to think about what the maximum rotation speed would be in any axis and the required accuracy.

Sorry if that doesn't answer your question directly

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Offline ChrisYardTopic starter

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Re: Angle Advice Please
« Reply #11 on: October 31, 2009, 02:42:57 PM »
Again thanks for the reply, yes both would be a luxury !! :-) but could be possiible if the future.

What I am trying to achive (all under control of my MCU & PC) is that the heli will take off and hover at a set height, now the height thing is not a problem as I have a couple of Sharp IR Range finders, (10cm - 80cm & 15cm - 150cm) I can control the main and tail motor speeds and I can control the two Servos.

But what some times happens is that the heli will roll and pitch with out any input for me... i.e. wind / me pushing it !!! what I was looking for was a gyro to detect this movement and correct it via my MCU...  So I think I might start with the 300/s first and see where we get.
« Last Edit: October 31, 2009, 02:45:29 PM by ChrisYard »

 


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