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CSU Chico Tilt Rotor Flying Machine, (Programming and CPU, 3 of 3).

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AndrewM

Wed Jul 11 2012, 01:17AM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362

In controls (maybe just aeronautics?) "dot" is the same as prime which is the same as derivative.

So theta_dot = d theta/dt (angular velocity)
theta_dotdot = d2 theta/ dt2 (angular acceleration)

Patrick

Wed Jul 11 2012, 01:44AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

AndrewM wrote ...

In controls (maybe just aeronautics?) "dot" is the same as prime which is the same as derivative.

So theta_dot = d theta/dt (angular velocity)
theta_dotdot = d2 theta/ dt2 (angular acceleration)

whoops! i see what you meant, yes i knew that, brain lapse... im not good at ASCII math anyway. do you know anything about programming in C?

ok so theta dot= (d theta )/( dt) which effectivley means: (change in angle theta) / (change in time)

therefore if the time interval is consecutive and constant: (d theta)/(dt) = (current theta - previous theta)/(time interval)

and i think thats what Brett Beaureguard means in this line :
[ double dErr = (error - lastErr) / timeChange; ]

AndrewM

Wed Jul 11 2012, 04:22AM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362

I've never been very good at reading other people's code, I usually just write my own... so I didn't read that page.

But yeah, looks like numerical differentiation to me.

Patrick

Wed Jul 11 2012, 05:10AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

well you and i are going to get this working so well need to figure out rolling, pitch collective and yaw and pid's and every other little thing we need, i want this done in less than one year from now.

I really appreciate your help, im going to stay on this everyday.

Carbon_Rod

Wed Jul 11 2012, 08:53AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Typically for UAV aerial acrobatics, people use Minimum Jerk Trajectory planning with Visual Servoing.

If you start to run out of time, openservo is a cheap mod that will reduce some of the errors that you are about to encounter...

Note that most gyros & some accelerometers will have oversampling error reduction, and low pass filter options...
i.e. simply use the on chip noise filters if you know the craft will not exceed a few g or high angular rates.

@AndrewM There are few robust alternatives outside the consensus of prior threads...
... the current approach will unlikely stay in tune very long...

Note a 200gram 1GHz wifi enabled mini computer is $68 delivered....

And it runs a popular distro:

Patrick

Wed Jul 11 2012, 02:26PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Carbon_Rod wrote ...

Note that most gyros & some accelerometers will have oversampling error reduction, and low pass filter options...
i.e. simply use the on chip noise filters if you know the craft will not exceed a few g or high angular rates.

@AndrewM There are few robust alternatives outside the consensus of prior threads...
... the current approach will unlikely stay in tune very long...

Note a 200gram 1GHz wifi enabled mini computer is $68 delivered....

And it runs a popular distro:

i will use the onboard low pass filter that my chips already supportand i still need to worry about gyro drift, but as for your 68$ computer thats not a real embedded system, and i cant configure pins on it or a RTOS like i can with a pic, ardiuno, STAMP or STM32.

edit, super dooper important:
]filter.pdf[/file]

Carbon_Rod

Thu Jul 12 2012, 05:04AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

In general, latency tolerant functions are located within an RTlinux kernel based OS with usb host stack and wifi.

Most RTOSs are not what the name implies, as the last real RTOS was MSDOS.

In general, people who believe otherwise are better off using multiple chips/boards....

A 12Mbps USB host link will add little latency to consumer sensors given maximum sample rates will rarely exceed 400Hz...

Note a 1.5GHz Cortex-A8 A10 with 1GB ram and a cheap interface chip for i/o is flexible...

Patrick

Thu Jul 12 2012, 05:50AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I dispute your claims, yet that clip was funny.

Carbon_Rod

Thu Jul 12 2012, 08:40AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Specifically, schedulers need to save multiple machine states for threading/message-passing, interrupts may overlap ISRs to randomize stack-pointer/register save times, and multi-core/GPU systems have several types of resource contention.

Most multitasking RTOS are approximating a fixed latency scheduler even if written in Assembly. If the accumulated errors from timing jitter are negligible/profiled than people sell it as an "RTOS".

"dispute" infers there is some inherent value in deception requiring negotiation...

Patrick

Thu Jul 12 2012, 12:11PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

dispute the meaning of dispute all you want

Ill stick with my STM32's for the time being since they handle GPIO, I2C and SPI nativley, and a traditional computer doesnt.

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