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Author Topic: Used a quadrotor before?  (Read 3639 times)

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Offline AdminTopic starter

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Used a quadrotor before?
« on: September 17, 2008, 04:11:29 PM »
I'm in the market for a quadrotor for under $200, and I'm browsing around.

I don't care about on-board electronics, just the chassis, as I'm robotizing it :P

Anyone with recommendations or advice?

Offline pomprocker

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Re: Used a quadrotor before?
« Reply #1 on: September 17, 2008, 05:56:16 PM »
On the robot society of southern california email list i think theyve been talking about one lately
read from the bottom up.

http://tinyurl.com/5j5vc9



Quote
Jim,

Thank you.

And yes the circuit board components are surface mount.

In fact, they also replaced the usual RC transmitter / receiver arrangement
and they are instead using an IR led transmitter for the joystick controller
with a single IR receiver on board the craft to receive the control signals.
This means that you have to keep the controller / transmitter pointed at the
craft never breaking direct line of sight or the craft is programmed to shut
off - but it actually works surprisingly well... and of course substituting
an IR receiver for an RC receiver really reduces the weight.  So they've
managed to pack an IR receiver, 3 rate gyros, a microcontroller, a voltage
regulator, 4 power transistors and probably 4 fly-back diodes onto a circuit
board that's just 1" square!  Amazing!!

The IR transmitter is interesting.  It looks like a typical 2 joystick game
controller - but as I mentioned it has 4 IR leds in front to transmit the
signal.  There's also a switch to choose "EZ" or "NORM" mode.  So all of
that information is being coded and transmitted on the IR light beam - the
mode, the position of the right joystick and the position of the left
joystick.... I assume that it's being sent as some kind of serial data
string.... it'd be interesting to break it down and decode it.  Also as I
mentioned, it's also being used as a "heartbeat" indicator - as long as the
craft is receiving a signal, it keeps running.... but if the signal is lost
or the transmitter is turned off, the microcontroller on the craft
immediately shuts down the motors.  Of course if the craft is in the air
when it loses signal and shuts down it's going to fall to the ground.... but
it really is amazingly durable and it has survived numerous crashes so far
without any damage!

Dr. Bruce.

==================

Bruce

I was very impressed with the 4 rotor helicopter you demonstrated at Sept
RSSC meeting!

The overall performance was good, it seems to rely on the same functional
principle that counter-rotating propellers - with independent speed control,
can be used to adjust pitch, roll, and yaw axis of the aircraft. If I recall
correctly, that is the same operating principal as the vehicles you
personnaly constructed.

Styrofoam (foamed white polystryrene plastic) is an amazing structural
material! It has a very high strength/weight ratio, even better than balsa
wood. Unfortunately these materials aren't very strong. But they are very
tough (they deform to absorb impacts, instead of breaking). Perhaps that is
why the material was chosen by the vehicle designer?

Did they reduce the weight of the electronics by choosing surface-mount
components?




=====================
Hi RSSC members!
 
The Senario Flying Saucer that I demonstrated at the last RSSC meeting is apparently very popular - it's currently sold out on most sites!  I bought mine from Amazon (not currently in stock), but I also found it in stock here:
 
http://tinyurl.com/5j5vc9
I'm slowly gaining proficiency flying it.  It has two modes: "EZ" and "NORM".  In "easy" mode, it seems to be integrating the rate gyro information to create a heading hold type action - it's more stable, but I almost feel that it's fighting me resisting my attempts to make it change position.  In fact, if I send it forward, then release the forward joystick, it actually backs up a little before stabilizing.  However, in "normal" mode I think that the rate gyros are acting like rate gyros - they're there just to dampen the motion... just enough to compensate for a human operator's slow reflexes.  In normal mode, I tell it to go forward an it goes forward more easily (it doesn't seem to be resisting me) and when I release the joystick, it goes forward a little further before settling down and stabilizing.
 
I won't tell you how many times I've crash landed this thing - but it's still intact and flying without any damage.... it's very well designed and made.
 
I'm sorry if this sounds like a commercial - I'm just excited to finally have something that I can actually fly!
 
Dr. Bruce.
« Last Edit: September 17, 2008, 05:57:08 PM by pomprocker »

Offline hgordon

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Re: Used a quadrotor before?
« Reply #2 on: September 18, 2008, 08:56:05 AM »
http://blog.trossenrobotics.com/index.php/2007/12/04/surveyor-srv-uav/

but it's a lot more than $200.

The main issue is that you will need gyro's to stabilize, so that adds a lot to the complexity and cost.   If you plan to operate outdoors, you might be able to use thermopile sensors, but I doubt they'll be sufficiently accurate.  Accelerometers don't work because there is too much vibration.
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Offline AdminTopic starter

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Re: Used a quadrotor before?
« Reply #3 on: September 18, 2008, 09:29:20 AM »
Quote
Accelerometers don't work because there is too much vibration.
Hmmm didn't think that would be a problem . . . I'll dampen out the vibration frequency with some caps on the outputs then. You wouldn't by any chance know the vibration frequency and expected g-force amplitude (I'm guessing no, but I want to work around it).

Quote
The main issue is that you will need gyro's to stabilize, so that adds a lot to the complexity and cost.
I was hoping to avoid gyros, so expensive! About which axis is it unstable? I can mod it mechanically to improve mechanical stability.

Jon, to be honest your UAV is horribly unstable mechanically :P

Also, what voltage and current draw are typically for each motor (average and peak)?

Offline Razor Concepts

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Re: Used a quadrotor before?
« Reply #4 on: September 18, 2008, 03:38:27 PM »
www.rcgroups.com

Check the multi-rotor helis and the aerial photography sections, theres a couple big threads about quads.

$200 for an airframe is WAY to high  ;D  Quadrocopters are probably the mechically simplest flying machines. Making your own airframe will be a peice of cake compared to what you have done. Just cut out something stiff in a cross shape, and drill some holes. As for the basic electronics, you need 4 brushless motors and 4 speed controls. www.hobbycity.com has the best place for cheap brushless motors, I suggest looking up the HXT Blue Wonders. As for speed controls, you need 4 with at least 10 amps continuous current (for the Blue Wonders), I would sugguest looking at Castle Creations line of speed controls. Do not buy speed controls from hobbycity, their power range isnt very smooth.

Also for $200 you can get the Silverlit X-UFO or the Walkera UFO. Those are both considered toy grade, but people upgrade them with better electronics.

There is nothing wrong with using accelerometers, all the X-3D users have accelerometers on board, along with gyros. The only moving parts on quads are the four brushless motors... and those produce almost zero vibration as long as your props are balanced.

Quadrocopters are unstable on the pitch and roll axis. It will be close to impossible to make a quad without gyro stabilization, how else will you get it to level? The toy quadrocopters use mechanical gyros and those barely work.

« Last Edit: September 18, 2008, 03:40:05 PM by Razor Concepts »

Offline AdminTopic starter

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Re: Used a quadrotor before?
« Reply #5 on: September 18, 2008, 04:14:54 PM »
Oh, I don't want to make my own - its a question of time and reliability, not just of cost.

Quote
It will be close to impossible to make a quad without gyro stabilization, how else will you get it to level?
It will stabilize like a non-inverted pendulum ;D

Wheres your faith in Admin? :P

Offline Razor Concepts

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Re: Used a quadrotor before?
« Reply #6 on: September 18, 2008, 04:38:53 PM »
Will the mechanical device thing give feedback to the main controller to level it out?

Offline hgordon

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Re: Used a quadrotor before?
« Reply #7 on: September 18, 2008, 05:11:24 PM »
Hmmm didn't think that would be a problem . . . I'll dampen out the vibration frequency with some caps on the outputs then. You wouldn't by any chance know the vibration frequency and expected g-force amplitude (I'm guessing no, but I want to work around it).

Even at very low angles of pitch or roll, the magnitude of gravitational force measured on the pitch or roll axis is really small in comparison to forces induced by motion of the craft and vibration.  I experimented with this first hand with my fixed-blade coaxial rotor ("baby Hiller"), and the accelerometer data was close to useless.

I doubt you can get anywhere close to enough accuracy with thermopiles, but at least they provide an absolute measurement that isn't susceptible to mechanical noise.

Systems such as X3D use accelerometers to cancel out gyro drift, but the core stabilization routines are based on gyros.
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