THE TRUTH ABOUT THE ITG3200

3689399270?profile=originalWell, to work in a spin stabilized mode, Marcy 2 would have to spin a
lot faster than a 3 channel coaxial copter can.  Without spin
stabilization, a $40 Syma S107 or a $25 Sky Invader didn't matter
because either way, we needed another gyro to know heading.  A 150
second flight time doesn't demand a very accurate gyro.

Mass produced Marcy 2's would use the cheapest single axis gyro
available, but suddenly a static proof bag of new gyros happened to
fall off a truck.  It's the ITG3200, another crazy small 0.5mm Invensense QFN. 

Decided to go ahead with it, to evaluate it for another 3 DOF IMU.  Have 5 years made

any difference with Invense gyros?

 

3689399198?profile=original

 

 

Unfortunately, it immediately showed a
large dead band, a convenient solution to the same old gremlin

of gyro 0 offsets drifting.  It automatically 0 centers itself, but it has to
rotate a large, minimum amount to detect anything.  You can rotate it
slowly enough, handheld, to go 90 deg without sensing anything.

It's intended for hand held motion sensing & gesture user interfaces,
not a heading hold gyro.  The deadband gets a lot

bigger as the lowpass bandwidth gets lower.

Direct analog pins would make this chip a lot more useful, but obviously
doing the samping on the die eliminated a lot of parts
that would be required for analog pins.

 

 

Through the IDG300, ADXRS150, LISY300, & ITG3200, gyros have gotten cheaper, but

they still use the same mechanism they did 5 years ago.  They can stack multiple gyros,

sample more bits, but the mechanism hasn't gotten any better.

 

 

UPDATE:


3689399348?profile=original

It wasn't a deadband as much as a mismatch between the lower & upper 8 bits.  It took a lot of rotation to get above 0.  Then the result was smooth from 0 - 255.  Then, it took a lot of rotation to get above 255.

 

It turned out the chip doesn't work in I2C burst mode.  You have to read the analog results 1 byte at a time.

 

 

 

MARCY 1

Read over the monocopter paper again, 2 years later, & figured out 3
factors affecting stability:

Wing pressure needs to go through the CG of the balance beam.

Coning angle needs to be minimal.

Balance beam needs maximum inertia.

The main advantage of a monocopter is having the most wing in the
fastest air for the least weight, but this results in a high coning
angle.  An ideal monocopter would have to be much bigger, have an IMU &
use servos for active stabilization.  The ideal, small vehicle is better
off eating the cost of a 2nd wing.

3689399361?profile=original

3689399284?profile=original

So the 2 flexing wings ended up pressing the fuselage onto the takeoff
rod & jamming it down.  Another problem was twisting of the angle of
attack to a level position.

3689399383?profile=original

3689399430?profile=original

It didn't have these problems in monocopter form, but we've also reduced
the wingspan & increased the RPM.

There's still hope for the lighter frame, if the design works & frees up
enough money for CF.  Time to dig out a tried & true brick frame.  It
was abandonned when we figured the monocopter was more optimum, but the
rigidity of balsa is really needed.

 

 

3689399455?profile=original

 

 

 

That definitely seemed to be more stable than the monocopter, but led us back to the actuator problem.

 

 

 

 

E-mail me when people leave their comments –

You need to be a member of diydrones to add comments!

Join diydrones

Comments

  • Fuse the ITG3200 with a mag to handle slow rotations. Will it compete with infinite budget 1960s military hardware? Certainly not, but it's still pretty fantastic for $12, compared to what we had 2 years ago.
  • T3
    I know that some point in the future I will get to see a video of a a single prop with all the control hardware sticky taped into the hub flying while being powered by the energy from a single laser pointer powered by a lemon.
This reply was deleted.