Re: Best gyro for frc.
 

What do you mean the most accurate timer was 1ms? Unless you meant microsecond instead of the millisecond I'm assuming that means.

Re: Best gyro for frc.
 

Hmm, I was using the millis() function and did not realize there was a micros() available. Reviewing the Arduino library I now see it is available, so I'll go back and modify my code to use it. This could help to increase heading sample rates.

Re: Best gyro for frc.
 

That's what I assumed, do note that micros() returns multiples of 4 (or 8 on 8mhz arduinos).

You might also want to look into using interrupt driven timers.

And while on the topic of timing and arduino, for timing dependent tasks write the code yourself. Tests I did a couple years back showed that there's a SIGNIFICANT overhead for the arduino digitalWrite compared to the comparable C code. I'd always assumed they were just macros but they actually include a fair bit of code.

Re: Best gyro for frc.
 

As in the long variable returned will always be a multiple of 4 (or 8), or a return of "1" actually means 4ms? If the former, no impact since I am just comparing time now to time at last sample collection.

I'm using SPI.transfer(data), not digitalWrite. Is there a more efficient method than this one?

Re: Best gyro for frc.
 

Has anyone thought about making an aftermarket board that plugs straight into the expansion port on the rRIO that includes a gyro built in as well as pwm expansion and dI/O and analog expansion?

Re: Best gyro for frc.
 

Gyros are very sensitive to electromagnetic fields, this may be a problem so close to the roboRio.

Even if it wasn't, the chip I tried in particular is a single-axis gyro and will require more precise mounting on the robot. Many teams like to mount cRios/roboRios vertically or in a way convenient for troubleshooting or maintanence. Maybe an embedded 3-axis gyro would solve that problem, like the rRio's 3-axis accelerometer.

Re: Best gyro for frc.
 

I added a calibration task that samples 5 seconds of data at 1kHz and calculates the bias from this. And I used micros() instead of ms counts and removed the smoothing, so now the heading is updated at 1kHz as well.

Result: ~1 deg drift in 10 minutes. I think that'll be good enough.

Photo of the setup (3D printed protective case):


Serial Output:

Re: Best gyro for frc.
 

Looks like you already figured it out, the returned value will always be a multiple of 4.

I'd be willing to bet doing the SPI write yourself would be more efficient but it's probably not a huge deal. The only reason I did any tests was I needed faster executing digital writes. It was mostly an example of how the wrapper library is pretty inefficient.





Mounting the gyro near the roboRio probably won't be an issue. Every time I've run a gyro has been an analog gyro, the issue was that the signal got messed up by the magnetic fields caused by currents driving motors. Minimizing transmission distance should help you there. But this gyro talks SPI so it's less susceptible to that issue.

Re: Best gyro for frc.
 

You can also throw a ground plane under the gyro to block most of the magnetic fields that might be there. That's good practice anyways.

Re: Best gyro for frc.
 

Not to bust your chops, but that's true for electric fields -- not so much for magnetic fields. Effective magnetic shielding requires the use of a material with a high magnetic permeability such as Mu-metal (Carpenter Specialty Alloys). Rolled foil copper such as that found on PCBs has little effect.

Re: Best gyro for frc.
 

I wasn't quite sure that I hadn't mixed the two up when I wrote the post. Thanks for calling me out on it :o

Re: Best gyro for frc.
 

Kauailabs will be announcing exactly what you describe on January 3.

Awesome, any plans to offer official Python support?

Re: Best gyro for frc.
 

What gyro specifically?

Thanks

Re: Best gyro for frc.
 

Invensense MPU-9250 (9-axis sensor).

Plus an on-board 32-bit ARM microcontroller, providing motion processing and calibration algorithms for accelerometers, gyros and magnetometers. Minimal yaw drift due to filtering/fusion algorithms. UART, SPI, I2C and USB interfaces. Open source hardware and firmware. C++, Java and Labview libraries for the Roborio will be available, too.