Chief Delphi - Best gyro for frc.

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Re: Best gyro for frc.

Figured I'd clear up a couple of responses in this thread.

Quote:

Originally Posted by seg9585 (Post 1415960)

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.

Incorrect. MEMS devices are manufactured using non-ferrous materials, thus making them immune to strong magnetic fields. A single axis gyro simplifies the mounting on the robot. You only have one axis to worry about! The ADXRS450/453 are "rate gyros" which mean that they are designed to only report back...rate... in one axis!

Quote:

Originally Posted by Bryce2471 (Post 1419178)

Sorry I'm a little late to the party on this thread. As far as this gyro goes (ADXRS453), it looks like there are two packaging options (ADXRS453BEYZ and ADXRS453BRGZ), I'm wondering which one you would recommend, and how you interface with it.

You probably want the ASXRS453BRGZ version since the sensor will be easier to solder onto a PCB and the measured axis is located through the center of the part. You would solder the sensor down to the PCB just like any other IC. I would recommend purchasing the breakout board, though!

The 450/453 differ from the gyros used on the AndyMark breakout board in that the Analog to Digital conversion is performed within the sensor. This makes them much less susceptible to EMI. In an ideal setting, you would want the accelerometer attached to a rigid portion of your robot, and the gyro would be located as close to the center as possible.

Although the 6-axis and 9-axis sensors are cool, they are not designed for precision navigation applications. Noise levels on those sensors are orders of magnitude greater than what's available on application-specific sensors. I would strongly suggest that teams invest some time looking into the 450/453 if they want to have a solid drive system.

Another caveat of systems such as the nav6 is that they are not calibrated. Each sensor is unique and will provide a slightly different response when used in different applications. In that case, an integrated IMU such as ADI's iSensor product line would be ideal.

Re: Best gyro for frc.

Quote:

Originally Posted by juchong (Post 1425003)

Figured I'd clear up a couple of responses in this thread.

Incorrect. MEMS devices are manufactured using non-ferrous materials, thus making them immune to strong magnetic fields. A single axis gyro simplifies the mounting on the robot. You only have one axis to worry about! The ADXRS450/453 are "rate gyros" which mean that they are designed to only report back...rate... in one axis!

You probably want the ASXRS453BRGZ version since the sensor will be easier to solder onto a PCB and the measured axis is located through the center of the part. You would solder the sensor down to the PCB just like any other IC. I would recommend purchasing the breakout board, though!

The 450/453 differ from the gyros used on the AndyMark breakout board in that the Analog to Digital conversion is performed within the sensor. This makes them much less susceptible to EMI. In an ideal setting, you would want the accelerometer attached to a rigid portion of your robot, and the gyro would be located as close to the center as possible.

Although the 6-axis and 9-axis sensors are cool, they are not designed for precision navigation applications. Noise levels on those sensors are orders of magnitude greater than what's available on application-specific sensors. I would strongly suggest that teams invest some time looking into the 450/453 if they want to have a solid drive system.

Another caveat of systems such as the nav6 is that they are not calibrated. Each sensor is unique and will provide a slightly different response when used in different applications. In that case, an integrated IMU such as ADI's iSensor product line would be ideal.

I absolutely agree that there are much higher noise levels on 6/9-axis sensors, and the dedicated yaw-rate gyro like the ADXRS453 is a very good sensor for the field-oriented drive application. The 6/9-axis sensors in the nav6 are consumer-grade (e.g., iPhone, Oculus Rift), rather than the industrial grade of the ADXRS453.

However - please be aware that the nav6 is definitely calibrated, as it features factory-calibration of accel/gyro biases, and also continually re-calibrates the gyro biases during periods of non-motion (accounting for gyro temperature changes). This behavior, implemented in the Invensense digital motion processor (DMP) silicon and the on-board microcontroller, is what enables the yaw error rate of approximately 1 degree/minute. The navX MXP features the 2nd-gen MPU-9250 w/even lower gyro noise levels - so we're seeing this technology continue to improve and mature as the MEMS noise levels decrease, and the implementation of the data fusion and calibration algorithms continue to improve. More info on the gyro/accel calibration is available at: https://code.google.com/p/navx-mxp/w...celCalibration

The nav6 technology does require about 16 seconds of calibration time before a match, during which the robot must be held still. The navX MXP lessens this period, but this may be a difference between the two approaches worth noting.

The nav6/navX MXP technology is cost-effective and viable for use in a field-oriented drive system. Several teams have been doing this successfully, and enjoying the ease of integration it provides. Sounds like a bake-off between a ADXRS453 and a navX MXP would be helpful to the CD community....

Re: Best gyro for frc.

Ok - so when wiring up this Gyro, what goes where?

Gyro Ground to Roborio SPI Ground
Gyro Mosi to Roborio SPI Mosi
Gyro Miso to Roborio SPI Miso
Gyro PDD to Roborio SPI 5V power (datasheet says 3.3 to 5)
Gyro CS to Roborio SPI CS0
Gyro Clk to Roborio SPI Clk

Do I have this correct?

Since my experience is with analog gyros, what type of data am I going to see over the SPI interface that I will have to use to calculate bias and integrate to angle with?

Re: Best gyro for frc.

Our team took up writing and providing decent drivers for the MPU6050 as one of our offseason projects last year (2014) and had good results. We have very little drift (ie a couple of degrees every couple of hours, though we have yet to record exact results). We have a nice, cheap, solution that has been tested on a BBB and a raspberry pi, and we have half ported working code for the roboRIO (also working on using the MXP breakout board with it):
Links:
For BBB and Raspberry PI: https://github.com/thedropbears/DropBoneImu
For roboRIO (WIP, but it works): https://github.com/thedropbears/lib-4774

Documentation:
http://thedropbears.org.au/wiki/index.php/DropBone_IMU

Edit: Add link to documentation

Re: Best gyro for frc.

Quote:

Originally Posted by Tom Line (Post 1431174)

We are wiring one up also. This pinout looks correct but I am unsure of one connection. Does MOSI connect to MISO on the other side? We'll find out this weekend I reckon. Has anyone written a class just for the ADXRS453 on the roboRio they might share? Will ADXL345_SPI (with relevant mods) work?

TIA

Re: Best gyro for frc.

Quote:

Originally Posted by wireties (Post 1439242)

Does MOSI connect to MISO on the other side?

No, MOSI connects to MOSI. It stands for Master Out Slave In. It's an output from the roboRIO and an input to the connected device.

Re: Best gyro for frc.

Quote:

Originally Posted by Alan Anderson (Post 1439359)

No, MOSI connects to MOSI. It stands for Master Out Slave In. It's an output from the roboRIO and an input to the connected device.

Thanks!

Re: Best gyro for frc.

Quote:

Originally Posted by wireties (Post 1439242)

There is demo software already written in LabVIEW for the 450/453, but I haven't seen anything for C++ or Java. Might want to check the examples!

I should also have a nice RoboRIO solution for the 345 & 453 that teams might be interested in looking at!