Need help with Gyro = Analog Devices ADXRS150EB

[Jack Jones]

I'm testing autonomous mode for IRI and "TURN" isn't working. Robot turns, but won't stop turning.

I'm working blind on this because our programmers were very capable, so I didn't stick my nose in the code, nor the control system. Also, I have no idea where the documentation for the gyro is.

What I do know is:

The code worked at the last regional, West Michigan.
A printf shows that Gyro_TImer() counts up as expected. However, Gyro_Angle() also counts up (but at a much slower rate than the timer) even though the robot was stationary. Is that normal? I expected to see the angle change only when the robot rotated.

[Mike Betts]

Originally Posted by Jack Jones

...The code worked at the last regional, West Michigan...

If the code once worked and has not been changed, then it is not the code...

Check the sensor and the wiring to the sensor for damage.

Regards,

Mike

[Jack Jones]

Originally Posted by Mike Betts

If the code once worked and has not been changed, then it is not the code...

...
Regards,

Mike

Not quite that simple. We're taking the practice robot to IRI. Practice robot's gyro came up missing sometime after WMR and end of school year. Pulled gyro from competition robot. Code changed slightly, but not autonomous part. Added two pots to lift mechanism to determine position, reading them on Analog #2 & #3 - but don't see how that'd interfere with the gyro.

Wires are good & VOM measures a few K ohms between supply and ground, a few hundred K ohms between the output and either of those. Other than that and looking for a change when active, I don't know how to check the sensor.

After it cools down a bit (it's been hot & muggy here) I may take a look at Get_Gyro_Rate(). However, I don't expect it to be any more informative than Gyro_Angle(), which doesn't care if the gyro is hooked up or not. It always drifts slowly upward.

We could, in case the gyro is DOA, resort to counting wheel revs. But like I said - it's hot here. So maybe we'll spend those first 15 seconds/match in silent meditation.

[Kevin Watson]

Originally Posted by Jack Jones

I'm working blind on this because our programmers were very capable, so I didn't stick my nose in the code, nor the control system. Also, I have no idea where the documentation for the gyro is.

Here's a link to the gyro data sheet: http://kevin.org/frc/adxrs150.pdf, and one for the gyro evaluation board: http://kevin.org/frc/adxrs150eb.pdf.

Originally Posted by Jack Jones

A printf shows that Gyro_TImer() counts up as expected. However, Gyro_Angle() also counts up (but at a much slower rate than the timer) even though the robot was stationary. Is that normal? I expected to see the angle change only when the robot rotated.

The gyro bias is drifting, which is normal. If your team used the code I made available, you can find the code and documentation here: http://kevin.org/frc. Here's the readme.txt:

 
The source code in gyro.c/.h contains a driver and supporting 
software to interface a variety of inexpensive gyros to your
robot controller. This software was tested with Analog Devices'
ADXRS150EB and ADXRS300EB gyros. Data sheets for these devices 
are included. Support for the ADXRS401EB is also included. By
default, this software is configured to work with a ADXRS150EB
gyro, sampling at 800Hz, downconverting to an update rate of
50Hz by averaging sixteen samples per update. These parameters
can be changed by editing gyro.h.
This software makes the assumption that when it's running, it 
solely controls the analog to digital conversion hardware and 
that only the gyro, on analog input one, is being sampled.
Calling Disable_Gyro() will disable the gyro software and
allow you to use the ADC for other purposes.
This source code will work with the Robovation (A/K/A EDU-RC) 
robot controller and the FIRST Robotics robot controller.
Wiring-up the ADXRS401EB, ADXRS150EB and ADXRS300EB gyro
evaluation boards is straightforward. Grab a PWM cable and cut
off the male end and strip the three wires back a centimeter 
or so. With a low wattage soldering iron, solder the white wire 
to the RATEOUT pin, solder the black wire to the AGND pin, the 
red wire to the AVCC pin, and finally connect a jumper wire 
between the AVCC and PDD pins. Plug the female end into the 
robot controller's analog input 1.
For optimum performance, you'll need to calibrate the scaling
factor to match that of your gyro's. One way to calibrate your 
gyro is to mount it very securely to a hefty, square or 
rectangular object. Mounting the gyro to a hefty object will 
help dampen higher frequency vibrations that can adversly 
effect your measurements. Place the mounted gyro against 
another square object and start the included demonstration 
software. To get good results, the mount must be absolutely 
still when the "Calibrating Gyro Bias..." message appears on 
the terminal screen. After a few seconds, the gyro angular rate 
and angle will be sent to the terminal screen. If the angle 
drifts rapidly while the mounted gyro is motonless, you need 
to restart the software to acquire a new gyro bias measurement. 
Again, gyros are very sensitive and must be still while the bias 
is calculated. Once the gyro is running with little drift, 
rotate the mount 180 degrees and note the reported angle. If the 
angular units are set to tenths of a degree, the ideal reported 
angle is 1800. If set to milliradians, the ideal angle 1s 3142 
(Pi times a thousand). For every tenth of a percent that the 
angle is high, decrease the GYRO_CAL_FACTOR numerator by one.
Conversly, for every tenth of a percent low, increase the 
numerator by one. Repeat until you're satisfied with the 
accuracy.
The included project files were built with MPLAB version 6.60.
If your version of MPLAB complains about the project version, 
the best thing to do is just create a new project with MPLAB's 
project wizard. Include every file except: FRC_alltimers.lib 
and ifi_alltimers.lib and you should be able to build the code.
****************************************************************
Here's a description of the functions in gyro.c:
 
Initialize_Gyro()
This function initializes the gyro software. It should be called 
from user_routines.c/User_Initialization().
 
Get_Gyro_Rate()
This function returns the current angular rate of change in 
units of milliradians per second. If desired, the angular unit 
can be changed to tenths of a degree per second by modifying
the angular units #define entry in gyro.h
 
Get_Gyro_Angle()
This function returns the change in heading angle, in 
milliradians, since the software was initialized or 
Reset_Gyro_Angle() was called. If desired, the angular unit
can be changed to tenths of a degree by modifying the angular
units #define entry in gyro
 
Start_Gyro_Bias_Calc()
Stop_Gyro_Bias_Calc()
These functions start/stop a new gyro bias calculation. For best 
results, Start_Gyro_Bias_Calc() should be called about a second 
after the robot powers-up and while the robot is perfectly still 
with all vibration sources turned off (e.g., compressor). After
at least a second (longer is better), call Stop_Gyro_Bias_Calc()
to terminate the calibration. While a calibration is taking
place, gyro rate and angle are not updated. Once calibrated, a
call to Reset_Gyro_Angle() should take place.
 
Get_Gyro_Bias()
This function returns the current calculated gyro bias. For
extra precision, this software internally maintains a gyro bias
value that is the sum of GYRO_SAMPLES_PER_UPDATE samples of the 
gyro's analog output. By default, GYRO_SAMPLES_PER_UPDATE is
set to a value of eight in gyro.h
 
Set_Gyro_Bias()
This function can be called to manually set the gyro bias. For
extra precision, this software internally maintains a gyro bias
value that is the sum of GYRO_SAMPLES_PER_UPDATE samples of the 
gyro's analog output. By default, GYRO_SAMPLES_PER_UPDATE is
set to a value of eight in gyro.h
 
Reset_Gyro_Angle()
This function resets the integrated gyro heading angle to zero.
 
Disable_Gyro()
This function should be called when the gyro functionality is
no longer needed, thus reclaiming the time spent servicing the
timer 2 interrupts.
 
Initialize_ADC()
This function initializes the analog to digital conversion
hardware. This is called by Initialize_Gyro() above and 
shouldn't be called directly.
 
Initialize_Timer_2()
This function initializes and starts timer2. This is called by
Initialize_Gyro() above and shouldn't be called directly.
 
Timer_2_Int_Handler()
This function is automatically called when timer 2 causes an
interrupt and shouldn't be called directly.
 
****************************************************************
Seven things must be done before this software will work 
correctly on the FRC-RC:
1) The gyro's rate output is wired to analog input 1.
2) A #include statement for the gyro.h header file must be 
included at the beginning of each source file that calls the 
functions in this source file. The statement should look like 
this: #include "gyro.h".
3) Initialize_Gyro() must be called from user_routines.c/
User_Initialization().
4) The timer 2 interrupt handler, Timer_2_Int_Handler(), must
be installed in User_Routines_Fast.c/InterruptHandlerLow().
See the accompanying copy of User_Routines_Fast.c to see how
this is done.
5) You must select the gyro you're using from a list in gyro.h
and if needed, remove the // in front of it's #define.
6) A gyro bias calculation must take place using the functions 
Start_Gyro_Bias_Calc() & Stop_Gyro_Bias_Calc() described above.
This must be done several hundred milliseconds after the gyro 
powers-up and is allowed to stabilize.
7) For optimal performance, you'll need to calibrate the gyro 
scaling factor using the instructions above or those included
in gyro.h.	
 
Nine things must be done before this software will work 
correctly on the EDU-RC:
1) The gyro's rate output is wired to analog input 1.
2) IO1 must be configured as an "INPUT" in user_routines.c/
User_Initialization().
3) The call to Set_Number_of_Analog_Channels() must configure
at least one analog channel.
4) A #include statement for the gyro.h header file must be 
included at the beginning of each source file that calls the 
functions in this source file. The statement should look like 
this: #include "gyro.h".
5) Initialize_Gyro() must be called from user_routines.c/
User_Initialization().
6) The timer 2 interrupt handler, Timer_2_Int_Handler(), must
be installed in User_Routines_Fast.c/InterruptHandlerLow().
See the accompanying copy of User_Routines_Fast.c to see how
this is done.
7) You must select the gyro you're using from a list in gyro.h
and if needed, remove the // in front of it's #define.
8) A gyro bias calculation must take place using the functions 
Start_Gyro_Bias_Calc() & Stop_Gyro_Bias_Calc() described above.
This must be done several hundred milliseconds after the gyro 
powers-up and is allowed to stabilize.
9) For optimal performance, you'll need to calibrate the gyro 
scaling factor using the instructions above or those included
in gyro.h.
 
Kevin Watson
kevinw@jpl.nasa.gov

[Matt Krass]

Originally Posted by Jack Jones

...Added two pots to lift mechanism to determine position, reading them on Analog #2 & #3 - but don't see how that'd interfere with the gyro....

Pure speculation here, but I seem to remember something about the gyro code locking the analog inputs to channel 1 for speed or something like that, perhaps in adding the pots you've accidentally disabled the sampling code? I could be way off so I wouldn't take it with too much weight, but maybe Kevin or Mike could share some insight on this one?

[Jack Jones]

Originally Posted by Matt Krass

Pure speculation here, but I seem to remember something about the gyro code locking the analog inputs to channel 1 for speed or something like that, perhaps in adding the pots you've accidentally disabled the sampling code? I could be way off so I wouldn't take it with too much weight, but maybe Kevin or Mike could share some insight on this one?

Well, there is something going on there. With pots disconnected, Angle counts negative to -1200 in the time it takes the timer to count 5K. With pots hooked up, Angle counts positive to 283 in the same amount of time. In either case, rotating gyro had no effect on the outcome. Was going to launch autonomous with pots disconnected, but it started to rain. Driveway test site

Been through most of Kevin's notes & code, which my kids had made use of to begin with. Nothing struck me as out of place; except that Start_Gyro_Bias_Calc()
Stop_Gyro_Bias_Calc()
wasn't called. Will give that a go, but seems to me that it's just fine tuning, not a show stopper.

[Joe Ross]

Originally Posted by Jack Jones

Well, there is something going on there. With pots disconnected, Angle counts negative to -1200 in the time it takes the timer to count 5K. With pots hooked up, Angle counts positive to 283 in the same amount of time. In either case, rotating gyro had no effect on the outcome. Was going to launch autonomous with pots disconnected, but it started to rain. Driveway test site

You not only need to disconnect the pots, but you must remove the calls to Get_Analog_Value from your code.

See this thread for more discussion about this issue and a few ideas for combining the gyro code with other analog sensors: http://www.chiefdelphi.com/forums/sh...ad.php?t=34500

[Jack Jones]

Originally Posted by Joe Ross

You not only need to disconnect the pots, but you must remove the calls to Get_Analog_Value from your code.

See this thread for more discussion about this issue and a few ideas for combining the gyro code with other analog sensors: http://www.chiefdelphi.com/forums/sh...ad.php?t=34500

Thanks for the info guys! Tested with Get_Analog_Value calls commented out and gyro appeared to work. However, pots are there, in part to keep the racks (double-double rack & pinion lifts) from bottoming out hard and breaking the FP transmissions, and to let the operator put the boom into position with one button press. So, given the high risk. limited time, and low payoff (maybe? 3 pnts/match) in making them work together, we'll either make the wheel encoders do the job, or scrap automode till the next competition.

Thanks again, OAO
Jack

[Kevin Watson]

Originally Posted by Jack Jones

So, given the high risk. limited time, and low payoff (maybe? 3 pnts/match) in making them work together, we'll either make the wheel encoders do the job, or scrap automode till the next competition.

I've been working on some code that will allow you to use your gyro while also using other analog inputs. Let me know if you'd like to try it out.

-Kevin

[Jack Jones]

Originally Posted by Kevin Watson

I've been working on some code that will allow you to use your gyro while also using other analog inputs. Let me know if you'd like to try it out.

-Kevin

I really should have looked into the automode a few weeks ago, but the school's robot was on display and I couldn't get at it to remove the gyro. Silly me, I expected it to plug n play; now we're out of time and cool-dry weather to do much about it.

OTOH, I've learned just enough to be curious so I'll take you up on the offer after we get back from IRI.

Thanks,
Jack