How do modern open source autopilots compare to aerospace-grade IMUs?

I noticed that Digikey is now selling Honeywell's newest aerospace-grade IMUs, which cost $1,328 each (note that's just for the IMU; it's not a full autopilot). How do the specs of these aerospace IMUs compare to those we use here? Are they worth the extra money? 

In terms of overall approach, the Honeywell IMU seem very similar to modern autopilots such as Pixhawk 2.x and 3.3: they both have MEMS sensors with internal environmental isolation and temperature compensation.

As for the sensors themselves, I'm no expert on specs, so I'll just post the basics here, comparing the Honeywell sensor to the Pixhawk 3

On the face of it, the Invensense and ST sensors in the Pixhawk 3 appear at least as good, if not better. But I imagine that there are some other factors that may be more important, such as gyro drift and vibration filtering. The Honeywell specs in drift are shown here: 

Meanwhile the Invensense ICM-20602 sensor in the Pixhawk 3 gives its drift in different units: ±4mdps/√Hz. I really don't know how to compare those.

Finally, I'm sure that a lot of the performance depends on the software running on the Pixhawk boards, be it PX4 or APM, both of which use GPS to augment the raw IMU data to compensate for drift, along with a lot of other smart filtering. 

So for those IMU experts out there: how do you think these two approaches compare? Are aerospace-grade IMUs worth the extra money?

Views: 3928


100KM
Comment by DavidJames on June 27, 2017 at 7:48pm

I logged some data from a Pixhawk 1 and found that the rate noise is close to the the 0.005 deg/sec/root(Hz), single sided level in MPU6000 spec.   A little higher than the spec., but I was bumping the desk at bit when I logged the data and it was connected to noisy USB power.     I'll try to do better next time.  :-)

Here is a link to the flash bin file.

https://cp.sync.com/dl/e7a323cc0#zjzzj4pc-k3r7smth-ek7w2sqi-fj92hh9v

It turns out that the GYR1 data is 1000Hz data but it is scaled in radians per second.

Comment by Anthonie Michael Muller on June 28, 2017 at 7:14am
@DavidJames That's how it's done :) could you do the same test with telemetry connected, servos moving and power from a single lipo? (from my measurements those 2 components generate the most noise)

100KM
Comment by DavidJames on June 28, 2017 at 2:57pm

@Anthonie That is the plan.   I was going to compare the Pixhawk1 with the APM2.6. I may be able to compare the Pixhawk2 on the solo too.    I am actually expecting things to be better on the battery.  USB power is pretty noisy compared to a battery, but you are right all the other stuff will contribute.

I have been trying to master controlling the flash logging process.   Do you know when flash logging is enabled and disabled and when the flash log is written with the fixed wing APM?

Comment by Anthonie Michael Muller on June 29, 2017 at 11:14am
Let me know where I can help, have access to lab psu, ossiloscope, apm2 and apm 1.4 (good for testing, learnt allot trying to diagnose baro drift) maybe PM from here?

100KM
Comment by DavidJames on July 1, 2017 at 3:16pm

I managed to get a 3DR Solo with the Pixhawk 2 logging high data rate gyro data.    The GYR1 data is logged at 1000Hz.   It looks like the Pixhawk 2 has a low noise setup and gets full performance out of the MPU6000.   Here is the MPU6000 root PSD from the Solo data:

So the Pixhawk 2 with the MPU6000 on the separate IMU board gets to the spec 0.005 deg/sec/root(Hz).   Angle Random Walk is then:

0.005 *60/root(2) = 0.212 deg/root(hr), which is nearly 3 times better than the best HG1120.   :-)

Comment

You need to be a member of DIY Drones to add comments!

Join DIY Drones

Groups

Season Two of the Trust Time Trial (T3) Contest 
A list of all T3 contests is here. The current round, the Vertical Horizontal one, is here

© 2017   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service