Airsim: ClockSpeed setting has no effect

Created on 5 Dec 2017 · 13Comments · Source: microsoft/AirSim

I've attempted to set the ClockSpeed setting in settings.json as explained in the docs, but this seems to not have any effect on the actual speed of the simulation. It is correctly read by AirSim, as evidenced by the on-screen output after startup. Regardless of the value I set, the drone is still flying at the same velocity. I would have assumed that with ClockSpeed: 3.0, a velocity command should result in the drone appearing to fly 3 times faster compared to real-time. Is this wrong?

Thanks!

Source

valtsblukis

Most helpful comment

Just fixed this issue. On a powerful desktop, I can run quadcopter simulation now at 100X clock speed!

Related: #901

Could you share the specs of the desktop?

tvturnhout on 9 Oct 2018

👍3

All 13 comments

Currently clock speed applies to only car physics. There is all internal infrastructure to apply to drones as well but that part hasn't been implemented and tested yet.

sytelus on 6 Dec 2017

I see. I wouldn't mind giving the implementation a go, if it's not terribly complicated, because I really need this for my project. Could you point me in the right direction? Any prior commits to refer to, or which files to modify? Thanks!

valtsblukis on 6 Dec 2017

I have added the change. It turned out to be pretty simple (please see above commit).

However you would probably want to know some pro and cons. When you increase the clock speed, you are in essence telling physics engine to use longer periods to compute new physics state. This means as you speed up the clock, the quality of physics simulation reduces and things starts diverging fast. This is especially impactful for drones (than cars) because drones require high frequency stabilization loop. So as you speed up the clock, drone would become more unstable.

sytelus on 6 Dec 2017

Thanks a lot, Shital! I appreciate your help and I understand the implications. My hardware allows me to increase the physics rate a bit, so I have some room to play with the clock rate.

valtsblukis on 6 Dec 2017

Just reporting my results. I managed to successfully set ClockSpeed: 10 and fly the drone just fine at a control rate of 5Hz (effectively 50Hz). The traced out trajectories are slightly different than at ClockSpeed: 1, but still very good.

To do this, I first increased the physics rate 30 times to 0.1ms / 10'000Hz. At this point the drone was still unstable if ClockSpeed > 3.0, which seemed strange. I found that PidController uses the wall clock to get the time delta, but if ClockSpeed != 1, then wall clock is inconsistent with the physics. This was causing the PidController to overcorrect and become unstable. So I multiplied the dt by ClockSpeed inside the PidController (patch attached) and now the drone is stable at any ClockSpeed < 30.

Finally, I had to make sure that the unreal FPS is higher than the rate at which I'm requesting camera images, and I also set the AutoExposureSpeed to 1, otherwise the images were too bright.

0001-Modified-PidController-to-take-into-account-ClockSpe.patch.txt

valtsblukis on 6 Dec 2017

👍2

@valtsblukis, did you modify the SimModeWorldBase.cpp ( getPhysicsLoopPeriod() ) to increase the physics rate?

cangokalp on 21 Dec 2017

@valtsblukis, I got some issues to speedup ClockSpeed. I followed your steps but still not working.
When the ClockSpeed <2, it is okay. When the ClockSpeed >=2, the drone is unstable. Even more, when ClockSpeed >=3, the drone hit into ground right after it take off.
However, i wish to speedup for a least 5 times.
Are these issues because of my computation power? I'm running on a PC (CPU: intel i7-7700 @3.6GHz, RAM:16G, GPU: GTX1070)
Have any advises for me to speedup my simulation?

Thanks!

Xking8 on 10 Jan 2018

@valtsblukis can you send a pull request?

cangokalp on 8 Feb 2018

👍3

@sytelus Is there some advance regarding drone speed up stability?

guillemhub on 2 Apr 2018

👍3

I too would really appreciate an update on this problem of instability caused by ClockSpeed > 1.0 in Documents\Settings.json. Or at least maybe a detailled explanation on how I can fix it myself.

Thanks in advance, would really help me out