Re: [PlayerStage-Gazebo] Get acceleration

[Luca R. <luc...@ho...>]

Hi Peter,
I'm facing the same problem with getting acceleration from gazebo and i'm
using a flying robot.
Do you think it could be possible to have your code (i mean the imu
interface and the gazebo files you modified)? I need to solve this problem
and a "starting point" would be of great help! 
(Obviously i'll share with you my solution when i'll come to one :) 
Thanks in advance.

Luca


Peter Nordin-2 wrote:
> 
> Hello
> 
> Unfortunately I do not think that I can help you, but I am having a 
> similar problem.
> 
> I am have been trying to use the IMU sensor, (I have added a few missing 
> player interface related files), but in my case the acceleration is 
> allways zero. Anyway I was not able to figure out why so I made some 
> minor additions to the gazebo code and differentiated the linear 
> velocity between each timestep. This way the reported acceleration will 
> be the actual velocity derivative. The problem is that I wont get 
> g=-9.81 in my output. This is OK in my ground robot case as I usually 
> just remove the gravity component anyway. For flying robots I do not not 
> know if this is Ok.
> 
> I tried adding an additional "artificial" gravity vector (rotated into 
> the curent body coordinate system) but realised that when the robot was 
> moving along the Z-axis (very rarely), I would get double acceleration. 
> -9.81 as well as the actual velocity derivative (-9.81 when free 
> falling). I the end I removed the artificial gravity vector, as I actual 
> have no real use for it.
> 
> It is probably possible to solve this in some smart way but I have not 
> had time to try and figure one out.
> 
> I am using a fairly recent Gazebo svn version and player 3.0.2
> 
> /Peter
> 
> 
> On 03/28/2011 05:26 PM, Neostek wrote:
>> Hello everyone,
>> i'm using Gazebo to simulate a PD controller on a quadrotor UAV.
>> The control evalueates the force and torque to apply to the quadrotor and
>> then i use the methods
>> dBodyAddRelForce(body_id, 0, 0, thrust) and dBodyAddRelTorque(body_id,
>> roll_torque, pitch_torque, 0).
>> Now i would like to get information about position, velocity and
>> acceleration of the quadrotor.
>> To do so, i use the methods:
>> body->GetPosition()
>> body->GetLinearVel()
>> body->GetLinearAccel()
>> and the last one appears to give practically nonsense results (gravity
>> acceleration depending on the mass for instance...).
>> Browsing into the code i found out that GetLinearAccel() simply does
>> return this->GetForce() /  this->GetMass();
>> That is " F = m*a "  as it should be.
>> Anyway the controller works and the quadrotor get still on the target
>> point,
>> but the acceleration i get on the z axis is positive (e.g. = 19.6) even
>> though the quadrotor is not varying its height.
>> I really have no point...please help me! :)
>> Thanks in advance.
>>
>> Marco
>>
>>
>> For the sake of completeness i'm using the following software version:
>> Gazebo - 0.9.0
>> Player - 2.1.3
> 
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