[WIP] Collision Prevention Update #3364
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… Acceleration based cp
| @@ -26,7 +26,7 @@ Multiple sensors can be used to get information about, and prevent collisions wi | |||
| If multiple sources supply data for the _same_ orientation, the system uses the data that reports the smallest distance to an object. | |||
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| The vehicle restricts the maximum velocity in order to slow down as it gets closer to obstacles, and will stop movement when it reaches the minimum allowed separation. | |||
| The vehicle restricts the current velocity in order to slow down as it gets closer to obstacles and adapts the acceleration setpoint in order to disallow collision trajectories. | |||
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The first bit makes sense to me - you're approaching a wall, so the vehicle reduces the velocity such that you stop before you hit it.
FMI, what does "adapts the accel. setpoint to disallow collision trajectories" mean?
Assume I'm heading towards a wall at a 45 degree angle, does this mean? I.e. I'm guessing it might mean that the setpoint is adjusted such that you curve into the wall and then move alongside it. Some images showing the behaviour might be nice.
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Also youtube the video to the PX4 account and include that in the docs too
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yea, some figures might actually help, but for that i first need feedback on my PR from Mathias, as its not yet set in stone how the compensation works.
Regarding "adapts the accel. setpoint to disallow collision trajectories", see comment below.
| @@ -57,13 +57,14 @@ If so, the vehicle velocity is restricted. | |||
| This velocity restriction takes into account both the inner velocity loop tuned by [MPC_XY_P](../advanced_config/parameter_reference.md#MPC_XY_P), as well as the [jerk-optimal velocity controller](../config_mc/mc_jerk_limited_type_trajectory.md) via [MPC_JERK_MAX](../advanced_config/parameter_reference.md#MPC_JERK_MAX) and [MPC_ACC_HOR](../advanced_config/parameter_reference.md#MPC_ACC_HOR). | |||
| The velocity is restricted such that the vehicle will stop in time to maintain the distance specified in [CP_DIST](#CP_DIST). | |||
| The range of the sensors for each sector is also taken into account, limiting the velocity via the same mechanism. | |||
| the restricted velocity is then transformed into an acceleration with [MPC_XY_VEL_P_ACC](../advanced_config/parameter_reference.md#MPC_XY_VEL_P_ACC). | |||
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FWIW as above, I don't really understand what this means. I think that perhaps we're always controlling the acceleration setpoint, so for our controller, so what this says is that we've worked out what our restricted velocity is supposed to be, and this converts it to the value that we need for our accel. setpoint?
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| the restricted velocity is then transformed into an acceleration with [MPC_XY_VEL_P_ACC](../advanced_config/parameter_reference.md#MPC_XY_VEL_P_ACC). | |
| The restricted velocity is then transformed into an acceleration with [MPC_XY_VEL_P_ACC](../advanced_config/parameter_reference.md#MPC_XY_VEL_P_ACC). |
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Yea, its a bit complicated. which is also why the rewrite has not been done before.
we have our velocity and acceleration setpoint coming from the operator. and the problem is that they can point into different directions. so we need to compensate the current velocity if its heading into an obstacle, and restrict the acceleration setpoint from the operator.
the current approach worked fine with velocities. which is why i take the constrained velocity with the old approach, subtract the current velocity to get a velocity error, and just add the proportional gain of the acceleration controller (the input to whom is an velocity error). you can kind of think of the gain as something which modifies the units, input is [m/s] output is [m/s²]. (in an abstract sense)
and for the setpoint of the operator, i just scale it in regard of the distance to the minimum distance. the closer the vehicle is to the minimum distance, the more the normal component gets scaled to zero.
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Looks good, though I have some questions.
As a post process I think perhaps we should also restructure this a little to "deprioritise" the companion side option, as it is untested. |
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hamishwillee
changed the title
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No flaws found |
adapted the collision prevention documentation to reflect the move to Acceleration based collision prevention
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