# Trampoline testing and virtual reality

With a little thought, I have a better idea of what’s required from the trampoline. Consider the following:

Height, Speed, and Acceleration

The top ‘picture’ shows flight – plotting height over time. The quad sits on the ground, then rises at fixed speed for a bit, hovers for a bit, descends for a bit. and sits back on the ground again – this is the external set of targets for the quad – what the human wants it to do.

The middle ‘picture’ shows the same, but plotting vertical speed over time. The sitting quad starts with 0 speed; a pulse of linear speed integrates over time to produce the sloped rise in height in the first picture. Descent is clearly the opposite. This is what the outer PID does – it takes the target set by the first picture to produce and output to achieve the desired vertical speed

The final ‘picture’ shows the same but from the acceleration point of view. Violent spikes of power are applied to the drone to change it speed as per picture two; momentum maintains that power to change it’s height as per picture one. This is what the inner PID does – it takes the output of the output PID as it’s target acceleration, and combined that with the gyro inputs to control the acceleration.

OK, in the real world, all the sharp corners will be rounded or wobbly depending on how well the PIDs are tuned. But the sharp diagrams provide excellent PID ‘targets’ for simulation – and that’s the next direction I’m going: using these targets, and some basic math(s) and a spreadsheet, it should be possible to tune the PID in simulation alone except for one missing link, and that’s where the trampoline steps in: I need a mapping between the blade PWM inputs, and the net acceleration that produces. That simply means that I do several runs at various PWM inputs, and use the accelerometer to measure the resultant acceleration.

Don’t think I’ll need it, but the drone currently weighs 1509g (1.5kg) currently:

Drone weight

That’s with the new case and corresponding diet Model A RPi, micro-USB adapter, carbon legs and the golf ball feet!

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