[PSUBS-MAILIST] Speed controllers

[Sean T. Stevenson via Personal_Submersibles]

Part safety, part allowing for future upgrades. In my mind, if you let go of the controls, the vessel should stop, period. If you have an alarm, leak, fire or something else that demands your immediate attention, you don't want to waste precious time having to null the thruster output before dealing with the other problem. Having the stick(s) spring return to zero output when you let go is just prudent, so you (hopefully) don't crash into anything when you have to let go in an emergency, or when you drop your pencil on the floor and throw your back out when you bend over to retrieve it.  I would employ self nulling controls regardless of whether I was using direct or indirect control.

With the indirect scheme I proposed, there is an additional advantage to be gained in the presence of sensing mechanisms for vessel motion (surge, sway, heave, yaw, roll and pitch) such as the ubiquitous pressure transducer for depth, gyro/fluxgate compass for heading, or e.g. Doppler velocity log for over bottom motion. In these cases, a control loop provides the ability to null vessel motion, as opposed to simply nulling thruster output, so that if you let go of the controls, the system can automatically apply reverse thrust to cancel headway or compensate for slight currents etc. to keep the vessel where it was when you let go.

This is particularly useful in the case of vertical motion. I intend to implement such a depth controller so that I drive up / down with the stick, with full range on the stick corresponding to 100% thruster output, but when I let go, the current depth becomes the setpoint and the controller takes over, commanding the vertical thrusters as appropriate to maintain that depth. Furthermore, in the event that maintaining that depth then requires a sustained thruster output in either direction, the variable ballast system will automatically adjust in order to bring that necessary thruster output down to zero and thus conserve power.

Sean



On April 22, 2016 11:13:19 PM MDT, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Not quite following that Sean,why not have a joystick without return to
>center function &leave it on that setting? I can see the sense in
>running the joystick throughthe PLC with an over-ride on the vertical
>thrusters when on the depth limit,I have seen commercial psubs with
>this feature.Alan
>
>
>From: Sean T. Stevenson via Personal_Submersibles
><personal_submersibles at psubs.org>
>To: Personal Submersibles General Discussion
><personal_submersibles at psubs.org> 
> Sent: Saturday, April 23, 2016 4:31 PM
> Subject: Re: [PSUBS-MAILIST] Speed controllers
>   
>Late to this thread, but I'll throw in my $0.02:I had envisioned a
>control scheme whereby the joystick inputs are decoupled from direct
>thruster / ballast control output. Instead, the PAC runs the thruster
>outputs on the basis of PID control loops, where the setpoints are
>adjusted by the pilot controls. Thus, the ramp rate of the target
>setpoint is dependent on how far e.g. the joystick is pushed or
>rotated, but on letting go, the stick springs back to center, and at
>that point the setpoint is overwritten with the current depth, heading
>or what have you, and the system automatically maintains that setting
>until you touch the controls again.  Manually commanded fully
>automatic.Sean
>
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