[PSUBS-MAILIST] Speed controllers

Sat Apr 23 11:21:11 EDT 2016

That's an interesting concept and has merit, but the question for me is
whether the need is important enough to justify additional complexity. I'm
trying to follow a very deliberate philosophy of extreme simplicity. The
idea is for Shackleton to be shipped around the world to interesting spots,
and because I'll be far from my workshop or supplies, absolutely everything
has to be simple, field replaceable, and with spares on hand. So for
example, I really like the environment monitoring package Jon's been
developing. Originally I was doing something similar, and the sub had a
touchscreen and everything controlled by a PLC. I still have a box full of
all the necessary parts, the ladder logic program I wrote for it, etc. It
was done, but I removed it because diving Snoopy changed my mind about the
feature/complexity balance. Which is not to say in the future I would never
ad any automation back in, particularly since I have all the stuff on a
shelf. It's just that if I ever do it would probably be as a redundant
ad-on, so that the boat could continue operating if the automation fails.
The other option is to build simple redundancy into the design. Whatever my
electronic controls and speed controllers end up as, they are going to have
a manual bypass that relies on nothing but switches. I was interested to
see the Triton subs do that as well, they have a PLC but also a switch
labeled "bypass" that turns the whole lot off and returns things to manual
control.

As an example of the feature/complexity balance, consider the compass. I've
got an off the shelf liquid-filled compass mounted outside a viewport,
that's it. In my box of automation parts I have a fluxgate compass with a
remote sensor that would go outside the hull. There are also way cooler
three-axis sensors available, like Cliff uses. But if I went the automation
route I would have failure points in the sensor, the cabling, the
through-hull, the PLC, the display, and the power supply. I'd need spares
on hand for all of those. My objective is to know my heading, but I can't
say I have any critical need for roll and pitch, for an autopilot, for
course-deviation alarms, or whatever else I could implement taking the
automation route. Don't get me wrong, they would be great fun to implement
and I encourage it! It's just that the simple solution has more utility for
the intended use of my boat. Shackleton's hull is currently being painted,
and it took only three hours working alone to take the entire boat apart
down to the bare pressure hull for sandblasting. If I went the automation
route, much as I'd enjoy it, I'm pretty sure that would not be possible.

Best,

Alec

On Sat, Apr 23, 2016 at 9:00 AM, Sean T. Stevenson via
Personal_Submersibles <personal_submersibles at psubs.org> wrote:

> 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
>> through
>> the 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. St! evenson 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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>>
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