<html><head></head><body><p dir="ltr">Your point about manual backups is spot on. As things get more complex, the failure probability increases unless specifically designed to provide component, system and/or mission failure redundancy. I'm not going quite that far (not designing the space shuttle), but will have manual overrides and backups - often low tech - in place for all critical functions. You have to be able to get yourself home assuming a complete loss of power, loss of lighting / visibility, etc. Being able to bypass computer control and go to direct proportional control wouldn't be a bad idea if only the controller had failed.</p>
<p dir="ltr">Sean</p>
<br><br><div class="gmail_quote">On April 23, 2016 9:21:11 AM MDT, Alec Smyth via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div dir="ltr">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. <div><br /></div><div>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.</div><div><br /></div><div><br /></div><div>Best,</div><div><br />Alec</div><div><div><br /></div><div> </div></div></div><div class="gmail_extra"><br /><div class="gmail_quote">On Sat, Apr 23, 2016 at 9:00 AM, Sean T. Stevenson
via Personal_Submersibles <span dir="ltr"><<a href="mailto:personal_submersibles@psubs.org" target="_blank">personal_submersibles@psubs.org</a>></span> wrote:<br /><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><p dir="ltr">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.</p>
<p dir="ltr">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.</p>
<p dir="ltr">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.</p>
<p dir="ltr">Sean</p>
<br /><br /><div class="gmail_quote"><span class="">On April 22, 2016 11:13:19 PM MDT, Alan James via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org" target="_blank">personal_submersibles@psubs.org</a>> wrote:</span><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div style="color:#000;background-color:#fff;font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px"><span class=""><div><span>Not quite following that Sean,</span></div><div dir="ltr"><span>why not have a joystick without return to center function &</span></div><div dir="ltr"><span>leave it on that setting? I can see the sense in running the joystick through</span></div><div dir="ltr"><span>the PLC with an over-ride on the vertical thrusters when on the depth limit,</span></div><div dir="ltr"><span>I have seen commercial psubs with this feature.</span></div><div dir="ltr"><span>Alan</span></div><div dir="ltr"><span></span><br /></div><div><br /><br /></div></span><div style="display:block"> <div style="font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px"> <div style="font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px"> <div dir="ltr"> <font
face="Arial" size="2"> </font><hr size="1" /><font face="Arial" size="2"> <b><span style="font-weight:bold">From:</span></b> Sean T. St!
evenson
via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org" target="_blank">personal_submersibles@psubs.org</a>><span class=""><br /> <b><span style="font-weight:bold">To:</span></b> Personal Submersibles General Discussion <<a href="mailto:personal_submersibles@psubs.org" target="_blank">personal_submersibles@psubs.org</a>> <br /> <b><span style="font-weight:bold">Sent:</span></b> Saturday, April 23, 2016 4:31 PM<br /> <b><span style="font-weight:bold">Subject:</span></b> Re: [PSUBS-MAILIST] Speed controllers<br /> </span></font> </div><span class=""> <div><br /><div><div dir="ltr">Late to this thread, but I'll throw in my $0.02:</div>
<div dir="ltr">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.</div>
<div dir="ltr">Sean<br />
</div>
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