Energy requirements for robot lost at sea

Given another 40 years of development of weather modelling and forecasting, an 'unexpected' severe tropical storm would stretch plausibility for me. But perhaps the container ship has lost communication through other factors? Or climate has become more unstable and harder to predict by then?

 

Thank you everyone for the helpful replies and direction. Here's a document that provides an overview of the robot, with calculations near the end, and a revised edition of the 3D model. I had mentioned that the robot would be shaped like a submarine, not like a box, but I guess posting a draft of the 3D model that was intended to guide the 3D artist caused some confusion. Sorry about that. I've corrected the model to be more submarine-shaped.

Automaton Overview

Somehow I overlooked needing four motors in my calculations. I haven't updated those particular calculations, yet. I calculated the buoyancy, and you all were right: it would have sunk. I've halved the motor's battery pack.

Here's an updated render, with an interior door for scale (keep in mind, it's a draft; arms aren't shown, the eyestalk can telescope into the body, the rotator for wheels aren't streamlined yet, etc.):

Correct. In the story, the ship leaves port a month or so before storm season begins, but a storm came "unseasonably early" anyway.

Interesting. I've made some modifications and recalculated the timing (see below). Your six days seemed to be pretty spot on. With the modifications and accounting for the current, I think it's now three days. In either case, it seems like there's plenty of time to make it ashore before there's not enough power anymore.

The robot wouldn't count on it; solar is a backup power source.

Good point. In my original design (version 1.0 in the PDF) the wheels doubled as propellers. I'm not sure why I thought paddle wheels would be a good idea. Version 2.0 iterates on the design and reinstates the propellers into the wheel.

I've extended the hull length to 3.0 m to boost it to around 4.2 knots, which is about 10 days of swimming time.

What current flow? Could the robot hitch a ride on the Pacific Equatorial Countercurrent, which goes directly to South America, narrowly avoiding the Peru Current? Would that mean not having to fight a current, but gain 2.9 knots for a total of 7.1 knots and swimming time of about 3 days?

I appreciate you taking time to respond. Please leave judgment statements at the door, though, they're neither helpful nor necessary.

 

I will do even better and say goodbye. Good luck to robot V 3.0, V 2.0 can't go anywhere.

 

I have to agree with Rumars. The pictured robot, as pictured, will not be travelling in the sea, much, or well.

It will need to have some ability to transform to a shape that is boat-like, and has some type of propulsion that would work.

The shape you propose looks like a shop vac. It is an objective comment.

If you come here for advice; try to avoid being offended. Rumars is a genuine and objective poster on this forum. Consider harsh critique as a positive; it may ultimately save the book from being preposterous.

 

The slower you go on electric propulsion the longer the range.

The longer the robot is in the ocean, it will have things growing on it, which will slow it down. I even had to dive over the boat mid-ocean to clean.

18 knots is very fast and even in 2063 would be a poor use of energy. Better 4-6 knots and the range will be 10 fold increase. Next, in favorable currents the "brain" can sleep allowing it to run indefinably given small solar area.

 

Obviously the wheels are hinged on 2 axes so they can rotate out, allowing the robot to travel 4 knots using 600 watts. It can maintain 3 knots in direct sun. They have low rpm turbines but they should have fewer blades to improve efficiency.

He claims a 1 ton battery with 2.2 megawatt hours not sure its possible even in 2063, but would give a 14,000-22,000 mile range at 3 and 4 knots. With intelligence, it could vary output allowing swell energy to be utilized (by speeding up at the right time to catch and surf waves at sea)

 

Apologies. I did not realize the wheels turned 90 degrees.

The aft engines are also in the flow of the forward engines; so from a technical perspective; the aft propulsion will not work well.

Maybe the rendering of the robot in water would be helpful.

 

On the positive side, Probably any shape or calculations will be accepted by the reading public, looking for entertainment, the huge majority of which have no science or engineering training or interest, maybe even revulsion of such, in this day and age.. (Lots of challenges / issues for legitimate hard science acceptance by the public; for example -claims that the age of the universe is less than 12k current calendar years, rejecting the "alternate" facts provided by science, etc)

I think of the hugely successful television series "Star Trek" and the exploration vehicle which was used named the "Enterprise". Although it had an attractive and cool looking design shape for some viewers, there were probably a lot of practical and Engineering flaws associated with it. Just one example was that there were no compatible Provisions in the pictured design for the artificial gravity required on the ship - needed for just about every episode, ha! I would suppose that a constantly rotating wheel construction would be required for Gravity effects- instead of a saucer -pontoon shape, and a few other science fiction outer space movies did incorporate that kind of wheel, which is a more realistic possibility?

 

Even with streamlining, the drag of the wheels is likely to be the largest component of drag. Would you consider having the wheels be feet you put on legs, like this?

Then those legs and wheels could retract into recesses in the body, except for the wheel(s) whose spokes you use as a propeller. For relative simplicity, I would go for two wheels on retractable legs in the rear, and a single wheel with propeller blade spokes in the front, though your robot might discover unpleasantly exciting aerodynamics when on the road at speed, unless those spokes can rotate to an angle that makes them not work as a propeller.

For a more futuristic look, there is the options of two wheels, the hip joints of those legs in the centre of the body, giving you T. rex proportions (well, also chicken proportions, but T. rex sounds better). Then if the propeller spokes in the two wheels are mirror images, their effects would tend to cancel when on the road. And the legs and can either retract so that they only let your propeller wheels stick out when the robot is in the water, or, depending on how you design the arms, you might also use them for propulsion, in a variety of ways, from paddles like the feet of waterfowl to flapping wings like those of a penguin. Then you could let the robot retract legs and wheels completely. I think that would cut drag by at least 80% compared to what you have drawn at the moment.

 

Yes, the wheels would cause drag. Would the amount of drag stop the machine from reaching shore before its batteries deplete?

Here's a depiction with two wheels swung around the rotator and one wheel turned 90 degrees:

Being able to swivel the wheel should take care of that?

The automaton is predominately ground-based.

 

I am thoroughly confused.

I assumed, after Sean D comment, the wheels swung out.

finger drawing in a Tesla, bumpy as hell.

 

Perhaps you could lighten the craft by substituting super-capacitors for batteries. That technology may be much more refined by the time your story takes place.

 

Your cross section is 0.8m * 0.5 = o.4m^2. Assuming a drag coefficient of 0.4, which seems reasonable seeing that this rounded stern will leave a turbulent wake, the body alone would have 0.16 times the drag of a 1m^2 flat plate, assuming full immersion. At the surface, wave making resistance could actually increase that.

Your wheels look to have a diameter of about 1.2m, and about 0.2m wide. Assuming the same drag as a flat plate for the two wheels in their default orientation, with the plane of rotation parallel to the flow, seems reasonable on the grounds that even though the wheel is rounded, the water flows around the front half of the wheel, then needs to flow around the rear half. Assuming each wheel is three quarters immersed, that gives us two wheels with a cross section of 0.9m * 0.2m = 0.18m^2, for a total of 0.36m^2, and a drag 0.36 times that of a 1m^2 flat plate.

Then there is the question of which of the other two wheels is in the water. You show the wheel that is in line with the body underneath, but then you would need the Voith-Schneider propeller that I suggested, and that is not what you have drawn. So I assume the wheel that should be in the water is the one sticking out above. Rim and tyre together look to be about 0.15m thick. Let's say you get that thickness down to 0.08m, and you give rim and tyre a teardrop cross section that has a drag coefficient of 0.3. With the outside having the tyre treads, I doubt you can do better. Then the area of the rim and tyre is ((0.6m)^2-(0.52m)^2)*pi = 0.0896m^2. Multiply that by the drag coefficient of 0.3 to get the drag of the rim and tyre, which then is that of an 0.0288m^2 flat plate. Add the drag of the hub, which has a cross section of about (0.08m)^2*pi = 0.02m^2. The hub is not streamlined at all. I am ignoring the flat blue plate parallel to the plane of rotation, which would add extra drag. Then the total drag of three tyres is that of flat plates with areas 0.18m^2 + 0.18m^2 + 0.0288m^2 + 0.02m^2 = 0.407m^2, which is 2.54 times as much as the body alone, under the most optimistic assumptions. Tyres and body would have 3.54 times as much drag as the body alone, a bit better than my previous intuitive estimate (I did not realise one wheel would be out of the water). I have not added the drag of the structure that holds the wheel. I have also neglected any drag from the propeller blades. And I neglect any drag from having the two passive wheels sticking out of the same side, which needs to be compensated for by vectoring the thrust of the drive wheel to compensate, which would make the whole thing travel through the water at a small angle to the longitudinal.

Go back to the energy requirements, multiply them by 3.5, then decide whether that is a problem. If not, the configuration you have drawn is fine.

The configuration with wheels entirely hidden away would have only the drag of the body (plus the drag of the penguin wings, but then, the drag of the propeller blades is not included in the above calculation either).

If you used two wheels of half the size, each acting as a propeller, you would have the equivalent of 0.16m^2 for the body, 0.0144m^2 for the two rims, and 0.04m^2 for the two hubs (I assume those would have to remain the same size), for a total of 0.2144m^2 equivalent flat plate area.

 

That's a great idea. I couldn't find any Moore's Law-like projections for supercapacitors. Earlier this year, lithium-air was touted to reach 1200 Wh/Kg (source and source) and has a theoretical maximum of 3623 Wh/Kg (source).

By 2064, it's not a stretch to imagine an energy storage medium having an energy density of 1890 Wh/Kg (540 * 3.5), be it from supercapacitors, lithium-air, a hybrid, or other technology (e.g., superconductors). I don't see a problem there.

I opted for a toroidal propeller, imagining it in the same efficiency ballpark as the V-S.

Probably neither. I imagined the entire machine being submerged for most of the travel, so that there would be at least two propellers working to move the hull. In any case, you've given me a thorough and amazing answer, Robert: Yes, it'd be able to reach shore, give or take some tweaking to battery life or reducing some of the dragging elements. Thank you!

I've added the axial flux motors, shrunk the panels behind the hub, and thrown on some arms and hands. Note that in the final form, the arms and hands will likely lay flat inset flush with the body and covered with a hatch curved to match the submarine contours (to avoid adding drag).

 

The solution is simple:

1. Make it run on the bottom. It doesn't need to swim.

2. Because solar power is unavailable at the bottom of the sea, assume nuclear power (fission or fusion) rather than solar.

It must be extremely sturdy - perhaps as yet undiscovered materials - so it isn't crushed by pressure.

Even hard science fiction can assume engineering capabilities that exceed current capabilities - e.g., Larry Niven's Ringworld assumed a rather strong material too.