School Project Requires Creative Solutions

It sounds like an ideal application for a Stirling engine

engine.https://en.wikipedia.org/wiki/Stirling_engine

http://brassgoggles.co.uk/forum/index.php/topic,18050.0.html

Very unlikely that you can generate enough force from rising flue gases to turn much of anything, let alone a chicken on a spit. Figure out the differential pressure between the ambient air and the flue gases and calculate the volume of flue gas you will need to exert your desired force. A hot air balloon should give you an idea of the relative volumes needed.

Have you quantified the forces necessary to turn a chicken on a spit yet? This is how you start to define your requirements. Be sure to do the systems engineering and lay out all your requirements and constraints.

Not that your idea is a bad one but if I were doing it, I would look at how you can use a "steam engine" that would take it's energy from the heat of the grill. You can also investigate thermopiles to see if you can make something work there. Also research Stirling engine.

Good luck with your quest. This is why we call it an "education".

Thanks. Semantics again.

I think a spring driven motor, as in an old phonograph, may bear consideration.

This was suggested earlier.

I like the idea of a hot-air balloon. You could tether it on a long string wrapped round a drum on the axle of the spit/rotisserie. When you release the balloon the spit goes round. The rate of rise of the balloon is limited by a governor which is actually a fan blowing air through the barbecue to ensure good burning.

If the goal of the project is to " make life better/easier" then I suggest multiple Hamster wheels connected to a gear box that drives the turning mechanism. This is a two fold winning approach.

1. It is innovative, at least never before done.

2. Hamsters are fairly ubiquitous and cheap. Get some and they will breed rapidly to produce replacement power sources.

3. Once the power source is depleted(dead) it can be cooked on the Bar-B-Q and eaten.

If this sounds silly, think about how silly a steam engine sounds.

Your first goal should be to select a feasible project.

Back to the drawing board.

While it may not have been done with hamsters, it was often done with small dogs.

There was even a breed of dogs developed specifically for the purpose.

Wow, who would have ever thought.

I recon that it would take 12 hamsterpower to equal one dogpower.

Quite. They've had (long disused) dogspits in a couple of old pubs I've visited. They've stiĺl had the fire and done roasts on the spit, but the treadmill's been disconnected and the spit was turned by an electric motor .

Two ideas come to my mind right away: a spring-drive mechanism, like in an old fashioned wind-up watch , that can be rewound as needed. The second is a weight-drive mechanism, like a grandfather clock, which also can be reset as needed.

But these are MY ideas, so you're not allowed to use them.

I agree with the spring driven device but you have to keep it wound. So my suggestion is design an added shelf with a special device that attaches to a can of beer. Now that device is attached by a string that when pulled, winds the spring. Obviously the spring will be wound at regular intervals keeping the rotisserie going as long as needed. Done.

The more 'Geewiz' technology, the more expensive...To keep something affordable and practical you need to stick with the KISS principle...There are plenty of battery powered rotisseries on the market....you could add a solar charger....15 watt motor can handle 25lbs according to the manufacturer...The rotisserie needs to be stainless touching any food surface....

http://spitjack.com/category/ROTISSERIES.html

Charge controller...

If you want to throw reason and practicality out the window, and you have nothing but time on your hands, and deep pockets, you could go with an organic rankine cycle device...

It doesn't seem very "innovative" when I can do a search for "Cordless Rotisserie" and get a bunch of hits.

But, has it ever been done with Hamsters?

Lots of things done with hamsters, but . . .

You should see the engine room on Holland America Lines' Hamsterdam.

Who shovels it out?

The same sort of guys that used to be called "stokers"; just shoveling out rather than in.

I have to admit that being able to eat the "power supply" when you are done with it is quite innovative!

A spinning marshmallow on a stick could be what you need.

It may sound like novelties, but it's simple.. Low cost and could be driven by a small fan.

I know there's market because I've seen a lot of people that couldn't roast one if their hamies life depeneded on it! ��

Once you have defined the required power to turn the spit, then you can look at what technologies will fit the application.

Since you are talking about a barbecue grill, the difference in temperature between the bottom of the pan and the ambient air suggests using a TEG.

Good luck!

Have a look at "Hero's Aeolipile" for some inspiration. The heat from the cooking creates steam and the direted outlets create movement.

You would need some gearing.

CAUTION: Since you say you are in year six, I'll state what will be obvious to others here. The steam device must NEVER be sealed.

A more complicated device could be based on the "Ctesibian Pump" connected to the rotisserie shaft.

I am suggesting that you use these for inspiration, not to copy. Innovation is he outcome of you seeing the hidden capabilities that have always been possible.

(The Egyptians could have produced functional hang gliders using bamboo and cloth that was available at the time, but nobody did since nobody recognised the possible innovation that would make the outcome possible.)

As a case in point, Time magazine once published a sidebar article that claimed that, according to court records, some bright someone actually did build (something similar to) a hang glider, somewhere in South East Asia, maybe a thousand years ago. Being justifiably proud of his creation, he took it to his (regional governor, local authority, grand poobah, other) and tried to give it to him as an honor to (the big-shot). However, the local (advisors) dismissed his claims as impossible, of course... But, the builder persisted, until the court business was all settled, and the advisors thought the (Big Deal) would enjoy a good laugh, while watching this presumptuous ignorant peasant make a fool of himself, and probably killing himself in the process. The relevant players in the drama gathered at a remote spot and bade the builder commence to demonstrate his contraption. But, against all odds, he actually flew the thing at some notable height for some notable distance. The court was shocked with disbelief, and furiously discussed what to do about it all. The (supposedly wizened advisors) finally told the (big Cheese) to confiscate the apparatus, throw it down the deepest well, and then, behead the builder for (disrupting the court's peace of collective mind), which was all subsequently done... It seems that they were afraid that if anybody else had seen the flight, that they too would dream of flying also. This could just not be allowed to happen. And so, in all their supposed wisdom, they lost a chance to gain potential (control of the air) over all their military opponents, and were eventually replaced by the next in a long line of conquerors, once again. So, it may not pay to create a breakthrough invention until the (power-structure) desperately needs it... (ie: it's not enough to have a great idea, if you don't have great timing, as well...)QED

The further point being:

Don't just ask what could be done;

Don't just ask what people want to be done;

Instead, ask what really needs to be done.

I don't know if this matters or not:

A. The weber kettle uses charcoal briquets.

B. Briquets in their burn process will produce different degrees of temperature and that will affect flue pressure.

C. A method would need to be devised to regulate the inflow of briquets to regulate a constant in the flue gas pressure and temperature.

D. Regulation would be necessary to ensure that the spit turns at a constant controlled speed and for the necessary duration as required to completely cook whatever food was placed upon the rotisseries spit.

Hamster on a stick, turn it yourself.

they make peltier run fans for wood stoves to circulate hot air. Take the fan off and put on a small pulley.

So, get on with it already...

Pick a method, any method, and build a simple prototype, fix it when it breaks and/or upgrade it if it doesn't break...

At least you'll have something done by the due-date...

(to a receptive inventor, failure can be a great mentor...)

(''tempis'' just keeps on ''fugit''-ing whether you watch the clock or not...)

(and show us some photos when you're done...)

The way I see it if people are too lazy to turn their own food over while cooking with a BBQ grill the odds are they are too lazy to ever bother cooking with a grill to begin with thus the whole food flipping problem is not a real issue.