Rover project idea

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Narius
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Rover project idea

Postby Narius » Tue Dec 01, 2009 6:12 pm UTC

So for one of my classes we have to design a 'mars rover' model. It cannot use any electricity, flammable liquids, must be at most 2' x 2' x 3' high.
It has to carry as much weight as possible, in this context the weights are circular like what you would see put on bench presses in a gym. You can't impart any initial velocity on it, other than holding a spring down or something like that (no push). It can't leave anything behind (like if you wanted to move the weights simply with a catapult, wouldn't work). How it scores is based off of its unloaded weight (the lighter the better), how much it can carry (the more the better), and how far it travels (the further the better). And you can't spend more than $80. My group is doing a CO2 powered vehicle. I'm not asking for suggestions, I just thought perhaps some people on here would like to come up with their own ideas. What would YOU do for this project?
And hey, if you're really bored you could build your own for the heck of it.

If I think of additional rules or instructions that make it clearer I'll make sure to add them.

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Velifer
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Re: Rover project idea

Postby Velifer » Tue Dec 01, 2009 8:09 pm UTC

Narius wrote:It cannot use any electricity, flammable liquids...

This is a solid... Though the propellant case would probably be quite heavy, among other problems.

I'd probably do it with springs. Wind up toy of mighty transport!

Outside? Check the weather and deploy a sail. Quite light, and the fuel is cheap.
Time flies like an arrow, fruit flies have nothing to lose but their chains -Marx

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Narius
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Re: Rover project idea

Postby Narius » Tue Dec 01, 2009 8:14 pm UTC

Velifer wrote:
Narius wrote:It cannot use any electricity, flammable liquids...

This is a solid... Though the propellant case would probably be quite heavy, among other problems.

I'd probably do it with springs. Wind up toy of mighty transport!

Outside? Check the weather and deploy a sail. Quite light, and the fuel is cheap.


Shoot.
That reminds me.
It's on a parking lot, and the vehicle itself without weights cannot weigh more than 40 lbs.

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Velifer
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Re: Rover project idea

Postby Velifer » Tue Dec 01, 2009 8:26 pm UTC

Narius wrote:It's on a parking lot, and the vehicle itself without weights cannot weigh more than 40 lbs.

Well, my midget on a tricycle idea just got a bit more challenging...
Time flies like an arrow, fruit flies have nothing to lose but their chains -Marx

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Kow
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Re: Rover project idea

Postby Kow » Wed Dec 02, 2009 1:41 am UTC

Velifer wrote:
Narius wrote:It's on a parking lot, and the vehicle itself without weights cannot weigh more than 40 lbs.

Well, my midget on a tricycle idea just got a bit more challenging...

You'll have to get an anorexic midget instead.
Image

Carnildo
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Re: Rover project idea

Postby Carnildo » Wed Dec 02, 2009 4:37 am UTC

I'd make a single wheel two feet in diameter and two feet wide. Inside would be the carrier for the weights, with the center of gravity being below the center of rotation. In between the carrier and the wheel would be roller bearing for support and the stiffest coil spring I could get my hands on. The spring would be rigged so that one end detaches when the spring is relaxed.

Assuming you're using metal for all parts, how much you can carry is limited only by the density of the weights. This give it rather incredible momentum once it starts going (even though it won't be moving very fast), so you'll get good distance out of it.

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Re: Rover project idea

Postby Mavrisa » Wed Dec 02, 2009 10:29 pm UTC

Get a tray. Place a bomb beneath said tray. Put the masses on the tray so they are slightly off center in the desired direction. Detonate the bomb.
Pros:
-Leaves nothing behind :P
-Could get the masses very far very quickly, if they survive.
-Explosion!

Cons:
-I don't know much about bomb making, but I imagine it would be hard to do it in under $80. Would someone more knowledgeable care to correct me on that?

Okay for a (slightly) more serious idea: Compress some hydrogen, create a ramjet type thing by releasing and igniting the hydrogen. That way, most of your fuel by mass comes from the air. Initially getting some airflow might be tough, but I'm sure you can figure it out. Hey, the rules say no flammable liquids, right?
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Re: Rover project idea

Postby frezik » Thu Dec 03, 2009 12:30 am UTC

I'd go for falling weights, like Hero of Alexandria's dancing robots. The unloaded weight can be very little with the right design, since you can use the added weights as your go juice.
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BlackSails
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Re: Rover project idea

Postby BlackSails » Thu Dec 03, 2009 11:32 pm UTC

You can make a stirling engine out of a parabolic solar mirror and a coke can. On a nice sunny day, this can get you as far as you would like.

Zalzidrax
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Re: Rover project idea

Postby Zalzidrax » Fri Dec 04, 2009 3:22 am UTC

Stirling engines aren't exactly known for their high power output--might be difficult to get enough output from a homemade one to keep up the speed. Though if you did manage to make it work well, it might be able to keep up the speed from a spring-loaded boost at the start or something.

It would be a really cool thing to try though.

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Re: Rover project idea

Postby PhoenixEnigma » Fri Dec 04, 2009 3:39 am UTC

I don't suppose you have the scoring formula available? That would allow some optimizations. It may be the best solution is to move a great deal of weight a short distance very rapidly, for example, or a light weight a very long distance at low velocity.

One idea might be to use the load to provide motive force by virtue of its weight. That way, the more load you add, the more force you get. I'm picturing a form of vertically-oriented rack and pinion system, but there might be other ways too. Using that for primary accerlartion and, say, a smallish sail as a sustainer could be a promising route to go.

I'm also trying to think of a way to ignite some solid rocket motors without electicity. Depending on how the criteria are weighted, it might be practical to send a couple dozen grams a few hundred meters in a handful of seconds.
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Re: Rover project idea

Postby wst » Sun Dec 06, 2009 12:23 am UTC

I have a Mamod brass stationary steam engine. Hexamine blocks are cheap fuel. Water is cheap. It runs for a few minutes at quite a high speed, and I'd gear it down with a pulley. It'd have 2 front wheels from one of those foldup scooters (low rolling resistance) and a small pedal bike wheel at the back, and a flat MDF deck around it with thin polycarbonate sides to give it a vertical carrying capacity without behaving like a game of jenga. And a small spring to start the engine.
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Re: Rover project idea

Postby eternauta3k » Mon Dec 07, 2009 2:43 pm UTC

PhoenixEnigma wrote:One idea might be to use the load to provide motive force by virtue of its weight. That way, the more load you add, the more force you get. I'm picturing a form of vertically-oriented rack and pinion system, but there might be other ways too. Using that for primary accerlartion and, say, a smallish sail as a sustainer could be a promising route to go.

How about this?
perspectiva.png
perspectiva.png (106.39 KiB) Viewed 2133 times

frente.png
frente.png (35.37 KiB) Viewed 2133 times

The rope should be set up so the thing can freewheel once the weight reaches the tray
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2.71828183
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Re: Rover project idea

Postby 2.71828183 » Mon Dec 07, 2009 6:51 pm UTC

Better, I think, would be to mount the load on a spindle and spin it up to a reasonable speed, using angular kinetic energy for motive force. Since your flywheel mass isn't part of the mass budget, and you can store a *lot* of energy this way, I think it'd be a very successful approach. After all, a 40 lb machine could easily contain, say, 50kg of flywheel, and if that's rotating at a reasonable 500 RPM and has a radius of 10cm, that's 1.234 MJ of energy stored, enough (with no losses or drag) to accelerate the whole 68kg machine to 190.51 m/s (a little over half the speed of sound in air at STP) from a standstill.

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eternauta3k
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Re: Rover project idea

Postby eternauta3k » Mon Dec 07, 2009 7:49 pm UTC

2.71828183 wrote:Better, I think, would be to mount the load on a spindle and spin it up to a reasonable speed, using angular kinetic energy for motive force. Since your flywheel mass isn't part of the mass budget, and you can store a *lot* of energy this way, I think it'd be a very successful approach. After all, a 40 lb machine could easily contain, say, 50kg of flywheel, and if that's rotating at a reasonable 500 RPM and has a radius of 10cm, that's 1.234 MJ of energy stored, enough (with no losses or drag) to accelerate the whole 68kg machine to 190.51 m/s (a little over half the speed of sound in air at STP) from a standstill.

Sure, the energy is enough to get to that speed, but how are you gonna extract that energy from the flywheel? You have to somehow make the rover accelerate smoothly while the flywheel is slowing down due to the load. I'm thinking either a clutch or a gearbox, connected to some sort of timing contraption.
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Re: Rover project idea

Postby 2.71828183 » Mon Dec 07, 2009 8:31 pm UTC

Since the object is distance, not speed, I think it would be enough just to have a large gear reduction between the flywheel and the drive wheels. Crank the drive wheels up to spin up the flywheel, then just drop it on the ground and let the wheels skid until it reaches a steady speed. This isn't terribly efficient, but it's simple and cheap.

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eternauta3k
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Re: Rover project idea

Postby eternauta3k » Tue Dec 08, 2009 1:41 am UTC

2.71828183 wrote:Since the object is distance, not speed, I think it would be enough just to have a large gear reduction between the flywheel and the drive wheels. Crank the drive wheels up to spin up the flywheel, then just drop it on the ground and let the wheels skid until it reaches a steady speed. This isn't terribly efficient, but it's simple and cheap.

Sounds interesting. It'd be great if someone could test this (maybe with lego) because I wanna know what happens when massive spinning object meets ground: skid, bounce, etc.
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Narius
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Re: Rover project idea

Postby Narius » Tue Dec 08, 2009 1:45 am UTC

PhoenixEnigma wrote:I don't suppose you have the scoring formula available? That would allow some optimizations. It may be the best solution is to move a great deal of weight a short distance very rapidly, for example, or a light weight a very long distance at low velocity.

One idea might be to use the load to provide motive force by virtue of its weight. That way, the more load you add, the more force you get. I'm picturing a form of vertically-oriented rack and pinion system, but there might be other ways too. Using that for primary accerlartion and, say, a smallish sail as a sustainer could be a promising route to go.

I'm also trying to think of a way to ignite some solid rocket motors without electicity. Depending on how the criteria are weighted, it might be practical to send a couple dozen grams a few hundred meters in a handful of seconds.


There actually is a formula, but I don't have access to it and I don't remember it unfortunately.
But we actually did something along those lines. We scratched the CO2; just couldn't get it working. We have a sort of pulley system in which one end of the chain of pulleys was tied about the back axle, and the other end had the weights tied on it, thus using the weights themselves to propel the axle.
They failed to specify the conditions (it was outside on a parking lot with an uphill slant) so we didn't do as well as we were predicting, but oh well.


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