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Rover Design essentials

Posted by: Rocket Scientist - Sat Sep 22, 2007 10:21 pm
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Rover Design essentials 
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Post    Posted on: Fri Jan 11, 2008 10:59 am
does any of this really matter to win the prize? what does it have to do to win? Could you not send it, let it crawl 10 yards, take a picture then die afterwards? im still thinking the rover much really try not to get the dust moving around into the parts or over the panels. Starting to sound like a transformer, sounds brilliant! but surely basic to win the task is the priority.

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Post    Posted on: Fri Jan 11, 2008 11:37 am
It has to travel 500+ yards.

If a small lightweight rover could survive a bumpy landing it would easily survive miscalculated leaps.

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Post    Posted on: Fri Jan 11, 2008 12:36 pm
idiom wrote:
It has to travel 500+ yards.

If a small lightweight rover could survive a bumpy landing it would easily survive miscalculated leaps.


Not if it is so small that any guidance system being used is only a couple of inches above the ground and consequently its camera cant see more than a couple of feet infront of it. A slight crease in the lunar surface would become a box canyon to a small rover. Why do all the hard work of getting there spending willions of dollars so that you can get stuck at the first obsticle.

Also any pictures are likely to be pretty rubbish without a bit of height, grains of regolith that look like huge bolders are not going to excite people.

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Post    Posted on: Fri Jan 11, 2008 1:45 pm
What about first selecting the lightest cam fit for the lunar environment, next selecting the lightest electronics and protections fit for the lunar environment and then - after that - determining the optimal ground clearing by applying what's left from the maximum possible weight of the rover? From that weight a motor also has to be subtracted as well as the antenna and the solar array powering that motor, the electronics and the camera and the antenna.

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Post    Posted on: Fri Jan 11, 2008 2:18 pm
I think the first step is to determine what I want to achieve.

Do I keep my rover just long enough alive to fulfill the 500 yards requirement?

Do I want to survive lunar night?

I guess 500 yards are doable e.g. in a few hours, so the electronics (starting with the cam) won't need to be very robust.

The longer I stay (and survice) the heavier my camera (and the other stuff of course) will get.

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Post    Posted on: Fri Jan 11, 2008 2:39 pm
the only prob is if u aim to only achieve the minimum you may fall short, if u build something to last then there is less chance of failing. Also agree that the main cost will be getting it there ready to move around.

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Post    Posted on: Sat Jan 26, 2008 1:11 pm
What if you took a mobile-phone sized "rover" and put it inside an inflatable transparent plastic cylinder? Deflate the cylinder to create a small and light package for transport, inflate it from a small pressure vessel inside the rover once on the moon (it wouldn't need much pressure in a vacuum).

The package itself would be a disc on its side, with the rim being able to rotate with respect to the centrally placed instrument package. Think of a ball bearing, with the instruments where the axle would go. The camera would look sideways, and the instrument package would have an asymmetric CG so that it would stay in a fixed position relative to gravity (i.e., your camera won't go upside down). The radio antenna could be on the other side.

A series of wires would extend from the disc's rim to the outer cylinder, like the spokes in a bicycle wheel. The rover would move by pulling on the wires, perhaps using solenoids, or maybe they're made from a shape memory alloy. An optical sensor could be used to sense the position of the outer rim relative to the centre instrument package, so that it can determine which way is down and therefore which wires to pull. Or, if the power supply is in the centre, there could simply be a sliding or rolling contact that powers any wire that is in the horizontal forward position.

If you want to be able to steer (rather than going 500 yards any which way) then the cylinder could be tapered towards the ends, and the rim could be connected to the ball using a double row of wires in a V-shape, so that you can pull asymmetrically and steer left or right.

One potential problem could be dust collecting on the outside. Shooting video of a dusty piece of plastic can be done on Earth as well, no reason to go to the moon for that. However, the camera will be looking out the side of the cylinder, which won't touch the ground, so it might work.

Image
Here's a quick picture. In the middle is the instrument package (it's green because it detects little green men). The inner lime portion remains still, while the blue outer rim rotates around it. The red arc is the contact strip that powers the actuators that roll over it, so that the entire contraption will move left. You can add another strip on the other side if you want to go backwards too, of course.


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Post    Posted on: Sat Jan 26, 2008 3:13 pm
Lourens

This is very complicated and any actuator failure is likely to mean that the rover becomes immobile, also its not going to be very fast getting anywhere so might need to survive longer than a conventional wheeled rover to achieve 500yards of distance.

Another thing to consider is that the moon regolith has very sharp edges which might wear a hole in the plastic causing it to deflate.

I like the idea of a 4 or 6 wheeled rover with each wheel being driven independently by its own motor. These could be small but geared down to give extra torque.

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Post    Posted on: Sat Jan 26, 2008 4:50 pm
hmm i seem remember some kinda tank toy when i was a child. It had such big tracks that no matter what it hit it would turn over and run along upside down. IT therefore had no top or bottom. MAybe something like that, though perhaps a track could cause probs.

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Post    Posted on: Sat Jan 26, 2008 5:26 pm
Complex? Each one of your motors has solenoids and sliding contacts, and you have a lot more moving parts if you add steering. The fact that it's hidden in a tidy box doesn't make it not there.

As I drew it, a single actuator failure doesn't have to mean the end, as there are always at least two active. If you go for the steerable version or add a few more wires then you get more redundancy.

As for speed, that depends on the speed of the actuators. Making the outer cylinder larger could help, but it would require larger travel in the actuators too, so that probably cancels out. Anyway, a permanent magnet inside a solenoid moves plenty fast if you put the power on, so I don't see why it should be slow.

Wear on the plastic could be a problem yes, but the weight of the thing is going to be very low in lunar gravity and the surface area touching the ground is going to be quite large. And with all the weight I'm saving for not having to bring four or six large rigid wheels, powerful motors and so on I can ship some nice thick sturdy plastic, at least on the running surface. The sides may be a bit thinner to help visibility.


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Post    Posted on: Sat Jan 26, 2008 5:50 pm
Your heay duty plastic is probably going to weigh more than my light weight wheels. :)

Also the difference between your 8 solenoids and my 6 motors is minimal, I would use brushless motors:- ie a permananet magnet on a spindle surrounded by a coil. These can be quite small and geared making the current consumption relatively small. A solenoid will probably take more current or have more windings making it heavier and you are right the amount of travel required could be a problem.

As for contacts I would use solid state motor controllers which contain no contacts.

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Post Re: Rover Design essentials   Posted on: Thu May 13, 2010 12:10 am
Well, most definitely, you're going to need an inertial navigation system of sort to fulfill the distance requirement. Off the top of my head I can think of the 3DM-GX3 made by Microstrain, which has a temp range of about -40° to +75°C, so temp control will be very important. Add internal AC for that. Looking at the reason why Mars Spirit got caught on the surface I would say that some fork level method of angling out of harsh terrain is also an important concern.

Data transmission will be more optimally performed utilizing the CCSPS Proximity-1 Space Data Link Protocol, so considering an...

an X Band transceiver
-- MACOM has the ~10.53 Ghz Voltage Controlled Oscillator Transceiver
-- ComTech EF Data has the ~8.4 GHz XSAT-7080 X-Band Transceiver
-- Depends on the strength of signal you want.

a UHF ProximityLink Transceiver
-- L-3 Comm has a C/TT 510 Elektra-Lite

a broadband traveling wave tube (TWT) microwave amplifier,

maybe an S Band converter(?) since Nasa also uses S Band for satellite monitoring


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Post Re: Rover Design essentials   Posted on: Mon May 17, 2010 11:44 am
A rover can be designed that weighs less than 50 grams, and if there are several, the chance one does the requirements should be high. The whole basic attempt can be done in the first lunar day, so surviving a lunar night would not be needed.

A short range RF link can pass the videos etc to the lander portion which would have a diode laser data link for transmission to Earth (RF is vwery difficult and has to be licensed while optical does not).

In the Microlaunchers website
( http://www.microlaunchers.com/7816/L3/l ... -link.html ) is the basic math for a 1/10 AU link for a NEO fly-by. Lunar distance would allow a higher data rate, as for a given transmitter the signal strength would be about 1600 times stronger.

About 2 years ago I posted something like this to see if there was any interest in developing a lunar distance version for an entrant. No response--maybe no interest. An RF system will be very difficult.


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Post Re: Rover Design essentials   Posted on: Tue May 18, 2010 4:53 pm
I find it seriously hard to believe a rover can weigh less than 1kg much less than 50 grams, given that the smallest X band transceiver I'm familiar with would weigh approx. 7.5kg. Remember, the goal of the lunar module is to travel x number of feet as well as capture and communicate data back via the lunar orbiter.

I'm sure that...

a.) given a rocket has the appropriate thrust to launch into orbit,
b.) a lunar orbiter obtains orbit around the moon,
c.) a lunar lander sucessfully lands on the moon,

having a payload of lunar rovers weighing only 50 grams, which essentially makes them just under the average size of a Hot Wheel car, it would be HIGHLY expensive and impractical if said rover were to be pinned and effectively stuck due to something as simple as a falling rock. Not to mention zero traction given the moon's powdery surface.


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Post Re: Rover Design essentials   Posted on: Tue May 18, 2010 8:50 pm
Whether you believe this is less important than if anyone does believe it. It will be done by those who believe, not by those who do not.

The ICs for short range RF weigh fractions of a gram. Look into the insides of a cell phone.

Several 5op gram rovers would be a good idea because only one has to succeed to win. As for traction--on level ground this will not be a problem. If the chance if getting stuck before traveling 500 m is 10%, 2 rovers should reduce the chance for both getting stuck to 1%.

Small motors? Google "sub gram rc planes" for a community building 2 channel RC planes which weigh less than a gram. Record now 225 mg. That included the motor and rudder actuator. Motors can be made which weigh less than 100 mg.

Again, this will be done by those who like and believe in the idea.

The rocket means for getting to the moon, landing is over 99% of the difficulty, and that is where the attention should focus. For a launcher system, the first stage is at least 2/3 of the expense, regulatory problem etc.

The technology to do all this is now available. When there is a "critical mass" of believers who get together, it will happen.


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