What are Some Resources for Designing a Moon Buggy Frame?

[Ari_mechie]

Hi everyone...

i have to design the frame of a moon buggy, which is a manually powered vehichle for 2... it is somewhat similar to the frame of FSAE cars... but the problem is... i don't know from where to start... i have ideas... but to design a proper frame... i need some study material...

so can someone suggest me a good book or reference material for frame designs or automobile frame design? would really appreciate if u provide a link for some e book... any other sort of help in this regard will also appreciated...
thanks :)

 

[Mech_Engineer]

Your biggest driving factors will be weight and size. With that in mind, you should look at the Apollo moon buggy, and then think about what you're trying to accomplish that is different than the real thing. It probably won't be very useful to study automotive manufacturing technologies; you should instead look into space frame design in my opinion.

Keep in mind you'll probably want to utilize materials with extremely high stiffness and strength to weight ratios. this probably means you should look into high strength steels, titanium alloys, and advanced composites like carbon fiber. Also keep in mind, your design should take into account the Moon gravity (approx 1/6g).

 

[Danger]

If your design includes moveable pieces such as suspension components, make sure that they are compatible with space-worthy lubricants. Zerk fittings won't cut it.

 

[Ari_mechie]

hey... thanks to both of u for ur consideration :)
the thing is... the buggy is to be designed for a competition, which is more of a race... where assembling the buggy on the spot would be included in the race time... so that too is an important aspect... n yeah... weight to strength is actually an important aspect... so materials to be considered have to be really strong... but cost of the buggy also has to be kept in mind...

the thing is i don't now how to start with the frame... as in my idea is to design it in 2 parts, which would be symmetrical (there's also a space constraint, that the disassembled buggy should fit in a box of 4'X4'X4')... so the symmetrical design would make the packing and assembling easier... but problem is... i don't now how to design the frame... i mean the various elements of the frame- how to place them, what should be the angles, how the stress should be distributed throughout the frame n all... n i need to study for this... but i just can't get the proper study material... n all htis hasn't even been done as a part of my curriculum...

so the thing is... how do i start, when i do have a basic idea in my mind that what should the buggy look like n what all features would it have!
any sort of guidance will be really appreciated :)

 

[Danger]

I suggest that you check into "Powerblocktv.com" as a starting point. All of their TV shows have featured frame builds in various episodes, which are available on-line. The one most suitable for your needs is probably "Xtreme 4x4", since it deals with all types of off-road vehicles. They go into a lot of detail regarding not only how to do something, but also why it should be done a particular way. It's also a great place to learn about things like suspension geometry, brakes, drivelines, steering systems... you name it. Of course, you would have to modify what you learn in order to make it "moon-worthy".

 

[john.phillip]

The frame geometry is usually a consequence of the components you want to carry, suspension type, driver and passenger seats and envelope, drivetrain supports, motor supports, drive controls, batteries, antennas, instruments, equipments, payload area, crash area and so on.

You might start by spatially distributing all parts that are already defined or required in your design, and elaborate a frame that connects everything together, providing adequate safety for the occupants. Then you distribute loads and add more stiffness where required, optimizing both weight and costs by choosing materials and manufacturing process, later you can go for vehicle dynamics, verify torsional stiffness, build prototypes and start testing.

For the frame cross section there are few options: Round or Square tubing; Open sections like "U" channels, "I" beams and angles; Sheet metal; Corrugated sheet metal and Composite sections.

 

[Danger]

Personally, I think that there's a glaring error in the basic concept of the project. You are supposed to design a vehicle for use on the moon, but actually use it on Earth. That automatically brings in a huge compromise factor. Things like component insulation, extreme dust-proofing, etc. aren't needed here, but more structural strength is.

 

[john.phillip]

I think they are supposed to demonstrate a fully working vehicle with all equipment and accessories, also there are good natural and artificial test beds on Earth that almost mimic the conditions on Mars or the moon.

The extra frame weight should not be a drawback as it is much less than the overall weight, also the vehicle performance will be very limited as it is human powered.

 

[Danger]

I disagree with your assessment, John, but understand why you see it that way. My reasoning is as follows:
Despite the frame weight being a minor percentage of overall weight, every single kilogram represents a huge amount of fuel in order to get it into space and decelerate it into lunar orbit and then onto the surface.
The only ways to simulate lunar gravity on Earth are through extremely well calibrated hyperbolic flight on something like the "vomit comet" or underwater. The first would be almost impossible to tune correctly and would last for only seconds. The latter would require some external ballast/floatation equipment in order to impart a semi-neutral buoyancy to the device. Even then, the internal stresses would still be at 1g. That implies that less structural integrity is needed in a lunar situation.
I realize that something like bouncing around over rocks would require something more solid, since inertial mass would be the same, but as you pointed out yourself the performance would fall far short of that due to it being human-powered. The suspension rates would be far different in each environment, as would be the structure of the wheels/tires.
That's how I see it, but I certainly welcome any counter-arguments and discussion.

 

[john.phillip]

Yes, during launch every gram counts, but he mentioned FSAE, which is for students. This is a chance to get involved in a real project before graduation, and certainly there are rules establishing all the requirements, which probably take into account everything you pointed out including self weight.

Talking about it, I found this link:

http://moonbuggy.msfc.nasa.gov/rules.html

 

[Danger]

Thanks for the link, John. I've never heard of FSAE and just assumed that it was some race car format like F1 or Midget or Legend.
From the rules, I can see that this has absolutely nothing to do with the thing being useable on the moon. It doesn't even say anything in there about there having to be room in the passenger section for their suits and environmental backpacks. It's just an engineering project that needs to look like something that might be used on the moon.

edit: Not that there's anything wrong with the concept, but it's very confusing to outsiders like me who take the OP at face value.

 

[Mike_In_Plano]

Cool Project!

Nasa has released some notes regarding the Old Rover:
http://www.history.nasa.gov/alsj/lrvhand.html

But it's very good to remember that you have a score card, and it probably leaves out a lot of the things you would need on the moon. Wanna win, design to the specs - not what a moon buggy needs.

Also, good design doesn't start in a vacuum. Look at what others have done. I'd suggest a couple of days digging in bicycle shops, camping stores (like REI), and looking at baby strollers. There's so many exotic interconnect schemes out there. Just study, absorb, and let your imagination react.

Best Wishes,

Mike

 

[john.phillip]

The same for me, I had the wrong impression by the project title and thought about something much more substantial, I should have researched or asked for the rules first.

About FSAE:

http://students.sae.org/competitions/formulaseries/

 

[Danger]

Okay... I'm going to save that link for perusal at a less fatigued time. Thanks, though... it looks interesting.

 

[Ari_mechie]

hey guys... first sorry for the late reply... n yeah... THANKS A TON for the help and the insight :D

actually you r right... its not as big as it sounds... you know... when you think of a moon buggy competition... things like low gravity, lunar rocks, etc. come to your mind... but its more of a race between vehicles that look like buggy's... but still... at graduation level... i think it still gives you enough scope to think out n use your creativity... i mean there's no restriction on the type of design... so u can innovate a lot!

also... they try to create moon-like surface with craters n ditches(which am not sure are there on the moon)... to give u a feel of it... n the restrictions they have posed in terms of the rules... are similar to the ones they had while taking the first moon buggy to moon... like 4'X4'X4' volume constraint... so i do hope it wud be some kind of a challenge! looking forward to it... n hope to start with the design soon... :)
thanks again guys... will come at the same place whenever i ll need any help :D

 

[Ari_mechie]

one question guys... do you think connecting a propeller fan at the back of a bicycle (powered by the pedals only) would anyways help in enhancing the speed of the cycle?

 

[Danger]

one question guys... do you think connecting a propeller fan at the back of a bicycle (powered by the pedals only) would anyways help in enhancing the speed of the cycle?

On the contrary. I rather suspect that it would rob more power from the driveline than it would provide in thrust. There are going to be losses in any transaction. Adding the necessary linkages would just introduce more friction. Let's say that you tap 1/4 hp from the driveshaft(s) to power your fan. That will drop to something like half (1/8 hp) by the time it gets to the blades of the propellor. Had it not been tapped off, the full 1/4 hp would have gone to the wheels. Anyhow, if this thing is supposed to look like a moon buggy, it definitely won't have a propellor. No air on the moon, remember?
Anyhow, keep us updated whether or not you need further advice. We'd like to know how it turns out.

 

[john.phillip]

According to the rules, flywheels are not allowed. If you implement a propeller, it will act as a flywheel also, even with a very low energy storage capacity and your design might not be allowed in the competition.

Also, the power source is the same both for the wheels and the propeller. Which one do you think will be more efficient, a small propeller trying to transfer the power to the air or the wheels to the ground ?

Try to estimate the minimum required propeller diameter to keep the cycle moving with the available power, is it within the 4'x4'x4' envelope ?

 

[Ari_mechie]

hmmm... quite right guys... it would only be wastage of energy... n yeah... i did remember bout no air on moon thing... but again... this is the paradox here... its a race here on earth!
but i think u guys are right... it would only add to the troubles... thanks once again guys... :D

n yeah... i wud surely keep u guys updated... n yes... will surely seek ur advice guys... u have been quite helpful... :D

 

[Danger]

Right, then... go kick some butt.

 

[Ari_mechie]

sure dude... ;)

 

[NikW]

Hi,
I'm also designing a lunar buggy (for a school project).
I have a basic idea design in mind, but if anyone could help provide some reference material? More than just the frame, something regarding more of the differences/ what to account for?
Thanks,