Hypography X Prize Entry

[Janus]

I don't think so? From the drawing below, doesn't the "downward" force on the pan lesten as the centrifuge spins it to a 45 deg angle? :eek: :esmoking:

 

 

No, the force felt on the pan will be the result of the vector addition of the centripetal acceleration and the gravitational acceleration. For the pan to tilt at 45°, the centripetal acceleration must be 1g. The resultant acceleration felt by the pan will then be 1.414g and your 5kg mass will "weigh" 7.07 kg.

[Roadam]

Well why do you all think that heat from the motors will be such a problem? A 5kg rover on the moon would have about 5N of force more than enough for driving(I think). If the motor is a stepper one like in GHADs thread then you dont even need high rpm. Consequentially mounting motors directly onto the axels. It doesnt need to be so speedy as earth counterparts, but maybe not so slow as mars rovers. Sojourner, weighing 10 kilos could move 1cm/s. Mars exploration rovers: 5cm/s. MSL : 2.5cm/s. Well the old Lunokhod2 had 50cm/s, and apollo rover something over 200cm/s.

Wow the more I read the less I see which speed would be the best. But given the delay in connection, which is about few miliseconds, I guess one could drive such rover at about few kph. It depends on refresh rate of the video and wether the rover is programable.

Lets say that it goes at speed .2m/s. And lets make even one more assumption that friction koeficcient with lunar regolith is .1(big, really). Then with rover weighing 9N, the power output of the motor is at about .2 watts. Not a lot, is it? Then with efficiency of the electical motor at about 90%(not really good motor), you get only about .02 watts of heating(radioisotope heater units on Spirit&Opportunity produce 1 watt of heat).

As for the battery consumption. Lead-acid battery has rating of about 30 watt-hours per kilogram, so if the rover had 1kg batter of such type it could operate its motor for 600 hours. At the speed of .2m/s or .72 km/h it could make about 400 kilometers :esmoking:. That of course is only motor power requirement, I dont even suspect how big would actual demand be.

If I made any mistake, please correct me.

[Turtle]

No, the force felt on the pan will be the result of the vector addition of the centripetal acceleration and the gravitational acceleration. For the pan to tilt at 45°, the centripetal acceleration must be 1g. The resultant acceleration felt by the pan will then be 1.414g and your 5kg mass will "weigh" 7.07 kg.

 

Thanks Janus. :) I knew the right answer had a "v" in it. :doh:;)

 

...As for the battery consumption. Lead-acid battery has rating of about 30 watt-hours per kilogram, so if the rover had 1kg batter of such type it could operate its motor for 600 hours. At the speed of .2m/s or .72 km/h it could make about 400 kilometers . That of course is only motor power requirement, I dont even suspect how big would actual demand be.

If I made any mistake, please correct me.

 

I have a deep cell battery charged by solar panels for home emergency and camping use. First, the liquid acid type is out for space I think, but they do have gel-type that function in any orientation.

 

My 12 volt battery is rated in "amp-hours" , not watt hours and has a 100 amp hour capacity. (Watts = Amps * Voltage) My panel is 15 watt (~ 1 amp/hr) for ~ 3 square feet of surface. The battery weighs 52 pounds. So without recharging I could run a 1 amp load for 100 hours or a 5 amp load for 20 hours, etcetera. With my single panel a full recharge takes 100 hours. :esmoking:: :eek:

 

edit: addendum: Mars Exploration Rover Technical Data

The Mars Exploration Rover Maintenance Manual

MER Technical Data ;)

[Jay-qu]

Excellent :singer: thanks for the info Janus!

 

Assuming we go with the russian option.. 673kg to lunar orbit should be more than sufficient. How do we go about calculating the mass we could deliver to Moon surface? this will place our limit on the rover/lander mass.

[CraigD]

Well why do you all think that heat from the motors will be such a problem?

I think I may have brought up that concern in post #106. My concern is based mostly on experience with small (1:10 - 1:28 scale) model cars and trucks. These motors get very hot – > 100° C, I’d guess from the times I’ve singed my fingers on them – and perform best when attached to large finned heat sinks (which only work well with air flow over them). They also have tremendous power to mass ratios – a good brushless RC car or aircraft motor massing .052 kg can draw 200 W of power, and produce much (80%+) of it as mechanical output – and are can be very small – eg: a cylinder .027 m diameter by .032 m length.

 

If one of these little motors were run stalled (no movement) at full power in a vacuum, and it were a perfect back body radiator, it would reach thermal equilibrium at greater than 900 K, close to the melting point of aluminum. As these motors are not perfect black bodies, the actual temperature would be greater – in short, the motor would melt.

 

None of this is a show-stopper. It only means that the motors on a lunar rover can’t be as powerful and/or as compact as those on a terrestrial RC vehicle. For example, unstalled and running at 10% max power, they’re black body equilibrium temperature would be only 345 K – barely hot enough to burn exposed human skin, let alone damage metal or plastic. I don’t think a complicated radiator cooling system will be necessary for the <10 kg rovers we’re envisioning.

 

The 210 kg Apollo lunar rovers were powered by 4 motors about as powerful as the above examples (attached to 80:1 reduction gears), but much larger – I’d guess about .1 m diameter by .075 m length, which would have given them a full-power stalled black body thermal equilibrium temperature of about 500 K. They had thermostatic switches that would cut off power when the motors exceeded about 530 K. I don’t recall that this safety system ever tripped – I suspect the rovers were never run flat-out in a jammed condition for extended periods – or at all.

 

Having done these rough calculations, I’m now more worried about COTS remote control receiver electronics than about motors – and eager to try putting one of my several cheap, tiny toys into a decent vacuum chamber to see what happens to it. Back-of-the-envelope, or even detailed engineering calculations are nice, but there’s no substitute for testing!

 

Sources:

• cyclonBrushless,cyclon Brushless for examples of COTS RC model motors
  
• wikipedia article “Stefan-Boltzmann law” for the black-body temperature calculations
  
• this NASA’s Lunar Rover page for rover information (including a link to a cool scanned copy of the LRV operations handbook :singer: )
  

[Turtle]

Excellent :) thanks for the info Janus!

 

Assuming we go with the russian option.. 673kg to lunar orbit should be more than sufficient. How do we go about calculating the mass we could deliver to Moon surface? this will place our limit on the rover/lander mass.

 

Agreed & agreed. Pretty hard to calculate without particulars but we can make some guesses. Suppose 2/3 of the 673 kg in lunar orbit is structure other than rovers, this gives us 222 kilos of rovers, or 55 kilos per rover if we have 4. (Mars rovers are ~174 kilos for comparison) Gives us an order of magnitude in breathing room over BigDogs original proposition. :singer: If there are no smaller rockets available, then not using the rated load is a waste, yes/no?

 

Not only do we need launch windows for the best trajectory to lunar orbit (perihelion best?), we have a less than 2 week window to land once there as we likely need to land in the daylight. This may be one advantage to going into lunar orbit?

 

The Moon's gravity is 1/6 that of Earth, so:

5kg*1/6=5/6kg=0.8333kg

 

Perfect! That is ~2.5 pounds which is the bare weight of the vehicle. I'll conduct some speed vs. terrain tests as well as battery life (the amp/hr rating is marked on them conveniently).

 

In reading at the link for the mars rover manual I gave (not an official site I now see), they gave very specific reasons for using the 6 wheel "Rocker-Bogie Mobility System Components" arrangement, i.e.

The RB system permits each wheel to independently conform to uneven terrain, allowing the rover to traverse obstacles twice the diameter of the rover's wheels.

MER Technical Data

 

We might consider copying the design for all the right reasons. :hihi: Any body know a page with more specs on the mars machines? :singer:

[TheBigDog]

I am guessing that only about 10% of the lander mass will be available as rovers. Much of the mass sent into lunar orbit would be lost as fuel for the landing, and as the rocket system used for the landing.

 

Let us assume that we send 673 KG of mass into lunar orbit, how much mass is required to slow and land on the moon? How much structure is required for the lander and its communications equipment, computer, batteries, and solar cells? How much mass remains for the four rovers, including how they are attached to the lander, and deployed from the lander. Since we are having diversity in our rovers, we may as well have diversity of size on the table. It adds to the research aspect of the mission. Once we find out the total mass we can have, we then horse-trade among the rover teams for allotment of mass, and see how it drives our designs.

 

I think that Craig is on the money about needing to do real world testing (as opposed to real lunar testing). We should form an environmental testing team. Any volunteers for that?

 

Bill

[DougF]

Here is a site that has good information that you might be able to use.

 

Rover mission analysis and design - Wikiversity

[freeztar]

I found this site that deals with dust experiments as well as solar cell longevity:

NSSDC Master Catalog Display: Experiment

[Roadam]

It looks just like we hit the hard wall as no one has posted for several days.

 

Idont think that copying mars rover design is to any good for this project. For one thing it greatly complicates things, and maybe isnt really needed after all. One of the goals in this xprize is to snap photos of older manmade things on the moon. So why not try to land near one apollo lander which is standing on reglith plain. There would be many things to picture and as far as I saw from apollo pictures, things arent so rocky that our rover would have to climb over.

[TheBigDog]

It looks just like we hit the hard wall as no one has posted for several days.

 

Idont think that copying mars rover design is to any good for this project. For one thing it greatly complicates things, and maybe isnt really needed after all. One of the goals in this xprize is to snap photos of older manmade things on the moon. So why not try to land near one apollo lander which is standing on reglith plain. There would be many things to picture and as far as I saw from apollo pictures, things arent so rocky that our rover would have to climb over.

I wouldn't say we hit a wall; we are just at the beginning. The official rules were supposed to be released on Thursday, but I have not seen them posted on the official site yet. In the mean time we have so math to do. Janus had mentioned that we could get 673 KG to lunar orbit. Of that, how many KG could we softly land on the moon? That gives us the mass for the lander and rovers.

 

I am going to build a rover. I am using Radio Shack as my outlet for all parts if I can manage. It will plastic rather than aluminum, but it will be my prototype rover. Once I have a prototype that I am happy with I will begin the process of conversion to moon safe materials. I will document the process online.

 

Bill

[Janus]

I wouldn't say we hit a wall; we are just at the beginning. The official rules were supposed to be released on Thursday, but I have not seen them posted on the official site yet. In the mean time we have so math to do. Janus had mentioned that we could get 673 KG to lunar orbit. Of that, how many KG could we softly land on the moon? That gives us the mass for the lander and rovers.

 

I am going to build a rover. I am using Radio Shack as my outlet for all parts if I can manage. It will plastic rather than aluminum, but it will be my prototype rover. Once I have a prototype that I am happy with I will begin the process of conversion to moon safe materials. I will document the process online.

 

Bill

 

Doing some research and some numbers, here's some rough estimates.

 

Using "off the shelf" rocket motors from Thiokol, the people who produced the RAD rockets for the Pathfinder mission:

 

Using a STAR 20 engine, we kill most of the orbiter's orbital motion.

We discard the used engine (28 kg) and its superstructure, say, 50 kg.

 

This leaves us with 325 kg after accounting for the fuel used by the STAR 20.

 

From here we use the Pathfinder landing procedure sans parachute. At the proper altitude (using a radar altimeter), we lower the main landing package by a tether attached to the RAD (rocket assisted descent) section.

 

Inflate the air bags

 

Using 6 STAR 8 engines (pathfinder used 3, but we don't have a parachute to help), we kill the remaining velocity just a little bit above the surface.

 

We release the tether and let the landing package drop to the surface, keeping the impact velocity under 100 kph (about the limit for air bags.)

 

6 fueled STAR 8's mass 105 kg, asuume another 50 kg for mounting super-structure, and this leaves us with an estimated 170 kg soft landed, minus the mass of the airbag system.

[TheBigDog]

What if we go Apollo style instead of airbags and rocket straight to the surface? There is a randomness to the airbag landing that really bothers me.

 

Bill

[freeztar]

I am going to build a rover. I am using Radio Shack as my outlet for all parts if I can manage. It will plastic rather than aluminum, but it will be my prototype rover. Once I have a prototype that I am happy with I will begin the process of conversion to moon safe materials. I will document the process online.

 

Awesome Bill! I admire your enthusiasm!

 

I look forward to your progress.

 

As far as the weight issue is concerned, I think the first step is to calculate the amount of fuel and type of rockets needed for the LM to make a soft landing, If indeed we plan on using rockets to slow and stabilize the descent. Specifications for the type of transmitter we will use will also be helpful in figuring our weight requirements.

[Jay-qu]

170kg thats great :confused:

 

I got emailed the official guidelines this morning. I will attach them to this document.

 

NOTE these are not set in concrete and may be subject to change, until jan 2009, up until then anyone can make suggestions to change these guidelines to help make them more fair and iron out any loopholes.

[TheBigDog]

I am looking at a 4wd electric monster truck as my starting point. I am going to remove every cosmetic feature on the thing, reducing it to a remote controlled moving platform. I am going to fashion an array of batteries instead of the single one that it normally runs on. My goal is to give it a range of 10 km on a single charge, twice the distance requirement for the range bonus.

 

Control will be as follows: we will have a website that is actually hosted by the lander. From there we will be able to look at live camera shots from the rover, and issue commands to the rover. A command can be a series of maneuvers. We might tell it to turn 30 degrees, then move forward for 30 meters. It will begin the maneuver and continue until it is complete, or until it either gets a signal to stop. When it stops we will evaluate the position and send a signal for the next move. The lander will have a wheelbase of about half a meter. It will have a mast that extends up where the antenna for communication with the lander will be located. There will also be a probe used for recharging. I am considering having the lander able to auto guide the rover to the recharger, so once we get it close it can do the final distance with precision.

 

We can indicate what type of photography for it to take along the way. It will have the low resolution navigation cameras on all the time, but we can choose to activate the HD camera and give it specific instructions as needed. The HD camera will be used for the HD movies, panoramic shots, and extreme close ups. All photography will be stored locally on the rover and uploaded to the lander. The lander will then relay the files back to earth through it's website.

 

My goal is to be able to complete the requirements of the mission on the initial charge in the rover, and the initial charge on the lander. If the solar panels fail to deploy on the lander, or the recharger fails to function, we will still have a successful mission and qualify for the prize. Assuming that those systems don't fail we then aim at the bonus prizes.

 

There will be four rovers, so we have ample opportunities, even room for friendly competition on the team. We should be able to control all the landers simultaneously.

 

My vision of the lander is the Eiffel Tower. Tall with four feet in a wide stance. It will unfold itself in space and fall feet first toward the moon. The rovers will be attached under the center of the lander and lowered or dropped the last distance to the surface after we have touched down. The top or the tower will be the comm antenna for controlling the rovers as far out as possible. The solar array for the lander will be as high up as we can keep it. There will also need to be a high gain antenna that points at earth for communications. The solar array on the lander should be large enough to run the main communications, with enough excess to charge the landers. I think that we should actually have a large array of batteries on the lander so it is always in the act of charging the low ones. We then run of charged batteries and even recharge the rovers from charged batteries as needed. This of course is all open to debate.

 

All systems will have some automation. The solar array should be able to rotate for best angle to the sunlight. Just before it loses sunlight it should rotate into position for when the sun comes back into view and wait. When the sun warms the equipment and begins charging things everything will wake up again. This too can be on a timer as we will know pretty much exactly when it is going to happen. The rover I build will have a fail safe in case it loses contact with the tower. If it determines that it has been out of contact for a default time it will plot a reverse course to the lander and self navigate until it restores communications. It will be using low powered signals to transmit telemetry to the lander, the antennas on earth should be able to snoop on those signals, so if the rover cannot regain contact with the lander we should be able to at least observe what it is trying to do to regain contact. This of course can all be tested prior to launch.

 

But I am getting way ahead of myself. I went out today and looked at various RC cars to use as a base. Lots to learn and lots to do. Before any of that I need to finish cleaning the garage and build myself a good workshop.

 

This is too much fun!

 

Bill

[Janus]

What if we go Apollo style instead of airbags and rocket straight to the surface? There is a randomness to the airbag landing that really bothers me.

 

Bill

 

From what I can figure, you could land about that same 170 kg.

 

The problem is that that 170 kg includes the landing motor, landing gear, fuel tanks, atitude control system, and the additional frame work to mount them to.

 

Plus the need for a much more sophisticated landing control system.

 

Leaving us with a much smaller "working" payload delivered to the Moon.