[TheBigDog]

Camera's and radios can be tested on any platform. We will move toward final rover designs with higher associated expense over time.

If 5 kg proves too low then we can change that. I think that the total engineering challenge will be similar in all sizes, but some of the costs can be constrained by keeping to a small size. A great deal can be done with 5 kg.

Bill

[Turtle]

Originally Posted by freeztar

Wouldn't you need an anti-centrifuge?

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?

Originally Posted by freeztar

You might be right, but we need a definitive parts list first to make that call, yeah?

Affirmative

Originally Posted by freeztar

Very good point! It would indeed require the same amount of joules to accelerate/decelerate the mass of the rovers wether here or on the moon. But weight should make a difference, particularly if we used a "hopper" design like CraigD suggested.

Since we have in mind to have multiple rovers, I see no reason to not have them all different? People can work on whatever team or teams they fancy. yes/no?

Janus gave some masses for operational LEO launch systems and I wonder if there is any advantage is going below what a particular system is rated for? Keeping in mind we will have a considerable amount of mass involved beyond that of the individual rovers.

Originally Posted by Freezta

Here's a nice comparison graph I found.

Acknowledged.

Originally Posted by Freezemeister

Which cars have you been looking at? I remember from my days as a kid that the higher-end RC's were almost exclusively metal (once stripped of their body). Of course, they are much more expensive and I'm not sure about their power.

I borrowed a big electric car (Jeep Grand Cherokee body which I removed). It is 2-wheel drive with fat off-road tires & powered by a 9.6 volt battery. Manufacturer is Scientific Toys LLC & made in China (I have not put it in my mouth. ) It has a two-channel radio. The motor has a metal case, but it is entirely contained in a plastic gear-box and has a protrudung cooling fin array. I think the all-metal cars you have in mind are the gas-engine models?

[Turtle]

Originally Posted by TheBigDog

Camera's and radios can be tested on any platform. We will move toward final rover designs with higher associated expense over time.

If 5 kg proves too low then we can change that. I think that the total engineering challenge will be similar in all sizes, but some of the costs can be constrained by keeping to a small size. A great deal can be done with 5 kg.

Bill

Acknowledged. What I see as a problem for a small wheeled rover the size of an RC is that the terrain is then much rougher by scale. When making my prototype video, the car high-centered at the end on a small hummock of grass on a 2 inch "cliff" down to raked garden soil. I drove it all of 20 feet. The Moon's surface is no backyard.

[freeztar]

Originally Posted by Turtle

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?

I see what you are getting at, but you have to consider the x-axis vector as well, no?

Since we have in mind to have multiple rovers, I see no reason to not have them all different? People can work on whatever team or teams they fancy. yes/no?

I agree, to a point. I think the basic chassis and electronics should all be the same for manufacturing cost reasons, but it would definitely be great to have versatility in functions.

Janus gave some masses for operational LEO launch systems and I wonder if there is any advantage is going below what a particular system is rated for? Keeping in mind we will have a considerable amount of mass involved beyond that of the individual rovers.

My guess would be that the advantage would be more velocity, but we only really need "enough".

I borrowed a big electric car (Jeep Grand Cherokee body which I removed). It is 2-wheel drive with fat off-road tires & powered by a 9.6 volt battery. Manufacturer is Scientific Toys LLC & made in China (I have not put it in my mouth. )

I suppose we should start testing the effect of Hg on regolith.

The motor has a metal case, but it is entirely contained in a plastic gear-box and has a protrudung cooling fin array. I think the all-metal cars you have in mind are the gas-engine models?

Yes, now that I think of it, I am thinking of the gas-powered models.

[TheBigDog]

I was thinking that the wheels would be very oversized compared to an off the shelf RC, but I get your point about the scale of obstacles. I need to get my hands dirty with this.

Another thought I have had... what if the drives are hydrolic, and the motor is submerged in the fluid to absorb the heat? This could provide both the cooling for the motors and the ability to have other ways of moving the rover around.

Bill

[Turtle]

Originally Posted by freeztar

I see what you are getting at, but you have to consider the x-axis vector as well, no?

I haven't a real clue. Just looking for an excuse to build an expensive science thingy.

Originally Posted by Frezolith

I suppose we should start testing the effect of Hg on regolith.

I wonder if the contest rules will have environmental standards we have to meet? No oil spills allowed!?

Originally Posted by Bill

I was thinking that the wheels would be very oversized compared to an off the shelf RC, but I get your point about the scale of obstacles. I need to get my hands dirty with this.

Then there is the matter of wheelbase length (front-to-back) and the "width" between wheels side-to-side(can't think of any automotive term for that measure just now). Another problem with smaller wheels is that for our given distance goal of 500 meters the smaller wheel/tire will experience more wear than a larger wheel/tire.

That's all I got. Ohh wait...it's not all. I found this camera looking for "miniature high resolution color video cameras". The only industrial source I found required registration. >> Sony EVI-HD1 HD High Definition PTZ Camera at a low price

[Janus]

Originally Posted by Turtle

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?

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 . 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]

Originally Posted by Janus

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.

Originally Posted by Roadam

...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. :

edit: addendum: Mars Exploration Rover Technical Data
The Mars Exploration Rover Maintenance Manual
MER Technical Data

[Jay-qu]

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.