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#101 2016-06-13 05:34:47

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 974

Re: Bikes on Mars? - Don't laugh!

Speed will be limited by the topography of the terrain, the surface conditions, weight of the vehicle and peddling power of the passenger.

Rolling resistance is equal to weight multiplied by rolling resistance coefficient.  According to engineering toolbox, the coefficient for ‘car tire on solid sand, gravel loose worn, soil medium hard’ is 0.04-0.08.

http://www.engineeringtoolbox.com/rolli … _1303.html

For vehicle mass 150kg (70kg man + 80kg vehicle), this would result in a rolling resistance of 22.4-44.7N on Mars.  Assume that cyclist power is 250W on average; this would put top speed at 5.6-11.2m/s (20-40km/h) on flat terrain.  On hilly terrain or sandy soils, speed will be lower.

4m2 of solar panels covering the vehicle would boost power by ~100W and may only weigh a few kg, so would be a worthwhile addition.  On the plus side, electric motors have excellent torque at low speed.  So even if power is low, the vehicle will not stop entirely.

Roll-out solar panels would increase weight, but would allow the vehicle to increase range by allowing drinking water to be recycled and oxygen supply to be regenerated.  The vehicle should probably stop between late morning and mid-afternoon when insolation is greatest.  If this were done, a lithium ion battery capable of storing 1kWh would weigh of a few kg and would extend daily range by ~100km and would greatly reduce reliance on pedalling.  All depends on how lightweight those solar panels can be.

I am assuming the astronaut could be equipped with a minimum counter-pressure suit that is relatively lightweight (for excursions away from the vehicle).  How much would this weigh?

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#102 2016-06-13 18:26:18

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 2,712
Website

Re: Bikes on Mars? - Don't laugh!

Bikes on Mars make sense with an MCP suit,  but not with any of the full pressure suit designs I have seen proposed.  Most of those would make it impossible to get up alone,  if you fell over.  Plus,  if you puncture a full pressure suit,  you are dead if you cannot get inside before it deflates,  period,  end of issue.  Not true with MCP,  which you can "patch" with a tight wrap of duct tape.  Fall over with a bike on Mars,  and the odds are very high you will suffer a puncture. 

I don't know figures for Dava Newman's modern incarnations of MCP,  but the old 1968-vintage version from Paul Webb was 85 lb for the vacuum-protective underwear plus a helmet and breathing bag,  plus a LOX makeup backpack.  To that you could add 15 lb of protective unpressurized outerwear,  and still fall near 100 lb "turnkey" for the suit.  Don't know how long Webb's backpack would supply oxygen,  though.  No air conditioner or water-cooled underwear needed.  You sweat right through the garment into vacuum,  just like here into not-vacuum,  just more efficient. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#103 2016-06-13 19:22:18

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 10,650

Re: Bikes on Mars? - Don't laugh!

Thanks Antius for the rolling resistance coefficient stuff as someday I may build something for earth bound use....

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#104 2016-06-14 08:32:06

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 2,712
Website

Re: Bikes on Mars? - Don't laugh!

For perspective on the rolling resistance coefficients, consider the rolling resistance coefficient for car and light truck tires on a hard pavement like asphalt or concrete:  0.014-0.015 typical.  I actually measured the forces with a spring scale,  and they do indeed come out pretty close. 

I can certainly tell a huge difference between riding a bike on pavement versus soft dirt,  even one with balloon tires.  I'd be surprised if the coefficient of a bike on Mars isn't above the range Antius quoted.  Maybe more like 0.10 or possibly higher still in really fine,  soft stuff.  The deeper you sink in and start plowing,  the higher it goes. 

The softer the sand,  the more the tires sink in,  and the higher the rolling resistance coefficient.  This can get to the point that the wheel quits turning,  and you are back to static/kinetic friction behavior,  complicated by a plowing force.  While weights are lower due to reduced gravity on Mars,  there's an awful lot of loose sand and fine dust in which to sink.  Any bike is going to need big balloon tires to stay on top where the rolling resistance is not too high. 

GW

Last edited by GW Johnson (2016-06-14 08:35:13)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#105 2016-06-14 13:33:45

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 974

Re: Bikes on Mars? - Don't laugh!

Most Martian terrains photographed so far are either sandy, as you have suggested, or rubble strewn.  In both cases, a two-wheeled bike would not appear to be very workable, from the point of view of surface pressure and rolling coefficient with sand, and stability in rubble strewn fields.  Seems more likely that something like a quad bike would work better, using balloon tyres and an Kevlar inner lining.

I did some research last night on P/W ratio of flexible solar panels and energy density of lithium ion batteries.  A 1kWh Lithium battery would weigh a minimum of 5kg.  The flexible panels I was looking at had an efficiency 22%.  They wouldn't say how much they weigh.

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#106 2016-06-14 14:32:28

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 2,712
Website

Re: Bikes on Mars? - Don't laugh!

Well,  given an lightweight MCP suit,  and a roll of duct tape to patch punctures "on the go",  something resembling a mountain bike with big "Fat Frank" tires might actually work on some of the mixed sand/rock terrains. 

It is amusing to think about a sight like that. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#107 2016-06-14 19:46:53

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 10,650

Re: Bikes on Mars? - Don't laugh!

I took the time to fix the artifacts and shifting for the first 3 pages....

I went back through the topic to see if we talked about tires but much to my amazement we did that in another topic....

So we will need to do some experimenting here on earth to simulate the conditions that have been putting holes in the Rovers tires so that we can make them to resist the terrain of mars.....

Agreed that the MCP suits would be the way to go.....this would allow for low pressure inside the car while pedaling so as to keep it on the ground if we bump or bounce.....

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#108 2016-06-14 21:00:22

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 2,712
Website

Re: Bikes on Mars? - Don't laugh!

Well,  rover "tires" have typically been metal of late.  I sure as hell hope they have learned driving Curiosity's aluminum tires on sharp rocks is a very bad idea. 

Quite frankly,  I think the Goodyear run-flat tire design would have been a more durable choice for a design startpoint,  even if they had to warm the rubber to keep it flexible.  Curiosity is nuclear-powered,  after all.  There has to be some heat to spread around. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#109 2016-06-15 17:58:12

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 10,650

Re: Bikes on Mars? - Don't laugh!

Antius I think these are about what you have discribed in "flexible panels of efficiency 22%" High Efficiency Flexible Solar Panels with SUNPOWER cells
http://rvsolarsupplies.com/wp-content/u … ebsite.pdf

SunPower 40W Solar Panel
Flexible, lightweight three panel design folds to 11" x 11" and weighs only 2.2 lbs making it ultra portable

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#110 2017-05-09 13:16:52

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 10,650

Re: Bikes on Mars? - Don't laugh!

Bump just wondering if a 4 wheeler built for two might work after modifications for mars....

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#111 2017-05-09 13:40:32

elderflower
Member
Registered: 2016-06-19
Posts: 558

Re: Bikes on Mars? - Don't laugh!

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#112 2017-05-09 16:06:53

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 10,650

Re: Bikes on Mars? - Don't laugh!

A single seat collapsed to save space while stowed is not a bad thing once we are in a dome but for safety 4 wheels would be safer.

This is an exaple of the adult sized vehicle that can be pedal powered....

1181681?$300$

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