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Bikes on the moon

Old 07-31-20, 06:14 PM
  #26  
Pop N Wood
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Originally Posted by DrIsotope
The single biggest force a cyclist has to overcome is wind resistance. The moon has no atmosphere, so that is off the table. The rider then only needs to overcome minimal rolling resistance, and account for equally minor mechanical losses. According to the calculator here, a combined rider + bike of 150kg, unrestrained by drag, requires just 176W to maintain 60m/s (117mph.)
Interesting. But that calculator didn't have a radio button for "moon suit".

I would imagine things quickly go non-linear at the near orbital speeds some of these guys are projecting. Even 117 mph is probably beyond the assumptions of that calculator. I'm projecting the mechanical losses will be more than "minor" at that speed.

Definitely need special wheels and tires. Ran my ebike up to 53 mph open loop speed while on a bike stand. Thought that sucker as going to vibrate right out of the garage.
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Old 07-31-20, 06:15 PM
  #27  
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Originally Posted by General Geoff
Regular pneumatic rubber tires would work fine on the moon IF there is a smooth, paved road there. The reason they didn't use em for the lunar rovers had more to do with avoiding potential flats and negotiating extremely rugged regolith terrain.
Well, plus the minor effects on rubber of vacuum and harsh UV radiation.
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Old 07-31-20, 06:35 PM
  #28  
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It would undoubtedly be solid tires on solid wheels, as there’s no need to save weight, and no need to worry about wind resistance. Wider tires would be better, something like one foot or more, for stability at speed.
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Old 07-31-20, 06:37 PM
  #29  
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Originally Posted by datlas
Pretty sure regular pneumatic tires would pop instantly in the vacuum of the moon. Solid rubber makes more sense. Hypothetically, of course.
Reduce internal pressure by one atmosphere. Gauge pressure is internal pressure minus external pressure. That is, gauge pressure uses atmospheric pressure as its zero point.

Otto

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Old 07-31-20, 07:03 PM
  #30  
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Originally Posted by woodcraft
to test, instead of a wind tunnel, need a vacuum tunnel.
A drag-free chamber would actually be better than a vacuum, and wouldn't be that hard to build.
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Old 07-31-20, 07:04 PM
  #31  
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Originally Posted by Pop N Wood
Interesting. But that calculator didn't have a radio button for "moon suit".
A man’s gotta know his limitations. I can make some estimates on the basic terms of cycling work: rolling resistance, air resistance and climbing/descent, but I have no data about pedaling work in a space suit! 😊

Otto
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Old 07-31-20, 07:22 PM
  #32  
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Well, maximum speed would be the same as on earth, as the stunt players filmed this in 1969 in Area 51.
So not really much of a vision.
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Old 07-31-20, 10:21 PM
  #33  
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Originally Posted by livedarklions
Well, it's a moon bike, so definitely not normal. Not sure how the stresses compare when the gravity is reduced and air friction is eliminated.
Damn it another new style of bike I need...cannot keep up. First it was a billion different off road road bikes now it is intergalactic bikes. 'You can't really ride on Mars with a Moon bike sure back in the day they rode Moon bikes but they weren't riding as technically as we do now" and then the other guy saying "moon bikes were the original Mars bikes just with slightly smaller wheels and no drop bars except for Neil Tomac but he was crazy"
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Old 07-31-20, 10:52 PM
  #34  
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Because it’s NASA the bike will mass about nothing and the moon suit will be a thousand lbm.

This is not as interesting as big air BMX or observed trials on the moon.
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Old 07-31-20, 11:01 PM
  #35  
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Further on the topic of the suit... space suits are pressurized at about 5 psi so the joints are holding hundreds of pounds and have some friction. The ideal thing for efficiency would probably be a pressurized rover where the rider is free to move inside and the only moving parts that go through the shell would be a driveshaft and steering
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Old 08-01-20, 01:37 AM
  #36  
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How slow could you go? Could you trackstand? How far could you lean?
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Old 08-01-20, 10:08 AM
  #37  
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Originally Posted by fietsbob
The bike will be feeling Lighter.. lower gravity..
Yes, but be sure to save as much weight as possible by using overpriced water bottle holders.
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Old 08-01-20, 10:37 AM
  #38  
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You absolutely do need to save weight. It's even more important than on your primitive Earth bikes. Weight is the thing causing your friction losses.

Tires will not explode. Vacuum is 0 psi, not minus infinity psi. (If anyone comes up with something that makes pressure below 0 absolute, patent it immediately.)

It's very likely you would need to take into account the time to accelerate up to the speed you want, and time to decelerate to reverse, because it's still only 1/4hp or something. The energy tied up in the wheels too. You will likely need to model a spherical Moon because by the top you're doing a pretty good percentage of the minimum orbital speed.

Added on edit: you don't need a rotating spherical moon because the moon rotating slowly enough to ignore and the effect is canceled on the return trip.
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Old 08-01-20, 10:39 AM
  #39  
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Old 08-01-20, 10:41 AM
  #40  
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Originally Posted by DrIsotope
It would undoubtedly be solid tires on solid wheels, as there’s no need to save weight, and no need to worry about wind resistance. Wider tires would be better, something like one foot or more, for stability at speed.

There's still gravity, right, so some suspension needed, unless the road surface is perfectly smooth, which takes the whole thing to an otherworldly place...


Also, you could go faster if the road was oriented on the side of the moon going down, rather than the top or bottom.
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Old 08-01-20, 11:50 AM
  #41  
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You need enough tire distension and road roughness to make traction to pedal and steer even if the road is perfectly smooth.
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Old 08-01-20, 12:26 PM
  #42  
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Originally Posted by Darth Lefty
Tires will not explode. Vacuum is 0 psi, not minus infinity psi. (If anyone comes up with something that makes pressure below 0 absolute, patent it immediately.)

It's very likely you would need to take into account the time to accelerate up to the speed you want, and time to decelerate to reverse, because it's still only 1/4hp or something. The energy tied up in the wheels too. You will likely need to model a spherical Moon because by the top you're doing a pretty good percentage of the minimum orbital speed.

Added on edit: you don't need a rotating spherical moon because the moon rotating slowly enough to ignore and the effect is canceled on the return trip.
As I said, you just need to lower internal pressure by one atmosphere although you could get away with more because the tires will be bearing one sixth the weight.

I didn’t show all my work but yes, available traction will limit your acceleration. My estimate was that I could increase (or decrease!) my speed by not more than 6 km/hr per second.

Otto
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Old 08-01-20, 12:58 PM
  #43  
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Yeah, sea level pressure over hard vacuum is about 14.7 psi. I'd use nitrogen to inflate the tires, but otherwise pneumatic will work fine. The unfiltered sunlight, however, will be hard on everything.
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Old 08-01-20, 05:22 PM
  #44  
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The more I think about this the more fun it is.

If all of your power output is being turned into friction losses you need to cool the drivetrain. That'd probably be tied into your life support, which is already managing something like 3x that much heat (following the power meter joule/calorie logic). Or maybe it'll radiate ok at a low enough temperature. The brakes are far more powerful and present a bigger challenge. But you do need brakes, slowing down by human power would be much less effective.
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Old 08-01-20, 06:09 PM
  #45  
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IIRC, the Lunar Rover has metal mesh tires
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Old 08-01-20, 07:47 PM
  #46  
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Fascinating history and current engineering

For rugged terrain without roads or tracks, spring mesh tires (made from nickel titanium memory alloy) is the best option, providing excellent traction without too much deflection, and able to 'heal' after rougher terrain.
The soviet rover used what is essentially a bare rim with treads, while a pneumatic tire has been used on the moon as part of a tool dolly.

All of these things work! It's up to the OP to specify the track material/surface. Maybe pine planks?
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Old 08-01-20, 08:13 PM
  #47  
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Originally Posted by Unca_Sam
Fascinating history and current engineering

For rugged terrain without roads or tracks, spring mesh tires (made from nickel titanium memory alloy) is the best option, providing excellent traction without too much deflection, and able to 'heal' after rougher terrain.
The soviet rover used what is essentially a bare rim with treads, while a pneumatic tire has been used on the moon as part of a tool dolly.

All of these things work! It's up to the OP to specify the track material/surface. Maybe pine planks?
I have no idea what materials could work in that environment, especially without water, but let's assume the same friction characteristics as an uncracked concrete road on earth.
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Old 08-01-20, 09:03 PM
  #48  
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LDL said in his first post, "Imagine that someone built a smooth, perfectly level 100 mile road on the moon" and that's why I was still assuming pneumatic tires. But that might not be a good idea north of three hundred miles an hour (dragster territory). I've been trying to find out more about the wheels on land speed record cars. This is what I found so far, in re: the Bloodhound SSC, which is aiming for 1000 mph with jet power and a rocket assist:

Wheels[edit]For low-speed testing at Cornwall Airport Newquay in 2017, the car was fitted with four runway wheels based on those of an English Electric Lightning fighter jet with refurbished original tyres.[44] These were replaced for the high-speed test runs in the desert in South Africa in 2019 by four 90-centimetre (35 in) diameter wheels weighing 95 kg (209 lb), forged from an aircraft-grade aluminium zinc alloy.[45] These were designed to spin at up to 10,200 rpm and resist centrifugal forces of up to 50000 g at the rim.[46][47]
Bold emphasis added by yrs. trly. Things get important that you might not expect.

This stuff is not easy. The TV personality Jesse Combs was killed last year in an attempt to break the four-wheel record run, in a car called North American Eagle, which was an ancient F-104 without its wings. Her run was awarded as a record posthumously because she did make the time over the track both ways before the crash, which was probably caused by some debris on the lake.
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Old 08-02-20, 11:17 PM
  #49  
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I see most people here do not understand the difference between Force (weight) and Mass.

Although gravity (acceleration downward) is 1/6 Earths, your MASS is unchanged. You still have to accelerate the same mass forward as you would on Earth. Your wheels have to accelerate the same mass rotationally. F=MA is unchanged for forward motion between the Earth and Moon.

Assuming a flat road on the moon, gravity isn’t much of a factor except for your friction to the lunar surface, which is something like loose dirt. So traction is a real engineering challenge. I’m going with my Fat tire bike.

The lack of atmospheric effects / wind resistance has been well covered.

I’m personally more interested biking on Mars

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Old 08-02-20, 11:39 PM
  #50  
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Originally Posted by General Geoff
I dont think any normal bicycle will survive much past 120 mph without wheel balancing and beefier bearings.
Nah, reckon it'll be all good on the bearing front at least. I've done 72km/h on 12" wheels before, and that works out to about 1200rpm. that'll get you up to 144km/h at least, with 700C wheels. And that's with the worst wheels ever, some kiddies wheels with pressed steel bearing cups, pot metal bearing cones, a wheel that wasn't ever round and 16 spokes made of fencing wire, straight laced, so any kind of vaguely well made bearings would cope I'd think. The 6809 bearings in my MTB are rated to around 28,000 rpm, so about 2,100mph on a 700C wheel!. With 1/6 the gravity I reckon the only issue would be wheel balancing and the gyroscope effect working against the reduced friction.A little unbalance could see you getting up a pretty good bounce, so well balanced superlight wheels would be the go.
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