Tracked vehicle construction?

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Postby carmatic » Sun Dec 27, 2009 7:07 pm

picture that the gears physically exist, floating in the space before your eyes....

start with the bottom-most gear, then add the next one, then the one after that and so on, and work your way towards the entire diagram
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Postby carmatic » Mon Dec 28, 2009 1:28 pm

i feel that my posts might have been somewhat inaccessible to you guys...

so i hope that i can clear some things up, and try to do a post that's slightly more enjoyable to read

consider this diagram:
Image

what you have is a round thing rolling betwen 2 flat surfaces... the surfaces continue on and on to the left and to the right....

now, those surfaces are moving... the upper , orange surface is moving in the opposite direction to the lower, purple surface... kind of like, rolling something between the palm of your hands

if the speed at which the surfaces move are exactly equal, but still travelling in opposite directions, the round blue thing will be rolling, but it will not be moving left or right
now, pretend that one of the surfaces has stopped moving... the blue thing will be rolled along at half the speed at which the surface is moving, in the same direction as the moving surface

if one of the surfaces is moving slower, but not stopped, it will be as if its somewhere between moving at equal speed and being stopped... as in, the blue thing will be moving, but it will not be as fast as when one of the surfaces has stopped moving in the opposite direction

mathematically, the blue round thing will be moving at the average of the velocities of the surfaces... velocities as in saying something like if it moves to the right, you add, if it moves to the left, you subtract....


now , imagine that the horizontal-ness of the diagram is wrapped into a circle... so the 2 flat surfaces will become circles, one inside the other, and instead of moving left or right, they will be rotating clockwise or counterclockwise ...

so the outer circle will be rotating in the opposite direction from the inner circle... the blue round thing will still be rolling between the circles which the purple and orange surfaces have become, and its speed will still be the average of the speeds of the 2 circles...

the speed is not to be confused with rotation rate.... rotation rate multiplied by the size of the circle equals the speed... a big circle rotating slowly has the same speed as a small circle rotating quickly
its the same thing as the speeds of the flat surfaces, except simply moving in a circle rather than a straight line...

---------------------------------------------------------------------

and if you've understood everything i've typed above, you will have understood how epicyclic gears work, and that is the gist of what i have been posting about all this time ... inner circle is called the Sun, the outer circle is called the Annulus, and the blue round thing is the Planet Gear ...
----------------------------------------------------------------------
so by having the Annulus and Sun rotate at different speeds, the Planet Gear will move in a circle, in the space between the Annulus and Sun gears ... it will move in the direction of whichever gear is spinning faster, at the average of the speeds of the gears, just like if it had been rolling between two flat surfaces...
if the Planet Gear is held by something, its movement can be harnessed... this is what the Planet Carrier is for, and it is what actually causes the tracked vehicle using my transmission to move


now, consider this diagram
Image
its a picture i posted in the last page, but edited...

the colour scheme is the same, and it would make complete sense if you have been following what i've been typing....
so you have the Sun Gear analogous to the lower surface, the Annulus analogous to the upper surface, and the Planet Gears... the yellow circle is the CVT , and the thick black line is the chain

because of the chain, the speed of the Annulus is equal to that of the CVT ... its rotation rate will be lower because of its bigger size, but that doesnt matter...
can you see now, if the Sun Gear turns at a constant speed, you can control the speed of the green brackety Planet Carrier by controlling the CVT? as well as making it stop and turn in both directions...
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Postby carmatic » Mon Jan 04, 2010 2:09 am

ok here we go

a rough idea of the partial parts list

Image

The planet carrier... this is the part which has to be custom fabricated, its represented by the red square in my diagrams.... it is basically the centerpiece of my transmission

a pair of these parts, one for each side, will set you back $344 ... aluminum 6061 T6 , for an epicyclic gear set with a 6 tooth Sun, 7 tooth Planet gears and a 20 tooth Annulus , at 2 teeth per inch pitch... the nubs will hold the Planet gears...

Image
gear housings, lifts the gears clear of the surface they are mounted on, roughly $190 for a pair, need 2 pairs

these are still imaginary parts, but at least now they have a somewhat tangible price (~ $724 so far)...


Image
an example of a sprocket which can be screwed into another coupling or something... just need one good, strong one , and a bunch of other cheap ones

still need:
the gears (of course) and the associated bearings,
a shaft in the middle of the transmission which keys into one of the gears and holds the sprocket as well, some way of connecting my Planet Carrier to the drive sprocket on the outside,
the drive sprocket itself and the tracks,
another shaft closer to the rider, holding the sprocket for the chains to the pedals, as well as 3 sprockets for chains into the transmission
and oh, the CVT's as well...

what do you builder guys think?
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Postby rodiponer » Mon Jan 04, 2010 10:28 am

The prices are from emachineshop, right? Their prices tend to be very high: they assume every part must be made as if it is going into a rocket ship engine.

I think the tolerances for these parts are loose enough that they could be made at home. The planet carrier would be easier to make if it could be two round plates and four clevis pins, with the gears between the plates, instead of being a single plate that is milled so the shafts stand out of it. This would reduce the cost to about $30 in aluminum, an hour of careful drawing with a protractor, and then drilling four holes.

The gear housing is even easier, just cut the rough shape with your favorite tool and then drill, right?

If the planet carrier needs tighter tolerances than can be done by hand, I will try to bang it out on my mill and gift it to the tracked vehicle constructor. Their money is better spent on a cool Cylon LED strip:
http://www.youtube.com/watch?v=VFd_H_RuwB8
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Postby carmatic » Tue Jan 05, 2010 12:53 am

lol@ the ice leds ... best thing i've seen today

yes, those are emachineshop prices...
but there is no point physically fabricating the parts until i can make sense of what they will be attaching to...
there are places to get custom gears and sprockets done, so i think that i will make everything conform to the shafts and couplings i can find...

any suggestions for those shafts and couplings? how do you guys attach your drive sprocket to your transmissions?

----------------------------------------------------------------------------------

the thing about the gear housing is that, you have to worry about aligning the gears , too far apart and you'll snap their teeth, too close together and you'll grind their teeth down ... since this design is a concentric gear design, i thought about doing this:
Image
a shaft going between the Sun gear and Planet Carrier ... i can specify that there be a hole in the middle of the gears to hold that shaft, which should keep the gears aligned even if the gearbox is abit sloppy... i could use something like this
Image
to hold the power transmission shaft, and a series of spacers on the shafts to stop the gears from moving side to side and touching where theyre not supposed to...

----------------------------------------------------------------------------------


but its all abit up in the air, until i can get a good idea about the shafts and couplings... for example, how should the Sun gear be attached? in the diagram its a simplified stalked gear... but it could be anything else, some examples from left to right:
Image Image Image Image Image
you could key the gear for the power shaft, that's what the thinner part of the shaft means ...

leftmost: keeping the power shaft and centering shaft seperate, this is probably the structurally weakest design, but also the most probable to be made, since the 2 shafts are independent of each other and the gears can be made in any way

second from left: extending the centering shaft into the power shaft, as in the power shaft is hollow so that the centering shaft can fit into it... the centering shaft would have a clip holding a groove in its middle to keep it between the gears... the hollowness might make the power shaft weaker, tho

middle: using the power shaft as the centering shaft... this would require a custom shaft, not too keen on having so much custom stuff in the design

second right: deleting the stalk ... so you dont hold the gear directly, but you hold it by the shaft... the gear would simply have a key notch in its middle, probably the simplest design

rightmost : depending on what the shaft is like at the ends, you could hold it with screws or whatever...

remember that the gears are completely custom, so it all depends on the shaft ... and the same thing applies to the Planet Carrier, since it is the 'output' of the transmission

---------------------------------------------------------------------------------

speaking of the Planet Carrier... i am worried about the twisting effect on the shafts of the Planet gears, thats the reason i avoided a 2-plate Planet Carrier, since the torque from the Planet Gears would be centered between the plates, while the torque from moving the vehicle will be on one plate only
i suppose you could mitigate the problem by somehow finding really thick Clevis pins, or by adding rectangular standoffs between the gears to resist the twist , like this
Image

really appreciate your mill offer, but im not worried about building it yet until i can get everything finalized... time spent searching for information is alot cheaper than parts which dont fit
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Postby carmatic » Thu Jan 14, 2010 11:27 pm

question to the builders....

im trying to work out the chains and sprockets for my setup

i am thinking of http://shakyparts.com/high_strength_alu ... ckets.html , availale in 35 and 41 pitch.... are there bicycle cranksets which work in that size?
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Postby Tiahaar » Sat Jan 16, 2010 2:13 am

Heya Carmatic, you're amazing, I like the way you think in gears! (wish I could grasp it all as easy)

The 41pitch chain is excellent to work into bikepart/drivetrain setups because it has the same 1/2" pitch as standard single-speed (bmx, cruiser) chain. Its a bit wider but you can work around that and it runs fine on the bike chainwheels. 40 is also 1/2" pitch but wider than 41. Elliot has told me of KSR folks who double-up the bike crank chainwheels and run 40 for extra strength. I used 41 chain on the tandem drive tank seen earlier in this thread.
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Postby carmatic » Wed Jan 20, 2010 11:15 am

Tiahaar wrote:Heya Carmatic, you're amazing, I like the way you think in gears! (wish I could grasp it all as easy)

The 41pitch chain is excellent to work into bikepart/drivetrain setups because it has the same 1/2" pitch as standard single-speed (bmx, cruiser) chain. Its a bit wider but you can work around that and it runs fine on the bike chainwheels. 40 is also 1/2" pitch but wider than 41. Elliot has told me of KSR folks who double-up the bike crank chainwheels and run 40 for extra strength. I used 41 chain on the tandem drive tank seen earlier in this thread.


cool, thanks for the kind words
i was trying to look for the pictures, but it seems that the links are dead... but its certainly surprising to me, the sprocket i linked to is for go-karts, and if '41 pitch' means the same thing as it does for bicycles, that means the same chain used in BMX is also used in go karts? or am i missing something...

anyway, here's a quote i came across today
Abraham Lincoln wrote:I'm a slow walker, but I never walk back

the thing about my transmission is that , when you are exhausted from pedalling through difficult ground , the kind which you need to be in a low gear for... and your arms are all shakey from the fatigue, trying to work the CVT's in that state means the difference between 'low gear' and 'reverse' is equally shakey...
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Postby Elliot » Wed Jan 20, 2010 1:17 pm

:D
I finally got back to this thread.

That was a nice explanation of how a planetary gear system works, by going back to flat parts! I learned those basics decades ago when I learned about automobile transmissions, but I had never seen it boiled down to the flat components. You'd make a good teacher -- or maybe you already "is" one? :lol:

BMX bikes use a variety of chain sizes, but they all have the same 1/2 " pitch as other bike chains -- and 41 and 40 chain. So 40, 41 and bike chains and sprockets (bicycle and industrial sprockets) can be mixed-and-matched, which I do all the time in Kinetic Sculpture Racing. The only thing that matters is the width.

The several different BMX chain sizes are mostly about fashion -- and resistance to damage when scraping the chain against rocks and treestumps. Some of them look almost like chain-saw chains, with wear surfaces facing away from the sprockets. But they are all 1/2" center-to-center distance between the pins.

#35 chain is 3/8" pitch, if I remember right, so it does not match any bicycle parts.

Steering is not an issue for me, so I'm leaving that to the Tracked Vehicle builders, Jafe and Tiahaar -- and others who may be lurking. I'm still in pursuit of an inexpensive and light-weight gear-shifting mechanism that will give me 2000 % range and can be shifted on the fly. Four ratios will be enough; it is the range, shiftable on the fly, that we need.

Recently, it dawned on me that I may be able to use a Chain Gang with 41 or 40 chain for strength, and shift THE INPUTS with bicycle chain and derailers. I may have mentioned this on an other thread already. I would run two chains off the crank (smallest and largest of a normal three-sprocket set), and split those with two derailers for a total of four gears. The big question is whether it is possible to shift the chain between sprockets that are NOT synchonized like the sprockets of a bicycle rear wheel cluster/cassette are. I think it can work if we learn to synchronize with pedal cadence, like heel-and-toe shifting an old car, and accept some "ugly noises".

But now I really MUST earn a living for a while.
:D
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Postby dragonfly Jafe » Wed Jan 20, 2010 6:59 pm

...I have given up on the 100% tracked vehicle for now...although I do plan to pick it back up one day. I am now torn between a big-wheel bike with fire effects or a half-track bike like the old kettengrad's of WWII for BM2010. However, I am fascinated by the talk and trying to follow...a CVT or larger moment arm DDSS wheel, with a stiffer frame and improved track retention features (combined with a weight reduction over my 2006 BioTrak) should do it...
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Postby gyre » Thu Jan 21, 2010 12:11 am

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Postby unjonharley » Fri Jan 22, 2010 12:12 pm

Tracks on the playa, ahla Dragonfly was my first passion vehicle.. But I run off to the next shinny thing.

Just to add an idea.. Take the weight off the tracks by sitting the driver/s in a sulky inside the tracks. The sulky seat would have an axel and wheels. The tracks would pull the sulky
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Postby Gryphon327 » Fri Jul 02, 2010 6:55 am

Wow. Just wow.

I've been thinking about a pedal powered tracked tractor for a few months now. It's nice to see that it would actually work. Thank you for the detailed builds!

Carmatic, your transmission is a work of art! In your first description you had a large gear moving at 1/2c. What is it for? Why not drive the annulus directly from the cvt and the sun from the pedals? Also, can you explain the variables in the equasion a bit more? And finally, is there an equasion that would calculate the torque?

I hope this thread is still watched occasionally. Thank you all for your posts! This has been an exciting read for me. Hopefully some day I will be able to afford a trip to actually attend a Burning Man, but at this point my hands are tied.

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Postby Elliot » Fri Jul 02, 2010 8:19 am

:D
Hey, welcome aboard!
Those who posted on a thread are automatically notified when a reply is posted -- unless they deliberately disable that function. So you should be seeing respnses to your arrival pretty soon.

You may have noticed that the tracked vehicles struggled to actually move much on the Playa. Horrendous friction. But fabulous engineering excercises!
:D
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Postby dragonfly Jafe » Fri Jul 02, 2010 12:48 pm

...yes, as a practical solution a tracked bicycle vehicle is not really viable. No need for brakes - BioTrak would stop the INSTANT you stopped pedalling. Also, even though I could turn at home (with some difficulty), it was at least 2x as hard on the Playa (maybe 3x). I managed a 20 degree turn before I threw a track (made easy by some missing spacer parts left at home by mistake). I think if I had everything properly installed, it would have worked. Decreasing the weight 50% would have helped also.

Tracked bicycle vehicles are possible...
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Postby carmatic » Sat Jul 03, 2010 1:09 am

Gryphon327 wrote:Wow. Just wow.

Carmatic, your transmission is a work of art! In your first description you had a large gear moving at 1/2c. What is it for? Why not drive the annulus directly from the cvt and the sun from the pedals? Also, can you explain the variables in the equasion a bit more? And finally, is there an equasion that would calculate the torque?


in my first transmission, the gearing of the CVT's control how much 'backwards' you go... as in, with a low CVT gearing, you go forwards, and with a high CVT gearing, you go backwards

there are 2 issues, one is that the gears have friction , especially the Planet gears... the second issue is that the CVT's dont have a 0 output, the lowest gearing of the CVT's will still have some rotation going on, resulting in a 'backwards bias' as in you will travel backwards faster than you do forwards
the variable 'c' , which is the rate of rotation of the constantly geared half of the diffrential gear, is supposed to address these issues...
it introduces a 'forward bias' via the differential gear, resulting in the Annulus rotating 'backwards' more slowly, and since the Sun gear is rotating 'forwards' at a constant speed this means you have that 'forward bias'... also you have less Planet gear movement and that means less friction
that (0.5x - c)/2 part is just how to calculate the rotation rate of the differential gear, which i have coloured brown... x is the ratio of the CVT, and the 0.5 part is because i have arbitarily chosen the differential gear to be twice as big as the CVT, and the divide by two is because the differential gear outputs the average of the two inputs i.e. you sum them then divide them by two, since the inputs are in opposite directions you subtract them instead

the (d + 2c - x)/4r is actually 0.5(1/2d - (0.5x - c))/r , just abit of algebra...it is the rate of rotation of the Planet Carrier... the 1/2d is the linear speed of the Sun gear, i.e. its rate of rotation (0.5, another arbitary choice by me) multiplied by its size (d) , as in how fast its teeth are moving... the (0.5x - c) part is the linear speed of the Annulus, wihch is the same as the linear speed coming out of the differential gear
you multiply it by half because the linear speed of the Planet Carrier is also the average of the linear speeds of the Sun gear and the Annulus
finally you divide by r , which is the radius of the Planet Carrier, to get the rate of rotation


but all that is deprecated because the second transmission is alot simpler , and alot more likely to be built, with no need for the big blue gears and the differential gears....
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Postby carmatic » Sat Jul 03, 2010 1:34 am

also, i would like to add that forwards/backwards movement of a tracked vehicle has no relationship with the friction of the ground, only with the flatness....

but when you are trying to turn the vehicle, the front and rear edges of the tracks will necessarily rub sideways against the ground... it is alot easier to turn when you move at the same time, so that you move in a circle rather than turn on the spot, and there will be alot less sideways movement between the tracks and the ground...
these people here are probably trying to turn on the spot , when it is actually discouraged to drive some real tracked vehicles (tanks, tractors, etc) like this

another thing which you could do is pleat the tracks with something like cupboard handles, something like one of these:
Image
Image
so that they 'cut' through or 'glide' across the ground sideways, but 'catch' it when you are moving forwards... you'll need a short and stout design and it should be made of a strong material... probably also put multiple handles per track section to keep the overall ground pressure low and to help these handles last longer, and maybe recess these handles into the track sections so that they are supported structurally
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Postby dragonfly Jafe » Sat Jul 03, 2010 7:58 am

....yeah, I theoretically could turn in place, but never tried. Moving forward was easy - BioTrak did that real well (about 2mph top speed the way I had it geared). My turning gear also had almost no leverage (about 6"). I had originally planned a vertical crank for everyone on board to be able to turn (like in the Hunley submarine) but had problems fabricating it.

conveyor belt material is a popular track material, with treads bolted on. Some guy built a 2/5 scale Sherman, with molded 1 piece hull and turret (he said he was thinking of selling those as a kit). Had a interesting belt transmission for the track drive, all powered off a lawnmower engine (3hp). His drove great.

http://www.youtube.com/watch?v=hlUbZhsxcWI
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Postby carmatic » Mon Jul 05, 2010 5:11 pm

i've seen that video before, that tank only goes at one speed , the transmission only has 'stop' , 'reverse' and 'forwards'... but you cant argue about how cost effective it is, just using some pulleys and tensioners, with some proper lubrication that transmission could be reliable for a very long time

im thinking that it would be alot more useful to take the chassis, suspension and tracks of an already existing small tracked vehicle, like maybe a bobcat or something, and build your vehicle up from that... this way, you have only the transmission to worry about since everything else is heavy duty and already tested to work with engine power , so it should be just about impossible to damage with pedal power

in fact , assuming that the transmission is up for it, you have the carrying capacity of the original vehicle you took the chassis from.... so a vehicle built this way could be used as a sort of 'green' transport, a cross between the NASA Space Shuttle crawler transporter and a bicycle... slowly hauling heavy stuff around the place using no fossil fuels...
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Postby gyre » Mon Jul 05, 2010 5:39 pm

They say the nasa crawler crushes 8 feet of paving with every pass.
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Re: Tracked vehicle construction?

Postby Tiahaar » Wed Feb 29, 2012 2:23 pm

a bump for my fave thread :-)

My terracrawler still waits patiently for its next incarnation, likely getting a lawn tractor engine and a convex track guide...so it turns better. Maybe for 2013. This year I have a 4 wheel tandem pedal thing to get built, will post pics here somewhere later on.
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