# hydraulic bike



## unknown52

want to make a hydraulic bike.  understand basic hydraulics and have access to everything i need to buyild one.  just need some help on what kind of pump and motor to get.  dont know how to calculate what rpm on pump (will be cranked by physical force, not an electric motor) will translate into gpm's.  and on motor,  what gpm turns into rpm's.


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## PCHiggin

How do you plan on transmitting hydraulic force to the rear hub? Let's see some sketches.

Pat


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## unknown52

dont have any sketches but kinda simple.  put a trike conversion on, weld motor to bike frame and then weld a sprocket on motor, connect with chain and shabami.


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## PCHiggin

HMMM, Sounds like you're in for a lot of fun. Let us know how it goes.

Pat


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## unknown52

we'll see.  i'll post a pic when im done, probably in 5 yrs or so.


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## PCHiggin

unknown52 said:


> we'll see.  i'll post a pic when im done, probably in 5 yrs or so.




You'll have your drivers license by then and will trade it for car parts.

Pat


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## Gordon

If you got a transmission from a hydrostatic drive garden tractor you could put a cog on the input shaft and use the chain and front chain ring to drive it. I think you would need to really get the rpm's up to get anywhere, so you would have to work on the gearing, perhaps even using a multispeed hub on a jackshaft or ?? I think a typical hydro garden tracter runs about 3600 rpms wide open. You should be able to buy a transmission for a Cub Cadet on ebay for $40 or so. The spendier ones are ported for hydraulic lift of the mower decks and other accesories, but you wouldn't need that option. Sounds like a fun project. Maybe you could put a blade on it and push snow in the winter!


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## militarymonark

my dad and brother made plans to make a hydraulic bike but the plans were stolen at my brother's science fair


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## unknown52

hey monark u a mechanic, was stationed at seymour with the 15's as a crew chief, now a hydraulic troop with the 130 and hh-60.

thanks gordon gonna look up prices, cheaper than i thought.


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## unknown52

found a pump operating at 3650 psi, 1 gpm.  also found a motor that gives me 884 in-lbs at 1300 psi, and 600 rpm's.  all sounds good but is the gpm too low on the pump.


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## Beaverdam

Doesn't sound like complete specs. What RPM is the pump turning to produce 1 GPM? What flow rate produces 600 RPM in the motor? Those are what you need to work with. All the ratios in the drive multiplied together and multiplied by the wheel size should get a number around 50 - 60 for most bikes and rolling terrain.

It would be cooler if you eliminate chains altogether.


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## unknown52

found a motor to operate the best at 11-12 gpm with 1300 psi.  giving me 807 in-lbs torque and 600 rpms.  to my math with a 26 in tire gives me 15 mph.  unsure on torque though,  800 seems to be good, but thats on my own estimate compared to a torque wrench.  so know im looking for a pump that fits the motor, without spending a ton of money.

no chains would be great but the expertise to put a pump in bottom bracket and the percision it would take to weld the motor in the exact spot for a gear drive at the wheels.  dont have money to buy an axle that would keep wheels moving together.


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## Beaverdam

OK, the important items are 11-12 GPM producing 600 RPM. You won't be providing 1300 psi at that flow rate (8+ HP), but you won't need to produce that much torque either. Is there something smaller you could use? A unit designed for 8 HP seems excessive.

Your best bet might be to re-engineer some automotive parts. Power steering, automatic transmissions and engine oiling systems are hydraulic, and the parts are cheap. Pumps and motors are similar, some units can do both.


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## PCHiggin

So,Are you going to pedal a hydraulic pump or have an electric motor turning it? I don't see it either way. If you're going to pedal @ all,and transmit the torque through a chain,why not just pedal through a standard set up?

Pat


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## unknown52

beaver.  looked at power steering pumps and although they are cheap, i cant find any specs of pressure flow or anything.  u seem pretty knowledgeable on this,  how to know how much force a pump needs.  figure with 6 inch crank arms i could produce a generous 4 hp (120 rpms X 180 lb-ft of torque(30 ft-lb from me)).  

PC.  gonna pedal (want to stay away from anything not hydraulic or man power).  and what do mean by standard set up?


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## PCHiggin

unknown52 said:


> beaver.  looked at power steering pumps and although they are cheap, i cant find any specs of pressure flow or anything.  u seem pretty knowledgeable on this,  how to know how much force a pump needs.  figure with 6 inch crank arms i could produce a generous 4 hp (120 rpms X 180 lb-ft of torque(30 ft-lb from me)).
> 
> PC.  gonna pedal (want to stay away from anything not hydraulic or man power).  and what do mean by standard set up?




The standard set up would be the bike as is,crank,sprockets,chain. I'm thinking you're going to be pedaling and the pedals are indirectly turning a chain and sprocket via a pump,right? Why not just pedal and turn the standard sprockets that are on the bike? I don't see any advantage to this idea. I understand the tinkering part but I think you're creating a heavy monster that will be way harder to ride versus leaving the bike alone. My $.02

Pat


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## unknown52

the addition of hydraulics turns my bike from 4 hp going to rear hub to (depending on psi and gpm) 8 hp, and could even get as much as 22 hp.  one pump and motor combo will give me 10 hp going 15 mph and 800 lbs torque,  granted it's expensive and i could probably pedal to those speeds.  but im a hydro troop in AF and it would just be cool (or at least interesting).  also live of the bay and the winds get pretty tough so with all that torque and weight even when winds pick up i wont have to pedal my ass off to go 2 mph.


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## Beaverdam

I think you are a little too optimistic:





How long do you plan to turn the cranks @ 120 RPM? 
How is "(30 ft-lb from me)" going to turn into 180 without a corresponding drop in RPM? 
Is your calculation assuming that happens 360*? 
Can you really do that @ 120 RPM?

If you could turn 4HP into 8HP using hydraulics we wouldn't need gasoline. The hydraulic system isn't going to be as efficient as a chain drive, and using two chain drives in addition, plus the added weight... well, it's a curiousity but not too practical.

My point with the automotive parts is, if you use the same parts for the pump and the motor you wind up with a 1:1 system. If you double the pump it becomes 2:1, a more useful ratio for a bike. Of course the pump would have to be modified to use it as a motor, possibly just using some of the internals in a custom housing. That could run into some expense unless you know the right people. I don't, right now.

ETA: A system using a peristaltic pump in the front and a similar motor in the rear would be doable, but would have to be totally custom. Still not as efficient as a chain, though.


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## unknown52

scratch earlier statement using wrong units of measurement.  the formulas im using are from a website forget http but it says ft-lb=lb of force X length of arm.  so im looking at 30 lb-ft with a crank arm measuring a foot.  then hp = (torque X rpm) / 5252.  so giving me .68 HP.  know depending on much horse power is required to turn, still cant find info on that.  but im figuring that hp equation has nothing to do with it.  think its all dependent on the measure of torque and the output of pump will depend on rpm (and all pumps are different).  the hp of pump is (psi X gpm)/(1714Xpump efficiency),  and with any hope ill find a low rpm pump that produces a good amount of gpm's.

and this might not work but hell if i get it running, it would be sweet.


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## Beaverdam

"the hp of pump is (psi X gpm)/(1714Xpump efficiency)"

That looks like an equation to figure out how much HP it will take to drive a pump to produce the GPM and PSI you want. Work it backwards with the .68 HP figure, and you'll see how much flow and pressure you can produce for a minute or so. The good news is you're not going to need much pressure to move a bicycle.


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## unknown52

To all the research i have now done, hydraulics is out of the question.  Seems only plausable use as stored energy, but that requires a gas motor and hydraulic motor to apply power together (dont know how) or apply hydraulics to front and gas motor to rear and that is too much money.

Got the trike kit so figure just gonna put gas motor on it and get 12 mph out of it.


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## Beaverdam

"... but that requires a gas motor and hydraulic motor to apply power together ... "

The only power available is the power you supply (via pedal or gas motor), the rest of the system is just transmitting it to the axle. The hydraulic motor can only put out the power spec'd if it has the input GPM & PSI spec'd.

The gas motor converts chemical energy (sunlight stored for eons) into rotary HP (torque and RPM). The hydraulic pump converts rotary HP to hydraulic HP (PSI and GPM). The hydraulic motor converts the hydraulic HP back into rotary HP. Each conversion has it's own (in)efficiency factor, as well as fluid drag in hydraulic lines, friction in shaft bearings and seals, etc. 

Regular bike drives convert rotary power to linear pull, and back to rotary power. But the conversions are more efficient, there is no fluid drag or shaft seals, and much less mechanical friction to deal with.


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## climbhike

Parker Hydraulics used to hold a competition for "chainless bikes" a few years ago search for "chainless challenge".  Web site had pics of two wheelers and trikes.  Interesting ideas but less than practical.  PapaG


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