What do you guys think of my final project idea?

[sdusheyko]

i'm about 1.5-2 years away from graduation and I'm thinking about what i might build for my senior project.

i was thinking of a pneumatic vehicle of some sort, maybe a go cart or motorcycle, which uses modified pneumatic wrenches as motors. some of these wrenches seem to make a decent amount of torque.

what do you think, PF?

 

[minger]

Why not just use the compressed air? You could run it through an air turbine or something like that.

 

[jack action]

It might not be a bad idea, but it is not the torque that you need to look at, it's the power. Once you have the power, you can convert it to the torque you want by using an appropriate gear ratio.

For example, a big http://www.redhillsupply.com/cpt7773.htm" is about 3 hp at the input (7.5 cfm @ 90 psi). With the efficiency loss, it is probably less than that at the output.

 

[sdusheyko]

air piston>turbine or piston<turbine for propulsion?

minger; the point of the wrenches is to take their air turbines which I'm assuming they're equipped with, and they're cheap and easy to find at flea markets. do you have any suggestions as to what kind of machine i can take apart to get a cheap and relatively powerful one?

jack; I haven't been able to find power output ratings for pneumatic wrenches, only the electrical ones. How did you figure out that the 1" is ~3hp? 3hp per wheel would be awesome...

thanks!

 

[jack action]

jack; I haven't been able to find power output ratings for pneumatic wrenches, only the electrical ones. How did you figure out that the 1" is ~3hp? 3hp per wheel would be awesome...

The power is equal to the pressure differential times the volumetric flow rate (Similar to the electrical power that is equal to the voltage difference times the current).

power = Force * velocity = (pressure * Area) *velocity = pressure * Volume flow rate

It is just a matter of using the proper unit conversion factor. I used http://www.wolframalpha.com/input/?i=90+psi+*+7.5+cfm" to calculate my example.

Remember, this is the power needed to compress the air, there will be losses upon transforming that energy back to mechanical rotation (depends on the efficiency of the power tool).

 

[minger]

Well first of all, do not think that even if you've been quoted 3 HP that it's the right number to go off of. I'm assuming that by wrench, you're talking about impact wrenches. They are also called pulse wrenches, you do not get the full torque all the time. The force/torque applied is very intermittent.

Look up an impact wrench in wiki to see how they work. I think you'll notice that it's probably not the "transmission" you want from your power source to your input.

So, to your original question, I'd say you'd be better off using the compressed air directly than using an impact.

 

[agurvinder]

hello guys.
the project he is trying to do was tried by me sometime back.
there are a lot of problems with such PURE vehicles as the economy obtained is very very low.
for example, you may get only 0.75 miles out of 1-2 gallons 15psi air. that's wat i got.
the weight of the vehicle increases if you make a high pressure vessel for storage of the air.
maybe you should try discussing hybrid vehicle where air is only a substitute along with some conventional fuel

 

[PaulS1950]

It would seem to me that a three cylinder compressed air powered motor would be far mor efficient than a number of vane motors to produce the same power. A vane motor does not have near as good a seal and works with smaller areas than even a small piston engine. The pressure required would be the limiting factor but may be partially overcome with bore size. As far as volume is concerned you can control the amount of air consumed with a compromise between bore size and stroke.
Mounting the motor transverse at the drive axle with direct drive would eliminate (drastically reduce) frictional losses. A regulated high pressure compressed air tank would be ideal for storage and maintaining as close to constant pressure output to the motor. Range is going to be limited as there is no "gas station" to refill a high pressure tank.

 

[agurvinder]

. Range is going to be limited as there is no "gas station" to refill a high pressure tank.

very limited..
read the post above paul

 

[PaulS1950]

very limited..
read the post above paul

I read your post, did you read mine? I am talking about 2000 psi "two gallon" tank and you were talking about two gallons at 15 psi.

 

[agurvinder]

I am talking about 2000 psi "two gallon" tank and you were talking about two gallons at 15 psi.

that pressure of 2000 psi with 2 gallons of air is a good range for operation. you did not mention that before. but i doubt it will give more than 2 miles for every 150 pounds of gross weight. because the size of the motor as well as the tank itself is quite large for higher power requirements.

 

[PaulS1950]

A three cylinder motor with a displacement of 12 cubic inches or less might be a good compromise between power and economy for a light-weight car powered by high pressure compressed air (2000 psi). It would have to be regulated to about 200 psi and use low friction components and seals but it could be built fairly easily from common supplies. No cooling is required because the air would provide that and the necessary lubrication would be minimal with the use of ball bearings only on the ends of the crankshaft and insert bearings on the rods. Needle bearings could be used at the piston pins with a press fit into the rod small end. The most difficult part would be the valves to open the cylinder pressure just prior to TDC and open an exhaust port just after? BDC.
A 60 degree crank would make the power flow reasonably smooth (with a two stroke cycle) and a small flywheel or gear train would further smooth the engine operation. The small size would allow for higher rpm although it should be limited to only that speed necessary for propulsion under the conditions of the test.