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B Leaking tank

  1. Apr 5, 2017 #1
    Hello. I am working on planning to build a small pnumatic tricycle. I got far in my calculations, but not quite finished because I am stuck. If someone could check my math, that'd be great, but my problem starts at the second line.
    1. Lets say that my air tank is 1064.54 in^3
    2. According to http://www.frightprops.com/faq/images/cylinderdims/1250DVS.jpg, it looks like the volume of the cylinder is 3.6 in^3
    3. Lets say im riding bike wheels (3 bike wheels) on concrete. My friction would be (0.002*791.78N*3=~4.57N)
    4. In the description, they say it has a push factor of 0.44. So 100psi in tank means 44lbs of push force. I made a table of that and found a bunch of values for y (100psi in tank means 44 lbs of push in the piston, 99psi in the tank means 43.56 lbs of push in the piston, etc...)
    5. I converted all the y values (the values that describe the piston push) into newtons.
    6. Then i subtracted the 4.75N of friction from the 195.7N (from the 100psi of air feeding the cylender and making it push 44lbs) and got the net force of ~196N if the tank was constantly at 100psi (195.7 is also the first on the list in the y table)
    7. Then i divided the net newtons (191.25) by the mass of the vehicle (80.7kg) and got 2.3366m/s^2.
    8. I also did this with another value on my table (180.1) so it is 2.17m/s^2
    9. The wheel is pi feet in circumfrence.
    I need to know my vehicle's speed, which is a problem if I dont know how much time it will take.

    From my understanding: Vf = Vi + at

    I averaged to 2 accelerations together and got 2.2533m/s/s
    I need to know how fast this thing is going to go and how far.
    I also need to know the formulas needed to get to the end of this problem. Thank you.

    I do not know what level of a question this is.
  2. jcsd
  3. Apr 5, 2017 #2


    Staff: Mentor


    Wind resistance will increase with the square of speed, so will rolling resistance force of the wheels. Acceleration will decrease and will reach zero when the motive force, balances the wheel friction and wind resistance. During that time, the air pressure in the tank will be decreasing.

    All the calculations you show are linear. Can you redo them assuming resistances varying with the square of speed and with tank pressure decreasing with time?

    I would also like to see how air pressure on the cylinder propels the bike.
  4. Apr 5, 2017 #3
    As for the first part, I dont know much math. For the second part, the cylinder is fed air and pushes (i have no clue why it pushes less than half of the pressure in there, but that's what the people doing the store videos said) the rod out. I will attach the device to the tricycle so that it pushes an axel.

    The cylinder wil push the middle part and then retract when i feed air into the other end of the cylinder, pulling that part in.....


    i can have a sealed wheel thingy. A gear-shaped wheel with much longer teeth, but not as many teeth that is surrounded by a matirial that seals it all the way. There would be 2 holes. Air gets fed into one hole and then turns the axel before getting out of it.

    I've been thinking that the second one would be more eficient since i dont need to put air in both sides. Sorry for the poor drawings.

    Again, i dont know very much math. Sorry.
  5. Apr 5, 2017 #4


    Staff: Mentor

    It sounds like you have a fun experiment ahead. Why calculate at all? Why not just try it out and see how good you can do.

    To really calculate the maximum speed, you need accurate numbers for wind resistance. Since you don't have that, calculations won't be very rewarding. So I encourage you, experiment.
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