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  1. #1
    Join Date
    10th January 2018
    Posts
    1

    Arduino controlled Altimeter for CannonBall

    Hello all and thanks for any help and direction.

    I have a cannon that shoots bowling balls. We have either paced out, used a range finder or satellite imagery to estimate average shot distances of 500-1000 yards depending on powder load. Most shots are made from a fourty-five degree angle. I would like to be able to have a recorded altitude of the ball. There is a forward directional rotation of the ball. As the ball spins the finger holes cut the air to make a whistling sound. Since the ball is spinning you can notice a volume difference in the whistle depending on which direction the finger holes are pointing at any given point in the spin. Using this as a very rough estimate I would say that the ball rotates at around 300/RPM. Surprisingly slower than I would assume, only a few revolutions per second.

    I have made quite a few arduino based projects. It recently dawned on me to use arduino based sensors to measure data from the cannon.

    My plan is to drill a hole in the ball to receive the arduino/sensors.

    I figure Rocketeers are the authorities on this subject.

    So my questions:


    -Does anyone know of a fast/reliable altimeter that is arduino compatable?

    -Will the rotation of the cannon ball affect the altimeter?

    -How sealed/unsealed can the altimeter be to be accurate? Does it need ~airflow to detect changes in altitude?

    -What are some some other questions I should be asking?


    Thanks again all, I really do appreciate any direction, insight and ideas.


  2. #2
    Join Date
    15th October 2016
    Location
    Huntsville AL
    Posts
    2,140
    If you're using a barometric altimeter, It needs sampling ports to judge changes in altitude via air pressure. This type of altimeter wouldn't be suitable for your application since it would have a massive pressure event at start, and combustion gases are corrosive to the electronics.

    There are some accelerometer based altimeters, but you'd need a 3 axis accel to account for the spin. The Jolly Logic Altimeter 3 has a Bluetooth interface, but its accel caps out at 24 G's.
    Other 3-axis altimeter's I'm aware of would require a large cavity in the ball. I've seen IMU units that have been slaved to an arduino, but again, they're not space friendly.

    "I'm at least 70% confident about whatever I say (90% of the time)"- college me

    NAR 101195
    Level 1: Big SAM, 9/10/16

  3. #3
    Join Date
    12th February 2009
    Location
    Oregon
    Posts
    96
    I had a stupid thought. If you can see the bowling ball in the air maybe the old fashioned Estes Alti Trak would work. With 2 of them/people on either side of the field you'd get a pretty accurate altitude. That is if you can see it.
    "Pay no attention to that man behind the curtain"
    the Wizard of Oz

    Member Oregon Rocketry and Eugene Rocketry

  4. #4
    Join Date
    14th March 2009
    Location
    Ohio
    Posts
    3,357
    Can't you just use math to figure out altitude? Time and distance traveled should be easy to determine. The ball follows a ballistic trajectory so basically a parabola. Pretty straightforward math gets you the answer.

    If you need more help, a forum on cannons or mortars would seem a better choice. I assume they know how to do these calculations. I've seen Civil War reenactors shoot cannon ball type mortars at targets. They are shooting at high angles so they must know how to determine the numbers to get even close to a target.
    Zeus-cat
    NAR# 92125 L1
    Total Impulse for 2018: 491.6 N/s Flights: 10
    2017: 1/2A:0, A:2, B:1, C:2, D:2, E:1, F:1, G: I have NEVER launched a G motor, H:0, I:1

  5. #5
    Join Date
    14th March 2009
    Location
    Ohio
    Posts
    3,357
    Duplicate post
    Zeus-cat
    NAR# 92125 L1
    Total Impulse for 2018: 491.6 N/s Flights: 10
    2017: 1/2A:0, A:2, B:1, C:2, D:2, E:1, F:1, G: I have NEVER launched a G motor, H:0, I:1

  6. #6
    Join Date
    13th October 2014
    Location
    SouthEastern, WA
    Posts
    6,097
    iirc Bob Krech has some experience with electronics and gun launched projectiles, he might be a good one to send a PM. I would think for a cannon ball the device would have to be accelerometer based and be potted in some kind of epoxy to keep the chips from ripping off the board at impact.
    Rich

    NAR# 99154

    L3-4x upscale Estes Cherokee-D- AT M1297W 5/28/2016 http://www.rocketryforum.com/showthr...r-rharshberger

    TriCities Rocketeers NAR section# 736 http://www.tricitiesrocketeers.org/

  7. #7
    Join Date
    14th March 2009
    Location
    Ohio
    Posts
    3,357
    I found a muzzleloading forum that has a cannon sub forum. I would ask these guys. http://www.muzzleloadingforum.com/fu...um.php?fid/20/
    Zeus-cat
    NAR# 92125 L1
    Total Impulse for 2018: 491.6 N/s Flights: 10
    2017: 1/2A:0, A:2, B:1, C:2, D:2, E:1, F:1, G: I have NEVER launched a G motor, H:0, I:1

  8. #8
    Join Date
    25th July 2017
    Location
    Colorado
    Posts
    58
    Check out J.E. Littlewood's artillery math from 100 years ago.

    Keeping it rocketry related, this has been explored before for (often ballistic) water rockets .
    https://www.et.byu.edu/~wheeler/benchtop/flight.php

    All you need is a stop watch (and in your case maybe a dusty lasting spot so you can visually stop the timer).

    hap = (g/8)(tend)2
    TRA 17281
    NAR 104429
    L1: 9/16/17, 4" Blue Angels Super DX3 - I345 to 1,733' (YouTube)
    L2: 12/2/17, 4" Blue Angels Super DX3 - J350 to 3,284' (YouTube)
    Alt/Speed: 12/2/17, 54mm MAC Scorpion XL - J357 to 7,884' at 637 mph

  9. #9
    Join Date
    31st October 2016
    Location
    N/A
    Posts
    238
    Since my students aren't posting any questions yet...

    Lets just take the OP at his/her word that independent measurements of maximum altitude, range, and time of flight are desirable for some reason.

    Back-of-the envelope, solving the range equation for initial velocity and computing for firing angle of 45, a range of 1000 meters over level terrain, comes to about 100 m/s.

    At maximum altitude, the ball will be moving with a speed of about 70 m/s. Say the bowling ball has a diameter of 20 cm, then 300 RPM (5 revolutions per second) gives it a circumferential translational speed of 0.3 m/s -- not a significant correction to the horizontal component of the ball's velocity.

    Assuming the barrel of the cannon is on the order of a meter long, the acceleration during firing will average about 500 g.

    All of these numbers are comparable those for a high power rocket, so we might guess that that barometric altimeters used for rocketry will work for this application. There are off-the-shelf options, as well as instructions for roll-your-own altimeters at the end of a google search.

    In addition to Nytrunnner's concern about the chamber pressures,I'd worry about g-load at impact. Neglecting drag, the bowling ball will hit the ground moving at the same speed with which it left the cannon. If the bowling ball were to crater the ground by as much 20 cm (just burying itself), the acceleration would be about 2500 g. Designing an energy-dissipating package to protect the electronics during impact is left as an exercise for the student.

    EDITS: Arithmetic, and acknowledging the previous contributions of others.

    Last edited by jlabrasca; 13th January 2018 at 06:03 PM. Reason: 100*100/0.4 = 25000
    NAR Level 1, Sheridan Oregon, 09/16/17 -- scratch built 7.6cm x 120cm rocket on an AT H182R.

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