Arduino controlled Altimeter for CannonBall

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Jan 9, 2018
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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.
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 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.
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.
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.
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 .

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
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.
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I am working on a similar problem. I am shooting bowling balls beyond 1 mile. My problem is simply finding the balls somewhere 2 to 3 miles down range. I am watching this thread for ideas i can use.

Why don't you join us on GBO Cannons. We are serious builders and shooters and always like new faces with similar interests.

I have recently moved to Montana where I had plenty of places to shoot to Oklahoma where i amm looking to shoot.

You altimeter question is interesting. How would mount it?
Huh. I find this problem rather interesting. Maybe a transmitter in the ball and three receivers to triangulate its position? Don't HAM folk do that sort of thing?

(subscribes to thread)

I'm thinking the g-force on any "on-board" electronics is going to cause a problem. Most of the accelerometers I've seen max out at +/- 35G, 70G, 120G, 250G. You'd have to pot whatever you used to keep the components from being ripped off but even then, you might limit out the sensors. Optical triangulation might be your best bet. Any who said you'd never use trig in real life?? How does it go....cosine theta equals adjacent over hypotenuse?
Still learning the software on the forum and the edit function. I recently Moved FROM Montana to Oklahoma.
Still learning the software on the forum and the edit function. I recently Moved FROM Montana to Oklahoma.
What part of OK? NE of Tulsa here.

The cannony bits -were- in MT, or -are- in OK?

<< suddenly intrigued >>

Edit: nm, on re-read I understand you're looking for a spot in / near OK
Yes Edmond is where I am. I am going run up Ponca City next week and see a farmer who says he has a mile we can shoot on.