Measuring Low Speed with Cellphone
Measuring Low Speed with Cellphone
(OP)
I have to design some shock bumpers to stop an 8000 pound X-Ray machine that has to be repositioned frequently to accommodate odd-shaped parts. We will move it on air bearings.
But I will need some means of knowing how fast this thing may move. Before I come up with a fancy engineered solution for measuring how fast this thing is moving, can I just put a cell phone on top of it with the right app and get the speed directly? I’m tentatively looking at a maximum speed of 3 inches per second. Acceleration doesn't matter. I tried asking some young techno people but they didn’t really understand physics so they couldn’t help. The shock bumper reduces the g’s to stop this thing so I can figure that but I need to know the speed based on actual tests.
I’m designing the shock bumpers using auto shock absorbers. There’s a race shop down the street with a shock dyno and a huge supply of used but still good racing shocks. I’ll submit my calculations for this shortly for everyone's critique. I think I can use a shock out of a SCCA Class D Modified, whatever that is.
Thanks all.
But I will need some means of knowing how fast this thing may move. Before I come up with a fancy engineered solution for measuring how fast this thing is moving, can I just put a cell phone on top of it with the right app and get the speed directly? I’m tentatively looking at a maximum speed of 3 inches per second. Acceleration doesn't matter. I tried asking some young techno people but they didn’t really understand physics so they couldn’t help. The shock bumper reduces the g’s to stop this thing so I can figure that but I need to know the speed based on actual tests.
I’m designing the shock bumpers using auto shock absorbers. There’s a race shop down the street with a shock dyno and a huge supply of used but still good racing shocks. I’ll submit my calculations for this shortly for everyone's critique. I think I can use a shock out of a SCCA Class D Modified, whatever that is.
Thanks all.





RE: Measuring Low Speed with Cellphone
Example:
Turn Your iPhone Into A Speed Radar
Pasted from <http://www.iclarified.com/14342/turn-your-iphone-i...;
Google: measure speed with android phone
Example:
SpeedView: GPS Speedometer
Pasted from <https://play.google.com/store/apps/details?id=com....;
For ultrasound method
Google: ultrasonic distance and speed sensor
Good methods using low cost Arduino computer
The project can be difficult if the load on air bearing has rotation and is free to move in many/any horizontal direction as compared to straight-line motion without rotation. You could check out robotics (Battle Bots) for ready-made components and computer code.
Walt
RE: Measuring Low Speed with Cellphone
Unless you get some sort of alarm rigged up to tell the "pushers" that it is too fast (that it is approaching a limit, BEFORE they exceed that limit), they still will go too fast by mishandling.
RE: Measuring Low Speed with Cellphone
RE: Measuring Low Speed with Cellphone
This is certainly in arduino territory and, unlike the phone, can also automatically apply braking, for example by cutting the air flow to the bearings.
If I was to look for a phone solution it would include visual flow analysis to pick up details on the ceiling, but I don't know that anyone would make an alarm for going too fast. It would also need a distance measurement to calibrate the flow speed.
RE: Measuring Low Speed with Cellphone
But the consensus is that cell phones won't work for slow speeds.
I'll rig up a Mythbusters grid and see how fast they can push it. There are OSHA rules on how hard an employee is allowed to push, so a little F = ma will get me started.
I've got the shock calculations done; the car shocks work quite well, at least theoretically. I'll send these when I get into the right format.
RE: Measuring Low Speed with Cellphone
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Measuring Low Speed with Cellphone
RE: Measuring Low Speed with Cellphone
Is the kinetic energy calc right? I recall a G/Gc as being part of using lbf weight calc. I usually use slugs to be sure.
RE: Measuring Low Speed with Cellphone
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Measuring Low Speed with Cellphone
But looking at it another way, again using energy, the machine will be moved by one man and has a maximum distance to move before hitting a wall of six feet. OSHA limits the amount a person can push an object to 50 pounds. So a man pushing the machine with 50 pounds of force for a distance of six feet imparts an energy of 300 Ft Lb. This would be an extreme case but still within the realm.
I’m trying to keep this graphic because that is how I design marine fenders, and I don’t know any better. And the shock dyno prints out a nice curve that I scan and insert into autocad, convert to a force-distance chart and read the energy and reaction values directly. And I like pictures.
Next step is to go back to the race shop and have him chart some more shocks. He also has a chassis dyno going all the time and feeling upwards of 800 horsepower thirty feet away makes for a great field trip.
RE: Measuring Low Speed with Cellphone
RE: Measuring Low Speed with Cellphone
A.
RE: Measuring Low Speed with Cellphone
RE: Measuring Low Speed with Cellphone
Greg....you're the car expert...does this make sense?
RE: Measuring Low Speed with Cellphone
I was conservatively stingy with my 4 inch stroke and will increase this.
Another guy is trying to design a sort of mechanized fence to sweep away anyone between the moving X-Ray and the wall. I gotta get this onto YouTube, it's getting hilarious.
RE: Measuring Low Speed with Cellphone
Your problem is identical to moving a load with a pallet jack. With a pallet jack one way of stopping the load is to lower it. You can stop your load by releasing the air to the air bearing. Have your bumper do this automatically if it touches anything.
https://www.appletonmfg.com/cart-mover.php
RE: Measuring Low Speed with Cellphone
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Measuring Low Speed with Cellphone
- How level is the floor? A small slope will impart a lot of KE to a 4 ton vehicle.
- Make sure you select a gas shock - the pressure will auto-extend it after each use. (or add a spring as suggested by Greg)
- Is the bumper mechanism attached to the wall or the vehicle? How do you ensure the correct location on the wall/vehicle is impacted? Is there another bumper for the return journey?
3DDave. I love the mouse encoder idea.
je suis charlie
RE: Measuring Low Speed with Cellphone
For Greg: I have shock reactions, what impact factors would be recommended? Shocks are typically rated up to 10 inches per second – is that the maximum expected shock speed in a vehicle or just a “rating” speed to calibrate shocks. I’m going to the race shop today for dyno curves. Will cold testing be different? I noticed previously that he cycled the shocks several times before recording. Our machine hopefully will never exercise its shocks, how will this affect the rate? We’ll cover the exposed shafts like the off-roaders do so they don’t freeze up. Thanks for your help.
We’ll make these up from telescoping tubing flanked by two or more car shocks and a light return spring inside the tubes. The owner likes the concept (they are low cost) and wants to build some more that are portable with aluminum tubes and frames and place them around the shop when he moves other equipment. There is a containment curb around the areas and I’ll size them to keep from blowing his curb out.
I like the mouse encoder idea also. I've got a spare mouse that I'm taking out to the garage to play with right now.
RE: Measuring Low Speed with Cellphone
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Measuring Low Speed with Cellphone
Every smart phone has a 3-axis accelerometer, and some apps take advantage of it. Most phones have a seismometer app available which will illustrate capabilities.
RE: Measuring Low Speed with Cellphone
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Measuring Low Speed with Cellphone
At 3DDave's suggestion, I visited Arduino territory. This is paradise! I need another lifetime to play with this stuff.
RE: Measuring Low Speed with Cellphone
RE: Measuring Low Speed with Cellphone
Care to mention how?
I did mention Arduino in the first response.
Walt