Measuring Acceleration/Speed for Small Vehicles? 55
stampfli_brit asks: "I am the captain of rowing at my local club, and was looking for a way to improve training. We have an NK SpeedCoach. However, I was looking for something that could measure the speed of the shell several times a second, more like this [pdf]. Any ideas on a cheap system using IC accelerometers or GPS, that could get this kind of information, log it for an hour or two, then dump it to an Apple Mac for analysis?"
Why not use a Powerbook (Score:2)
Re:Why not use a Powerbook (Score:1)
One idea (Score:2)
Either delegate people from your team, or hire some local person (IE: College student looking for a little extra cash) to point a radar gun at the boats, and have the radar gun output to something.
So which is it? (Score:1)
Re:So which is it? (Score:2, Interesting)
Re:So which is it? (Score:1)
Re:So which is it? (Score:1)
Re:So which is it? (Score:2)
</nitpick>
Re:So which is it? (Score:1)
use GPS VTG (Score:1)
The message provides the current speed and heading.
A standard (>$200) GPS receiver should give this information. You will need a more expensive one if you want to save the data and sync it to your computer.
If you want a real cool rolls royce solution you could contact my company - we'll write PDA solution for you.
http://www.sapien.com.au/ [sapien.com.au]
GPS Handheld (Score:2, Informative)
How about.... (Score:3, Informative)
How about one of these [vernier.com] attached to one of these [vernier.com]? Together you are looking at about $500 but compared to the alternative
Re:How about.... (Score:2)
I'm also not sure what kind of accuracy you get on the x(t) and v(t) by integrating off of the a(t) the acceleremeter gives (haven't had a chance to play with one yet). You'd have lots of oscillations in the a(t) due to the oars cycling, right?
We measure accelerations in physics l
Re:How about.... (Score:2)
Re:How about.... (Score:2)
You can integrate a(t) once to get v(t) and twice to get x(t), but I wouldn't recommend it. I've tried it (not with a boat) and it just plain doesn't work very well. At all. Period. Even with very high quality accelerometers and a very high acquisition rate, yo
Re:How about.... (Score:1)
Serial Accelerometer (Score:1)
Scroll down, and they have accelerometer you can just plug into a serial port. You'd want to have a laptop on board, and some simple software to interface with the serial port...but serial port interfacing isn't to hard, so this might work for you.
oh, and it's like $45 or so.....
Re:Serial Accelerometer (Score:1)
Any ideas on where to buy a similarly cheap data logger for serial? Or software for a PDA to do the same thing?
Re:Serial Accelerometer (Score:1)
Yes, it would be convenient to have a handheld data logger that you could dump later....but I think that would just add to the complexity of using something like this device.
I think the simplest solution would be to plug it into a laptop, and either capture the data with a serial terminal (which are easy to get/use on any system) then dump it to some kind of software and plot it....or write something to intercept the data in real time and plot it. The latter would probably be the most usef
Speaking as a rower myself... (Score:1)
The only way it would work is if it was very light and very waterproof, or better yet, if it floats and is waterproof.
I'm surprised nobody mentioned this, although geeks who row are probably a rarity.
Re:Data Rates (Score:2)
Oh, that's easy! (Score:3, Interesting)
Make a crossbar out of the poles, and mount the protractor to it, with 90* facing downward. Tie the weight to the string, and hang the lot right next to the protractor. Align the contraption such that the length of the protractor runs parallel with the keel of the boat.
With some (very) simple fizzix, you've just built an accelerometer.
B
Re:Oh, that's easy! (Score:1)
Re:Oh, that's easy! (Score:1)
How fast? (Score:2)
Re:How fast? (Score:1)
Re:How fast? (Score:2)
Tricky (Score:4, Informative)
It's very useful info but you also learn rather quickly that it's full of errors. Consider that the wind speed and direction is usually read from a anemometer/vane at the top of the mast (often on a small pole to attempt to keep it out of the wash of the sails). Speed through the water is done ultrasonically or with a paddle wheel. All these direct measurements are converted to things like true wind speed, true wind direction, velocity made good and so on.
Damping is a huge problem. You may think that several readings a second is good but as the boat rides over waves and heels to varying degrees all of your measurements will be off. Wind due to the mast swinging (doesn't take much heel to really move things around 7 stories up - I've been there many times), boat speed due to water-flow differences at different heel angles (some boats average readings from multiple sensors to combat this issue), and even magnetic heading due to compass-dip if the compass sensor isn't gimballed or otherwise compensated. Essentially you become limited to short-term running averages of the readings.
You don't have quite as many inputs but still need to be concerned with yaw and tilt of the shell, turbulence from the oars and so on. Boat motion will be especially problematic if you are trying to directly measure acceleration.
I suspect that an appropriately designed towed speed sensor might get you the data you desire (though the data-quality will still be sketchy). Perhaps a small propellor/chopper-disk/optical sensor. You could probably build one for a few dollars. The problem then will be to convert the pulses to something you can use.
GPS for gross approximation only (Score:2)
Normally I'm a big proponent of GPS units. I think they are very cool, and they have a lot of inherent functionality.
For this task they are probably a poor choice. Typical GPS unit uses algorithms for determining speed which will filter out minor changes, or delay their appearance in the data.
They do a very good job of giving an accurate speed when they are neither accelerating nor decelerating. (more accurate than your average speedometer in good conditions). But it is unlikely the data will show any det
Why? (Score:4, Informative)
Having been a varstiy cox for a top D1 rowing team I've never needed such information to make my boat faster.
The speed coach is a very good device. Short of rebuilding it, you will not find anything that will come close to it's level of accuracy (or durability). If you're looking for a device that can dump to a PC (presumably Mac as well) have a look here [nkhome.com]. It's not that expensive and comes with all of the hardware that you would have to build yourself.
Your only other option is to find an impeller, and get a data logger and make it waterproof. You'll also need a display and a C compiler to drive the impeller -> display conversions.
I guess the question is how much is your time worth?
Re:Why? (Score:2, Informative)
Example: If the cox calls "send the boat off the finishes", to see what effect that has on the force curve, and boat speed.
Ball bearing solution (Score:3, Interesting)
Re:Ball bearing solution (Score:3, Informative)
So my advice - go back to what works. Slide plates have very few moving parts, and do
Re:Ball bearing solution (Score:2)
Seriously, why is this even a question?
Re:Ball bearing solution (Score:1)
Re:Ball bearing solution (Score:2)
can be done... (Score:2)
that said, once you have the sensor, you can talk to it pretty easily using a standard serial interface.
More than Accel (Score:4, Informative)
My immediate thought would be to go grab a few Vernier sensors (as someone else mentioned) and a TI-92, and do it on that. However, NK has spend a whole lot of time and cash making sure their impellers work perfectly for what they're supposed to do, and produce the minimum drag possible. I know if I was rowing at that level (I rowed in HS for a while), I wouldn't want some homemade impeller giving me excess drag.
Upon further though, why would you want that much resolution in terms of speed? The SpeedCoach measues at the midpoint of each stroke, as the power phase is finishing. If you want something more specific than that (maybe to analyze for the effect of small changes in stroke shape or recovery speed), I would think that you'd be using a tank anyways, and you could do something with video for that (not needing an impeller at all).
Also, think about this: most national teams use SpeedCoaches for their training. If it's good enough for them, why do you need more prescision?
I think you need to rethink your problem. If you're measuring for the impact of rudder usage on speed, you can do that with models in a flow tank (go talk to your hydrodynamics departement). If you're doing stroke geometry, use an erg (or a tank, a videocamera, and a few Vernier probes). I can't think of a good reason for needing that much prescision in an on-water situation.
Re:More than Accel (Score:2, Informative)
I want the ability to be able to compare the power curve on the water to that on the erg. And see how specific changes in the stroke make the boat slower / faster, and compare that to the rowers' perceptions.
Re:More than Accel (Score:2)
One option (Score:3, Informative)
A good system would be GPS coupled with an accelerometer and microcontroller. Use the GPS for absolute positioning, and to calibrate the accelerometer. Use the accelerometer for speed and position updates as quickly as you need them.
It would probably take about 40-60 hours of work to develop and test the concept, and probably cost about $200 per prototype unit. Thereafter one could probably make them for $100 apiece. Assuming a cheap engineer at $60/hr you're looking at $2,800 to $4,000 for the first 2 prototypes.
If you want to go the cheap and quick route, you can skip the GPS and simply use an accelerometer. One such gizmo is here [myplace.nu]. This person created a simple acceleration meter that analyzes a few car parameters by monitoring acceleration during a 0-60 test. This doesn't match up directly with what you need, but with some work you can take this and make it do what you're looking for.
-Adam
Gyro Plug (Score:1)
What I do: (Score:2)
cheap, fun, dorky (Score:2)
Uhh... sure, GPS (Score:2)
It's very simple to use.
GTech-Pro (Score:3, Informative)
It's a set of precision accelerometers designed for car racing, but it might give you enough detail that you can use the output to suit your needs.
Looks like it only works with a PC, but for $300 you can't have everything.
GPS (Score:2)
Optical solution (Score:2)
Data logger (Score:1)