How do you... measure Speed?

[niterider1]

Although not a newbe it's been a while since I ran a FE Hydro or Rigger. Last time was during the time when Ed Hughey had the top hardware and you used a radar gun to measure top speed (With the help of some tin foil). Now I would love to get back to running riggers and hydro's but I'd love to be able to find out how fast they actually go!
I have heard about using GPS I have also heard something about Eagle tree but no idea how they are used or work.
Can someone fill me in?

Alex
From the frozen a$$ North

[Boaterguy]

there are many ways, some more accurate than others.
Time between two known points
GPS (i think the new Eagle tree v4 e-logger has a GPS, steven sells it on OSE), never used it, looks like a great unit.
if you aren't too concerned about your phone, there are GPS apps, of course 99 cents isn't a great, accurate GPS.
this all depends on your budget and the amount of accuracy you want.

where in the north? i feel your pain, it gets cold here too

[m4a1usr]

You want to be accurate? Use 2 bouys and a clock. It does require you to have some extra bodies to aid though. Because time over distance doesnt lie. GPS will work but its too subjective. No sanctioning body that measures speed for actual records uses GPS. Not one unless its a dual receiver setup using differential measurements.

But in defense of GPS do you have to be 100% accurate? Its "close enough" for most folks.

John

[Boaterguy]

time isn't always accurate, you have to make sure the clock is started excactly when the boat crosses the bouy, and acceleration is also a problem, of course you could accelerate first, but that would bring up the first issue

[niterider1]

I live near Niagara Falls, Our building season is from November to May.

So if I wanted to be kinda accurate I could use a mini GPS? Is there something small enough to fit in my Renegade Rigger? Or would a 1/16th hydro be better sized?

Alex
GWN
Great White North

[m4a1usr]

time isn't always accurate, you have to make sure the clock is started excactly when the boat crosses the bouy, and acceleration is also a problem, of course you could accelerate first, but that would bring up the first issue

Why is time not accurate? Thats how real races are done? If you mean the clocks have to be coordinated for starting and ending, thats obvious. Measured time over distance is the ONLY accurate method to measure speed. All boating records are done this way.

John

[Boaterguy]

I'm just saying, sitting there with a stopwatch and a calculator isn't the best, it's accurate if done correctly, but can be skewed slightly.

[Fluid]

Up until a couple of decades ago, official world records for R/C boats were measured by analog stopwatches triggered by two observers using different sight lines. This method left PLENTY of opportunity for inaccurate readings - you can guess most of them - and so records "eclipsed" from the books after a few years.

Now with infrared digital measuring systems the times measured are accurate - but only to a point. The problem now is one of resolution. To tell the difference between 140.0 mph and 140.5 mph over 330 feet, the resolution needs to be less than 0.006 seconds. To tell the difference between 140.00 and 140.05 mph requires a resolution of less than 0.0004 seconds. Many timers do not have resolution this high, so there is no way to accurately determine the difference between 140.0 and 140.05 mph. Reporting speed records to the thousandth of a mph is just fooling the fools.



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[Boaterguy]

I see.

[Gary]

Although not a newbe it's been a while since I ran a FE Hydro or Rigger. Last time was during the time when Ed Hughey had the top hardware and you used a radar gun to measure top speed (With the help of some tin foil). Now I would love to get back to running riggers and hydro's but I'd love to be able to find out how fast they actually go!
I have heard about using GPS I have also heard something about Eagle tree but no idea how they are used or work.
Can someone fill me in?

Alex
From the frozen a$$ North

Niterider1....I would go with the Eagle tree. First off its alot of fun and interesting to have all that information to go buy and makes it easy to make adjustments and see your improvments. Now, as far as it being accurate..........I can tell you this with no BS.......I can go 2-3 times a week and get the same readings within 1-2 miles per hour so to ME its pretty much dead nuts day to day. I have also checked this with a radar gun as well.That does not mean its 100% dead on and that you can go out and say you have the mph as a record....it is not. But to have for yourself numbers to go by its fantastic. I would recommend it 100% for Sport Boating. Have fun!!!

[LuckyDuc]

Although not a newbe it's been a while since I ran a FE Hydro or Rigger. Last time was during the time when Ed Hughey had the top hardware and you used a radar gun to measure top speed (With the help of some tin foil). Now I would love to get back to running riggers and hydro's but I'd love to be able to find out how fast they actually go!
I have heard about using GPS I have also heard something about Eagle tree but no idea how they are used or work.
Can someone fill me in?

Alex
From the frozen a$$ North

Here is an example from my Eagle Tree data logger. It shows continuous Amp usage, GPS speed, and number of satellites locked. You can easily see the corner vs. straight away speeds too. The Average Speed, Amps, etc are summarized at the bottom of the chart.

It is a very useful tool and reasonably accurate. If you look at the charts you can easily detect speed anomalies.

[graill]

We got into a detailed discussion a couple or three years ago on rumrunner about gps verse time traps. The end result was the timetraps being the mechanic of choice for the racer records.

Gps is to this day is still very much guess work on the part of the sat and the subject, the sats "assuming" all things staying the same for the next measured "tick" what the next increment of speed increase, time and distance will be. the best gps for civilians that i have seen is a 25 hz unit. maybe better ones are out by now, i still use the 10 hz eagletree.

However when we finally get to play with 1000 hz or higher gps recievers in the mundane world we will have some fun and can then start the argument on time traps verse mobile gps again. (grin)

[rc2266]

A calibrated eye

[pescador]

Besides GPS and timing nobody has mentioned radar yet.
I've been using this radar gun this year, it's been working great and it fits in your shirt pocket. A little pricy but it's been pretty convenient to use, it picks up boats from about 100 ft and it has made testing easier when we are out with a bunch of boats.

[Fluid]

Plenty of us have used radar in the past and know its limitations very well. Unless the boat is coming directly at the unit head-on, the speed readings will be off - the more the angle the less the accuracy. Plus it takes time to measure the boat's speed after the radar picks it up at 100 feet. Think about it - a 60 mph boat travels 90 feet in one second. By the time the radar gives a reading the boat is in your lap. Safety concerns and poor accuracy are reasons radar has limited use for boats if you care about accuracy. It works a lot better for cars and planes.


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