I was reading an article in the latest issue of MRR which included an evaluation of a loco’s scale MPH.
How do you measure scale MPH other than using something like a stop watch to measure the time it takes to travel over a section of track?
Rich
I have an Atlas sound loco that has one of the functions is to tell you how fast it is going but I am not sure how common that is. And then there is the MRT AccuTrack Speedometer which I have not used but I have read about using for speed matching locos, I found it on line for about $65.
LION uses a stop watch. He made a table calibrated for a 300’ train. (That is the size of my trains, and exactly half the length of a B division NYCT train.) I can time in HO or in 1:1, it all comes out the same since it is the length of 300’ that is fungible.
Stopwatch is the only true way of finding out the loco’s speed. That is unless you have a radar gun, lol.
Quicky way is to count the number of seconds it takes for a 40 foot car to pass a specific point and divide into 30. 1 second for the car = 30smph, 2 seconds = 15smph, etc. 2 cars in a second = 60smph. Or use 36 for 50 foot cars.
–Randy
Rich,
I also employ the stopwatch method. I have two marks on my track that are 3’ apart. I created a sMPH chart (that hangs up on the wall) with times (in seconds) how long it takes the nose of a locomotive to go from Point A and Point B. Once I know the time, I look up on the chart for the sMPH. I’d be glad to send it to you, if you’d like.
Tom
Tom,
Thanks. I sent you a PM.
Rich
I use a stop watch. I have one, it’s easy to use, it’s easy to check that it is keeping good time, and the equation of speed is really simple.
Speed = Distance / time.
A ruler will give me the distance traveled, the stop watch gives me the time. To get velocity in scale miles per hour (as opposed to furlongs per fortnight) just convert the distance into scale miles and the time into hours.
5280 feet to the mile. 12 inches to the foot. Distances in HO scale are 87 times the distance in real world (1:1) scale.
60 seconds to the minute. 60 minutes to the hour.
In the old days I worked this sort of thing on a slide rule. Now I use a hand calculator.
I use this Scale Speed Calculator program from Western Reserve Division.
On it’s way, Rich. [:D]
Tom
Sorry, it is NOT the ONLY way.
I made a speedometer car using a bicycle speedometer and calibrated it for a 33 inch wheel.
Works great !!!
Did someone try to use a pair of detectors like the ones that trigger grade crossing gates ?
Martin4
That’s how the speed unit from TDP worked. Unfortunately they’ve gone out of business. But JMRi does the same thing, you cna set up a pair of block sensors, which a known distance between them, and it will calculate the speed for you.
–Randy
Interesting, how accurate is it?
How do you trip/activate the speedometer, a magnet has to go by the sensor on my bike?
Richard
I ran a speed test on all 3 locos. All three are Atlas Dash 8-40B with Dual Mode Decoder set to factory defaults.
I measured over a 15’ long straight section of track.
The two fast locos ran at a top speed of 81.16 and 80.98 scale MPH. The slower loco ran at a top speed of 74.23 scale MPH. Running at a top speed around the entire 164 foot main line, the two faste locos would, of course, eventually lap the slower loco.
I am not sure if the Atlas Dual Mode decoder has the speed adjustment capability in terms of CV’s that would permit me to match speeds on the 3 locos.
Rich
Hi:
Do you have a marker on the wheel to trigger it? You can also claim that it is prototypical. I remember talking with an old timer that said many of the tourist lines use bicycle speedometers on their steam locomotives that didn’t come from the factory with speedomters.
Another way is to measure the wheel diameter and the rpm of the wheels.
Lets say the wheel is 40" diameter. That’s a circumference of 125.6" or about 10.5 ft. 504 revolutions is one mile. Divide by 60 gives you 8.14 rev/minute = 1 mph.
Measure the rpm of the wheel and divide by 8.14 to give the speed in mph. If at 4 volts the wheel turns at 400 rpm, the train is going about 49 mph. At 650 rpm its going almost 80 mph.
Of course, that poses another question. How do you measure the rpm of the wheel?
Rich
There was an article in MR some years ago about using the bike speedometer method, and also I think one that used an optical sensor. The bike speedometers work by a magnetic sensor, on a bike you attach a magnet to the spokes, for the model car you attach a magnet to the axle. The speedometers are usually quick enough even though this causes a sense far more often than a much larger bike wheel.
Side note, the counting how long it takes a car to pass a point method works regardless of scale - even for the real thing.
–Randy