The Home Machinist!

I plan on installing a bicycle speedo/odom on my locomotive.
Not being able to browse such products in stores these days, I am concerned with the units' ability to program for small diameter wheels.
That programing range data is been difficult/impossible to determine online.
I also can't use a wireless unit, due to the steel tender floor. Sooo...

What wired units can people recommend that will work for our 4.5" diameter tender truck wheels?
Thanks.
RussN

I have looked in the past and decided that it would probably be necessary to 'scale' the indicated speed as none that I found would work with our diameter wheels.

Russ,

Haven’t looked at bicycle odometers, but have installed a couple of cheapo rpm sensors on two lathes. These things work well with small diameters- from 4” cone pulley’s down to 1” shafts. Now, with an rpm sensor, you could theoretically program a multiple relating to your wheel diameter to get an actual speed measurement in MPH.

The trick would be to find a gauge to express your indicated MPH. Seems like any digital speed sensor gauge should report whatever you program the speed sensor to show.

Glenn

As to "programming speedometer for small wheels", on my Northern, I ended up putting two magnets on the axle (instead of one) and the set the wheel diameter such that it read in Scale miles per hour.

Let's say that your wheel is 4" diameter. With one magnet on the axle the wheel would rotate this many times in one scale mile:

1 scale mile = 5,280/8 = 660 feet = 7,920 inches

4" wheel circumference = 3.14159 * (4/2)**2 = 3.14159 * 4 = 12.5664 inches wheel circumference

Rotations in 1 scale mile = 7,920 / 12.5664 = 630.25 revolutions per scale mile

To find the diameter of a wheel that would do 630.25 revolutions in an actual mile (so that the speedometer will indicate "MPH"):

5,280 / 630.25 = 8.3776 feet in circumference = 3.14159 * (D / 2)**2 ... solving for "D":

D = 2 * sqrt( 8.3776 / 3.14159 ) = 3.266 feet = 39.19 inches in diameter

39.19 inches in diameter is probably outside the range of the capability of the speedometer but, if you put two magnets on the axle you only need a wheel with half of that circumference or:

D = 2 * sqrt( (8.3776 / 2) / 3.14159 ) = 2.3 feet = 27.71 inches which is probably in the range for the speedometer

Note: The above assumed a wheel diameter of 4" and would have to be adjusted for a different diameter.

Hope this helps ...

Russ...have used both wired and wireless bicycle 'puters. Purchased some Sunding brand bicycle computers on Ebay. These were typically around $8 each. They can be programmed for our sized wheels...nominally 4.125" diameter => 330 mm circumference (and you're right...need to make sure the wheel size of any bicycle computer for our trains is NOT limited to bicycle tire sizes).

Originally had a wired computer, but that was a PITA when the front tender truck needed to be removed for service. Since the sensor is nothing more than a magnetic reed switch, would imagine the wire could be cut so a small 2-pin connector could be installed. Later on, switched to a wireless computer. The transmitter is on the lead tender axle. Pretty much directly below the receiver. The steel tender deck was not an issue. However, some of the wireless computers do have a distance limitation as a friend of mine found out.

Made a split disk out of nylon that was clamped around the axle for the magnet. The pickup sensor/transmitter was mounted on a bracket attached to the truck bolster. Need to position the wireless transmitter so you can easily access/replace the battery (#A23). This is slightly smaller than the "normal" garage door opener battery. For the wireless versions, the receiver uses a #2032 battery. Batteries will easily last a year and are readily available at most big box stores.

It will take a while to get used to the programming and then sequencing thru the various display parameters. Like so many other things, you get used to the sequence after a while. Can select speed readout in mph or Kmph...but these are actual speeds. One of the handier aspects is the "wheel(s) turning" indicator. Easy to determine if sensor and display are working.

Have some photos somewhere if you're interested. Carl B.

I bought a wired one many years ago at Target that would go to the small diameters we need. It was a Target house brand. Sorry I don't have any more info than that. There are no marks on the unit to give any idea who made it.

Gang: Thank you for your useful input. Thoughts in several directions.

Carl's setup is precisely what I had in mind.
In 2006 I purchased (yes, I actually found the receipt!) a TopPeak Comp 150 wireless cycle computer which I dug out of storage today. I had originally determined it could be programmed for small diameters. We all see if that is indeed true.
I will test it through the tender steel floor to see if it will work. If yes, I will create a setup and see where that takes me. I like the plastic disc idea for holding the magnet.
My concern remains the wireless data transfer through the steel, because I have specifically read of problems with that. Thus my quest to locate a wired unit.

I'll share my results here, when I get to this project. Several weeks downstream?...
Thanks all.
RussN

Carl ... if you can find the photos of your installation, I would like to see what you did.

Probably won't work through the steel.

John Hasler wrote: ↑Mon Apr 12, 2021 9:20 am Probably won't work through the steel.

And yet Carl B's did work through the steel deck.
We'll see. I have my hopes up...
RussN

Reporting back already...
The bicycle computer I have can be adjusted for wheel circumferences between 0mm to 3900mm! So no problems there.
With new batteries installed, everything works.
The 4" diameter tender wheel has a circumference of 319 mm, which entered into memory easily.
And preliminary hand-held tests show that the sender unit does communicate with the receiver through the steel tender deck/floor.
So next task is to access the bottom of the tender truck to design and install the holder for the sender unit and the magnet holder on the axle.
Eventually...
RussN

George and Russ...
Some bicycle computer reference photos attached...

The transmitter comes with a double sided sticky foam. That sort of works. I put some small Ty-raps thru the slots to really hold the transmitter in place. think in the 1st photo, one of the Tu-raps already broke off. Might have even put some RTV in there as well.


Next photo shows minimal clearance between the magnet in the nylon disk and the transmitter. If I remember, the distance is something like 3mm. Need to make sure there's clearance for any axle side play.


Here's a bottom view looking up at the transmitter.


Last photo shows the LCD display. The "wheels in motion" is a pair of bicycle tires spinning in the upper left corner. During the next photo, was clicking along at 6.2 mph. Below the speed, is the total distance traveled since the odometer was reset at the start of the run.

When programming the receiver, need to hold both buttons down for something like 3 seconds. Once in "program mode", you set the circumference of the wheel with the magnet. The digits are set one at a time. If you don't touch any of the buttons for a short time, the display is kicked out of the program mode. You get used to this after a while. While programming, the left button selects the parameter to be set. The right button is used to set the numeric value.

Had an incident several years ago when the computer stopped working. The LCD display was working, but getting no "data". Replaced the transmitter battery...but that didn't help. When I got home, on a hunch replaced the battery in the receiver display...and everything was back to normal. For my purposes (other than knowing how fast I can get going on a straight away), use the odometer to stop every 5 to 6 miles to "lube around" the loco. So for those (2) purposes...it's a great tool.

Keep in mind, there's nothing really fancy here. The transmitter (wired or wireless) is nothing more than pulse counter. Total pulses yields distance (based on wheel circumference). Total pulses over a fixed time period yields speed (again based on wheel circumference).

Hope that helps. Carl B.