This entry covers the details of my digital weighbridge which is a simple thing to adapt to fit any loco stand. It's very simple to build too, it uses components readily available, you don't need to be an electronics tech to build your own. Ok, so mine has been built to fit my new alloy stand, kindly built for me by Nick Elliot. It took my weight easily but I have had added a little more to it to suit my needs. IE, I have added cross bracing to allow me to wheel the model around the workshop (very uneven floor) safely and also to hoist the model on and off without being worried about any mishaps during the lifting.
So the first picture shows the stand itself and for this stand I'll be making two modules, one for the weighbridge and the other for a rolling road which will be for another day. Note the flat section of alloy near mid point, this is for the base of the weighbridge to sit on.
Now for the easy bit, buying a cheap pair of digital bathroom scales, these I bought off eBay and this particular set was chosen for its blue tooth ability which makes reading the weights very easy. IIRC these scales cost £15, I have seen them for less. I chose these as I could see in the images that the underneath was easy to detach from the glass, basically it was as simple as using a scalpel to tease the 4 sticky pads that held the base away from the glass top.
Here is what remains of the scales now fitted to the stand, the four sensors on this particular model were just clipped in and thus very easy to remove. The digital readout and electronics board I have left in their place and cut around them to remove the unneeded parts of the plastic base. I then drilled and tapped the stand cross brace to secure this section to the stand. The sensors will be siliconed to both the weighbridge base and top plate, thus sandwiched in-between. I have cut a rectangle out of the top plate for the battery box to fit in, I still need to file a small section away so that I can use the original battery box clip in lid. The battery box will also be siliconed in place once the stand has been painted. My eldest son has kindly said that he can paint the entire stand in an epoxy paint for me, once that is done I'll do the final assembly of the weighbridge to the stand.
This picture shows the top plate in position, later I'll also make a small box to cover over the electronic board and display for protection. As things are seen here, the loco can be pushed along the track without touching the weighbridge.
with the basics done as far as they could be until painted it was time to test the weighbridge's operation. First job was to put the loco on the stand, this was very easy using the hoist and swinging jib, here the model sits on the stand for the first time. Something to note here is that the model only takes up half the length of the stand which is 7 feet. Having a stand of this length and with the weighbridge close to centre, allows me to weigh all axles without the need to turn the model around.
Just to show that the stand is strong and mobile I have detached the model from the hoist and pushed it to the end of the workshop.
Now to weigh the model I slip two steel plates onto the weighbridge plate, this picture hopefully shows that when the wheel is pushed over the weighbridge with the plates in place it will rise up onto it's flange and thus will be weighing the axle involved. To weigh the axle I used two plates of the same thickness, if wanting to just weigh one wheel I'll only use one plate, thus leaving the other wheel still sitting on the rail. I have pulled one of the sensors out a little to give an idea of what's going on here. Later I'll make up proper plates that sit over the top plate so that they can not slip, I'll also chamfer the ends to aid the wheel rising onto the plates although the wheels went over the plates very easily without.
Ok, so on to the test itself, as mentioned I have chosen a set of scales with blue tooth capabilities, you don't really need this but since they are so cheap anyway and since the scale display isn't easy to see with the loco sitting on top having the ability to read the weight on ones phone makes a lot of sense. This picture shows the reading on the phone, now most of what's in this app is not required, I may try to see if I can get my IT son to look into writing an App for this purpose but for now the standard app does the job. So ignore BMI etc...:) One part that may be useful is the 'last time' figure difference as it shows the difference between the axle measured and the last axle measured.
Ok, so what did the test reveal? here's the results...
Bogie Front axle = 21 lb
Bogie rear axle = 19.8 lb
Main driver leading = 44.4 lb
Main driver crank = 16.8 lb
Main driver trailing = 16.8 lb
Trailing axle = 29.8 lb
Total = 148.6 lb
I took these measurements 3 times and got the same readings each time. The results don't surprise me as currently the model is very nose heavy now that it has the 3 cylinders fitted. It will continue to grow in weight at the front until the boiler is fitted were things will balance out more as this is very tail heavy due to it's large/wide firebox.
When the model is complete I'll revisit this test and see how well I can set the springs to give me the required chassis balance.
My aim will be as a starting point to mimic the prototype's weight distribution percentage wise with the model
The prototype weights come in at: (as published in the 'Flying Scotsman pocket book' by R.H.N. Hardy
Bogie (both axles) 17 ton 18.5%
Leading Driver 24 ton 26 %
Crank Driver 20 ton 21.7%
Rear Driver 20 ton 21.7 %
Trailing axle 15 ton 16.3 %