1:450 Scale Road and Rail

[martink]

My second linear motor layout featured a working level crossing (grade crossing to you North Americans) at its heart.  This video is just a rough before-and-after cut showing it in action.  As a first attempt, it had numerous problems with the stop sections for the cars, with vehicles creeping forward and stopping too far apart.  In its final form with some electrical and software changes, the car-to-car spacing in the queue is better, down to about half that seen in the video.   I have since reworked the track and control designs to completely avoid these problems so the road vehicles can be tightly packed and well behaved.  Unfortunately, I cannot retrofit it into this layout unless I pretty much start again from scratch, but the next time I build something with a level crossing....

[Chris333]

But you're on the wrong side of the road 

Love the track speeder traveling the road.

[martink]

But you're on the wrong side of the road 

Love the track speeder traveling the road.

You could always just flip the video to swap left and right!  And during testing, I use whatever vehicles are at hand - one of those was the fire patrol trolley from Monbulk Creek.  There are even some bare magnets trundling along by themselves.  Oddly enough, making model cars or whatever at this scale is harder than doing the trains - they are so small it really pushes the limits of what my 3D printer can produce, and then trying to squeeze in the magnets...

[davefoxx]

Impressive.  Downright, and no buts about it, impressive.  I'd upvote your post, if I could.

DFF

[Mark W]

Wow.  Incredible!



I'm guessing the magnets need to be pretty strong, and/or specific polar orientation?  I'm also guessing something like iron or stainless steel powder additive to the resin, to make a magnetic print itself, would not work either (ignoring the more rapid wear it would likely cause to FEP). 

[martink]

I'm guessing the magnets need to be pretty strong, and/or specific polar orientation?  I'm also guessing something like iron or stainless steel powder additive to the resin, to make a magnetic print itself, would not work either (ignoring the more rapid wear it would likely cause to FEP).

The field generated by the coils in the track is very weak (it won't have any effect on an iron object placed on the track), so the magnets have to be the strong rare-earth type to compensate.  They have to have their magnetic axes aligned vertically, so the north or south poles are touching or almost touching the track surface.  So, trying to 3D print with a magnetic resin wouldn't work - too weak, no orientation, etc.  I design suitable holes into the bases of my models and glue and press-fit the magnets into place, so the vehicles can slide along on the smooth polished nickel surface of the magnets.  While things run happily enough on the bare track, using a protective surface avoids any long term wear problems and looks more realistic.  However the slightly increased distance between the coils and magnets reduces the drive force slightly so the system needs an extra Volt or two to compensate.

Practical vehicles need multiple magnets, with alternating N/S poles on 3mm centres to match the coil spacing, and the more magnets the better both for the extra traction and for steering.  Something light enough with one magnet will move, but will point in random directions.  Two are theoretically enough for directional stability, but the discrete drive pulses will tend to spin the model around from time to time.  Three is almost good enough, and all I can fit into smal road vehicles, but they sway badly and you still occasionally see a car doing a handbrake turn.  Four is great, since that also matches the 12mm repeating pattern of coils in the track.  Longer vehicles can use 6 or 8, with two groups of 4 being the best of the lot.  Think of each magnet as an axle with a very loose back-to-back spacing on the wheels, and then consider all the different wheel arrangements on trains, rigid wheelbase versus bogie/truck, minimum curve radius, etc.  The same basic issues and trade-offs apply.

[Mark W]

Cool, thanks for the explanation!

@tom mann, let me upvote this!