Cheapest easy DC motor to survive locked rotor

Sounds very interesting. I will ask at work if they have throwaway cdrom drives.

Sounds fantastic!

The recorder is gone... But a good idea. Thanks Nick.

Enough to build a Zuse?

Nick

You mentioned using a solenoid earlier. They're terribly inefficient, but they're generally built for this kind of load. They have lots of windings that bulk them up and would slow them down if they should go fast, but give lots of actuating force and a high resistance to limit current. You may even want to use separate "open" one and "close" ones; this will let you use two single-acting solenoids and would simplify your switching.

If you don't already know about it you want to check out Herbach and Rademan:

I checked them out and did not find 12 vdc solenoids. McMaster has them, see item 70155K2, for $8.82. I may use them on railroad switches. I hope that they can stop in an intermittent position (if the part being moved does not want to move further) without trouble. But that will come later.

Just had a quick look. I have one marked 24 V and two which are unmarked. I'm guessing that the unmarked ones are either 12 V or 24 V from the thickness of the wire. Interestingly one is branded "Playmatic". Two have mechanisms which turn the reciprocating action of the solenoid into a rotary action. Stroke looks to be about 1" on all of them. Weight is probably 0.5 - 1 lb each. I can investigate further and take some pictures over the weekend if you like. What gauge is your son's railway? Unless it is fairly large you might need to build a model shed to house these in. They are pretty chunky.

Chris

Yes, looks like they are a bit too chunky. I would guess that the track is about 14-16 mm wide. I think that I will look for something smaller, and I'd need them for something else anyway (switching tracks).

Why not get a small bit of Nitinol (Memory wire) and use the relay to apply voltage, heating it up and causing it to shrink, pulling the gate down

Maybe add a cheap linear regulator and either use the built-in thermal shutdown protection or wire the regulator as a current limiter. Look up the National LM7812 etc...

Most solenoids will overheat if they remain energized with the armature prevented from fully seating in the coil.

Ned Simmons

Unless the armature provides a thermal path that cannot be the case in a DC solenoid. AC, yes -- the inductance would go up, and the current down. DC, no -- after you get past the R/L time constant the inductance doesn't mean anything.

Thanks Dave. I will try using a resistor, if that does not help, I will explore your proposed route.

According to Ignoramus8558 :

Enjoy, DoN.

So after looking at all these electrical solutions I have to wonder why you can't just do it mechanically. Put a pair of washers on the shaft and a jam jut. Tighten the jam nut just enough to hold the gate at any position. Power to motor only to move the gate and de-power it otherwise. 'Course this assumes that the motor torque capability is way more than you need for a simple model railroad gate. Very cheap. OK reliability. May have to play with it to keep it from loosening up.

Have fun in any event.

Or build a small servo controller and just use the servo as it was intended. I once built a small circuit that used a potentiometer to let me "control" a servo. I can't imagine it's a hard circuit to find, nor would it require any expensive components (nor very many components). Then just find an RC servo "big enough" to handle the size of the gate, which also shouldn't be hard to find (and I'm sure used ones are dirt cheap on eBay).

The circuit I found used a potentiometer, but it wouldn't be hard to hack it to have a switch change the resistance appropriately for the circuit to move the servo to the right place (hint, use a pot to find the proper resistance values for "open" and "closed" gate positions and then use a switch with NO and NC terminals and wire the proper resistance to each one).

You can likely also drive multiple small servos off the same signal from such a device, though I never tried it. That way you could use a gate on each side of the crossing, just like real life.

I mean if Iggy can build his own 17.5HP RPC, this is child's play. Pun intended. ;-)

--Donnie

Thanks to all. I added two 100 ohm resistors in parallel (R=50) and the motor works with minimal torque and no overheating. The resistors (25W rated Dale resistors) stay quite warm but no more). It's now tricky to have a gate that actually opens and closes, but I like it this way.

Use pinball solenoid parts. Fairly cheap and built to last. Pinball flipper solenoids have two sets of windings...one to "hit" and the other to "hold". There's lots of pinball information on that great world wide web thingamabob.

As for track switches, what scale are we talking? I can't imagine a scenario where hacking your own is cheaper than buying the canned stuff that exists. I do G-scale railroading and those little solenoids they have aren't really cheap, but damn if they aren't very well packaged for the application and just plain work.

I suppose if it's just for one or two and you just want to DIY...

--Donnie

You are kind of right, but it is tricky to automatically turn it off so that it can later be reversed. Much work. See my other post, a resistor worked great.