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Rotating Beacon on Model Railroad Problem
Bob models S scale and sent in this question for readers:
“I have a rotating beacon that does not rotate. No sure how the fins on the top should be angled? The beacon is connected to 18v on my transformer. I have adjusted the vanes but still does not rotate.”
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This beacon appears to be like or identical to the rotating beacon made by Lionel in the 1950’s. The rotation was caused by hot air rising from around the light bulb and flowing through the “fan” in the upper part of the beacon housing. The bulb itself had a little dimple in the top in which a pin at the middle of the fan rested. The entire housing with its colored lenses balanced on this pin. Because the only point of contact for the housing was that pin, there was very little friction and the movement of the rising hot air was able to spin the fan and the housing.
It would not matter whether the blades on the fan were bent up (to the outside) or down (to the inside), but to keep an even flow of air they should all be bent the same amount. Up or down would change the direction of the rotation. If the blades are not bent enough, not enough air will flow; if they are bent too far, the air will rise without exerting much force on the blades. As I recall the beacon we had, they were bent up about 1/8 inch.
In troubleshooting why your beacon is not rotating, first check to see if it spins freely when you spin it gently by hand. If it doesn’t, it won’t spin on its own. Something is interfering with its motion. Is the pin too short so that part of the fan is rubbing on the bulb? Is there a dimple in the bulb? Is the beacon housing able to swing a little bit like a bell if you bump it gently? If it doesn’t, then it has more than one point of contact (which should be the pin at the middle of the fan), and it will not spin.
Or, perhaps, you’re not waiting long enough for the bulb to heat up. The bulb needs to be warm enough to get the air moving, and that doesn’t happen immediately. Any drafts (a fan to keep you cool, perhaps?) can also interfere with the rising hot air off the bulb. The air around the beacon needs to be relatively still. The hot air rising off the bulb does not have much force; therefore the friction on the beacon housing needs to be almost zero. To overcome the inertia of a non-moving beacon you might just start it rotating by hand and let the heat from the bulb keep it going.
One final thought. Is your bulb a traditional incandescent bulb or an LED? An LED will not produce enough heat.
Follow up: Actually, it’s not just the air right next to the bulb that heats up, but all the air inside the housing. That’s what takes a while. When the air inside the housing is sufficiently warm, it rises through the fan. Therefore, another reason the blades of the fan cannot be bent too far is that if they are, too much air escapes, too much cool air enters from below and the air inside the housing is no longer hot enough to keep flowing up. You may have to experiment a bit to see how far the blades on the fan need to be bent.