minimum radius tester

Discussion in 'Getting Started' started by 60103, Jun 19, 2006.

  1. 60103

    60103 Pooh Bah

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    I've been thinking about this device for years, but i haven't had the base or the huge amount of track it would take. It might be fun to take to a show; a use for the old code 100 track after you switch to fine scale.

    What I would start with is a 4 foot square sheet of Homasote or such. In the center mark 4 points in a 1" sqaure. One should be in the center of the sheet.
    Pick the point farthest off center and draw a quarter circle at 24" radius in the opposite quadtrant of the board, let's say upper right. Now shift to the point to the right; reduce the radius by 1"; and draw another arc. Keep shifting the center around and reducing the radius. The centers wikk rotate in the opposite direction to the arcs. When you get to the first quadrant again, you'll be in 4". 4 times around and you'll be doing streetcar radii. You may want to put a large radius or straight track before the beginning.
    Now just lay and wire the track. You have built a spiral (not a helix!). Put a loco on the starting track and slowly wind it into the center to see where it binds, derails or shorts out. Run it in again backwards.
    A second spiral in the opposite direction would also be handy. Can you get a buddy to do it?
    I think 4 feet square would do for HO, be very generous for N, and be totally inadequate for O.

    Did I explain it clearly enough? :wave:
  2. b28_82

    b28_82 Member

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    That sounds like a good idea! I never thought of testing a car or locomotives ability to handle a radius through a test track specifically made for this. Usually just see how well it navigates the club. In a few weeks though i'll be clubless:cry: :cry: Oh well i guess that just means i'll have to put a layout in a room of my new house. Yeayyybounce7
  3. Russ Bellinis

    Russ Bellinis Active Member

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    You need to run the locomotive with at least one car. Often the locomotive will make a tight radius, but coupler overhang will result in it not being able to pull or push any cars through without derailing t\or even flipping over the cars.
  4. BigJim

    BigJim Member

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    Good idea but that will not test the straight to curved transistion problem. A train may do fine on an 18" radius circle but have problems changing from straight to 20" curve. Trains are more sensitive to the difference in radius from one unit to the other.

    That said try a string and a 1.25" rod (Closet pole?). Pencil in loop at the end of the string. String attached to the rod. Place the rod upright in the center of the 4' x 4'. Wrap the string around the pole as you draw the spiral. It will be about 3.9" less per full circle.

    Many layouts are limited to trying to do a 180 degree turn in 48". Using 2" minimum edge clearance that means a 22 degree maximum radius. Using a spiral in and out of the curve can help.

    This tecnique works well for "spiral" track curves. For example you can use a 1 gal paint can (6.75" diameter) for a 180 degree loop. Make sure you decrease to the mid point and increase out of the turn. NEVER DO AN S CURVE AT THE SMALLER RADIUS. With a 44" track center width you can enter at about 25.5" radius. Reduce down to 20" at the middle and back to 25.5". This should make things much more realistic than going from straight to 22" and the gradual change helps the coupler problem. Reducing to 25" and 19.5" will give you an extra 1/2 inch for an easement into the 25" point (shown below). I think the black line in the picture below looks and will work better than the red one:)
    [​IMG]
  5. Biased turkey

    Biased turkey Active Member

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    As mentioned by Russ, running the loco is not enough, it must be coupled to at least 1 car.
    "the straight to curved transistion problem" Worse than that, on my N scale micro layout I have a right curve directly followed by a leFt curved turnout. Some small cars and locos can make it, but some longer loco can't.
  6. fsm1000

    fsm1000 Member

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    I made a radius tester of sorts for my shay and porter
    http://fsm1000.googlepages.com/mylocos
    Click the bottom picture and then enlarge it in explorer or double click it in firefox. It is huge so beware on dialup.