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Wobbly Wheels

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  • Wobbly Wheels

    I have been scratch-building 1/32nd cars to compete in the IHSR series, creating custom chassis components, many of which are parts made on a filament 3D printer.

    One car I have created is based on a Monogram model of the Cooper Monaco racer. I have used the body as the main structure of the car -- a monocoque design. There are three sub-chassis attached to the body, a motor pod, a center module that carries a rattle pan, and the front sub-chassis that includes the guide and the front wheels.

    That front sub-chassis mounts the front wheels on a pair of stub-axles. Each wheel has its own ball-bearing fitted into its hub. Those ball bearings are a loose fit on their stub-axles, so the front wheels are a bit wobbly -- they don't have to spin exactly square with the chassis. They have some ability to self-steer. At least in theory they can steer and roll rather than slide when the car drifts a bit in a corner. And that, in theory, should reduce the front-end drag in cornering, making the car less likely to spin out.

    That front end wobble was not intentionally part of the design. It just seems to have happened. But that car has started to perform really well, and I am beginning to think the wobbly wheels are -- to coin a phrase -- not a bug but a feature.

    They are not the first set of wobbly wheels in slot racing -- not by half. The 1970's HO TycoPro chassis designed by the legendary Pat Dennis featured skinny front wheels loosely mounted on plastic stub axles. Those wheels most definitely wobbled. Was that by intent? Nobody ever seemed to mind, and the TycoPro chassis was a definite success, even if its pickup system was not so stellar.

    One of the top competitors in the IHSR club has pointed out to me that when a slotcar enters a curve there is a conflict between the guide and the front wheels. The guide is trying to turn the car while the front wheels want to keep going straight. That appears to be the reason why there is so much emphasis on keeping the load on the front wheels light and the front tires slippery -- so they put up the least amount of resistance to the guide's efforts to steer the car.

    I'm thinking my wobbly wheels are helping in that direction. Rather than get dragged sideways they'd self-steer into the corner. One can hope they have a bit of gyroscopic action so their ability to wobble doesn't have them flopping chaotically either in the corners or in the straights.

    Add to the list of the mundane superpowers I crave would be the ability to actually see what those front wheels are doing at speed. In my prior life as an engineer I once had access to high speed cameras capable of thousands of frames per second. It would be just the thing.

    A little bit of online research has turned up the fact that the current iPhone models can take 240 frames per second in Slo-Mo mode. But I don't think that would be fast enough. There are high speed video cameras that cost less than a thousand dollars, but Santa would have to be very, very happy with me for such a thing to come into my life.

    Anyway, at the moment it appears that my car's wobbly wheels are part of a package that is performing really well. If they aren't helping it does not appear they are hurting.

    Ed Bianchi

    Last edited by HO RacePro; September 4, 2021, 09:29 AM.

  • #2
    Originally posted by HO RacePro View Post
    One of the

    Kevan - Isle of Man
    Print It, Build It, Race It, Improve It, Repeat...


    • TuscoTodd
      TuscoTodd commented
      Editing a comment
      I run into that as well - will be great if you can adjust that sir!

    • SCC_Steve
      SCC_Steve commented
      Editing a comment
      Per vBulletin Tech Support:

      With the default settings, the log in session terminates after 15 minutes of inactivity. Activity includes actions like loading pages and clicking interface buttons. When composing your posts within the editor, it happens solely on the end-user's computer. It does not necessarily contact the server while doing this. There is auto-save functionality that is on by default which saves a post draft every minute. Plus the notification indicators will refresh for up to five minutes after a page load. I am not sure if these trigger last activity updates though. If a user takes a long time to compose here posts, then they can be logged out.

      The remedy for getting logged out is to use the "Remember Me" checkbox on Login. This will store the user's identity as secure HTTP Only cookies on their computer. Both a userid and a password token (not the actual password). When a session timeout occurs, instead of asking the user to log in again, the system will use these cookies to perform a log in behind the scenes. When you click the logout link, the cookies are deleted. Remember Me will be active for up to 30 days.

    • SCC_Steve
      SCC_Steve commented
      Editing a comment
      The default automatic logout was set to 15 minutes of inactivity. Per the comment above, keep in mind that when you are creating or editing a post, this is being done on your computer. If you have take more than 15 minutes to create a post, the server is not seeing activity so you get logged out. I have increased the default auto logout value to 60 minutes. Let's see if that resolves, or at least minimizes, the issue some forum users are experiencing. Be sure to click "Remember Me" as well when you login.

  • #3
    If you are using a computer to do your post you could compose it in Word Pad, then copy and paste that into the BB post. I have Microsoft Word, so I use that and I also usually save long posts to my hard drive.


    • #4
      With slot cars that have their front tires touching the track those should have as little grip as possible. Some people coat front tires with nail polish. makes Zero Grip rubber front tires and there are extra hard low grip urethane front tires from Quick Slicks and Super Tires.


      • Pappy
        Pappy commented
        Editing a comment
        I put silicones on the front of a car and it didn't seem to make any difference. My line of thinking was maybe grip on the front tires would eliminate some of the side loading on the guide flag. I also run both of my front wheels independent of the axle.

    • #5
      I would be conserned about the wheels vibrating on a straightaway but hey if it ain’t broke why fix it
      Peterborough Ont


      • HO RacePro
        HO RacePro commented
        Editing a comment
        I'm concerned about that too, which is why I'd love to get some close-up high speed video of those wheels. Failing that, I guess I just have to race it and see how it finishes.

    • #6
      To follow up...

      I didn't need a high-speed camera to discover an issue with my wobbly-front-wheel car. My home track has four corners, and on three of them the car performs brilliantly. That fourth corner, however is a large-radius high-speed sweeper. Apparently the car hits a critical speed in that corner and the front end gets squirrely, to the point where it sometimes deslots. As best I can tell those wobbly front wheels hit a resonance and upset things.

      So, to answer my own question, it appears that wobbly front wheels are okay, and maybe even an advantage at some speeds, but not at all speeds. And at those critical speeds they really foul things up.

      I'm going to rework the front end and tighten things up.

      Ed Bianchi