Announcement

Collapse
No announcement yet.

Let The Gearing Experiments Begin

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Let The Gearing Experiments Begin

    I am having a blast, even considering the struggles, learning to scratch build (inline-chassis) slot cars. My first two scratch builds were built to be legal for Proxy Races, if I choose to participate. After that, what's been most-especially fun, is building my cars, experimenting with different MOTORS, as I narrow down, THE Motors, I choose to build with, for my small Scalextric Sport road course layout! I've decided on two different short can motors, and one long can motor (the long can comes in two different rpm/torque ratings). So, now, I'm ready to Experiment With Gear Ratios, which is where I need you hobbyist's help !! For general, basic home plastic track competition, I personally think whoever came up with "standardizing" the 9/27 gear ratio, nailed it/ got it right ! So I'm using that 3 to 1 ratio, as my base. Question One : 8-tooth pinion/ 24-tooth crown is 3 to 1 ratio, also, but won't that perform differently than 9/27 on the track ?? Question Two : what if I go up one tooth on the crown and one tooth up on the pinion, for 10/28 (2.8 ratio) ?? Will I gain acceleration at all/lose top speed ? Remember, my layout is smallish. Maybe just go up a tooth, or maybe two, only on the crown gear ? Question Three : or how about something a bit Wild, to gain acceleration, but not lose too much top end, which I hope you all could suggest ?? Anyway, I have built several pretty fast scratch builds, and they handle well, too. The one's I've built on the LVJ Champ and Cruiser chassis, are fast too, with a very slight handling advantage over my total scratch builds. Built one LVJ car, with a paper-laminated Super Modified body, featuring a Slot.it 29,000 rpm short can motor, that is a total rocket !! I'm not touching the gearing, on that one, lol.

  • #2
    A 3:1 ratio is a 3:1 ratio, whether it is 7/21, 8/24, 9/27, 10/30, 11/33 or 12/36. At least in theory. There is likely a minor loss of efficiency with the smaller pinion gears. And you may need the higher tooth-count gears if you want to build an anglewinder or sidewinder. Otherwise there won't be clearance between the motor can and the rear axle.

    What limits the tooth count on the crown or spur gear is the diameter. Too many teeth and the gear will be larger than the rear wheels and rub on the track.

    Going from a 3:1 ratio to a 2.8:1 ratio should reduce peak acceleration and increase top speed. Again, in theory. And it is a pretty good theory.

    Going from a 3:1 ratio to --say -- a 3.5:1 ratio will increase peak acceleration and reduce top speed. But here theory can run into issues with reality. You may lose any gain in acceleration if the added torque just spins your wheels. And that reduction in top speed may not matter if the track isn't large enough for your car to reach its top speed.

    I am going to suggest that you want to gear your cars so that you get a moment of wheelspin starting at full throttle from a dead stop. Your tire grip limits your peak acceleration which happens at full throttle and low speeds. Once your car is rolling you should no longer see any wheelspin, which means you are not wasting any power. That power you aren't wasting adds to your top speed. And you should also have good braking without any skidding.

    Increasing/decreasing the tooth count on the pinion gear has a much bigger effect than changing the tooth count on the crown or spur gear. Fine tuning of your gearing should probably be done by changing the tooth count on the crown or spur gear.
    Ed Bianchi
    York Pennsylvania USA

    Comment


    • #3
      Thank you, VERY much, Ed : your answers are exactly what I wanted and needed to know : and I suspected that the crown gear/spur gear, was the one to really be tuning with, too !

      Comment


      • #4
        Slot.it's 28:9 in their Group C and DTM cars is a nice ratio that allows the teeth to mate with different teeth during each revolution which can help slow premature wear.
        Bram,
        CHCH NZ

        Comment


        • 6666hotrod
          6666hotrod commented
          Editing a comment
          Wow, now that's interesting !

      • #5
        Smaller gear ratio = higher top speed, less acceleration, less brakes, smoother drive.
        Bigger gear ratio = lower top speed, more acceleration, more brakes, less predictable drive.

        Smaller diameter gears should spin up quicker and in some cases where space is limited is the only option

        I prefer starting at 10/28 for the motors I prefer (NSR Shark 25)

        N.B. tyre diameter has a big say in overall gearing, the gear ratio itself is only one part of gearing, true 'net' gearing is called rollout, the distance the car travels for one full rotation of the motors rotor.
        Last edited by Kevan; August 17, 2022, 04:20 AM.
        Kevan - Isle of Man
        Life is like a box of Slot cars...πŸš“πŸš—πŸššπŸšœ

        Comment


        • slothead
          slothead commented
          Editing a comment
          Can you define smaller and bigger? Does going from 8:26 to 8:27 count as an increase or decrease? What about 8:26 to 9:27?

          26/8 = 3.25, 27/8 = 3.375, 27/9 = 3.0

        • Brumos RSR
          Brumos RSR commented
          Editing a comment
          The actual diameter of the pinion can alter acceleration and top speed along with the number of teeth. So a 9/27 gear and a 12/36 although the same ratio may accelerate and brake at different rates if the diameter of the pinion and spur or crown are not equal in size to the one it is being compared to. This is the way it works in the karting world which is closer to the slot car world than 1:1 cars. Size Matters.

          Kevan is correct here

        • Kevan
          Kevan commented
          Editing a comment
          @slothead
          2.8: is a smaller ratio than 3:1...and 3:1 is a bigger ratio than 2.8:1

      • #6
        Some notes about gearing efficiency...

        Full sidewinder setups are the most efficient, especially when running 'involute' gears. Theoretically perfect 'involute' gears do not rub -- they roll. Watch the animation in this Wikipedia page:

        https://en.wikipedia.org/wiki/Involute_gear

        Slotcar crown gears, used for inline drives, all-too-often have primitive teeth with 'saw-tooth' shapes. Probably the least efficient, especially when mated with small pinion gears. There are, however, crown gears with better tooth designs -- typically aftermarket. Especially gears designed for drag racing.

        Crown gears also lose efficiency due to the sideways thrust they create. That thrust has to be countered, which causes drag. In the worst case there is a flange on the crown gear which rubs against the motor shaft. The best setup uses ball bearings and axle sleeves to counter that sideways thrust.

        For inline crown gears with a flange the flange and motor shaft tip should be greased.

        Anglewinder setups typically have efficiencies intermediate between those of sidewinder and inline gearing. Tooth forms are typically better than crown gears but may not be true involute. Sideways thrust exists but is typically less than in a inline setup.

        Efficient gearing has proper spacing, with a small gap between the gear teeth. A common trick when setting up gear spacing is to feed a thin sheet of plastic film between the gears. The film sets a small clearance between the gears while you tighten things up.

        Last edited by HO RacePro; August 17, 2022, 05:11 AM.
        Ed Bianchi
        York Pennsylvania USA

        Comment


        • slothead
          slothead commented
          Editing a comment
          "thin sheet of plastic film" is non-specific. Is there an ideal thickness?

          Also, I assume the sideways thrust is due to the crown or spur gear (anglewinder) being pushed away from the pinion gear. What grease is recommended to use on a crown gear flange? Does using an axle stop on the side of the chassis the crown gear is facing produce a better solution? What about putting spacers behind the crown gear, between it and the chassis/bushing?

        • Bal r 14
          Bal r 14 commented
          Editing a comment
          I use Kleenex to space gears. Started doing that many years ago when I flew RC helicopters. Works great on slot cars, too. If it still feels tight, fold the Kleenex over to double the thickness and do it again.
          Last edited by Bal r 14; August 17, 2022, 08:41 AM.

      • #7
        An ideal thickness of film? I don't know about ideal, but at a guess only a mil or so. Maybe use a section cut out of a plastic sandwich bag. You're only looking for just enough clearance so things don't rub. More clearance doesn't help.

        As for grease, again, don't know about ideal. You want a thin grease that stays put on the flange rather than getting flung away. Have you heard of 'Lubriplate'? It has been around forever and should do the job just fine. Look for Lubriplate 630-AA in the handy small 3/8 ounce squeezable tubes. Great addition to your pit box.

        If the car doesn't have ball bearings on the rear axle, a brass tubing spacer that pushes against an oilite bushing should be the next best thing. A dab of grease there won't be amiss.

        Don't take my recommendations on plastic film and grease as gospel. Lots of room here for experimentation and debate.
        Last edited by HO RacePro; August 17, 2022, 09:26 PM.
        Ed Bianchi
        York Pennsylvania USA

        Comment


        • #8
          Thanks for the replies to my questions. I'll definitely get a small tube of grease for gears, and remember the storage bag plastic for gear mesh.

          Comment


          • #9
            Back in the day lots of guys used cigarette paper to set gear mesh😏.
            Mike V.
            Western North Carolina

            Comment


            • #10
              So would there be a really noticeable difference between 9:27 (3) and 9:28 (3.11)
              What about if you went 10:28 (2.8) compared to 9:28 (3.11)

              cheers
              DM
              Dangermouse to the rescue.

              Comment


              • 6666hotrod
                6666hotrod commented
                Editing a comment
                See, now y'all are getting to The Nitty Gritty Of It, for Me !!!

              • Bal r 14
                Bal r 14 commented
                Editing a comment
                Ideally, you want to optimize gearing to match the length of the track. If you are getting out-accelerated badly on the straights, you aren't going to catch up on the turns.

            • #11
              DM, it's not easy to predict how a gearing change will affect a car's performance. A lot of it has to do with the track rather than the car. There are cases where a relatively minor change in gearing has a major impact on how well a particular car navigates a particular track. Not to mention the fact that different driving styles may favor one gearing over another.

              While many slotters prefer a car with snappy acceleration and strong braking I have noticed that the best drivers have a smooth driving style, turning in fast laps consistently and without drama. Their gearing choices may be closer to 2.8:1 rather than 3.11:1.

              A couple years ago I experimented with direct drive in custom-built 1/32nd scale cars. No gears. Rear wheels mounted directly on the motor shaft.

              While the cars were not competitive, they came much closer than you would have expected. A lot of that had to do with very high top speed and lots of coast. There was something like 'turbo lag' where I'd pour on the power early exiting a curve. And coasting into a curve made the most use of the tire traction available.

              I should mention I had a lot of success oval racing with direct drive in HO cars, which inspired my experiments in 1/32nd. Those cars required a complete rethink of driving style. Almost opposite of driving a geared car. Full power on the banked curves and coasting down the straights!

              Ed Bianchi
              York Pennsylvania USA

              Comment


              • 6666hotrod
                6666hotrod commented
                Editing a comment
                Yep : The Nitty Gritty of it. Thanks, guys !

            • #12
              I set backlash by feel, when the wheel can be rocked back and forth a tiny bit in various positions around its rotation without moving the pinion I know its right.
              Kevan - Isle of Man
              Life is like a box of Slot cars...πŸš“πŸš—πŸššπŸšœ

              Comment


              • 6666hotrod
                6666hotrod commented
                Editing a comment
                Lovin' this Education, hobbyist's !

            • #13
              One of the oldest and most successful gearing tricks involves heating the plastic to improve the mesh. This comes back to the fact that slotcar gears often have primitive tooth profiles.

              When you have a car with a metal pinion and a plastic driven gear -- crown or spur -- you apply heat to the plastic teeth while the drive is spinning. You do need to have the heat focused on the gear teeth to avoid damage elsewhere. As soon as you hear the noise of the gears change remove the heat. And you will hear it change -- very noticeable. They'll get quieter.

              If you look at the plastic gear teeth under magnification you'll see where they have been deformed by the heat and pressure. It won't be a big change -- you want to avoid that. But just where the pinion gear teeth were in contact with the plastic.

              Like I said, you'll hear the difference. The gears will run quieter, and that means they'll be more efficient. A small change, but small changes can win races.
              Ed Bianchi
              York Pennsylvania USA

              Comment


              • #14
                Originally posted by Mickey thumbs View Post
                Back in the day lots of guys used cigarette paper to set gear mesh😏.
                And were their cars smoking fast? πŸ™„

                Comment


                • waaytoomuchintothis
                  waaytoomuchintothis commented
                  Editing a comment
                  When we used ZigZag Wheat papers doublewides, it sure seemed like they were, but then, everything, including slot cars seemed extra fast when we were mellowed out.

              • #15
                While using kleenex/paper/saran wrap etc. to set your lash is OK (and was done for several years), you are assuming that both your pinion and spur have been produced with the bore drilled absolutely dead center, (they are sometimes off) and that the pinion has been installed perfectly squarely.......I have seen tons of pinions installed with a bit of "wobble", and if is the case, you will end up with varying amounts of lash as the pinion rotates.

                Most of the more experienced racers, will set the gears with just a touch of lash manually, and then check the lash a every couple of teeth on the spur to see if the lash increases or diminishes at any point over 1 full rotation of the spur.......if you wish to set the lash using tissue paper or whatever, make sure you set it at the "tightest" spot that you have identified.
                While a perfectly non concentric Crown is far less of an issue than with a Spur, Crown gears often exhibit some wobble,....and this also requires checking the lash at several points around a complete rotation of the Crown.......always set the lash at the tightest point.

                While it is aways much more beneficial to use perfectly concentric gears that have been installed correctly, minor variances can be overcome using the method above.

                To keep grease/oil etc. on the tiny points that the gears actually touch is wishful thinking, and even the vast majority of "Eurosport"/"Wing car" racers do not "lube" their gears (using 150K + motors).

                cheers
                Chris Walker

                Comment

                Working...
                X
                UA-149438709-1