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  • Shimming Axles

    Shimming axles between the wheel hub and the cahssis give you a perfect distance if you use the same shim for shim on each side. the distance will be exactly the same. I don't understand why people are not doing this on every car that they own. It not only sets the distane equally but it keeps the crown gear groove and motor shaft properly aligned and does not allow the axle to slide from one side to the other putting any frictio on the crown gear form the motor shaft. IF the shims have soem sort of lubricatin on them ther should be no friction and only the best times that a car can acheive should result. I always shim the front even if it is a minimum 0..5 shim pt prevent any friction from the wheel to chassis. sometime the front wheel adjust ment can be .125' on each side to set it up perfectly to be just inside the fenderwell and it also prevents the axle from moving from side to side. IF there is any reasons for NOT doing the setup this way PLEASE enlighten me. I'm VERY CURIOUS and very serious about my slot cars and performance. Thank you in advance,
    Lindsey "Kansas" Angell

  • #2
    Shims, spacers, stoppers ... for sure, it's only a good thing to build a car with virtually zero lateral movement possible in the rear axle.

    If this isn't done with an inline, then the pinion shaft will gradually (or maybe not so gradually) start chewing away on the hub of the crown gear; those lightweight aluminium ones from Slot.it seem particularly susceptible. Besides, a car in a corner is loading the gear - or not - with the force from the lateral g's, and this can't be helping performance.

    Shimming externally (between the wheel and the outside of the bushing) isn't always the best choice, particularly when trying to stuff the wheels under the bodywork; especially with some sidewinder or anglewinder setups.

    Personally, on builds that are really important such as proxy cars, I like to use stoppers, the ones that were developed for anglewinder setups; both Slot Car Corner and Sloting Plus have these available in reasonably priced packets - though I still use a shim or two (if there's room) between the stopper and the bushing surface, in the belief that several provide less chance of binding if the lubricant is being spun off over time.

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    • #3
      I couldnt agree more!!

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      • #4
        Basically, IMHO, you're right. I probably have more spacers/washers of varying thickness, diameter, and material than all the other parts put together (I buy 'em in bulk when I need parts). But you're assuming symmetry, which is not always true, I'm afraid.

        On sidewinders, the distance between wheel hub and axle mount on the chassis will vary because the axle mounts are offset to one side or the other. And on RTR cars with splined axles and pressed-on plastic wheels, sometimes all you can get in there is one very thin spacer on one side. And sometimes there are just enough differences in the body and chassis because of molding issues and wide tolerances that your theory breaks down in the face of reality.
        Last edited by JML; 03-21-2010, 06:00 PM.

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        • #5
          The body is off center on plenty of slot cars, so an extra .010 or so on one side is often called for.

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          • #6
            My reference to al of my cars are for INLINE setups, so please...I don't need the confusion of angle winders right now...

            http://www.torquemadaslot.it/Test%20...slot%20uk.html

            Does this setup keeps the lateral forces from eating up and loading up the crown gear? I suppose IF I saw one...actually installed one I might better understand how it works...IF this is what you are refering to then I can see how they retain the 300-400 rpms better in the corners because the loading is on the ball bearings and not put into the squish and friction of the shims. I am seriously interested in the physics and science more than just winning a race because I have some $6.00 part installed.

            I don't see or understand how at this moment HOW any lateral loading (going around corners forcing the axle to shift to one side) as long as my shims are taking up all the slack space and therefore taking up the lateral force and any friction how any loading can be put on the crowngear/motor shaft/pinion gear. I can see that even IF my shims are actually compressed enough there may be some friction but I cannot see how any compression would be enough to allow any loading on either side of the gears with them in place.

            IF someone could explain how then I would seriously appreciate their explanation. TOO, I cannot see how the piece I have at the beginning the shortcut keeps the loading off of the gears.

            Lindsey "Kansas" Angell

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            • #7
              ANOTHER minority report!

              Seems like I am destined to be the frequent "odd voice out" these days...

              Sticking with inlines and assuming both the wheels and crown gear can be moved/adjusted: to my mind there are two principal objectives in shimming the drive axle of an inline car: to improve mesh and to lessen friction. And before we get to why you would do that, let's take a look at other reasons and comments on why you would shim the axle:

              Originally posted by lindseyangell View Post
              Shimming axles between the wheel hub and the cahssis give you a perfect distance if you use the same shim for shim on each side. the distance will be exactly the same. I don't understand why people are not doing this on every car that they ownl
              Originally posted by Robert Livingston View Post
              The body is off center on plenty of slot cars, so an extra .010 or so on one side is often called for.
              If spacing the rear axle were the only objective with shimming, I consider it redundant. There is absolutely no reason why you cannot obtain perfect wheel spacing by using the adjustment on the crown gear and wheels. And you can quite easily accomodate the common situation that Robert mentions: it is my experience also that it is pretty rare to find a situation where you add equal thickness spacers to both sides to get the spacing perfect. Slot car life just does not seem to be that balanced! And in rereading this sentence: that statement is pretty ambiguous, isn't it? My slot car life certainly is not that well balanced....

              Originally posted by lindseyangell View Post
              ....but it keeps the crown gear groove and motor shaft properly aligned and does not allow the axle to slide from one side to the other putting any frictio on the crown gear form the motor shaft. IF the shims have some sort of lubricatin on them ther should be no friction and only the best times that a car can acheive should result.
              Originally posted by Wet Coast Racer View Post
              Shims, spacers, stoppers ... for sure, it's only a good thing to build a car with virtually zero lateral movement possible in the rear axle.

              If this isn't done with an inline, then the pinion shaft will gradually (or maybe not so gradually) start chewing away on the hub of the crown gear; those lightweight aluminium ones from Slot.it seem particularly susceptible. Besides, a car in a corner is loading the gear - or not - with the force from the lateral g's, and this can't be helping performance.
              OK, when it comes to mesh and the mess that friction could possibly make of performance and component wear:

              1. With good quality components (assume for instance a Slot.it motor with a Slot.it bronze hub crown gear), I do not believe the you can significantly improve the mesh by adjusting the crown gear to pinion position with shims/stoppers. You certainly also do not get excessive side play on these quality components. I believe this setup is pretty much as good as it gets. However: with lesser quality components you could have less than perfect mesh and possibly sideways "slop".

              Case in point: I recently had a Fly Racing Aluminium hub crown gear that was ludicrously tight. I had to sand the inside of the groove to loosen up the mesh for it to run properly. Another option would have been to cut off the part of the motor shaft engaging the crown gear and set the mesh "manually" with shims.

              Another case in point: I put a Slot.it offset crown gear in a MRRC/Rev-Mon Sebring chassis with their FF50 size motor. Slot.it gears are designed for 2mm motor shafts while the small can motor has a 1.5mm shaft. So I shimmed the axle for decent mesh.

              2. Friction: OK, this is where I think it gets somewhat complicated: you have two distinct sources/types of friction on the gear/back axle: i) the reaction force due to acceleration/deceleration of the motor and ii) the friction due to sideways forces due to cornering. Note that I am assuming a good mesh either way (with or without shims), so the friction of the actual gear engagement is so close to the same that the differences could be ignored.

              And note that my following "arguments" are based on properly lubricated surfaces with proper clearances.

              Friction "drag" is given by the product of the normal force that would be "pressing" the two surfaces together multiplied by the friction coefficient. And BTW: the word "normal" refers to the fact that the force is directed perpendicular to the surface, not as opposed to "abnormal". In either case (shimmed vs shimless), the sideway forces are the shimilar... well, actually, they are identical, but I wanted to use the pun, so there!

              So the question becomes: are the friction coefficients significantly different between the motor shaft pressing on the sides of the crown gear groove compared to the wheel pushing on a shim pushing on the bushing? And don't be misled by the fact that in the one case the contact surface area is significantly greater than the other: unless you are getting up to large enough forces that you are starting to plastically deform the material, the surface area is not relevant. And in this case, I do not believe that is happening.

              So from this perspective, I believe the friction coefficient and the consequent "drag" is pretty much the same whether you use shims or not.

              Aahh, but what about the "groove wear" that Paul has mentioned, I hear you say (and that is quite a feat, seeing as some of you are thousands of km away from me!)? The main issue here is poor tolerances (typically found in Fly Racing Al hub crowns) combined with inadequate/non existent lubrication. In those cases the softer Al. is prone to excessive wear. In cases where you have correct tolerances and you keep the hubs adequately lubed, I personally have not experienced any wear problems, and I run a number of Al-hubbed Fly Racing cars. HARD!



              So bottom line for me is:
              • Shimming can certainly do no harm.
              • There are some situations where it is absolutely essential.
              • It definitely has benefit in cases where cars might not be "optimally maintained", for instance during extended racing that you would find in proxy series
              • I defy anyone to notice the difference between a well set up, decent componented (is that even a word?), well maintained car with or without shims. If there is any performance difference whatsoever it would be small enough to be masked (if not totally overwhlemed/dominated) by any number of other factors.
              So for me: I do it when there is a specific other need for it, otherwise I do not bother. But I do set up my cars well and I properly (some less-kind souls may say excessively or even compulsively) maintain my cars.
              So my take is: a few instances where it is essential, no reason not to do it, always some value in doing it, but in most cases do not expect heady performance improvements.

              One man's opinion.

              Comment


              • #8
                OK, I have been meaning to come back to this Thread for a while now, but been a bit busy trying to put some cars and trucks together and like that.

                Real ones as well as 1/32, I might add. I actually do have a 1:1 life, believe it or don't.


                So bottom line for me is:
                • Shimming can certainly do no harm.
                • There are some situations where it is absolutely essential.
                • It definitely has benefit in cases where cars might not be "optimally maintained", for instance during extended racing that you would find in proxy series
                • I defy anyone to notice the difference between a well set up, decent componented (is that even a word?), well maintained car with or without shims. If there is any performance difference whatsoever it would be small enough to be masked (if not totally overwhlemed/dominated) by any number of other factors.
                So for me: I do it when there is a specific other need for it, otherwise I do not bother. But I do set up my cars well and I properly (some less-kind souls may say excessively or even compulsively) maintain my cars.
                So my take is: a few instances where it is essential, no reason not to do it, always some value in doing it, but in most cases do not expect heady performance improvements.

                One man's opinion.
                Alwyn, try this. Simply hold a motor with a pinion gear on it in one hand, with a crown gear held between your finger and (presumably) opposable thumb in the other hand, so that they're located in space in more or less the same way as they would be in a slot car chassis or pod. Push one gear toward the other, then use a spare digit to rotate the crown in a forward direction. Pretty easy, huh? Now, try pushing the other way, and see how easily that same pinion shaft lets the crown gear/rear axle turn. End of story.

                With good quality components (assume for instance a Slot.it motor with a Slot.it bronze hub crown gear), I do not believe the you can significantly improve the mesh by adjusting the crown gear to pinion position with shims/stoppers. You certainly also do not get excessive side play on these quality components.
                Forgive me, but that's carp. There's already visible, and physically detectable, movement of a few thou even with brand new gears; it's only going to get worse with use, and I don't care what kind of super grease you use to try to counteract it.

                This isn't rocket science!

                Slot cars spend most of their track time, or certainly a large part of it, going through corners. At the front end, the sideways friction is essentially against the sides of the guide flag. But at the rear, where it really counts, the friction is going to be against ... what? Some different metal surface, spinning at a 3:1 differential speed in the opposite direction? This being (in the setup you seem to think is just ideal with those quality components) the micro surface of a motor pinion shaft against the surface of the hub, is what.

                So I'll favour having this side load spread over a larger surface - such as the outside of a brass bushing, or an axle spacer, or a stopper, any day of the week.

                I have seen the hubs of crowns - and in particular, those expensive Slot.it Aluminium/Teflon crowns - utterly destroyed because I relied on lubrication to prevent it. Doesn't work, never mind what you think you may be detecting from car behaviour on the track.

                Slot.it setups, with those spherical bushings, present a bit of a challenge - regular bushings with a large external surface area make it much easier to install one or two or a dozen spacers, in order to spread the load.

                So although, personally, I still haven't technically gotten my head around anglewinder setups, the invention of the axle stopper has to be the greatest thing since sliced bread. Here's a picture of a car I set up recently for the Slot.it Summer Shootout Series proxy:



                In that series, Slot.it parts are essentially mandatory. Blame the Rules Guy. I tried various spacer variations inboard of the right rear wheel, but no matter what, the M2 screw on the stopper was going to bind on the pod. So I ended up putting it on the outside of the left rear wheel, with a couple of 0.10" spacers between the stopper and the bushing.

                I really like using stoppers; you can mess around for ages with various spacers, but with stoppers setup is just way easier, to my mind; you can oh so carefully adjust the sideplay on the axle, just by 'feel'. I've used Slot.it, SlotCarCorner, and Sloting Plus stoppers (which feature an inbuilt bearing - very clever).

                But any way you look at it, if you want a car to be fast and smooth - and remain fast and smooth over the long haul, particularly when the lubricants haven't been reapplied in many scale miles - then the answer to this Thread has to be "Shim, baby - Shim!"

                Comment


                • #9
                  Another thing I know nothing about!

                  Comment


                  • #10
                    I use brass tubing and a stack of steel washers (you guys call them shims) as thrust bearings to bear the load of cornering forces. I feel this is superior to using the shaft-in-groove arrangement which is so common in RTR cars, and in the race-quality, tunable cars from Slot.It and others.

                    First reason is that the opposing rotation of the hub and the motor shaft, in left hand corners, is extreme. It is an accepted fact in mechanical engineering that frictional losses increase as the speed of sliding parts increases. Various people have shown, on skid pads, that friction in the gear train of inline cars (with shaft-in-groove alignment) tends to decrease forward velocity (cornering speed).

                    Second reason is that the width of the groove in the gear hub is, of necessity, larger than the diameter of the motor shaft, which allows measurable side play in the rear axle, and more importantly, allows the gear teeth to move away from optimum mesh. More friction is created, gear tooth life shortens, and with high power motors, you get teeth being decapitated.

                    While it is probably easier to use collars with set screws (called "stoppers"), I find it easier to cut brass tubing to length, and add two or more steel washers for exact spacing and to lessen friction. A stack of washers will create less frictional loss than a single spacer, as the most easily sliding surface will do most of the sliding. Another age-old principle of mechanical engineering.

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                    • #11
                      I purchased a set of "leather punches", at Hobby Lobby, for under $5, (w/coupon), and a similar, but larger set, from Harbor Freight, (again, around $5). Using a common paper punch and the "axle size" punch from one of these sets, allows me to make spacers as thick or thin as needed, using various thicknesses of plastic (credit cards, etc.), and as many as I want, when I want, and at the right price. Making a "C" out of the "O", allows you to snap it over the axle. It just takes a little practice lining things up. So easy it's boring.

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                      • #12
                        A stack of washers will create less frictional loss than a single spacer, as the most easily sliding surface will do most of the sliding.
                        Definitely, that's why I used a couple of spacers as well between the stopper and the bushing.

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                        • #13
                          makes the car drive like butter....

                          Originally posted by Wet Coast Racer View Post
                          Definitely, that's why I used a couple of spacers as well between the stopper and the bushing.

                          Agreed!!

                          Try running a 200 gram Super Truck on the skid pad, if you don't independently fix the rear axle the gears are TOAST in about the time to make some, hold on...wait for it...toast.

                          Cheers!
                          Paul




                          Funny how some think of this as "over thinking" the problem

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                          • #14
                            Originally posted by Wet Coast Racer View Post
                            Alwyn, try this. Simply hold a motor with a pinion gear on it in one hand, with a crown gear held between your finger and (presumably) opposable thumb in the other hand, so that they're located in space in more or less the same way as they would be in a slot car chassis or pod. Push one gear toward the other, then use a spare digit to rotate the crown in a forward direction. Pretty easy, huh? Now, try pushing the other way, and see how easily that same pinion shaft lets the crown gear/rear axle turn. End of story.
                            You guys are right. I am still not sure physics-wise why, but having tried it in my Slot.it McLaren with the wheel adjusted to run against the bushing vs. not when pushing the "wall" of the hub (not the teeth) against the motor shaft, there is a palpable difference in resistance.

                            There is clearly something that I am not seeing theoretically, because in looking at some reference stuff, the kinetic friction coefficient does not change with speeds in the m/s zone (and we are talking about around a 5m/s relative speed of the shaft against the counter-rotating hub).

                            Ahh well, we live and learn.

                            Originally posted by Wet Coast Racer View Post
                            Forgive me, but that's carp.
                            I find something fishy about this statement though..

                            Comment


                            • #15
                              My feeling about the friction inherent in the shaft-in-groove gear align feature, compared to thrust bearings elsewhere on the axle, is that thrust bearings show less friction primarily because they can be set up with closer spacing. A properly tight bearing does not vibrate, while a loose fitting bearing (shaft-in-groove) does vibrate, causing extra frictional losses in the form of vibration.

                              And, extra friction is caused by ill fitting gear mesh. When the gear teeth are permitted to drift in and out of optimum mesh (as in shaft-in-groove), you get extra friction.

                              Also, when axle-mounted thrust bearings are used, the motor shaft is relieved of side load caused by cornering forces, beyond any loading caused by the gears trying to separate under drive load, which side load is absorbed by the armature bearings. This introduces more severe friction than the motor needs for free operation.

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