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  • #46
    A few fun facts about magnetic flux...

    - Magnetic flux, like electrical current, flows from a positive pole to a negative* pole. It has to travel through a complete circuit, just like electrical current.

    - Magnetic flux prefers to flow through ferromagnetic materials -- steel, iron, nickel, that stuff. But like electrical current it can also flow through open air.

    - Magnetic flux flows much more easily through air than electrical current. The magnetic flux that leaks out into the air is typically far greater than in an electrical circuit.

    - When the ferromagnetic paths open to the magnetic flux "saturate" -- reach the limit of how much magnetic flux they can carry -- the remaining flux will leak out and flow through the open air.

    - In a can motor design the steel can is intended to be the return path for the magnetic flux that has passed through the armature. With high-strength magnets the can might "saturate" and flux leak outside it, where it can create downforce through acting on the steel rails. A thicker can will not saturate as fast as a thin can, and will leak less flux.

    - A cooling hole in a can motor will leak some magnetic flux, but far more flux will travel around the hole, like water around a rock in a stream.

    - A barrier made of ferromagnetic materials can act as a shield against air-conducted magnetic flux. It can be effective as long as it doesn't saturate. Such a barrier completely enclosing a magnetic field will completely isolate that field from the rest of the world. The electrical analogy would be a Faraday cage.

    Ed Bianchi

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    • #47
      Typically I cut a hole in the top of the can of my M20 motors. I do not cut one in the bottom. With Neo magnets I find I have to apply at least one layer of ferromagnetic tape under the motor to pass the pin test. All my racing is done under the HOPRA Gravity rules so I am running my cars at 18 volts. I do use choke on my controller and at times I use a resistor of 1 - 3 ohms on the motor. I have not found that the wipers in the motor wear out fast in general. It seems they fail quickly or last for at least a season of racing if not longer. I have also replaced the wipers on motors that have a good magnet and armature combo. I have replaced arms where the com has become overly worn. I have found that once you establish a good can with magnets, it can be refurbished as needed. Motors are cheap so I don't find it cost prohibitive to buy motors and just use the endbells.

      Comment


      • #48
        Originally posted by SouthShoreRacing View Post
        I don't agree that all neo magnet motors have brushes. I have not seen any M10 or M20 motors with brushes regardless of the type of magnets. They all have wipers. I can't comment on the energized motor providing more downforce, I have not done any testing of that theory. Personally I want the motor as low as possible so that means no chassis parts under it. I have had to use shielding tape on some motors to pass the pin test.
        Yes, agreed. My bad. Somehow during cut and paste/editing; my "N-20 N-30" designation vanished to the ether and I didnt catch it. I had intended to be more specific.

        My observation is that the energized motor does provide additional down force. I never thought about it, until one day it bit me. Seriously. I have to qualify this with the note that the effect is easier to feel on models without traction magnets.

        Feeling a bit nostalgic one night, I was warming up some AMRACs. I had nicked one of my fingers working that day, so the digit was tender. Easy enough to lift the chassis up and warm it up per usual. Once warmed, I gave it a couple of quick blips, and the ensuing increase in downforce instantly snatched the chassis down onto the rails. It dragged one of AMRAC's blade style flux collector right through the fresh flesh wound in my finger tip and pinched it for good measure. I smarted pretty good when steel met nerve, and quickly let off the throttle. The effect is instantaneous, and might be considered violent at scale.

        Moronic yes, so food for thought In my world. I recollected a short piece by one of the smart guys on the subject of the combined magnetic field. THAT was what they were on about.

        Naturally I tested something else, after putting a band-aid on my piddy. A low-belly brass tube frame affair, with a modified box motor using Tyco guts. Being somewhat the same as the AMRAC, with and open field, good arm, and peppy motor magnets, but no traction magnets. It also got grabbier as the revs climbed, so long as the rails were within proximal reach.

        I filed all that away for a rainy day such as one does, until I revisited it on HWP's SL-1 3-D Chasssis. A closed can polymag N-20 set right on the rail exhibited the same trait.

        A short ways back I sorted out a twin motor gravity sled for a friend. Sporting twin N-20's on a flexible bulkhead, you could actually see the chassis grunt down as it was forced to flex when powered.

        So that's the actual prelude to my wondering about a known attractive effect, that isnt tested for, in an essentially non attractive class.

        The lift pin test is an unpowered test. Im tumbling a combination breakin-box/scale contraption that would indicate both the static lift, as well as any added energized lift. Not saying it's a faster way 'round, might even slow ya down LOL, or the result could be negligible. Probably worthless in practice, but thinking is still free.

        I just like cool little brass slotcars.
















        Last edited by model murdering; 10-16-2020, 07:26 PM.

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        • #49
          I took some readings of my four gravity cars yesterday. Two of the cars have Slide Guides and can't be measured on my scale, which was made for cars with guide pins. I did take gauss readings of the motors in all four cars. The gauss readings were the highest ones that I could find on the bottom of the motor when it was not running, if I get a chance will take readings with the motors powered up.
          My old Riggen car has a Slide Guide and an M20 motor, it read 5 gauss. My inline Landshark also has a Slide Guide and the N20 motor reads 3 gauss. The Direwolf has an N20 motor with a small hole in the bottom of the case, it reads 40 gauss, so probably it has neo magnets. On the scale I read 19.6g of downforce. The Thurman center hinged anglewinder has an M20 motor that reads 20 gauss, possibly it also has neo magnets. The car measures only 0.1 grams of downforce.
          The 19.6g that the Direwolf reads is in in the same ballpark as several of my SS T-Jet cars. Those cars have magnets that read 900-950 gauss on the side that faces the armature, I have not taken any measurements on the rail facing sides.
          The possibility that the downforce would increase when a motor was powered up could open up a real can of worms. Taking measurements with the motor running would be more difficult for a start.

          Comment


          • #50
            This whole business of a running motor contributing additional magnetic downforce caught me completely by surprise. It is something I had never considered.

            But I have my own reasons to believe it is a real effect. Two reasons I'll give right now:

            1) There is such a thing as "soft" magnetic materials. "Hard" materials stay strongly magnetized once they have been "zapped". Those are the things we make magnets out of -- ferrite, neodymium, ceramics. "Soft" materials include ordinary steel. "Soft" magnetic materials become momentarily magnetized when inside a magnetic circuit but then quickly lose that magnetization once the magnetic flux is removed. "Soft" materials are the stuff we make armatures out of, because reversing their magnetic orientation hundreds or thousands of times per second requires little energy. A good thing because it allows electric motors to be very efficient.

            But the short time these materials remain magnetized is not zero time. So the can of a slotcar motor -- a "soft" material -- will remain magnetized for a short period of time, probably enough to add to the downforce of the car while cornering, even though the car might be unpowered at that time, or even braking.

            2) I have recently begun to suspect that the motors of the 1/32nd scale slotcars I have been racing recently are contributing downforce to the cars. At least some of the tracks that IHSR races on have steel braid. While we remove the traction magnets from our cars I think they might still have significant downforce due to their motors. In one of the last races IHSR held before the ceiling caved in my car -- a SlotIt anglewinder -- was uncharacteristically fast through the corners. So fast I looked likely to score my first win ever in that club. A problem with my pickups ruined that chance, but I was still intrigued by the unexplained boost in cornering power.

            Since then I have come to believe what happened was my car's sponge tires had worn enough that the motor was down very close to the braid, and its magnetism was giving me significant magnetic downforce.

            Now I think the "soft" magnetization of the motor can may have added to the "hard" magnetization of the motor magnets, to create more downforce than would be perceptible with the unpowered car just sitting on the track.

            Was my car sitting lower than legal during that race, due to worn tires? Dunno. My car was never teched. But in the future I am going to be much more careful to keep its ground clearance as low as I can get away with -- down to thousandths of an inch. Then we'll see.

            Ed Bianchi

            Comment


            • #51
              Yay! You're Approved!

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              • #52
                Originally posted by HO RacePro View Post
                2) I have recently begun to suspect that the motors of the 1/32nd scale slotcars I have been racing recently are contributing downforce to the cars. At least some of the tracks that IHSR races on have steel braid. While we remove the traction magnets from our cars I think they might still have significant downforce due to their motors.

                Ed Bianchi
                All motors used in Slotcars do provide some level of magnetic "downforce" when used on plastic track (steel rails) or on tracks with steel braid, and this varies by,... the strength of the magnets, their length, their orientation to the track (inline, sidewinder.anglewinder), and, track/motor clearance.


                As far as current "plastic car" motors, a typical ceramic magnet FC-130 will produce roughly 4 to 10gms. of downforce, again , depending on the above mentioned factors, while typical FK-180 motors (longer/stronger magnets) will produce in the range of 10 to 40 gms.,............and is he reason the FK- 180 (in an anglewinder configuration) finds favour with most of the "Euro" plastic car guys, when running on plastic track. Coupled with a soft longitudional flexing chassis, once on the track, the motor will "bow" the chassis, increasing the "downforce" even more..........sort of non magnet, magnet racing..............I am not fan, but, to each his own.

                While the FK -180 motors do weigh considerably more than a typical FC-130,...not the hot tip for handling on a taped or non magnetic braid track, the benefits of 40+ gms of magnetic downforce on steel rails/braid, far outweigh the increased polar moment of inertia disadvantages of using the heavy FK-180's in the back of the car.

                There are a few "current" motors that have Neo magnets, and these, produce significantly more downforce than their ceramic brothers/sisters.........The MB Slot "Dodo" motor (FC-130) produced 60/70 gms. of downforce, it is no longer produced, as it was outlawed by most clubs. Similarly, the currently available Piranha 25K FC-130, has Neo magnets, and offers more magnetic downforce than most FK-180 motors.......while it is used by many home racers, many clubs have similarly banned this motor on steel rail/braid tracks.
                The Slot-it 25K Flat 6 RS, also produces considerable downforce, and the can cutouts are different either side, with differing downforce levels.

                So yes, slot car motors do produce "downforce" on steel rails/braid,.........how much you want, and whether your club allows this, is the question.

                Cheers
                Chris Walker






                Last edited by chrisguyw; 10-17-2020, 02:51 PM.

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                • #53
                  Ed: " ... I have my own reasons to believe it is a real effect."

                  Better not tell Riggen, Aurora or AMRAC. By longitudinally orienting the power plant just off the rails in the open frame arrangement, they cashed the check on exploiting the combined field decades ago. The primordial flux collector designs mark the birth of H0 magnatraction as we know it today.

                  Focusing flux is magnatraction. The added inertial dampners came later to control the off throttle kiting.

                  Anytime I see a motor slung down like a pregant ant in open space over the rails, I see lines of force.

                  Comment


                  • #54
                    This is one of the main uses for the Magnet Marshal. Motor magnet strength makes a huge difference on steel rail tracks or magnetic braid tracks. The Slot.it Flat 6 r motor can create over 30 grams of downforce which is a serious advantage against zero magnetic downforce motors.
                    I was able to see in lap times a noticeable difference in performance with only 5 grams more downforce. This magnetic pull creates more tire grip so everything else being equal lap times were better. The car handled better in the turns. Or should I say the magnetic pull kept the car on the track.
                    We measure magnetic pull from the motor as part of tech in most classes we race. It can have a real impact on lap times.

                    The BRM mag motor depending on tire size can create up to 500 grams of downforce if I remember right. I will check tomorrow and post.

                    But yes magnetic pull of the motor even with fairly high clearance can make a big difference on 1:32 and 1:24th scale cars.
                    Alan Smith
                    SCI Owner.
                    www.scaleracing.com
                    www.slotcarillustrated.com
                    www.facebook.com/scaleracingcenter
                    www.132slotcar.us

                    1-253-255-1807

                    Comment


                    • #55
                      I knew long ago that the motor magnets could produce high levels of downforce on steel rail/braid tracks. What I'm wondering about is whether electric current inside the motor adds to that downforce.

                      Hey RickD, could you do me a favor? You've mentioned you have a magnetometer. Could you try measuring the gauss underneath a can motor with and without it running? It should show if the current affects the magnetic downforce the motor can generate. It would also be interesting to see if there is a delay in the change in downforce once the current is shut off.

                      Ed Bianchi

                      Comment


                      • #56
                        OK, I broke out my gauss meter which is generally accurate +/- 1 gauss.

                        As a quick test, I tested the following chassis that are depicted at the beginning of this thread. I took the highest gauss reading unpowered, and then again the highest reading when powered at 6.0 VDC. This voltage level was selected so as to avoid over-revving these little motors. Data is reported as gauss unpowered/gauss powered.

                        LS #1, in-line configuration with a lead weight under the motor: 11/14

                        Dire Wolf, in-line configuration with the stock supplied motor mounted flush with the bottom of the chassis: 28/39

                        Bulldog, in-line configuration with the stock supplied motor mounted flush with the bottom of the chassis: 13/13 (very interesting!)

                        Bulldog, sidewinder configuration with the stock supplied motor mounted on top of the brass chassis: 27/101 (a real eye-opener!)

                        As an interesting aside, I did check the bottom of the Viper Retro magnets and got a high reading of 6 gauss. I've not yet testing this car under power. This car is quite interesting. I will post a full review write-up on this chassis probably no later than Thursday of this coming week.
                        Last edited by gmcullan; 10-18-2020, 05:54 AM. Reason: Corrected a couple of typos.

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                        • #57
                          Thank you Gerry!

                          Observation #1: Yet more proof that when you do research to answer a scientific question you end up with more questions than when you started. And usually far more interesting questions!

                          Observation #2: Holy cats! Powering up a motor -- at half power! -- can produce almost 4 times the surrounding magnetic field!

                          Observation #3: There can also be zero impact on the magnetic field! Hey what!?!

                          Observation #4: Confirmation that a lead weight under the motor -- which is NOT ferromagnetic -- does not shield its magnetic field.

                          Observation #5: Something very weird is going on with the stock Bulldog motors. Huge impact or no impact at all!

                          As for those questions I mentioned in Observation #1...

                          - How much will the increase in the magnetic field under these motors increase the downforce? Will it be a linear relation or a power relation? If a power relation, by what exponent?

                          - If the voltage applied to the motor is increased, as it would be under racing conditions, how much will the magnetic field be increased? Again, linear or exponential? Maybe not increased at all?

                          - What the heck is controlling the increase in the magnetic field? Why does it vary so much?

                          - Is there any time lag in the increase/decrease of the magnetic field? How much and why?

                          - Will the increase in the magnetic field be uniform across all samples of a particular chassis/motor? I strongly suspect not, but why?

                          - Will the increase in the magnetic field be the same if the motor is run backwards?

                          - What happens under dynamic braking? Is the magnetic field still increased, decreased or unaffected? Could this have an impact on cornering?

                          *******************
                          If we get any answers to those above questions -- and it is certainly not a comprehensive list! -- those answers will almost certainly generate still more questions.

                          Oh, and one last observation. Here we are about sixty years into slot racing history, and we are still discovering new phenomena to research and discuss!

                          Ed Bianchi

                          PS - To those who don't know Gerry personally, despite the rumors he is not the genetically enhanced mutant cat of a Bond villain. He is instead a genuine, certified slotting Graybeard of the first water, with an illustrious history in both the MARC and HOCOC HO racing series. He is one of the pillars of the HOCOC community. And he is a skilled modeller, guitar craftsman, VW beetle modifier, drone and model helicopter pilot and mechanic, and talented in other ways that I am simply in awe of. Really.

                          PPS - Gerry, doest thou have a means to data log off your magnatometer, so we can get time/speed/gauss curves off it?

                          PPPS - Rich, love to see what your magnatometer might teach us!
                          Last edited by HO RacePro; 10-18-2020, 09:37 AM.

                          Comment


                          • #58
                            As promised I checked the gauss readings of a number of motors, both unpowered and powered. I moved the probe around the bottom of the motor case and noted the highest reading. Tiny movements of the probe could have a large impact on the reading, if I was making a living taking these readings I would build a jig that kept both the probe and the motors in a fixed position.
                            I only tested loose motors and I used 8 volts for the powered measurements.
                            A black endbell N20 mystery motor bought directly from China measured 115 gauss unpowered and 52 gauss powered. A yellow N20 motor directly from China has round holes in the case, it measured 8/13. This motor got very hot in the short time that it ran, I have one of them in my Riggen car. A black endbell HOST M20 read 39/32. A black endbell Quicker neo M20 from Lucky Bob"s measured 72/106.
                            I also got a lift pin, the Quicker M20 barely lifts the pin. I would not be willing to conclude that a closed can motor would always have more downforce when it was powered.
                            I will bill Ed at my usual rate for this work. Strike that, he sent me some nice samples of his 3D printed stuff, so we are square.
                            Last edited by RichD; Yesterday, 07:09 AM.

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                            • #59
                              I think the difference in magnetic fields, or lack there of, boils down to phasing. If the can magnetic field and the armature magnetic field are in phase, the field effects are cumulative. If the fields are out of phase, the fields can be cancelled or even negated.

                              Something very similar happens with the winding and construction of guitar pickups. You might think something out of phase won't work, but they can and do. In regard to guitar pickups, out of phase windings can present some very interesting tonal colors. Think of Gary Moore with his Gibson Les Paul "Greenie" with its unique out of phase pickups. Check out his "Still Got The Blues For You"

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                              • #60
                                Unfortunately, my gauss meter does not feature data logging or output. As Richard Dumas has noted, a VERY small change in probe placement can have a significant effect on readings. All the readings I took were fishing for the highest readings.

                                As for equating the gauss readings to downforce, while it is somewhat easy to measure static downforce, measuring downforce under power presents more of a challenge.

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