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  • slot car motors and brakes

    What or how does a slot car motor have brakes? is this provided by the motor, controller or track? Can braking be put back in?
    I just got a car that ran in a proxy and it has no brakes. When the car as set up for the proxy, it had braking.

    We have been setting up 1/32 cars using many NSR 30k short can motors but cannot get a handle on braking. Some have good brakes, some have weaker brakes, some have almost no brakes. All same settings on the controller and adjustable brakes on controller is on full.
    These cars has very similar gearing about 11/34 and similar weight ( no heavy cars causing car to have little braking gars weigh 77-90grms.
    I dont notice this on other motors like pirana, scalextric, slot it. lance
    Last edited by lance; July 16, 2020, 05:27 PM.
    Lance Sofa racer

  • #2
    Good question!! Let's wait for one of the gurus to answer that one!

    Comment


    • #3
      "Brakes" are actually back-EMF generated by the rotation of the motor with no power applied. Because the coil (armature) is still rotating through the magnetic field it generates a small current that then "pushes back" against the power supplied, which in turn forces the armature to slow down (vs freewheeling). It's the same principle as used in diesel electric locomotives, and why they replaced steam.....while steam engines had larger tractive power they had no braking, and the electrical "brakes" provide a huge advantage.

      So...while all motors have some "brakes", the slowing is affected by the strength of the magnets, the wind of the armature, the air gap between the arm and the magnets, the strength of the friction between the brushes and the commutator, the alignment of the can and endbell bearings, the gear mesh, the weight of the car, etc.
      Also, if you have a poor connection on the controller you will feel like you have lost brakes.

      Generally on a proxy car, I would suspect the motor brushes to be significantly worn which reduces their pressure on the commutator and can reduce braking, as well as having the gears worn in which also reduces friction.
      But you will see variability in brakes with different motors, just because of magnet/air gap/wind/stack length differences. In the old days, that's why we blue-printed motors....getting them set up with consistency improves the performance.

      I am sure there will be a more detailed discussion, but that's the basics of brakes relative to the motor function.
      Come Race at The Trace!
      Timberline Trace International Raceway - SW of Mpls, MN

      Comment


      • lance
        lance commented
        Editing a comment
        Thanks chappy. Your explanation is really good and could explain what happened to the motor. This proxy was the GT3 and it was 10-12 rounds (10 rounds and shakedown and a final) so i dont think the motor was old and wore out the brushes. In this proxy many different cars and handling, it may have deslot and hit something and shifted a magnet in the motor. it so weird that it is really noticeable on the NSR 30k motors. i dont notice it on NSR 25k, pirana, scalextric, carrera slot it motors.

    • #4
      When braking goes down from what it was on any car believe it or not the first thing to check is the braids
      ALL of the brakes a car has is provided by the motor alone but gearing weight and tire diameter all have effect on the perceived amount of brakes the car has
      As for the track and controllers the controller activates the braking at closed throttle buy shorting the two contacts of a lane together. Since the motor is spinning and has no voltage applied it is now a generator trying to apply voltage to the track which is shorted by the controller, this drastically reduces the rpm of the motor ( brakes). The track is simply the conductor to supply a circuit to the motor weather it’s powered or shorted is up to the controller
      Any adjustments on the controller will lessen the braking a motor is capable of but never increase it
      There I think I got all that right!

      Comment


      • #5
        I thought braking was provided through controllers that applied a slight reverse voltage when the trigger was released. Notice I said 'thought' because I never had any evidence or info to base this assumption on. If as described above, what's actually happening is the controller merely shorts out the rails so the EMF created by the still spinning motor is cycled right back through it, that also suggests that a properly designed controller could also modify things. A pure short means there's zero resistance in a circuit. Very low resistance would also mean any current in the circuit still returns directly to the source, but a with a slight voltage drop depending on just how low the resistance is.

        The point being, it seems controllers 'could' provide different levels of braking depending on if any resistance is still present when the controller is off.

        Also, wouldn't a small amount of reverse voltage (opposite polarity) provide ideal braking? This could be provided by a capacitor discharge so it was a short lived event. This could also be variable based on the capacitor(s) used.

        Comment


        • #6
          i think that there are some controllers that work that way. i have one, but haven't dissected it.
          heck, back in the 60's we used to put a D cell backwards to apply reverse Voltage on braking! it was pretty funny on the starting line sometimes when somebody forgot and took their finger off the trigger and the car backed up before the power came on. later we didn't make it illegal, but peer pressure sufficed. it was difficult to handle anyway, and easier just to build a good motor. with a few exceptions, good power and gearing also gives decent brakes.
          me, i just try to provide as good a short as i can under full braking when i need it when i build my controllers.

          Comment


          • mattb
            mattb commented
            Editing a comment
            There were a couple "add on" boxes in the 60's that you could put inline on your controller brake lead. Those boxes usually used one or two "C" batteries to reverse power the motor when brakes were applied. This is pretty simple to do and home made designs were covered in the magazines. I saw a few guys try them, but they weren't any more successful at racing than the good drivers that learned their cars limits. I don't remember a production based controller with that built in. There were controllers with different resistors so you could switch while running. Classic made a box the controller hooked to and Cox and MRC made adjustable controllers with all the hardware in the handle.

            All car setups have a different braking action. Just about every variable in a car can make braking a little different. Obviously weight and gearing probably make the biggest difference.

        • #7
          In the early days of the hobby I remember adding “power brakes” to our controllers by wiring a battery into the brake wire. Can’t remember the details, but I remember the cars creeping backwards when not applying power.

          Comment


          • #8
            that's odd. Creeping backwards? heck, given that you had made the start line error braking with the reverse D cell, ours tried to parallel park back into the adjacent lane behind the start/finish line! Lol.
            it wasn't death, but you'd surely get to the first corner behind everybody else because you were too sideways (and behind everybody as well) off the line.
            and that was from only a single cell 1.5V battery. i can't imagine anything less strong in terms of backing up unless the controller wasn't working properly (or the braids maybe?).
            i spent two races trying to make it work and got it pretty good at the sharp corners but trying to go through the road course part, i quickly ditched it.
            if i hijacked this thread, i apologize.
            Speed

            Comment


            • slothead
              slothead commented
              Editing a comment
              Actually, if anyone did the hijacking it was me.

          • #9
            The setups that were tried at our little track had a switch on the brake wire. It was turned off at the starting line and turned on once the race started. No creeping that way.
            Matt B
            So. In
            Crashers

            Comment


            • #10
              Normally with standard controllers that have a third connection, when the controller trigger is in the all the way off position it completes a circuit with the ground wire which provides a path for the current generated by the spinning armature which slows the motor. That's why disconnecting the brake cable disables the braking action. And, yup in the good ole' days some tracks allowed battery powered brake boxes but I never had one.

              Comment


              • slothead
                slothead commented
                Editing a comment
                Glad to see you contributing again.

            • #11
              If you want to try an experiment connect the shafts of two motors together and apply ~12 volts to one of them. If those were regular Scalexrtic black stripe motors they would be spinning at about 20K RPM. If you were to measure across the terminals of the driven motor you would read about 8 volts, but the polarity would be the opposite of the applied voltage. If you were to short the terminals of the driven motor both motors would slow down considerably and the amp draw of the drive motor would go up.

              Comment

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