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Keeping your MAC cool with ATF

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    Keeping your MAC cool with ATF

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ID:	56263 Below are the details and results for my experiment using Low Viscosity ATF to cool a MAC IGH motor. The small diameter rear wheel was used because with an IGH motor, changing the diameter of the rear wheel is the only way to change the gearing between the electric motor and the ground. A word of caution...it only takes a tiny amount of ATF on your brake rotor to cause a serious loss of braking capability.

    MAC ATF Cooling Experiment

    Objective:
    The objective of these experiments was to determine if adding Automatic Transmission Fluid to a MAC Internally Geared Hub (IGH) motor can sufficiently reduce the temperature of the motor to prevent potential damage when riding off road.
    Equipment used and starting conditions:
    A. The motor used was a 12T MAC Internally Geared Hub motor installed in a 20” rim. The wheel assembly was mounted in a Mongoose Terrex bicycle. The rim is 57 mm wide (internal) and the tire is 4" wide.
    B. A Cycle Analyst v3 was used to display the temperature and the wattage.
    C. The battery used was a nominal 52v 14s6p configuration.
    D. ATF being used was “low viscosity” and meets the Dexron VI and Mercron LV spec.
    E. The ambient temperature for the entire experiment was 20 degrees C (67 F).
    F. The starting motor temperature was 70 degrees C every time the experiment was conducted. This was accomplished by riding to the starting point and if the motor was too hot then it was allowed to cool until it reached 70 degrees C and if it was too cool then the brakes were applied along with the throttle and the bike was allowed to roll slowly until the motor temperature was 70 degrees C.

    Procedure
    A. Record the full throttle no load wattage with no ATF added.
    B. Add .5 ounces of ATF and record the full throttle no load wattage.
    C. Lean the bike 30 degrees from vertical and visually determine if any ATF runs out of the fill port with the fill port in the 6 o’clock (lowest) position. The fill port being used was one of the brake rotor bolt holes.
    D. Record the full throttle no load wattage.
    E. Ride the test section and record the temperature.
    F. Add .5 ounces of ATF and repeat steps C thru E.
    If at any point ATF runs out of the fill port when the bike is leaned 30 degrees with the fill port in the six o’clock position, the experiment is complete. A 30 degree lean angle is beyond any expected riding condition but was selected to allow a sufficient safety margin to prevent leakage under normal operating conditions.

    Test data/results
    Based on past experience the temperature of the motor with a lithium based grease in it for lubrication resulted in motor temperatures around 110 C when the test section used for this experiment was ridden.

    Run #1 - Internal components of the motor were clean and no ATF was added:
    Full Throttle No Load Wattage: 90 w
    Temperature at the end of the test section: Not ridden due to a lack of lubrication in the motor.

    Run #2 - 0.5 ounces total ATF in the motor:
    Full Throttle No Load Wattage: 90 w
    Temperature at the end of the test section: Not ridden due to a lack of lubrication in the motor.

    Run #3 - 1.0 ounces total ATF in the motor:
    Full Throttle No Load Wattage: 100 w
    Temperature at the end of the test section: 105 C

    Run #4 - 1.5 ounces total ATF in the motor:
    Full Throttle No Load Wattage: 90 w
    Temperature at the end of the test section: 110 C

    Run #5 - 2.0 ounces total ATF in the motor:
    Full Throttle No Load Wattage (FTNLW): 80w
    Temperature at the end of the test section: 110 C

    Run #6 - 2.5 ounces total ATF in the motor:
    Full Throttle No Load Wattage (FTNLW): 100 w
    Temperature at the end of the test section: 96 C

    Run #7 - 3.0 ounces total ATF in the motor:
    Full Throttle No Load Wattage (FTNLW): 110 w
    Temperature at the end of the test section: 86 C

    Run #8 - 3.5 ounces total ATF in the motor:
    Full Throttle No Load Wattage (FTNLW): 107 w
    Temperature at the end of the test section: 83 C

    After adding 3.5 ounces total ATF to the motor a very small amount of ATF was observed departing the motor when the bike was leaned 30 degrees therefore this ended the experiment by definition.

    Conclusions
    A. 2.5 to 3.5 ounces of low viscosity ATF can aid in cooling a MAC IGH motor.
    B. Minimal increases in the viscous drag were observed as expected but considered acceptable based on the decrease in temperatures.
    C. 2.0 ounces or less of ATF does not appear to add any cooling benefit.
    D. More than 3.5 ounces of ATF could lead to leakage and the associated safety concerns regarding braking.

    Recommendations
    A. Conduct similar experiments in a laboratory setting where all of the variables could be controlled, monitored and recorded. This experiment was conducted as carefully as possible utilizing the available resources.
    B. Utilize additional fluids to determine if low viscosity ATF provides the best benefit based on viscous drag and temperature reduction.

    Supporting Data and information
    Dimensions:
    1. Motor Case ID ~ 5.85”
    2. Outer Motor OD ~ 5.76”
    3. Internal Case Width ~ 1.55”
    4. Initial fill volume is .5 ounces…this should provide some lubrication for the planetary gears but not provide any additional cooling. The approximate volume between the Motor Case ID and the Outer Motor OD is 1.24 cubic inches which is equivalent to .7 fluid ounces.
    5. ID of the motor copper windings ~ 3.68”
    6. OD of the motor copper windings ~ 5.15”
    7. Break Rotor bolt circle diameter ~ 1.68”
    8. With the Mongoose 20x4” tire being used: 10 mph = 150 rpms of the rear wheel.
    9. ATF being used is “low viscosity” and meets the Dexron VI and Mercron LV spec.
    10. Permatex Ultra Gray was used to seal the interface between the hub and the motor cover.
    11. Permatex Ultra Black was used to seal five of the six brake rotor bolts. The sixth bolt was not sealed and use for the fill port.
    12. No leakage of ATF was observed other than that stated in iteration #8.

    These experiments were conducted on 22 November 2017.
    Last edited by Bullfrog; 01-22-2018, 07:35 AM.

    #2
    Warning Warning Warning...if you follow my recommendations for adding ATF to a MAC to keep it cool, eventually it will leak on the brake rotor and you will lose your back brakes.

    The good news is that adding 2.5-3.5 ounces of low viscosity ATF to your MAC will keep it cool with the max temps never going over approximately 85C.

    The leakage didn't occur while riding on relatively smooth paved surfaces but over the last couple days I have ridden off road on some pretty rough ground with exposed roots and rocks...my guess is the rough surfaces caused the ATF to splash around inside the motor more, therefore it came in contact with the opening in the axle where the wiring exits...and eventually started to seep out of the left side of the axle and onto the brake disc.

    For anyone riding off road at relatively slow speeds and needing high torque...my recommendation is to go with a Mid-Drive motor like the Bafang BBSHD because you can utilize the bikes gearing as well as the motors gearing to keep the motor spinning at an efficient rpm and produce less waste heat.

    What seemed like a great idea has its limitations...whatever you do, have fun, be careful and try to learn from my mistakes.

    Comment


      #3
      Nice methods applied, and explained so well.

      Good contribution.
      Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

      Comment

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