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Old 12-11-2017, 07:36 PM   #31 (permalink)
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Originally Posted by Grant-53 View Post
Putting fluid in a motor casing is not an industrial practice. I would suggest mounting metal wheel disks to the sides of the motor as fin area and reducing drag on the wheel assembly. Heat comes from the current in the windings under load.
A lot on Endless Sphere recommend it for geared motors, because there's virtually no contact between motor and casing. The sides of the motor can be cool to the touch, while the windings are in excess of 100c.

Either that, or drilling holes in the sides and installing fans.

Probably won't matter until after winter though.

EDIT: Some interesting reading on potted motors, ferrofluid and oil cooling:


Last edited by Ecky; 12-12-2017 at 07:56 AM..
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Old 12-16-2017, 02:25 PM   #32 (permalink)
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Originally Posted by Ecky View Post
After playing with GRIN's motor simulator, I'm thinking the difference in efficiency won't be nearly so large as you're predicting. It appears that the MAC will actually have an edge in efficiency while getting up to speed, and in some hill-climb scenarios, while the Leaf motor pulls ahead in cruise, but only slightly. I'll get regen braking with the Leaf motor, which may make up for the difference in efficiency in a stop and go "city" drive cycle.
Interesting. I didn't run a simulation with this tool with your parameters and was taking a guess based on earlier simulations I did using this tool where I used parameters suited for my requirements when I was initially considering a MAC(I was going for fastest overall 0-30 mph acceleration time possible with the controller I planned to use, while allowing a 50 mph top speed, which at 30 mph cruise, greatly hurt efficiency). The increased thermal efficiency for your parameters versus what I assumed they would be makes a big difference. However, I am curious if that simulator factors in losses from the composite gears, or just spits out the motor's efficiency by itself based on what it is calculated to be?

So based on your simulation's parameters for 30 mph, 83% eff for the MAC, 87% for the Leaf. Your preliminary 21 wh/mi at 30 mph figure is drawing 630W from your pack. At an assumed 5% electrical losses in non-motor parts(controller, wiring, ect), assuming 83% efficiency for the MAC, we get 497W at the wheels to move at speed. The Leaf motor at 87% efficiency should lower the power from the battery pack to 601W or reduce your energy consumption at a steady 30 mph by 1 Wh/mile, using the same methodology that I used earlier to estimate a larger difference between the two.

1 Wh/mi is still noticeable. There's a lot more to be gained by working on the aerodynamics though.

The simulator seems to be over-estimating your power requirements when comparing with your preliminary data, but then again your vehicle's actual CdA/Crr parameters are still unknowns and that will modify the simulator's performance, temperature, and range calculations in an undesired direction versus the real results.

I think the regen will be a huge asset in stop and go city driving or for reclaiming range while going down long hills when not wanting to exceed the speed limit.

Please, get some videos showing us your acceleration, and have a speedometer of some sort in the video as well when you do it so we can see it climb up in speed!

I think 0-30 mph in under 7 seconds is easily within reach right away for you with the Leafbike motor(and much faster is possible later). You will want to modify the dropouts with torque arms before you abuse them too much. These motors(as well as your MAC) can twist them, and then you're in the market for another trike, so be careful.
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Old 12-16-2017, 03:40 PM   #33 (permalink)
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I began building and modify DC permanent magnet motors when first racing slot cars in the 1960's. To stabilize the armature windings at high RPM (+100k ) we would apply epoxy. The field magnets were held in place with spacer clips and the motor shell was used to concentrate the the magnetic field. Air flow was primarily axial. Automotive alternators and most industrial motors I have worked on in robotics follow this practice.

Heat conduction of the stator or field windings passes through the casing to the external heat sinks. Axial air flow may be increased by a fan blade mounted on one end of the armature. This is common on electric drills. Since magnetic field strength follows the inverse square rule great care is given to minimizing the air gap. Dynamically balancing the armature and installing high quality bearings reduces the range of motion of the armature in the air gap.

The inquiry becomes how best to minimize temperature rise in the windings which reduces current flow and shortens motor life through the breakdown of wire insulation. The other question comes in discovering the relative merits of ferrofluids in the air gap. Does the improvement in field strength outweigh the viscous drag as the air gap is reduced?

Last edited by Grant-53; 12-16-2017 at 03:45 PM..
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