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Step 11Boundary Conditions for Your Motor
We have reached the last and most important part of the motor: the endcaps.
Okay, I lied. EVERYTHING on your motor is the most important, but this one is the MOST important!
The motor endcaps are what bridges your motor shaft and the rotor can. Because they are large in diameter and disc shaped, they are often the most difficult parts to get right on a motor. They have to stay concentric and without axial wobble. Usually, they'll have rotor attachment features machined in them too.
Referencing figure 1 on the bottom, there are a few characteristics of every endcap design.
ý The Bearing bore is a precisely machined surface, that is, +/- 0.001 or less, into which the bearings fit. Usually, this is a press fit, but can be a tight slip fit if one side needs to be removed for servicing.
ý The Bearing shoulder might or might not be present. If it is, it's usually just a small extension that brings the thickness of the bearing bore to the width of the bearing. It might not even be needed if the bearings are press fit into the bore. It can be on the outside or the inside.
ý A winding relief cut is usually made so the magnet wires bulging out from the stator don't interfere with the rotation of the endcaps. If your motor is sufficiently wide, this is unnecessary, but space-constrained motors like my scooter motors needed the endcaps to sort of conform around the stationary internals.
Making the winding relief results in a dish-shaped endcap.
ý Can mounting surface and provisions. The surface is the broad cylindrical face that mates with the magnet can itself, and provisions is just my term for describiing how the can is held in place. Regardless of how the can is physically mounted, the surface itself should be smooth and well fitting: unless you are purposefully going for the permanent press method, leave this a smooth slip fit, which indicates a diametrical difference of .002" or less.
In terms of how to actually mount the can, there are a few approaches. Shown in Figure 1 is "radial threaded holes" which go through the can and into the endcap.
Shown in the other pictures of my scooter motors are axial holes which either let me bolt through the can or around it.
Through-can axial screw holes, which make the can itself structural, are the most common method for large bike and car motors. If you have the space available, it is also the strongest!
The BWD scooter is a great example of through-can axial screw mounting. The endcaps also prominently feature an external bearing shoulder.
You have the option of integrating wheel mounting facilities into your endcaps, which is what I did for RazEr. Speaking of which...
Okay, I lied. EVERYTHING on your motor is the most important, but this one is the MOST important!
The motor endcaps are what bridges your motor shaft and the rotor can. Because they are large in diameter and disc shaped, they are often the most difficult parts to get right on a motor. They have to stay concentric and without axial wobble. Usually, they'll have rotor attachment features machined in them too.
Referencing figure 1 on the bottom, there are a few characteristics of every endcap design.
ý The Bearing bore is a precisely machined surface, that is, +/- 0.001 or less, into which the bearings fit. Usually, this is a press fit, but can be a tight slip fit if one side needs to be removed for servicing.
ý The Bearing shoulder might or might not be present. If it is, it's usually just a small extension that brings the thickness of the bearing bore to the width of the bearing. It might not even be needed if the bearings are press fit into the bore. It can be on the outside or the inside.
ý A winding relief cut is usually made so the magnet wires bulging out from the stator don't interfere with the rotation of the endcaps. If your motor is sufficiently wide, this is unnecessary, but space-constrained motors like my scooter motors needed the endcaps to sort of conform around the stationary internals.
Making the winding relief results in a dish-shaped endcap.
ý Can mounting surface and provisions. The surface is the broad cylindrical face that mates with the magnet can itself, and provisions is just my term for describiing how the can is held in place. Regardless of how the can is physically mounted, the surface itself should be smooth and well fitting: unless you are purposefully going for the permanent press method, leave this a smooth slip fit, which indicates a diametrical difference of .002" or less.
In terms of how to actually mount the can, there are a few approaches. Shown in Figure 1 is "radial threaded holes" which go through the can and into the endcap.
Shown in the other pictures of my scooter motors are axial holes which either let me bolt through the can or around it.
Through-can axial screw holes, which make the can itself structural, are the most common method for large bike and car motors. If you have the space available, it is also the strongest!
The BWD scooter is a great example of through-can axial screw mounting. The endcaps also prominently feature an external bearing shoulder.
You have the option of integrating wheel mounting facilities into your endcaps, which is what I did for RazEr. Speaking of which...
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