Shaft specs for CIM motors

[Andy Baker]

Originally Posted by Cal578

I'm looking for specifications for the shaft loading on CIM and mini-CIM motors. In particular, we'd like to know how much axial and radial load the motors can take.

Please reference actual, quantitative specifications.

Thanks for sending an email to us at AndyMark about this also. We never really looked at this, as we have not had issues with side loading the CIM motor (and hence, one of the reasons we all love the CIM Motor).

Here is my answer to Gerry in my previous email. I figured that the rest of you folks may like this:

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We don't currently have any specs for this. However, we have not heard of this being an issue with this motor, when it shot poof balls in 2006, basketballs in 2012, and driven many high-load gearboxes during the years. This sort of shock load to the CIM is significant this year, but I believe that the CIM motor can handle it. The bearings are bronze bushings, which have high load ratings. Here is some analysis and explanation on the from one of the bearing manufacturers:

http://www.buntingbearings.com/data.html

If we consider this example, we can plug in some numbers:

• PV is a means of measuring the performance capabilities of bearings.
  
• P is expressed as pressure or pounds per square inch on the projected area of the bearing. V is velocity in feet per minute of the wear surface (surface feet per minute).
  
• For sleeve (plain) bearings, the surface speed is .262 (pi ÷12) x RPM x shaft diameter in inches. P is equal to the load on the bearing in pounds divided by the projected area in square inches. For sleeve (plain)bearings, the projected area is the length x the inside diameter of the bearing.

PV is then obtained by multiplying P x V as shown in the following example:

Assuming that the contact force between a shooting wheel and the frisbee disc is 30 pounds (which is a high guess)...

5/16 (8mm)" shaft @ 4500 RPM, 30 lb. total load, bearing length 1/2".

V = .262 x RPM x shaft diameter, or .262 x 4500 x .312 = 370 sfpm.

P = total load ÷ projected area (area = .312 x 0.5 = .156 sq. in.), or 30 lbs. ÷ .156 = 192 psi.

PV = 192 psi x 370 sfpm = 71,000 PV

Looking back at the web link's PV chart, I see the weakest bearings at 75,000 for their max PV ratings.

So, with this analysis, I think that we are ok for this application. If this was something that happened to this mechanism 24/7/365, then I would recommend a motor with a larger diameter. Since this is a very infrequent use of this motor, I think that we are good.

Sincerely,
Andy Baker
AndyMark, Inc.