Custom or Off-the-Shelf?

Custom or Off-the-Shelf?


Today I want to follow up on a discussion of an often debated topic: do you want a custom motor or should you buy a standard (stock) motor?

The reasons to purchase a stock motor are simple and convincing, e.g.: stock motors are built in large quantities which means they are typically lower cost than a custom motor; and stock motors are inventoried, which means you can get them quickly without the need to carry a large inventory in-house. Lastly, there may be multiple manufacturers that produce the identical frame motor, which results in competition and a secured supply chain. All these factors translate into cost savings and risk reduction.

Given all of these benefits using a stock motor, why would you even consider a custom motor design? The obvious reason here is that you cannot find a motor that fits your application. A recent example comes to mind where a customer required a small-HP, very high-speed motor for a new product development which simply was not available as a stock model. Needless to say the solution was fairly expensive and carried great risks due to the limited supply chain for certain components which, once again, supports the notion that you should use a stock motor if it is available.

In another example the customer was looking for a custom motor and drive to improve system efficiency by several percentage points above those available with standard stock hardware. In this case a unique value proposition could be made to offset the higher acquisition cost.

A third reason why a customer may want to go with custom motors and drives is legal- or marketing-related; I am thinking of a case where the customer was looking for a large airgap reluctance motor to avoid potential patent conflicts, and we were able to find a suitable custom motor solution. In another case a customer simply wanted a switched reluctance motor in their product that they could offer as a “new” technology for marketing reasons.

Once a customer decides that they want a custom solution it is important to make sure that the resulting product is cost-effective, with a reliable and stable cost structure and supply chain. To accomplish this, the customer may wish to only purchase a design and manufacture it in-house, or find a specialty motor supplier who is interested in providing small-volume production. Most likely, neither the customer nor a small specialty motor house will be integrated enough to supply all the components, and most will rely on a third-party supplier for magnet assemblies, laminations etc. — which can be a challenge.

We have typically chosen the classical approach in that we generate the prints, have parts quoted, and then perform the final assembly for both the components, sub-assemblies and final assembly. This is a process that is generally considered to be the lowest cost, but that premise needs to be re-evaluated.

First, consider the handling costs: shipping charges, packaging, inspections etc., where multiple shipping and handling charges can accumulate for a single subassembly.  Consider a high-performance, wire-EDM’ed lamination stack for an example; first you acquire the laminations, then you have squares cut, then the stack gets welded or glued, and finally the stack will be wire-cut. This requires laminations to be shipped out for the square cut to perhaps a laser facility; then the laminations will be annealed at a different facility, then they will be stacked and glued at yet another facility, and finally they will be sent to the wire EDM facility. If you fully account for the shipping and handling charges, the costs will be quite high. An alternative is to work with a partner that can provide you with the finished lamination stack. Our preferred method is to work directly with the steel manufacturer, as they are the most experienced resource with the best knowledge how to best handle their material. Some manufacturers now offer the capability to provide you directly with high-quality sub-assemblies (i.e. lam stacks) where they supply a finished sub-assembly that needs only to be shipped and inspected once — and where you can have the added comfort of knowing that all processes were performed per the manufacturer’s prescribed methods and specifications.

There are two main advantages to the latter method: first, when you fully analyze and allocate all costs you may find that this is actually a less costly process and, second, it may be a much faster way to procure the required components.

What does this all tell us?  The main point is this: use a stock motor whenever possible, but if you need to go the custom route you should not be averse to a custom motor and drive, as it may well benefit your business. What’s more, if you go the custom route work with partners who have a solid track record and whom you can trust to provide higher-level components and sub-assemblies whenever possible, as this will reduce your cost, speed up delivery and improve the success of your custom motor.

About Author

George Holling

With over 70 publications and 9 U.S. patents on sensorless and efficient motor controls and low-cost power circuits to his credit, George Holling (PI) is an in-demand consultant to many major U.S. and International corporations for motors and drives. At present he holds significant influence in two companies — as technical director of Electric Drivetrain Technologies (2011– present) Moab, UT and as CTO of Rocky Mountain Technologies (2001– present), Basin, MT. Holling is a graduate of the University of Aachen, earning his B.S. (1974), M.S. (1978) and Ph.D. degrees there, while picking up his MBA here at the University of Wisconsin. His career has spanned both the commercial and academic arenas, the latter including stops at (Dean, Computer Science & Engineering) Utah Valley University, 2001 – 2003; and (Adjunct Professor), Western Michigan University, 1997 – 2002. From the commercial side, apart from his current positions, Holling has served as Project Engineer and Product Line Manager, UNICO; Franksville, WI (1978-1981); Project Engineer, General Electric, Medical Products Division, Milwaukee, WI (1981-1983; Manager R&D, Pacific Scientific/Honeywell Motor Products, Rockford, IL (1983-1985); Vice President of Engineering, Regdon Solenoid, Brookfield, IL (1988-1990); President, Advanced Motor Controls, Sun Prairie, WI (1990 – 1999); and Vice President of Engineering, Cordin Company, Salt Lake City, UT (1999 – 2000). Holling has also spearheaded projects for the development of high-efficiency motors and drives up to 400 kW, and has successfully negotiated licensing agreements with U.S., Chinese, Japanese and Indian customers for the licensing of motor and drive technology.

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