.Actually, you are on the right track about gluing the set screws in place. It sounds to me like the set screw fits loosely inside the threaded hole in the wheel hub.

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computer or access to the Internet.

— Clint Ramsey Quincy, CA

^ .There are a lot of companies that will sell these parts via mail or telephone. Table 1 contains a list of companies that I have worked with in the past that have printed catalogs you can request. Stock Drive Products, W. M. Berg, and Nordex will have a much larger selection of drive components, since this is their specialty. Small Parts, Inc., McMaster Carr, and Grainger have a smaller selection of 0.2" (1/5) pitch belts and pulleys, but they have a very large selection of other types of parts that can be handy for your other projects. All of these companies take phone orders and I know Small Parts, Inc., takes mail orders.

When the motor shaft repeatedly reverses directions, it oscillates the forces from one side to the opposite side on the set screw, which slowly loosens it up. Gluing the set screw in place is one of the common fixes for this problem.

Loctite® (www.loctite.com) makes a product called Threadlocker that is used to glue fasteners in place. They have many different versions of this product — from low strength, removable adhesives to high strength, permanent adhesives. I would recommend that you use the Loctite 222 generalpurpose Threadlocker. It is purple in color, sets up in about 20 minutes, and can fill some fairly large gaps between the threads of the set screw and hub. It is not a permanent adhesive, so the set screw can be removed using regular tools, but it will be a lot "gummier" than without it. Only a couple of drops are needed to "lock" the set screw in place. So far, the tiny 0.5 ml bottle that I have has lasted three years. Loctite products can be found at most well stocked hardware, automotive, and fastener stores. I purchased mine from McMaster Carr (www.mcmaster.com) for a couple of dollars.

Another option is to replace your current set screws with "self-locking" set screws. These set screws have a nylon patch on the side that is used to keep the set in place in high vibration applications. You should be able to get the same size self-locking set screws for your hubs, but they are usually harder to find than regular set screws. McMaster Carr will most likely have the size you need.

.Do you have any recommendations for a small, low ^k cost gear motor that has a built-in encoder? I am not interested in surplus motors since I want to always know that I can get a new one when I need one.

Cathy Novak via Internet

Solutions Cubed (www.solutions-cubed.com) has one of the best deals for motor-encoder combinations — the Easy Roller Motor with the Easy Roller 200 CPR Quadrature Encoder combination. The encoder comes as a kit that is mounted directly on the motor shaft that extends out of the rear of the motor. It took me about 10 minutes to assemble and mount the encoder to the motor. The Easy Roller Encoder is a two channel quadrature encoder that uses a 200 count per revolution encoder disk. Only four wires are needed to use the encoder: +5 V, GND, and channel A and channel B quadrature signal lines. The Easy Roller Motor is a 12 V, 200 RPM gear motor that has a 30:1 gear reduction that can produce at maximum torque of 50 oz-in (at stall). This motor/encoder combination has the ability to monitor 6,000 counts per revolution, which can enable some very precise positional control; $52.00 for the set makes this one of the best low cost, high resolution motor/encoder combinations available.

Q.I would like to know where to go for 0.2" pitch cog belts and pulleys. I would like a supplier that has a mail order catalog, since I do not have a




Small Parts, Inc.

(800) 220-4242


Stock Drive Products

(516) 328-3300


McMaster Carr

(562) 692-5911



(800) 323-0620


W. M. Berg, Inc.

(800) 232-2374


Nordex, Inc.

(800) 243-0986


Table 1. Mail order parts suppliers for cog belts and pulleys.

Qqn answer yoi

.In the August issue of SERVO Magazine, I saw a question from Steve Anderson asking if there were ^ny "free" oscilloscope programs for the PC. In your you said, "What you need is a data acquisition system called a PC Oscilloscope, which is not just a program."

I agree that the PC scopes you mentioned are good choices, but - if your budget is limited to zero dollars - here is an alternative that you might try. In the past, I have worked with kids at the high school level and we were able to use a free oscilloscope program to do many "basic" experiments using just the basic PCs in the science lab and their internal, standard PC sound cards. Though there are inherent limitations to this method (For example, you are limited to the frequency response of the sound card "line in" jack.), the display rendered is a good way to view various basic waveforms and the price is right.

A free oscilloscope program (WINSCOPE) can be found at http://polly.phys.msu.su/~zeld/oscill.html and at www.geocities.com/nlradiofm/winscope.htm If a Fast Fourier Transform (FFT) is more in line with your needs, a free FFT frequency analyzer can be obtained at www.relisoft. com/freeware/ I hope this information is useful. Thank you for a great magazine. I look forward to every issue!

— Vern via Internet

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