Servo - October 2011

the design for the most part, while substituting more reliable materials to strengthen the design where needed.

Despite the improvements, there were still some weak points in the Gold Sparks gearmotor, mainly gears occasionally stripping out and breaking due to the small pitch, along with the output stage breaking loose of the drive shaft. Built to combat these issues, the main feature of Fingertech’s newer ‘Silver Spark’ motors are the larger pitch of the gears (Figure 2) compared to the Gold Sparks, while keeping the same basic dimensions, 11 mm mounting pattern, and not adding more than a few grams for the equivalent gear ratio. In addition to all of this, they’ve added a whole new batch of gear ratios, ranging from half of the lowest Gold Spark ratio to twice its highest.

In the months leading up to their release, Fingertech has had a number of these motors going through rigorous testing in the arena. I’ve tried out a number of the new models in some of my recent small bots. In August ‘ 11, I wrote a build report for SERVO on one of these bots — an Antweight wedge. I had been running surplus Maxon 17:1 gearmotors for years, and with the Maxon stock starting to dwindle, the lower ratio Sparks now available, and the FK-050’s ability to run off of 18.5V without burning up, it seemed the perfect opportunity to switch over and begin looking for an alternative drive motor. There are more details on the build itself in the mentioned article. Overall, the 11.1:1 Silver Sparks have handled more abuse over a dozen fights that it’s taken to kill at least one Maxon motor in the same time frame.

A few months before building Rudy, I first tried out the Silver Sparks in a much more abusive testing application,

namely using them as the drive for my three pound weaponed robot, Misdirected Aggression. I was stepping down from the B16 motors that were usually the standard for a Beetle spinner’s drive train in an attempt to put some more weight into the armor. I had already tested some 50:1 Gold Sparks in the application, and they had stripped out after a few seconds of driving around, so I wasn’t too confident in the newer gearmotors at first.

Despite this, the final Silver models eventually proved their worth, and held up fine until a massive impact ripped the motor from the gearhead, despite the red-Loctited mounting screws. This issue was eventually fixed by press-mounting the full gearmotor in a 1” wide UHMW block (Figure 3) similar to how I had previously secured the B16s.

FIGURE 2. The final stage of the Silver

Spark gearbox compared to the smaller pitch of its predecessor (left).

In addition to eliminating the need for mounting screws to the gearmotor’s face, this press-fit supported the FK-050 motor, preventing it from being removed from the gearhead. The Silver Sparks have worked great from then onward, with no motor or gearbox failures not related to the bot’s unprotected wheels. I’d recommend a similar mounting method for anyone planning on using a single pair of Silver Sparks in anything over one pound.

To conclude, the Silver Spark gearmotors have proven their value, holding together in applications where most similar small gearmotors would have failed. The Silver Spark gearmotors are currently available from www.fingertechrobotics.com, and Finger Tech’s US distributer at www.robotmarketplace.com. SV