Servo - January 2013

Mind / Iron

FOR THE ROBOT INNOVATOR

ERVO

by Bryan Bergeron, Editor ;

Cutting Corners Experimenting with robotics — for the most of us — is a 'nice to have' activity that is stimulating, challenging, and rewarding on several fronts. Unless you're fortunate enough to work with robotics as a career, components and platforms are not a 'must have' when the end of the month rolls around and it's time to budget expenses for your next project. So, it's tempting to cut corners here and there in order to stretch available funds. However, there's a limit to cutting because at some point, you'll limit the possible success of your project.

For example, I just finished assembling a robotic arm and mobile platform that I purchased from an established robotics company. I had picked up the equivalent earlier model before the economic downturn, so my expectations of build quality and components were set by that experience. In short, I was disappointed.

Starting from the user interface, instead of using set-screw knobs with D-shaft pots, the pots featured smooth round shafts. Within minutes of working the robot arm controls, the knobs began to slip. I suppose the D-shaft pots might have cost the manufacturer a few cents more than the round shaft version, but at the expense of a workable user interface. I flattened the shafts with a Dremel and reattached the knobs. The knobs are now workable with no detectable play.

Then, there's the base of the arm controller. It was nicely painted with smoothed corners, but unlike the previous model there were no rubber feet. At best, the unit slides around on a hard tabletop. At worst, it mars the finish of a wooden tabletop. Self-adhesive rubber feet were an inexpensive but bothersome fix.

Moving inside the arm and controller unit, I noticed that the power supply components were lacking the thermal grease that was used in the previous model. It probably takes a few more seconds to assemble the unit when messy thermal grease is used, and labor is undoubtedly expensive these days. The downside, of course, is that the temperature of the power supply components is greater, and component life suffers.

Another disconcerting shortcut was the wiring. Several of the 16 gauge connections from the power supply had been replaced with more diminutive 24 gauge wires. Worse yet — from a maintenance perspective — the power supply connectors were replaced by direct connections.

The main point in all of this is that cutting corners is a natural reflex to the increasing cost of components and limited resources. However, you have to know what to cut and what to leave as-is. In the examples above, the mismatched shaft and knob could have been a constant annoyance, but wouldn't have resulted in catastrophic failure. The lack of rubber feet is more problematic, especially if they prevent you from scarring the kitchen table. Failing to use thermal grease when it's clearly called for is simply unconscionable. Why not invest in a few dollops of grease today to double or perhaps triple the life expectancy of a component?

Skimping on wire gauge and connectors seems almost as egregious, depending on the average and peak current drawn by the servos in the robot arm. You don't want to endanger lives by creating a fire hazard.

It's a good idea to have a 'no cut' list that contains the components and accessories that shouldn't be subject to skimping. And it should be adaptable to context. For example, skimping on lock washers may be okay for a carpet crawler, but not for a four pound quadcopter that could come smashing down with the loss of a nut. The best way to cut back on a complex system, of course, is to simplify the design. Engineer out what you don't need and take some of the savings and invest them in higher quality components, cables, and connectors. SV

6 SERVO 01.2013

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Bryan Bergeron

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