Mind / Iron
by Bryan Bergeron, Editor ;
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
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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