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[DPRG] jbot twists off

Subject: [DPRG] jbot twists off
From: David P. Anderson dpa at io.isem.smu.edu
Date: Fri Jun 24 15:07:03 CDT 2005

Howdy,

jBot now has a working sonar array and can be let loose
to run autonomously in dangerous places like the junkyard
where this morning in the middle of a spectacular run
over a pile of broken pallets and tangled metal pipes
it managed to twist off the rear left driveshaft.  Plastic.
Twisted it up like a piece of black liquorice and snapped it
off at the ujoint:

<http://geology.heroy.smu.edu/~dpa-www/robo/jbot/jbot_twisted_driveshaft.jpg>

So I thought, must be that we are putting a whole lot more torque on the
driveshafts than they are designed to handle, and headed off to the
hobby shop to buy replacements.

There the R/C car guy told me that the Nitro cars twist off their driveshafts
all the time (which made me feel better), and he sold me a set of steel constant
velocity joints to replace the plastic driveshafts (so THAT'S how they make their
money!!):

<http://geology.heroy.smu.edu/~dpa-www/robo/jbot/jbot_cvjoint.jpg>

An interesting sidenote for those contemplating using R/C suspension and
drive parts for an offroad robot.  Evidently designed for high speed
(35~40 mph) and low torque, while our robots generally tend toward low 
speed (4~5 mph) and high torque, hence the broken driveshaft.  Seems to
be a problem that the R/C nitro guys have already neatly solved.   Just
send money... ;)


best regards,
dpa


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