DPRG mailing list archives: [DPRG] RE: .Parallax Robot

Sat Jan 5 22:22:00 CST 2008

Hello Ron and Glenn,

You hit the nail on the proverbial head...   I don't know if you know but I
have done some experimenting on making a APU for my sojourner robot project.
It is basically a gas driven electrical power system for long range high
power generation.

One of the items that a coworker of mine introduced me to is that of tuned
exhaust systems.   It is much easier for a constant RPM system than for a
dynamic RPM system like the one on that robot, however the idea is to remove
all of the back pressure from the motor, and then in the exhaust system to
generate a small amount of back pressure by carefully reflecting a certain
amount of the exhaust pressure wave back to the engine.  The careful part is
that the wave front being reflected back is adjusted such that it creates a
nodal point or standing wave in the appropriate part of the muffler /
exhaust system.  If it is done correctly the nodal / standing wave can be
adjusted to disrupt a significant amount of sound energy.

The guys who build those large scale replica airplanes have been doing this
for years, but rather they tune them to create more sound to get that deep
throaty replica sound.

Anyway, when the volume of exhaust is kept constant due to constant RPM this
can be done fairly effectively.   In the case of the Parallax robot the easy
way to do that would be to run the engine consistently in its power band and
use a needle spool valve to regulate the delivery of power.  Ultimately this
would lead to higher gas consumption which is probably why they did not do
it, however it would allow them to tune the exhaust system to something
extremely quite.

>From my tracking the project, the production version is no where near Gen-I
of the project but I am sure there are versions I've not been privy to as I
don't work there and am not affiliated with the group in any way.   I'll bet
however that the significant feedback they receive after field launching a
few thousand Gen-XI robot leads them quickly to considering this for
implementation in the next Gen product.

If you care to see, my prototyping was done on a configuration that looks
like this.  (Link below)  That is a weed whacker motor, read = loud.   I am
most definitely *NOT* a small engine guy.  One of my coworkers is a
mechanical engineer who works on forward field emergency power generation
systems and way (way way) back in the day they used to use small gas
engines.   He turned me on to the technology.  I haven't modified mine yet
but he had me over to his shop and showed me what he has done on several of
the gas powered scale race boats that he runs.  It is quite amazing.   There
are just tooo many fun (read = lots of research) avenues of technology to
track down related to robotics and this is just one of them that I have not
had the time to finish up on yet.  I wish I lived closer to a big group like
the DPRG where one can find like minded people to work with and share out
little bits of the research work.   Man you guys are lucky, that is one of
the things I miss about moving away from Pugetropolis.

http://nikita.argia.net/kmaxon/soj_pwrplnt_007.jpg

One company out there that makes this sort of mufflers that can be modified
to tune for standing wave noise cancellation can be found at the following
link.

http://davisdieseldevelopment.com/muffler/giant.htm

BTW, I don't mind if this is reposted to the list, some others out there may
get some info out of it or it may spur follow on conversation, I'll leave
that up to you...

-Kenneth

-----Original Message-----
From: DeltaGraph at aol.com [mailto:DeltaGraph at aol.com]
Sent: Friday, January 04, 2008 7:33 PM
To: kmaxon at qwest.net
Subject: Re: .Parallax Robot

Hey Kenneth,

Very interesting.
Very nice on your generator setup.
Interesting on RC mufflers too -- my other thought -- how could you make it
sound cool.
Like professor Fate's car in the Great Race -- if per chance you ever saw
that movie -- from 60's
Dim memory was that car sounded cool -- twin V-8s as I recall...

sure post what you like -- maybe this what I wrote:   ;)

Ron

Hey Kenneth,

Neat platform, but seems a bit noisy.

If I had to use a gas engine I would waste some payload on a really good
muffler.
Maybe go with some kind of active sound suppressor?

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