Motor Costs Comparison (more pro-electric)

Fri Sep 17 17:18:52 AKDT 2004

Dean & Matt,
 Yes. I forgot to mention the the "programmability" factor of an electric
motor. Whereas a glow motor's characteristics come from mechanical things
(bore, stroke, port timing, etc.), an electric motor and speed controller
can work together to alter the torque curve. Some speed controls take
advantage of this now, but most people don't realize it. The better speed
controls use a non linear type of output (I'm oversimplifying here) to make
the electric motor "feel" more like a glow motor. I haven't worked much with
the brushless motors but I have a bit of experience with the can motors
(from R/C car racing). It seems like what we need is a speed controller with
a P.I.D. control loop. The currently available ones are one dimensional /
open loop. The throttle stick simply increases or decreases the output of
the motor. The speed controller just changes the PWM duty cycle in direct
response to the stick position. We need some feedback and Fuzzy Logic to do
this right. Dean: If you design the hardware, I'll work on the code...
John Pavlick
http://www.idseng.com

  -----Original Message-----
  From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]On
Behalf Of Dean Pappas
  Sent: Friday, September 17, 2004 12:55 PM
  To: discussion at nsrca.org
  Subject: RE: Motor Costs Comparison (more pro-electric)

  Hi Matt,
  I suspect that you're right, even if the timeframe is a little longer.
Some pieces of hardware are still lacking. The first among these is a speed
controller that offers braking. Probably the easiest way to do this is to
make the controller so that stick position actually controls the motor RPM,
and then mess with the timing to get braking when the RPM is above the
target. The potential for slow downlines is staggering. For the geared
motors, an RPM limit would also allow the selection of a lower resistance ,
higher Kv, winding and corresponding change in prop or gear ratio that would
overspeed the motor under a W.O.T. dive, but will improve efficiency
everywhere else.

  just some ramblings,
      Dean
  Dean Pappas
  Sr. Design Engineer
  Kodeos Communications
  111 Corporate Blvd.
  South Plainfield, N.J. 07080
  (908) 222-7817 phone
  (908) 222-2392 fax
  d.pappas at kodeos.com

    -----Original Message-----
    From: discussion-request at nsrca.org
[mailto:discussion-request at nsrca.org]On Behalf Of Rcmaster199 at aol.com
    Sent: Friday, September 17, 2004 1:13 AM
    To: discussion at nsrca.org
    Subject: Re: Motor Costs Comparison (more pro-electric)

    John there are at least a couple more good points:

    Throttle response of an electric can be made more effective compared to
most engines, even many four strokes. You don't get the wind up on downlines
like you do on 2 strokes, and you don't need to wait until the 2 stroker
settles down on landing

    I doubt we will ever have to worry about the motor "flaming out" on
take-off, 10 feet off the deck in no man's land, even if one cell drops. Or
the motor going fat or lean and flaming out somewhere in the flight.

    There are many more good points to be made. It makes sense for pattern
even if initial cost or the cost per flight is prohibitive for many right
now. Consider the afforementioned flame-out on take off, or flame out on
landing approach that got a little too far away. A cracked pattern plane is
often the result of either condition.

    I still hold to a statement I made more than a year ago: in five years
more than half of us will be flying electric

    MattK

      Here are my thoughts on electrics:

      Good points:

      1. They are VERY quiet. This is a good thing. I've never heard of
someone
      losing a flying site because the planes were too quiet.

      2. They are clean. The airframe will last longer because there's no
danger
      of being fuel soaked. Electrics are more "politically correct" in that
they
      don't pollute the air (although the energy required to charge the
batteries
      my come from something that does), and most of the new batteries are
safe
      when disposed of properly (to the best of my knowledge).

      3. They produce less vibration, even when the motor is mounted
directly to
      the airframe.

      4. Modern brushless motors have as much usable power as glow motors.
When
      properly matched to the airframe, an electric motor feels almost like
a glow
      motor.

      5. They are easier to fit with a gear drive. This allows a wider range
of
      props that may be used.

      6. Brushless motors require very little maintenance.

      7. The C.G. doesn't change as the battery discharges.

      8. They are easy to start.

      Bad points:

      1. An electric power system for large airplanes is VERY expensive. You
can
      buy a lot of glow fuel for the cost of a few battery packs. Batteries
are
      reusable, but they don't last indefinitely.

      2. Power system design is much more critical. Props, gear ratios and
current
      draw must be considered very carefully.

      3. Batteries must be charged. This takes a long time compared to how
fast
      they discharge. Owning a lot of battery packs merely delays the
inevitable
      truth: If it takes 10 times longer to charge than discharge,
eventually you
      will end up waiting for something to charge.

      4. With LiPO's the energy density is fairly high (capacity wise) but
it
      normally takes quite a few packs in parallel in order to handle the
required
      current loads.

      5. LiPO's must be handled with care. I don't need to elaborate on this
one
      although I personally don't think they're DANGEROUS. People are more
      dangerous.

      6. High output electric power systems are relatively heavy, although
this is
      improving at a rapid rate.

      To sum things up - I fly glow and electric. I like them both. I have a
few
      S400 planes that fly very fast and track very well. I also have a few
slow /
      park flyers that are great when the air is calm. Small electrics are
great.
      Most of the time, however, I prefer glow motors. Mostly because of
cost and
      ease of use. A .40 glow motor costs $50.00 (used) to $100.00. A
brushless
      motor and battery that provides equivalent power could easily cost 3
times
      as much. I don't like to wait for batteries to charge. I hated it when
I
      raced R/C cars and I hate it even more now. I don't mind wiping the
slime
      off of my plane at the end of the day. I do believe electrics may be
the way
      of the future. The key word is future. At the present time, I think
the best
      bang-for-your-buck comes from the glow stuff. There's a lot of energy
stored
      in dead Dinosaurs, and we pretty much perfected how to extract it in
the
      '70s. If money is not an object and you want to be a pioneer then fly
2
      meter electrics. I think I'll wait until technology catches up with
our
      expectations.

      John Pavlick

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