[TriEmbed] Pinewood derby help

[Alan Smith]

Depending on when the race is, I did this in a similar Dad's race (except
our rules our less than 5oz, fits in the box, bring it.) but I used a motor
and fan out of an RC electric jet.   I had lithium ion battery pack (to be
able to supply instantaneous current), and a board I laid out with an
attiny to give the right signals to the embedded speed controller that
handled driving the motor.

I had a switch on the front of the car so when the pin dropped, the switch
would open.   I had the motor spin up to idle speed when the switch was
pressed (ie, car first put on track) and then go to full power when it
opened.

I got a little nervous because we have a group of boys that congregate at
the bottom of the track.   So I went the night before to test it out on the
track.   I went to go test it and nothing.   I hadn't brought anything with
me and was stunned.  I finally saw a wire crossing and used my pocket knife
to clean it up.    I then started it up.   I hollered for people to watch
and put it on the track.

In a typical pinewood derby race, the car picks up speed going downhill and
then slows down on the straight piece.  This car picked up speed the entire
time until it hit the end where there was a plywood board.   The battery
wasn't connected well enough, and it flew up into the fan blade knocking
out half the fan blades and causing the car to fly off the track across the
room.   Luckily I have several dependable eyewitnesses that will swear that
it was scary fast.   Unfortunately there is no video, and I entered the car
with torn up blades in the race the next day under the name "Heartbreak"

--Alan


On Tue, Jan 10, 2017 at 1:27 PM, John Vaughters via TriEmbed <
triembed at triembed.org> wrote:

> > I hadn't considered the motor actually slowing the car down though.
>
> It wouldn't really slow it down, but it would prevent it from speeding up,
> or become a dragging force once you reach the top RPM the motor will run
> with the applied load at the top voltage. It is a significant force to
> consider. The extreme example would be a 100:1 gear ratio on a motor. You
> get to top speed quickly, but just try to speed it up with another force,
> it is difficult. The motor and gear leverage is the limiting factor.
>
> Probably the best sensor you could use would be an acceleration sensor.
> Then you could play with the gear ratio that gets you to a constant
> acceleration and top out near the finish line. It would be fairly clear
> that you top out with the sensor. Between the best time and acceleration
> measurements you will find the best gear ratio. Also, consider ramping the
> voltage with your PWM to prevent wheel spin. If you really want to go all
> out and do not care about the motor, test over driving the motor with
> higher than rated voltage. They can take it, but only for so long before
> they spark themselves short.
>
> Good Luck and Have fun!!!!
>
>
> On Tuesday, January 10, 2017 12:56 PM, Craig Cook via TriEmbed <
> triembed at triembed.org> wrote:
>
>
> >Still go down hill, but now you have a motor and not just gravity as a
> force.
>
> Correct.
>
> If I can make it work I also want to be able to ssh into the CHIP when at
> the race track so I can make tuning adjustments.
>
> Race day is 27 Jan.
>
> It's going to be a power-to-weight and traction problem.  I hadn't
> considered the motor actually slowing the car down though.
>
>
> If there is interest I could do a TriEmbed presentation on "How I made a
> block of wood into a Race car with the help of TriEmbed".
>
> My Son's car is going to have LED headlights and tail lights.  That is run
> from a CR1616 battery I already had.  Will be run in a parallel circuit
> with resistors.  Already have that working on a breadboard.  Fitting 5mm
> LED's into a block of wood and hiding wires is interesting.  I sacrificed a
> cat6 cable for it's wiring.
>
>
>
> Got a note today that my digikey order has been shipped.
>
>
> Thanks
>
> Craig
>
> _______________________________________________
> Triangle, NC Embedded Computing mailing list
> TriEmbed at triembed.org
> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
> TriEmbed web site: http://TriEmbed.org <http://triembed.org/>
>
>
>
> _______________________________________________
> Triangle, NC Embedded Computing mailing list
> TriEmbed at triembed.org
> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
> TriEmbed web site: http://TriEmbed.org
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20170110/5b09d44f/attachment.htm>