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PICList Thread
'[EE]: Speed and Distance Measurement.'
2001\02\02@103543 by Bourdon, Bruce

(Note: Some of you may have already recieved this, I appologize if that is
the case. -Bruce)

A friend of mine is into (mostly stock) tractor pulls, and he actually
volunteers a lot of time and effort to help out with many of the areas

He is interested in learning about the PIC and is thinking making a device
that could be used to help display the tractors speed and distance as it
travels down the track.

We've tossed several ideas back and forth, and would like to hear any ideas
or similar applications that anyone has attempted.

A few notes:

* the event is public, with a significant level of noise coming from the
crowd, PA system, tractors & engines, etc..

* distance is the main criteria by which pulls are judged.

* a full pull (max distance) is typically about 200 feet.

* the course is straight, and movement on the course is controlled (i.e.
roped of area - public cannot walk onto path).

* the towed sled can be modified, adding reflectors, sensors, etc..

* the speed is a significant bonus, as the max speed gives a relative figure
of merit of the tractors horsepower (a published figure from the factory) -
making it easier to spot cheaters (dynomometers are rarely provided).

* the speed is on the order of a few miles per hour, therefore any acoustic
methods should attempt to cancel air movement (which could easily exceed
this value).

* the towed sled has a standard truck rear end and differential which turns
a drive shaft to a transmission which turns a shaft that a cable is attached
to and winds up on - pulling a weighted box up an incline - all mounted on
the "sled."

* distance resolution should be sub-foot (i.e. tenths of foot).

* speed resolution should be at least tenths of a mph, though this is not
critical to the project.

The ideas that we've seriously considered include:

- mounting sensors (hall-effect or opto-but shileded from dust..) on the
drive shaft of the towed sled

- mounting onto the sled, a swingarm with a wheel that has sensors to
measure the distance and have a pic take this, calculate speed and display
or transmit this inofrmation to a remote pic/display.

- mounting a flat reflector on the sled, and using ultrasonic pulses to
measure the distance, calculate speed, etc. (the advantage to a remote
ultrasonic tranciever is that it any component of the wind that is in the
direction of the sleds path will be cancelled by the other "half trip").
Disadvantage: extreame distance and environmental noises.

- aquiring a radar gun and modifying it to provide a pic with the speed,
have the pic accumulate distance by combining speed measurements with time.
Disadvantages: resolution of most radar guns probably not sufficient for
speeds involved, distance measurement questionable, cost, etc..

- laser rangefinder and speedometer... possibilities include measuring the
time of travel (about a foot per clock at GHz frequencies), triangulation,
counting the audible "pops" from a setup that has the beam split, one
portion travels to the sled and back and is then recombined with the other
beam and then passed to an opto sensor & amplifier then pic counter (this
would count each time the distance moved through one wavelength as the
relative phases combined to modulate the beam at the sensor).

- placing trancducers/sensors along the track with complimentary
sensors/transducers on the sled, with the pic monitoring distances between
each along the way...

- purchase a large quantity of pics on a tape reel, mark the tape in


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2001\02\02@110111 by M. Adam Davis

Since the rope being pulled by the transmission (pulling the weight up the
inline) is a function of tire movement, you can measure that to  the
thousandths of an inch and extrapolate all the information you want out of
it - truck speed, distance, etc.

Just mount a big display on the trailer for all to see.  As a bonus you
could even generate electricity with the system to power the device/charge
a lead acid battery for when it's not moving.

And you could mount a bull horn and an ISD recording system to taunt the
tracter operator
Not moving:"C'mon, start your engine already!"
Moving slowly:"[yawn] Y'know, I could probably walk home and back before
you're done."

The crowds would love the talking tracter pull trailer.  You could even
log the whole event onto an eeprom or flash and graph the pull.


"Bourdon, Bruce" wrote:
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2001\02\02@110931 by Bob Ammerman

picon face
Just a general thought -- the more direct you make the measurement the

I'd go for something either tied to the 'drivetrain' in the sled, or perhaps
driven off a separate tracking wheel attached to the sled the runs along the

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level

{Original Message removed}

2001\02\02@112353 by jamesnewton

face picon face

Seems like it might offer the best solution.

James Newton (PICList Admin #3) 1-619-652-0593
PIC/PICList FAQ: or .org

{Original Message removed}

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