Here is my modification to the MOMO racing
pedal set. I wanted to have a force sensitive brake pedal for
some time. I had seen all the articles on the Race Sim Central
message boards and thought this would be a great next project.
In starting the project I decided to get a few different
loadcells. I bought them from here:
http://www.scales-r.us/loadcell.htm
I ended up doing the modification on the
MOMO wheel pedal set instead of building a stand alone pedal
set. The main reason I did this was cost and time. Since the
pedals are built well enough for my taste and I am not hard on
my equipment I didn't have any concern. I also used Leo's load
cell board for the control of the accelerator and loadcell
brake. His website is here:
http://www.lbodnar.dsl.pipex.com/USB-load-cell/
The basics of this are pretty
straight forward. The harder you push on the pedal the more
braking force you get. You can read more about how a loadcell
actually does this by reading the Wiki out take below.
"A load
cell is typically an electronic device (transducer)
that is used to convert a force into an electrical signal. This
conversion is indirect and happens in two stages. Through a
mechanical arrangement, the force being sensed deforms a
strain gauge.
The strain gauge converts the deformation (strain)
to electrical signals. Normally, a load cell consists of four
strain gauges in a
wheatstone bridge
configuration, but is also available with one or two strain
gauges. The electrical signal output is normally in the order of
a few mill volts and requires amplification by an
instrumentation amplifier
before it can be used. The output of the transducer is plugged
into an
algorithm
to calculate the force applied to the transducer."
Wikipedia
The first step was to choose
the correct load cell. I tried the 30KG,10KG and 3KG. For this
application the 3KG turned out to work perfectly. The 10 KG
would have worked as well, but the 30KG was just too much force
for the plastic pedals. Also since I am a Formula 1 driver I
didn't want a lot of pedal movement since a real formula car has
only a few mm of actual pedal movement There are many schools of
thought on how to implement the actual loadcell, but I went for
the tried and true method of having the pedal press down on a
shock and spring combo from an RC truck. Here is a diagram to
help visualize.
|
|
 |
|
|
|
The actual process is pretty simple.
First I took the pedals apart. Since I
have my pedals in a cockpit the supplied carpet grip on the Logitech
pedal is not needed. Once I removed this grip it gave me a large
cavity to install the loadcell. I built a small bridge to hold the
loadcell in the cavity on the pedals base. |
 |
 |
 |
|
|
|
After I had figured
out the attachment of the load cell to the pedal base I then had to
drill a HUGE hole on the pedal bottom and attach the RC car shock to
the loadcell. I have a set of taper drill bits and taking my time I
was able to open up the plastic without breaking anything. |
|
|
|
|
 |
 |
 |
|
|
|
Now that I have the
shock and the loadcell mounted it is time to connect the pedal to
the shock. I did this by taking a piece of brass rod and threading
it to go through the shock. I then drilled a hole through the pedal
so I could send the threaded shaft all the way through the pedal and
into the top of the shock. Then with a nut on each end I was able to
tighten the two up and reassemble the unit. |
|
|
 |
 |
 |
|
|
|
The only thing left
was to connect the loadcell and potentiometer to the loadcell board
from Leo Bodnar. Once I connected the 4 wires for the loadcell and
the three for the pot I was ready to test it out. I connected it all
up, and booted the computer and went into the joystick calibration
menu in windows. Calibrated the load cell and accelerator pedal and
was off and racing.
The feedback and
tactile feel from the brake pedal is great and provides that extra
bit of realism. Also the damping provided by the shock is a very
real feeling and you can really tell when you are getting on the
limit of the brakes. In truth I can say this has provided me a much
greater feel for the car and if my lap times at San Marino mean
anything I have removed a full second from my times.
I highly recommend
this modification to anyone, and in the future I might build a full
set of pedals, but for now these will do just fine! |
|
|
