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!
