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Load Cell Braking Modification

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.
loadcell_05.jpg loadcell_06.jpg loadcell_07.jpg loadcell_08.jpg loadcell_10.jpg
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.
loadcell_11.jpg loadcell_12.jpg loadcell_13.jpg loadcell_14.jpg  
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!
 
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