| Constructing Pedals |
| First, let's take a look at the basic operating concept of the pedals. The picture to the left shows how the pedals are linked to the pots. This setup is taken verbatim from Walt Ottenad's design, which is very effective and very reliable. The idea is simple: when the pedal is pressed downward, the eyebolt that extends from it's front edge rides in the slot of the backboard and simultaneously moves the control arm downward. This translates into radial movement of the potentiometer, thereby, yielding variable resistance. This resistance is sent to the simulation and is translated as acceleration or braking. Here's an actual photo of the back of my pedals which includes some details that I left out of the illustration above. This photo shows two bungee cords attached to an eyebolt at the bottom of the backboard, and then extended over two pulleys and down to the eyebolts of the pedals. This is the spring mechanism that returns each pedal to it's original position when letting off the gas or brake. By using different gauges of bungee cord, or by pulling them tighter, you can change the tension of each pedal to suit your needs. For example, you might want more tension on the brake than the gas pedal. Using two cords allows for a little more variation in this respect. You may eliminate the bottom eyebolt and just run one bungee cord from the gas pedal to the brake pedal, but I found the other setup more suitable for my needs. I also had a problem with the bungees popping off the pulleys, so I used wooden drawer pulls instead. It worked great. I included two wooden stops on each slot to restrict the up and down movement of the pedals to coincide with the limits of my pots. I had made the slots too long and the potentiometers were turning way too far for their own good. The message here is to do whatever you feel will get the job done better. Don't be afraid to experiment a little, and keep an open mind toward your approach. Every homemade wheel and pedals that I've seen are different in some way. That's what makes all of this so interesting! Control arms can be made from many different materials. Mine are 1/8" thick plexiglass strips 7/8" wide by 6" long. I drilled two 1/4" holes about 2" apart and made cuts between them to create slots. A little sanding on the cuts is needed to make them slide nicely on the eyebolts. Next, I drilled a 1/4" hole at the opposite ends for the pots. I like using plexiglass because it's strong, flexible, and moves noiselessly on the eyebolt shafts. Also, it can be bent or curved by heating it with a heat gun or boiling water to fit the situation. You can see in the picture that the arms are slightly S-shaped which keeps them from binding on the eyebolts, when they're in the uppermost position. The control arms are attached to the pots with nuts and lockwashers. You must, however, thread the shafts of the pots with a 1/4 20 die. This is a little tricky because you must restrain the shaft from turning while doing this or damage may be done to the internal workings of the pots. Just take your time and use a little common sense and there'll be no problem. The 100K pots that I purchased from Radio Shack have very long shafts which makes gripping them with a small vise or pliers more feasible. Attach the pots with L-brackets, or make your own as I did from sheet metal. Wally makes extensive use of radio straps for this purpose as well as for control arms and many other items. Use whatever means you have best access to. As for myself, making my own brackets to fit each situation poses no problem, since I have the tools and materials for doing so. But, as I said before, go with whatever fits your own situation. To attach the bungee cords, simply thread them through the eyebolts, slip a washer over the end and tie a knot. The washer keeps them from slipping through the large opening of the eyebolt. Adjusting the tension is done by stretching the bungee a little more before tying it off. The pedals are attached to the base with regular hinges. I made my own with L-brackets and threaded rod for pins, but it's more trouble than it's worth. Use ordinary 3" door hinges and you'll be happier. Drill a 1/4" hole on the toe end of the pedals for the eyebolts. Take care in drilling them straight and as far as the drill will go. Drill a 3/8" hole to intersect the end of the 1/4" hole. Here you'll place a 3/8" metal insert to screw the eyebolt into. If you can't find the inserts, a bolt will do just fine. I put a nut at the end of the pedal which allowed me to tighten the eyebolt securely, but it's not necessary. Here's another set of pedals that I made, and as you can see, are gear driven. The pots are located in back of the gears, and between the shafts of the pedals. In this way, your feet never come in contact with the mechanism itself. The shafts are made from heavy duty mending straps that can be found in any hardware store. They extend through the base where they're attached to the springs. However, all this could be located on top of the base, which would eliminate the need for slots and make construction easier. The pedals were made from carriage bolts with rubber hoses slipped over them. Dampers can be used in lieu of springs for a more realistic effect as seen in the simulator built by Stefano Tovagliari in the "Simulators" section of this page. I like this idea very much and will include it in my next set of pedals. Stephano used dampers from a car hatchback, but anything like this is possible as the type used on aluminum stormdoors. If you know of other examples, preferably smaller versions of these, let me know. My thanks to Mark McGranahan who sent me this excellent idea! - "In regard to your quest for smaller dampers for pedals, have you ever considered the radio control car industry? A few manufacturers produce some very high quality miniature oil filled coil-over shock absorbers that just might do the trick. These are fully adjustable units. You can use different viscosities of oil....different piston valving....different spring rates/lengths etc. I think you should check them out. What the hell...they just might work. Your best bet would be to go to a hobby shop and just see what they have to offer." My hinges are L-brackets that I cut down to fit with 1/4" bolts as pins. The gears were attached to the ends of the bolts which I tightened securely on each side with nuts. Smaller L-brackets hold the pots in place (you need to enlarge the holes to accommodate the threaded part of the pots).NOTE: The one thing that I need to do to my pedals is to tilt them forward a little. When at rest, it's uncomfortable for the pedals to be at the 12 o'clock position, because your ankles get tired. It's more natural for your feet to slant forward rather that at a 90 degree angle to your leg. Trust me! I've included a photo of the underside of this setup which shows the springs and the stops that limit the movement of the pedals. Below is a alternative approach to using gears by simply linking the pedal to the pot via an arm made of plastic or metal. It's much easier than gears, but it limits you to only a 1:1 ratio between the two. In other words, the arm will move at the same rate as the pedal. Adding a slot to the control arm of the pot will increase this ratio which allows you to use more of the resistance potential of the pot. This is effectively illustrated below when you compare the two at the neutral position (white) with the pedal pushed forward (blue). The angle between the blue arms is greater than the white ones. This translates into more "turn" on the pot shaft resulting in additional resistance and better sensitivity. It's important, however, to insure that there is no slop in the connection at the pot arm. Make sure that it fits close, but not so tight that it binds or impedes smooth action.