While i’ve been tinkering with many things over the time since my last post. Most of it has not really been very noteworthy or at least nothing that would probably be of interest or use to anyone else.
However, inspired by now owning a 2L turbo sports car and some recent participation in some motorsport events i’ve decided to build a racing simulator. It’s nothing new, i don’t claim it to be but i’ve decided to collaborate some of the things i have done in hope that it might help someone else going down the same path.
The aim of this project is to produce a somewhat life-like simulator without using a standard shop bought wheel/pedal set. I’ts not going to be real, i know, but here’s my ‘requirements’:
- Realistic steering wheel with as much rotation as possible
- Analogue Clutch
- ‘H’ pattern gear shifting
- Analogue Hand/E brake
- Force measured brake (not movement like normal pedal sets)
- Small/Storable/Disassembleable (I don’t have a spare room for a sim cockpit)
- Strong/Durable
- Cheap!
The intended target platform is a PC running ‘Live for speed’
I started this project a couple of months back, starting with the wheel and now i have just completed the pedals. The steering mechanism was construced utilising a 2:1 ratio cam belt driven gearbox giving a theoretical ‘lock to lock’ of 540 Deg. A little less than i wanted but it works ok. There’s nothing too technical about it other than the gear reduction. It uses a real sports steering wheel too. A keen eye might also be able to tell what the bearing/shaft supports are recycled from 
The pedals were heavily based on the design of the commercial product from http://www.cannonsimulationtechnologies.com. Todd of CST also sells a ‘DIY’ guide for making a pedal set that is somewhat comparable to his commercial product for only US$12. I probably could have constructed my pedals without the need for the guide but i went and bought it anyway. I saw it like paying royalties for his design and i think it’s only fair he gets some reward for his efforts.
The main difference with my pedals are basically the fact that i have constructed them almost entirely of things i had at home already or i could acquire for free. The problem for someone attempting to replicate what i have done is, not everyone would have the stuff lying around like i do but parts can easily be substituted.
So far, the build has only cost me about $80. The bulk of that cost is for the rod ends that go to the tops of the pedals at ~$16ea. The springs were about $7 each. The steering mechanism has been totally free so far.
All these mechanics are no good without some way to interface them with a PC. I tinkered with the idea of using an optical mouse to track an encoder mounted to the steering wheel at first but this was not far from epic fail. It worked but was too unreliable, lost it’s center and basically sucked. One advantage it did have was an almost unlimited number of rotations. Pity it sucked everywhere else. Abandoning the optical mouse idea, i moved to the old pot style joystick. I happened to have an old E-Sky USB trainer in the cupboard that i never use anymore so i gutted that – The result is the ability to have 4 axis analogue joystick control. Only problem was that ideally i needed 5 analogue inputs but it was enough for ‘proof of concept’ for now.
Not long after destroying the USB trainer I came across Leo Bodnar’s site. He sells a generic USB interface that provides 6+ Analogue inputs as well as 32 odd buttons. While his product is good, it did not really follow the rule of cheap. At about $80 to get one to my door, it would have doubled the current cost of the build. Some more googling turned up a ‘product’ called Mjoy by Mindaugas Milasauskas. It’s a DIY USB joystick interface based on an Atmega8 AVR. It seems that his legacy goes on but for some reason his website is gone. I am making Mindaugas’ and version of the joystick interface (for a fraction of the cost of Leo’s). All of my designs and ideas will be published here.
The interesting thing with the CST pedals is the use of a load sensor for the brake sensing. This is a superb idea (Although Todd admits it was not his). This will give a much more real feel to the brake pedal. I managed to salvage a load sensor from some industrial scales some time back – I knew it would be good for something! The problem is the interface between the load sensor and the joystick controller. The load sensor only puts out ~2mv at full load, we need 0-5v scale for the joystick interface. Some more googling dug up an ‘off the shelf’ chip designed for this exact task. It’s an INA122 by Burr-Brown (owned by Texas instruments i believe). As it turns out, this appears to be the chip Leo uses in his controller with load cell interface. The difference with me is, i’m going to give you all the info you need to get it running with Mindaugas’ design for free.
Details to come….
