The throttle servo was a cast iron bi*ch to sort out. The trouble was due to three different technological hurdles to jump. Physical hardware, electrical hardware and virtual software. .... plus add safety, speed and durability.
The first-generation of the throttle servo started by harvesting a stepper motor and gearbox from a laser printer. A wooden baseball bat was the primary harvesting tool. A complex gizmo consisting of gears pulleys and cables was constructed and but was ultimately scraped. The total cost was $0.00
The second-generation servo uses a powerful stepper motor directly coupled to the throttle shaft. For safety, the stepper motor can be deactivated and the throttle return spring will immediately close the throttle. The associated software takes up 18 lines of code for manual mode. A few more lines of code will be necessary for automatic mode.
Total cost was a budget busting $45.00. I know it seems cheap but free is always better when possible.
Load cell and amplifier
The load cell is actually unremarkable in the sense it works right out of the box. The $40.00 load cell and the $23.00 amplifier are wired together and the output is wired into the ardureno. A few lines of code converts the voltage into pounds.
The load arm on the PAU measures exactly 14 inches.. I built a second 14 inch calibration arm on the opposite side of the PAU. The idea is to apply a known weight to the calibration arm and tweak the amplifier (if necessary).
The loadcell is rated for one kilo Newton ...that works out to 224 pounds in dog years or something like that. Metric weights don't make any sense.
Just for giggles, I weighed myself on a UPS scale then climbed a ladder and stood on the calibration arm. Close enough. I figure I can eat 100 more Big Macs and I will weigh enough to full range the load cell or I need to buy a calibration scale. Decisions...
Anyway, the real calibration will be done at some point but for now I'm happy the load cell and amplifier appear to work. Due to the 14 inch load arm, the actual torque generated by the PAU has to be multiplied by .86 to convert to foot pounds. This is just one line of code and never has to be an issue.
At this point I had enough stuff cobbled together to do some basic testing. Getting all the ducks in a row is about as complex as launching the space shuttle but I managed. Long story short, it all works!
With the engine running I can dial in a load and advance the throttle electronically. So far I'm at 65 lines of bullet proof code.
The next step is getting the shaft speed sensor sorted out. I have all the parts in stock however this last hurdle is massive and I'll explain when this thread gets updated again.
Let's look at some pictures...
Getting the parts to build the first generation throttle servo. I had to beat the E36 M3 out of a laser printer to harvest the stepper motor and some gears. If you seen Office Space, you know the song....
Gears and motor in hand
The first generation throttle servo was insanely complex and eventually ended up in the scrap bin.
The second generation servo is simple, fast and safe.
Stepper motor directly coupled to throttle shaft makes life a lot simpler. Flipping a bit in the software will disable the motor controller and the throttle will snap shut in the blink of an eye. Nice!
Meh, no drama no surprises. The load cell and amplifier work perfectly out of the box. Five lines of code and it was time to move on.
This is the nearly complete dyno controller. The knob on the left is for manual load control and knob on the right is for throttle control. The manual controls are for trouble shooting and setting up the dyno. Flipping a switch will disable the manual controls and a PC will automatically take over.
I'm going to try to shoot some video tomorrow and let you folks get a look at this thing in action.
Stay tuned!