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Topic: Automobile Cruise Control Project (Read 2 times) previous topic - next topic

bobp0303

I'd like to develop an automotive cruise control using a 5.25" floppy stepper motor -- the general idea seems simple enough (particularly since I have no experience building computer hardware  ;) ) -- I'm a computer programmer who has also remodeled, rewired, and replumbed my previous house, so I'm comfortable with the overall project idea.
Has anyone already done this?

My general plan is to:
1 determine all the ways to instantly disconnect the device -- brakes, manual switch, etc.
2 build or obtain a clutching device that defaults to a physical disconnect.
3 figure out the interface required to interface with my tachometer signal or a single spark plug impulse (manual transmission, so I definitely don't want a speedometer connection!)
4 write or obtain arduino software to recognize current frequency of tachometer impulses.
5 modify arduino software to drive stepper motor to control throttle.

Bob.

Orac

Wouldnt you want to find vehicle speed instead of engine rpm?


agent_orange

You need to learn negative feedback and control mechanisms for the software part. There should be some stuff on the web or maybe on this site for negative feedback control algorithms.

bobp0303

Thanks for the tip on specific topics to learn -- they've been added to my research list.

KirkCharles

Check out this article called PID Without a PhD

http://www.embedded.com/2000/0010/0010feat3.htm

Also a recent avrfreaks.net post has a PID control library

It is very unlikely that a small step motor will be able to operate the throttle of a car.
One of the several sub problems is to make a test rig to open an close the throttle with engine off.
Test the throttle with a fish scale to determine the force needed. That way you can be sure.

Also consider a DC motor with a pot for feedback.
Perhaps you can tap into the TPS which is a pot on the throttle shaft used by the Engine control computer.
Many older cruise units use engine vacuum to pull a cylinder for the throttle.  Perhaps a junkyard trip is in order

If you keep the gear ratio low on the actuating motor it will return to idle by just removing power.  Find a motor that you can spin the shaft by hand and test to see if the throttle return spring will back drive it.
Good luck

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