Making an engine governor

[FFMan]

I'm making a small honda strimmer engine into a compact generator for topping up batteries in the field. It uses a motorbike stator, flywheel and rectifier/regulator.

This small engine has no governer so I know that as the battery charges up, the load decreases, the revs will rise and as i want to leave this unattended that could be bad news.

It feels as though i could make a governor by using a servo to drive operate the throttle and a simple rpm pickup to establish speed. I could also add a timed shutdown or a shutdown when the throttle has reduced to a preset limit.

Is driving servos from zbasic easy, i couldn't find any examples after a quick look through the app notes.

[dkinzer]

It feels as though i could make a governor by using a servo to drive operate the throttle and a simple rpm pickup to establish speed.

It is quite feasible. Many years ago I did the same for a 12KW diesel genset using a magnetic pickup mounted near the flywheel for the RPM input and a linear actuator to control the throttle. My implementation was so long ago (pre-ZBasic) that I used a Basic Stamp II having no floating point and extremely limited RAM. Because the RAM was so limited I needed an external RAM chip to store the historical information to implement the PID control loop algorithm. There is some information, including photos, at the page below.

http://kinzers.com/don/GenSet

There is a good article on PID control on wikipedia and a lot more information is available elsewhere. Tuning the algorithm will be a trial and error proposition due to the reaction time of the various elements of your particular system (throttle positioning, throttle response, generator output curve, etc.).

[FFMan]

thanks Don.

Nice project of yours, different scale to mine but principal is similar. I was going to use a magnetic pickup also, perhaps even using the existing stator magnets which are 3 pieces.

I am familiar with PID as i got part way through building a cruise control which is a very similar proposition.

Are you able to point me in the direction of any servo control example code ?

[dkinzer]

Are you able to point me in the direction of any servo control example code ?

I don't have any particular examples. Much depends on the stepper/servo that you choose and whether you choose to use a control chip (as I did - Hurst 220001, now discontinued) or produce the phased drive signals directly. You should be able to find good information about the drive requirements for the motor that you choose. I suspect that you can find some Arduino code for stepper control.

[FFMan]

ok - i rather thought servo driving was a regular zbasic thing and i would be able to drive it using some pulseout commands.

If not this looks usable http://www.ebay.co.uk/itm/282345296797? ... EBIDX%3AIT

and with the clutch disengaged gives manual control

[rosariote]

Hi,
Since it is a trimmer engine you may use this 2-phase 4-wire Stepper Motor DC 5v 12v linear Actuator Telescopic Position Rod . Do a search in ebay using the above description. By using the stepper you may adjust the speed more accurate,