engine RPM control solenoids controlled by PWM.

BrendanP

Senior Member
I'm thinking of getting a couple of these linear actuators to use with a petrol powered motor for throttle and choke control. Here is the link to the pdf. data sheets.

http://www.woodward.com/pdf/ic/52132.pdf

I was looking at the APECS 2000 controller on page 74. (APECS- advanced proportional engine control system) I think picaxe should be able to do what it does. As far as I can see PWM command should be able to do the job.

I propose to use the APECS 0175 series linear acutator on page 84. This actuator isn't a thread turned by a motor as are most linear actuators but seems to be a solenoid. I thought solenoids simply pulled in or out.

Can a solenoid be partially 'open' or 'closed' by use of PWM? Am I missing something?

I don't want to spend the money for nothing so any advcie is welcome. I thought some of the robotics guys would have done stuff with this sort of thing..

http://www.woodward.com/pdf/ic/52132.pdf
 

BeanieBots

Moderator
Can a solenoid be partially 'open' or 'closed' by use of PWM? Am I missing something?
They can be 'controlled' to mid postions but it is often rather sloppy.
PWMing a solenoid is a bit like having a leadscrew type actuator connected to the load via a length of elastic.
Not impossible but be cautious. If the load varies, so will the position.
 

moxhamj

New Member
To expand on that, a Servo is a device that moves to the position you ask of it, no matter what the load. For a model plane that is fine as the load is wind resistance and the servo can always overcome that. Pushing a throttle requires a lot more force and solenoids have a quite non linear force curve. It is possible (I have a magnetic globe hovering on my desk under active microprocessor control) but it becomes very complex. I don't think a solenoid is the right device.

I'm in the process of building a throttle controller at the moment and I'm using a cheap cordless drill diving some threaded rod with 2 aluminium tubes to provide stability. There is a microswitch at each end of the travel which act as limit switches.
 

BrendanP

Senior Member
I've spoken to Woodwards reps/agents here and they say their unit can do the job as its purpose made for that task. But, that is in conjunction with their controller which might have the sophistication to do the job.

Whilst at work today I was thinking of making just the unit that Dr. suggests. I remember someone else the forum made one and posted a link to the picture. Can't remember who but thanks you anyway.

Are you using the gear set that came in the drill Dr. or is it 'direct drive'. I guess you'll pwm it?

Can anyone suggest high quality small 12V DC motors that can take heat and vibration?
 

premelec

Senior Member
I'm not discerning what the engine is doing but if it is on a vechicle drive or something else that needs to shut down fast that's a special conditon... I installed a cruise control on a 1970 VW van which had a combination of lead screw and solenoid - the solenoid performed the fast dropout function when you hit your brakes - the lead screw did the heavy pulling and slow releasing... it was a commercial after market unit and worked very well. [$120US]...
 

leftyretro

New Member
Well there may be a fundamental semantics problem here.

I worked for many years in the process control area at a oil refinery. We used all sorts of solenoids and many types of magnetic linear actuators.

All solenoids we used were of the on/off type, open/closed only control, but there were also magnetic actuators that were simple wire windings that could position a soft iron actuator rod mechanism through a 0-100% travel range. These were usually part of a larger servo control mechanism where there was physical position feedback of the final control element that would then tell the PID controller to move the move the commanded magnetic actuator one way or the other to eliminate the error between desired and actual position.

So for my definition solenoid = digital output device, magnetic actuator = analog output device.

Lefty
 

BrendanP

Senior Member
Thanks Lefty, Woodward lists them all as 'linear actuators.'

Also thanks to Prem , your idea of using a automtotive aftermarket unit is brilliant suggestion.
 

premelec

Senior Member
BTW on the 1970 VW Bus I just picked off the RPM from the points rather than sensing wheel RPM - So it regulated RPM instead of speed - I installed it 11 years ago - cable actuator - many units use vacuum but VWs don't have any vacuum most of the time :) . Company name was "Rostra Precision Controls" model 'Ultra Cruise' [Laurinburg NC 28352 USA]. be careful!
 
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