solenoid with basic stamp2

Borna

Hello all,
I'm very new to PIC programing and my knowledge of electronic is very limited
I'm working on a project to build a small model 4 cycle engine and I want to operate the exhaust valve with solenoid.
I'm planning to use basic stamp2 to control the timing and the operate the solenoid.
I'm thinking to have 2 hall sensors to control the closing and the opening of the exhaust valve.
The first hall sensor is located at 0 degree on a wheel, and whenever the magnet passes by, it set a pin to low so the solenoid is not powered, therefore the valve is closed. Whenever the magnet passes the second hall sensor located at 170 degree on a wheel, it set a pin to high so the solenoid is engaged to open the valve.
However the second hall sensor only set a signal if it is on the second rotation after the valve is closed.

Sensor1 at 0 degree
LOW 1 ' so no power to solenoid

sensor2 at 170 degree
if (counter = 1)
HIGH 1 ' power to the solenoid
counter = 0
else
counter = 1

The max RPM on the engine is 3000, however most of the time engine will run at 1800 RPM.

This means at 3000 RPM, the exhaust valve has to be opened every 29 ms and stays open for 10 ms.

Questions are:
Is basic stamp2 fast enough to handle this?
Do you see any issues with what I'm planning to do?
This meas the solenoid has to go from low to high 34 times in one sec. Is this possible?
Can you provide an idea how I need to make the circuit to control the solenoid?

Thanks
Borna

Franklin

You will need a transister, mosfet, or relay to switch the power the solinoid needs.

Mike Green

Look at Nuts and Volts Column #6.

Go to the main Parallax webpage and click on Resources, then click on Nuts and Volts Columns. That'll take you to the index.

The Stamp is fast enough to do this, but the solenoid may not be fast enough. You'll have to look at the spec for the solenoid.

erco

Assuming you are talking about regular automotive poppet-type valves, IMHO you're paddling toward the falls. There's a reason why valve springs are so heavy, you need lots of force in both open and closed positions. You'll need at least a quarter-inch of valve travel, probably more. A solenoid is a terrible actuator. It has a non-linear force/stroke curve, very weak initial pull, and uber-strong slamming force when it bottoms out. You need smooth valve motion, easily controlled by a camshaft but a solenoid (even ignoring the impossibly large initial opening force) is not up to it. It will slam the valve open, then slam the valve closed when it shuts off. Lots of valve float and bouncing. Exhaust valves run VERY hot and are usually close to their mechanical limits when properly cam actuated. If you add the solenoid's mechanical shock loads on top of the valve's already fragile existence, my guess is that you'll have a valve stem failure in short order.

Leon

Pneumatic valve operation is used on some MotoGP bikes; that would be better than using solenoids for direct operation. The bikes presumably use small solenoids to control the pneumatic actuators.

Borna

Hi Erco
I agree with what you said, but those are already taken under consideration. I'm using a sliding exhaust valve rather using tradition poppet valve, so valve slamming is not an issue here.
Also This is a home made model small engine with .875X1 bore and stroke and performance is not an issue.
My main concern is to be able to find a solenoid that can cycle 34 times per sec at max RPM and to build the circuit to drive the solenoid. Looks like Mike Green suggestion on Column is a good one too.

erco

Slide valves are definitely better than poppets here, but they still have mass; the acceleration forces are not trivial. Keep in mind that your 34 cycles per second is not SHM, the valve sits patiently closed for 1.5 revolutions, then slams open and close in half a crank revolution. A solenoid actuator will by nature generate violent velocity profiles on both opening and closing. You may need some mechanical damping for longevity, which will further affect your valve timing.

Neat project, please keep us appraised of your progress. Good luck!