So I am designing a project where I need to remotely control a butane lighter, disposable bic kind.
Will a servo motor produce enough torque to push the lighter button down? Not a piezo igniter button which requires a bit of force, just the gas spring lever like on a standard bic. Ignition will be controlled by ni- chrome heated wire.
I tried using a small 12v push pull solenoid but it was not strong enough.
I can't find any information online about how much force is needed to press a lighter button down.
which is rated at stall Torque : At 4.8V: 1.8 kg-cm / 25 oz-in. At 6.0V: 2.2 kg-cm / 30.5 oz-in
Anyone here have any experience with how much force could be applied using a micro servo and if this would work? The idea would be to place the lighter and servo in a jig, and then the servo would rotate with a horn attachment that would press down the lighter button.
Hold the lighter upside down over a set of kitchen scales, and press down so that the button on the lighter is pressed by something on the pan of the scales. Note the reading on the scales when the gas valve opens. You'll probably find that it opens progressively, i.e. the harder you push, the wider it opens, until it gets to the fully open position, so decide how wide open you want it to be. Also, if you're not sticking to one particular lighter, there will probably be quite a wide variation in opening forces between different lighters, even of the same type / model, so allow a bit for that, or perhaps do tests on a number of examples of lighter.
Then measure the radius of the horn, and do the sums.
So if we assume 400 grams is needed ( as someone mentioned above) and the torque specifics of the motor, are listed " at 4.8V: 1.8 kg-cm / 25 oz-in. At 6.0V: 2.2 kg-cm / 30.5 oz-in"
And there are 28.35 grams in an ounce, x 30.5 = 864 grams,
Then if i position the horn to strike the lighter< or drive a push rod> at 1inch radius or less , then it would push with 864 grams of force < or more if a shorter radius> , which would give me more than my 400 grams needed.
So the motor rated at 30.5 oz-in should work. Am i thinking this through correctly?
Looks correct to me.
Now all that's left for you to do is actually try it out and see how it works in the real world.
Do remember to connect the servo to an outside power supply, not to the Arduino's power outputs, and to connect the grounds.
you not only have to press the butane valve, but have to roll the igniter wheel as well...
(Edit: Just saw the note about nichrome igniter... Wll that work?)
But it would still be as well to measure the lighter(s) you plan to use. These are not precision devices and a sample of one is not really enough to base a design on. The two I just tried seemed to need more like 550-600 grams to fully open. Fortunately that's still within range of your servo.
You also need to consider how long the valve must be open for. Servos don't like being held close to Stall Torque for a long time and may burn out.
For this application I'd want to suggest a linear actuator. I assume OP is only interested in on/off, which is what a solenoid is very good at. Very simple to program (just set the control pin HIGH/LOW as needed), very simple to build, probably uses less power than a servo and designed to not burn out when powered constantly.
Hi,
How long do you expect the lighter to be burning at a time, they are not built for extended lengths of time due to heat build up in the burner jet and the metal shroud.
LOL. Put an off-center wheel on a geared stepper shaft as a cam and use it to press and hold the button.
Be sure to a slippery plastic over the button so the cam doesn't wear the button down.
Thanks everyone for your feedback! getting closer to making this a reality.
It has already been done, as shown here :
But key differences I want to make are:
make it smaller, using a bic instead of a whole butane can, so way smaller flame, like a candle instead of a flamethrower.
using a smaller servo or motor, so it can fit in a smaller more compact package.
automating the process using arduino, so the whole sequence is triggered by one remote button press, which turns on motor to press bic to open gas, heats up nichrome wire, stays on for 5 seconds, then shuts down. Instead of manually controlling it with an rc transmitter.
The lighter only needs to be on for 5 secs maximum, is that too long to hold a servo at stall torque?
I am not attached to using a servo, so yes I could try a geared stepper shaft with an off center wheel. I am concerned about size, I wish to make it as small as possible. That is why I am initially attracted to the high torque, mini servo.
Or a linear actuator stepper motor slider could work, although I am having trouble finding any information in descriptions about the force ratings for linear actuators, such as this one
You'll be much better off with a solenoid type actuator. Basically an electromagnet with push rod, that's pulled down (or pushed up) when activated.
The one you link to looks pretty powerful to me, but also very slow. It'll have great position control and has a long range but you only need up and down for a few mm for your lighter, and you don't want to wait ages for that to happen.
That YouTube video is extremely dangerous as they are burning LIQUID PROPANE, not gas, hence the LARGE flame.
If you use a BIC type lighter, the construction of the lighter should not let you burn liquid PROPANE, thank goodness, but I don't know if you will get reliable ignition of gas with a hot wire.
A solenoid concept is more fail-safe than a servo or motor cam.
Power failure;
Solenoid OFF.
Motor and servo, stalled in ON.
Hi, in the video they are using butane with a nichrome wire to ignite the gas straight from the bottle, no venturi valve.
So the proof of concept is there. It works.
Yes, there is a danger of the motor burning out leaving the valve stuck open. So yes a solenoid would be best. The micro push pull i tried was not strong enough, so perhaps i could use a bigger one.
Also, i just had the idea to use mechanical leverage to amplify the power of my tiny solenoid. So I will try using the solenoid to push on a lever which will then push on the lighter.
I just wish to make it smaller and automate the whole sequence using arduino, instead of manually controlling the process via rc transmitter and receiver as they do in the video.
Sequence as follows:
one external remote button is pressed, transmitted via rf to arduino.
2)nichrome wire heats up
bic lighter valve is pressed down,
valve is kept pressed via motor for 3~4 seconds
nichrome wire shuts off
valve is no longer pressed
end sequence, ready to receive remote loop activation again
