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Linear Actuator

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Is it OK to connect the 12V Supply directly to the Actuator, and not via a relay?

That depends on the version you get. For versions B, S, and P you will need something to interrupt power to the actuator. However, I think you are referring only to version I. For that version, you can leave the power attached and the drive will not function without a signal. For either microcontroller or 555 control, you would be using the RC or PWM mode. Is the speed OK for you? The fastest is 11 mm/S, which is pretty slow compared to a standard servo.

John
 
Hi John,
Thanks a lot!

Yes, i'm interested in I mode.

The reason for my question is due to what the Datasheet says:

"When the actuator is powered up, it will repeatedly scan leads 1, 2, 4 for an input signal that is valid under any of the four supported interface modes.
When a valid signal is detected, the actuator will self-configure to the corresponding interface mode, and all other interface modes and input leads are disabled until the actuator is next powered on.
"
 
Yes, I read that, which is why at power up, I assume it just idles, much like an RC servo idles without a signal. An RC servo when powered without a signal may turn a little in an unpredictable direction, but it will still be easily moved by hand. That is, it is not "stalled," and there is no opposing force that resists moving it by hand to any position.

Since you do not know in which direction it will move, if any, I suggest having a signal for the open position sent at power up. You can then turn off that signal or keep it on. If you turn it off, the device will be dead and act as if there is no power to it. If you give a continuous signal, it will move to the appropriate position and will require substantially more force to move it from that position. If you are using PWM for the signal, the datasheet doesn't say how the device will behave. Will it interpret "no signal" at start up as zero PWM and forcibly move to the open position? I doubt it, as it will be scanning for a signal. Once it gets a signal, then turning off the signal entirely may make it move to the zero PWM position. I don't see that that will make any difference. Your concern should be the stalled position (i.e., the force against movement exceeds the motor's ability to move it).

John
 
What actuator? L16-P? Stroke?

Note you need the LAC board with the L16. The internal board available with some other actuators does not allow PWM.

The internal board available on some actuators don't accept PWM as input.

Before you key too carried away, you need to find:
1. The stroke of the push button.
2. The push button size (round, square?)
3. The force to operate the push button

The actuator stroke will have to be longer than the push button stroke.

Here is a spring calculator: https://acxesspring.com/spring-calculator.html

F=kx where x is displacement for a spring.

Spring vendors are another issue.

If you have to push this to management, I would add the fact that the LAC board contains stall protection and electronic limits.

Your conceptual design has to include a "Local Push button"

Your programming has to assume that a power failure happened just as the actuator was fully extended. i.e. On BBB power up the actuators have to retract.

It's noted that "stall" is not reportable with the boards.

Let's ask, how might you set/adjust the limits?
e.g. (just an example) Position at touch
Spring Travel
Spring k constant
Button travel

Gotta go.
 
john

I thought I read that the actuator will stay at the current position when powered off and will resist up until the max force it usually can resist. The question is, what position is 0 PWM which is at power up? Something is missing in the datasheets like "Power up behavior" when powered down at some position.

The board seems to lack a NOT ENABLE input too although 0V, 0 Ma, 0 PWM can be considered stay at the same position at power up, until one is commanded to move, Then that mode is selected. If PWM is used to move the actuator, then 0 PWM is considered 0 position.
 
At power on, the device doesn't know or hasn't determined whether it is PWM, RC servo, voltage , or current controlled. Once one line shows a signal, then the device switches to that mode. Presumably, the PWM mode must show a non-zero value at some point. Zero PWM is fully retracted, as is 1 mS in the RC servo mode, as I read the datasheet.

At first. I thought the actuator may have been a worm gear or screw drive, which would give tremendous resistance to movement when turned off. Now, I think it may just be a spur gear and rack. Still, the ratio is pretty high to get 1 second for 11 mm, so passive resistance is probably pretty high.

As a premise, I would not recommend designing something to duplicate the actions of a human fingers, i.e., pushing a key. But since electroRF seems intent on doing that, I think the type "I" device (i.e., a servo with either PWM or pulse time control) is the way to go. Since current draw on the signal is probably negligible, except for the current mode, I have a hard time understanding why we are even discussing a signal-off condition.

John
 
John:

Power on SEEMS well defined which I interpret as mode selected by first non-zero signal.

Power down seems not well defined. The info shows it keeps the position with the same resistance to movement.

In USB, RC and 4-20 mA, it's possible to have an OFF state which could mean STAY AT POSITION.

Verified - No

For PWM or voltage mode there is no OFF state. As the BBB and actuator controller are powering down there could be movement toward 0 position.

Controlled power down MAY not be possible without cutting power to the actuator.

What is the effect of power fail? We can assume no Power switch for now.

Power Fail could occur at any time. At rest. During movement. At full button press.

What I think this says is that the BBB has to reliably detect a power up which usually means a good power on reset IC and it must command the actuator to the retracted position (touching the power swich at a minimum) on power up.
 
Me again. I see where you wanted to use the L12 series actuator.

Here's a quote from the datasheet:

PWM Mode: This mode allows control of
the actuator using a single digital output
pin from an external microcontroller. The
desired actuator position is encoded as
the duty cycle of a 5 Volt 1 kHz square wave

on actuator lead 2, where the % duty cycle
sets the actuator position to the same %
of full stroke extension. The waveform
must be 0V to +5V in order to access the
full stroke range of the actuator.

A square wave by definition is a 50% duty cycle wave, so how can you encode anything?
They should have said rectangular.

You will also need some sort of level translator to get from 3.3 V of the BBB to 5V. Can I assume that the BBB is Beagle Board Black?

Under the 0-5 V section:

and I quote again:

The setpoint voltage must be held on
lead 2 until the desired actuator stroke po-
sition is reached. Lead 2 is a high imped-
ance input.

So, what does that mean?

Does "disconnecting" mean the position will "stay" or does disconnecting mean it would go to zero if using this mode? Same question is true for PWM.

The integrated controller lacks stall protection:

Stalling the actuator under power for short peri-
ods of time (several seconds) will not damage the
actuator.

I think they did a pretty good job, but I'll analyze details like no tomorrow.

In your situation, actuator movement toward retract 0% on power down is not an issue if it happens at all. I would have made the 0-5 V linear mode, a 1 to 5V signal, so that 0 V is OFF.

Electrical limits don't exist in the internal version.

Other general comments about their controllers (embedded or otherwise) is:
a) A NOT ENABLE pin would be useful. 99% of the time it could stay at ground.
b) A STALL or NOT STALL output would also be useful.
c) DIRECTION AWAY FROM STALL would also be useful.
d) USB should also implement a, b and c.
e) A 5 V Ref signal so level translation would be easier.

Probably around 100 g-force or less is a ball park number for push button activation. I was unable to find any PC power switch specs.

Here is a force conversion website http://www.unitconversion.org/unit_converter/force.html and 100 g-f is about 1 Newton so you could really smash the button.
 
Me again. I see where you wanted to use the L12 series actuator.

Here's a quote from the datasheet:



A square wave by definition is a 50% duty cycle wave, so how can you encode anything?
They should have said rectangular.

You will also need some sort of level translator to get from 3.3 V of the BBB to 5V. Can I assume that the BBB is Beagle Board Black?

Under the 0-5 V section:

and I quote again:



So, what does that mean?

Does "disconnecting" mean the position will "stay" or does disconnecting mean it would go to zero if using this mode? Same question is true for PWM.

The integrated controller lacks stall protection:



I think they did a pretty good job, but I'll analyze details like no tomorrow.

In your situation, actuator movement toward retract 0% on power down is not an issue if it happens at all. I would have made the 0-5 V linear mode, a 1 to 5V signal, so that 0 V is OFF.

Electrical limits don't exist in the internal version.

Other general comments about their controllers (embedded or otherwise) is:
a) A NOT ENABLE pin would be useful. 99% of the time it could stay at ground.
b) A STALL or NOT STALL output would also be useful.
c) DIRECTION AWAY FROM STALL would also be useful.
d) USB should also implement a, b and c.
e) A 5 V Ref signal so level translation would be easier.

Probably around 100 g-force or less is a ball park number for push button activation. I was unable to find any PC power switch specs.

Here is a force conversion website http://www.unitconversion.org/unit_converter/force.html and 100 g-f is about 1 Newton so you could really smash the button.


Hi,

Yes but when you see "square wave" and "duty cycle" in the same sentence that usually implies that it is really a rectangular wave. We find this slight of pen from time to time in the literature.
Maybe a better way of explaining it would have been to say that it is a pulse duty cycle modulation, but im sure there are other ways too.
 
Hi,
KISS, Jon, MrAl
I thank you so much.

I ordered the BeagleBone Black, and the **broken link removed**

Thank you KISS for noticing I'll need a level-shifter 3.3V -> 5V.

It seems i'm gonna have some hard time when it arrives, and will need to work it out.

I very appreciate your advices, and i'm gonna update you all on the progress.
 
Springs

I tool a look at my "junk box" and found a spring about 1/4" diameter, 0.026 diameter wire and 12 coils/inch that seemed to work on a tact switch, The deflection seemed to be OK,like 4-5 mm eyeballed, not measured. It was just too long, About 2 inches.

The mounting scheme could be a spacer of the right ID. I tried a 0.187 hex spacer and it seemed to hold. I'd probably use a bit of epoxy.
 
Hi,
KISS, Jon, MrAl
I thank you so much.

I ordered the BeagleBone Black, and the **broken link removed**

Thank you KISS for noticing I'll need a level-shifter 3.3V -> 5V.

It seems i'm gonna have some hard time when it arrives, and will need to work it out.

I very appreciate your advices, and i'm gonna update you all on the progress.


Hi again,

You are welcome, and do you think you can post a few pictures when you get this thing build so we can see what we helped with? Thanks much if you can, as it would be nice to see it in real life now.
 
Hi,

With everyone here helping you i dont see how it can fail although it may take some trial and error.
 
Hi
Were you able to complete this project ?
I am looking to develop a similar button push actuator. Would like to learn from your experience. Can u share an update ?

Hi,

With everyone here helping you i dont see how it can fail although it may take some trial and error.
i
 
This thread ended over 2 years ago. If you have a similar question, the recommended practice is to start your own thread. You can put a link to this thread in your first post as a reference.

ak
 
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