18" linear actuator help

[boyntonstu]

I am looking for ways to raise and lower an upside down periscope video camera.

What comes to mind is a power antenna from a car or a power trunk lifter; both 12V.

My boat is 12 Volts.

Any DIY ideas or products?

BoyntonStu

P.S. On Tuesday made the semi-finals in Tampa for the ABC's American Inventor show!!!

[patmat2350]

The antenna sounds good to me... check for new ones at any auto parts store or jcwhitney.com, or your local junkyard. Just loosely coil the camera lead around antenna.
Or, modify a servo to act as a mutiple-turn winch; make a loosely telescoping mast from brass tubes with a heavy weight on the end (gravity fall, winch it up).
PM

[boyntonstu]

Thanks,


Good idea.

A reversing esc would allow up/down.


A square tube for the perisciope with window out the side would be great.

The "tube" into which it slides need not be complete, [ with a little return would allow the camera to 'see' out.

Know of a good reversing esc?


BoyntonStu

[patmat2350]

Don't need an ESC, just get a servo. Attach the winch drum to the output end; "hack" the servo by disconnecting the position sensing pot, then as long as the Tx stick is held to one side or the other, the servo will run continuously that way.

PM

[LtDoc]

Or, a 'take-off' on another telescoping device, using 'all-thread' and a 'nut'. The 'all-thread' spins, raising and lowering the 'nut' attached to the moving section of tubing. The tubing (whatever shape) doesn't do any turning so could have conductors glued/molded into it's surface for connection to the camera. Works okay in air, not sure about water - lol.
- 'Doc

[Umi_Ryuzuki]

What they said... :)

Use the servo to spin the all thread clockwise or anti clockwise, and that will run the nut, or threaded insert up and down the thread.

:cool:

[boyntonstu]

What they said... :)

Use the servo to spin the all thread clockwise or anti clockwise, and that will run the nut, or threaded insert up and down the thread.

:cool:

OK

I use the servo as a motor. I am a newbie to RC.

Does the transmitter control forward and reverse?

[Umi_Ryuzuki]

OK

I use the servo as a motor. I am a newbie to RC.

Does the transmitter control forward and reverse?

Yes servos operate in both directions, and are controlled by the transmitter.

A sail winch drum servo will rotate continuously either direction out of the box, and have plenty of torque.

Most other standard servos need to be modified to be able to run in this manner.

something similar to this
http://www.geocities.com/patsmodels/servo/
http://www.mhsd.org/model/howto/servo.htm
http://www.rcgroups.com/forums/showpost.php?p=7130746&postcount=40

[boyntonstu]

Yes servos operate in both directions, and are controlled by the transmitter.

A sail winch drum servo will rotate continuously either direction out of the box, and have plenty of torque.

Most other standard servos need to be modified to be able to run in this manner.

something similar to this
http://www.geocities.com/patsmodels/servo/
http://www.mhsd.org/model/howto/servo.htm
http://www.rcgroups.com/forums/showpost.php?p=7130746&postcount=40


Thanks,

That is a big help.

What about limit stops?


How do you limit the lift distance if you are winching the periscope?

BoyntonStu

[Umi_Ryuzuki]

You would have to create your own limit switches.
Perhaps some switches that ground the circuit once it reaches its extents.

[MILLERTIME]

Parallax (Futaba) Continuous Rotation Servo. $12.95

http://www.parallax.com/detail.asp?product_id=900-00008

[Kmot]

GWS, of foamie airplane fame, is also coming out with a continuous rotation servo:

[boyntonstu]

Thanks again.

Servos receive a number of pulses to move.

Is there an adjustable pulse counter so that one could limit the number of

pulses/revolutions/periscope travel?

This would be better than a limit switch IMHO.

[patmat2350]

Servos receive a constant pulse train at 50 Hz (20 ms intervals), with pulses usually varying from 1 to 2 ms, and 1.5 ms is "center".
Normal servo with a limited throw will move to a specific position based on the length of the pulses.
Sail winch servos have, instead maybe a 120° throw, maybe 5 full revolutions. But again, the target position is fixed by the pulse length.

If you hack a servo by disconnecting the position sensing pot, then any stick motion will make the servo spin continuously one way or the other, with no stopping. In this case, you either move the stick to neutral when things get where you want them, or you set up limit switches... your choice.

PM

[Brooks]

Blue Point Engineering makes a device that de-sensitizes the "center=neutral" stick position, esentially widening the neutral boundary. This is handy because once you remove the pot from the feedback circuit (to make the servo continuously rotatable), the center neutral can become tricky to find when you want to stop rotation.

For a jack screw arrangement without limit switches, how about making the connection slippable? Rather than connecting the nut to the servo with gears, use a pully on the servo (cut a pully groove in the nut) and connect both with a rubberband. This way you can simplify your system: merely time the normal rise/fall and then count to yourself when operating the periscope. If you get off a second or two, the rubberband will just slip, so no harm comes.

servo neutralizer for center-desensitizing, servo stretcher to double normal servo throw:
http://www.bpesolutions.com/rcequip.html

[boyntonstu]

Blue Point Engineering makes a device that de-sensitizes the "center=neutral" stick position, esentially widening the neutral boundary. This is handy because once you remove the pot from the feedback circuit (to make the servo continuously rotatable), the center neutral can become tricky to find when you want to stop rotation.

For a jack screw arrangement without limit switches, how about making the connection slippable? Rather than connecting the nut to the servo with gears, use a pully on the servo (cut a pully groove in the nut) and connect both with a rubberband. This way you can simplify your system: merely time the normal rise/fall and then count to yourself when operating the periscope. If you get off a second or two, the rubberband will just slip, so no harm comes.

servo neutralizer for center-desensitizing, servo stretcher to double normal servo throw:
http://www.bpesolutions.com/rcequip.html


Any slip clutches or designs?

Like a torque setting on an electric drill/screwdriver.


Reach the limit and the servo slips.

What happens if the servo runs against a 'stop'?

Will it stall and/or burn out?

[Brooks]

If a servo reaches some physical barrier to further rotation before the pot tells it to stop, several undesirable things happen: a) it will try to rotate further and this "stalls" the servo; it draws excess current trying to turn further, which would wear out your batteries faster than normal. b) the torque will try to twist the servo mount out of allignment, racking the system, possibly causing damage. c)while I've never stripped servo gears with a stall, I suppose it's possible (my gear dammage has only happened when the servo experienced some sort of shock loading; metal gears are more resistant to stripping).

I think it's best to design to avoid the stall, or at least make the system slippable to absorb the momentary stall until you get your thumb off the joystick. If there is a lot of resistance to raising the periscope, and you have to use a high torque servo, then maybe it would be better to install limit switches. Of course, lots of resistance will eat up amps, making the batteries wear out, so it would pay to work on the mechanical aspects of your design to make it as free-moving as possible.

[boyntonstu]

If a servo reaches some physical barrier to further rotation before the pot tells it to stop, several undesirable things happen: a) it will try to rotate further and this "stalls" the servo; it draws excess current trying to turn further, which would wear out your batteries faster than normal. b) the torque will try to twist the servo mount out of allignment, racking the system, possibly causing damage. c)while I've never stripped servo gears with a stall, I suppose it's possible (my gear dammage has only happened when the servo experienced some sort of shock loading; metal gears are more resistant to stripping).

I think it's best to design to avoid the stall, or at least make the system slippable to absorb the momentary stall until you get your thumb off the joystick. If there is a lot of resistance to raising the periscope, and you have to use a high torque servo, then maybe it would be better to install limit switches. Of course, lots of resistance will eat up amps, making the batteries wear out, so it would pay to work on the mechanical aspects of your design to make it as free-moving as possible.


Would this slipper clutch on Ebay be applicable? 130106572404

Unfortunately for the servos, the boat will be carrying a pair of SLA 6 Volt 4-6 Ah batteries and high current draw will be possible.

In order to have a limit switch, a multi-wire controller is needed, I believe.

In order to come down, and release the up limit.

These are photos of my $100 elevator. It stops automatically at the top with a limit switch.

[Umi_Ryuzuki]

The servos will only draw as much power as they need. So the battery doesn't matter.
I run servos on 6v gel cells all the time. 4-7ahr.

It is just better not to stall them. Since you have the elevator limit switches figured out, the periscope limit switches should be simple.

Just take the time to explain how the limit switches work for the rest of us. :p

[boyntonstu]

The servos will only draw as much power as they need. So the battery doesn't matter.
I run servos on 6v gel cells all the time. 4-7ahr.

It is just better not to stall them. Since you have the elevator limit switches figured out, the periscope limit switches should be simple.

Just take the time to explain how the limit switches work for the rest of us. :p


There is a $59.00 Harbor Freight 3/4 hp 440 pound capacity hoist at the top.

(Aren't hobby motors expensive!!?)


It reverses via the switch in the yellow controller handle. (BTW I paralleled the switch to 2 wall switches to send the empty elevator up or down.)


When the elevator reaches the top, there is a red disk that is wider than a pivoting bale. When the disk hits the bale, the pivoting arm pushes a NC micro-switch and it opens. Thus the hoist cannot pull into itself and burn out.

The elevator cannot go up further and can only go down. When it does, a spring return the bale to neutral and the upper limit switch is now closed.

I call it my "Dental Floss" elevator because if the winch cable breaks, it brakes.


In use almost 5 years. Lifts 350 pounds, 8 feet in 12 seconds.

My funnest project.

My best invention is now (as of Tuesday) in the Tampa semi-finalist category in ABC's American Inventor.

Wish us luck!

Stu