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3 linear actuators in parallel to lift a small mass. can this be done easily?

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lots o' tots

New Member
Hello all.
I want to start off by saying that I am a very beginner level hobbyist.
I am looking to hook up 3 linear actuators (or something similar) in a simple toggle switch circuit. I do not need to control the actuator speed, so no control boards are desired. The simpler the better. Just a simple on and off, most likely using a DPDT switch.
The goal is to lift (push) a metal tray with a sample that weighs 50 grams in the air so that it is above a precision balance. I want to weigh the tray and sample but it will be inside an environmental chamber so i can't open the door which is the reason for using an linear actuator or something similar. After weighing, i would like to lift the tray back in the air so the balance is at 0 g.

Limitations/requirements:
  1. My total height cannot be more than 4" which includes the extension.
  2. Currently, I have 2 wires available to me that passes from the outside to the inside of the chamber. I can make more openings but only if i have not other choice. It is a real pain in the butt to do.
  3. 3 actuators will have to work in parallel. Exact timing is not critical as i believe there is a small amount of room for error, but it should be pretty close so that an object can be lifted.
  4. Duty cycle is not important. It may be cycled ~100 times in ~2 months. that is about it.

I was looking at two types of linear actuators
http://www.robotshop.com/ca/en/firg...-12v-potentiometer.html#Supplier-Product-Code

and

No laughing, but i was looking at the LEGO linear actuator. they are hard to find, but still out there.
due to low duty cycle and lifting such a small mass, maybe this can work

http://www.robotshop.com/blog/en/lego-linear-actuator-3837

Can this be done? If so, could you please direct me how this sort of thing is wired or any other useful information.

thanks for your time
 

cowboybob

Well-Known Member
Most Helpful Member
Welcome to ETO, lots o' tots!

Given your specs and examples, this actuator seems to best fit your requirements. Price may be a deterrent. I didn't thoroughly search for examples.

Simple ± 12VDC forward/reverse actuation, limit switch control and adequate range.

Wiring simple. Once you decide on a device, we'll be glad to help with control wiring.
 

cowboybob

Well-Known Member
Most Helpful Member
... My total height cannot be more than 4" which includes the extension. ...
Misread this spec. as a "4" extension. Anyway...

These units are designed work with just a two wire arrangement to the motor, like this:
upload_2017-5-21_19-5-17.png
(limit switches are not displayed, as there is no need - they are internally configured to perform as below).

When powered, the actuator shaft fully extends (or retracts) until the limit switch for that direction is tripped, causing the motor to stop.

When you reverse (or "toggle") the DPDT switch, the shaft goes fully in the opposite direction until, as above, the other limit switch is tripped.

If you use a DPDT switch with a "Center OFF" position (3 positions total), you can easily remove all power from the circuit.

All three actuators can be wired in parallel.
 

lots o' tots

New Member
there seems to be alot of switch options. which should be used? also is there a similar drawings that shows how this is wired in parallel ?
 

cowboybob

Well-Known Member
Most Helpful Member
This is just an example switch. Stall current for the actuator you want is only 200mA (@ 12VDC) so this switch is more than adequate. The "center OFF" option is just a suggestion - it is not a requirement. Just my conservative way of doing things such that ALL power is removed from within the environmental chamber when not moving the weigh tray.

Matched to the previous wiring schematic, below is an example of parallel wiring:
upload_2017-5-22_8-30-54.png

<EDIT> If the "Momentary" feature (you have to hold the switch in position until the actuator is fully extended/retracted) annoys you, this switch might might better suit your needs.
 
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Colin

Active Member
Just use an arm on a servo motor. It costs just $2.00
Connect the wires directly to the motor. It will be very fast acting on 5v.
 

lots o' tots

New Member
would the servo motor will be too fast acting? i dont want the sample to fly in the air. also as interesting as it sounds, i unfortunately have to keep my labor time on this down to save cost. good suggestion though

is that switch a non-momentary switch? I don't want to hold the button. I suppose if you turn it ot the off position, it will not move. Is the is correct?
 
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Pommie

Well-Known Member
Most Helpful Member
Agree with Colin. If a 3 armed lifter is above the mass then the servo will easily lift it. Small problem is the servo needs 3 connections, 5V, Gnd and signal. However, you may be able to use the body of the device as the ground connection.

Edit, by lifter I was thinking 3 bit's of wire twisted together at one end and bent under the "plate" at the other end so as to form a pyramid.

Edit2, go to your local model shop, buy servo, battery and servo tester and have a play. Probable <$30 all up.

Mike.
 

lots o' tots

New Member
It worked like a charm!. Thanks.

i have a side question. i have a peltier cooler that draws 11amps at 12volts. The wire is 6" long and only 22 gauge to my disappointment. I have checked out some wire charts online for DC power and the extension would bring this near the capacity of the wire (especially since it will be embedded in insulation). I need to extend the 6" wires to a total length of 2 feet.. Can i use a thicker gauge wire closer to the power supply? I have 16 gauge stranded lying around. Do the wires need to be soldered? I wanted to just use wire nuts and no soldering if possible. I am not interested in aesthetic value.

Please let me know if this extension using a 16 gauge stranded wire with wire nuts and no solder is safe.
Thanks
 

Pommie

Well-Known Member
Most Helpful Member
I would shorten the 22g wire to around 3" and extend with the 16g and try it. I hope you have a very good fanned heatsink on the hot side otherwise that peltier will run extremely hot and melt it's own soldered connections.

BTW, what solution did you go for? Could you use the chassis as the GND connection?

Mike.
 

lots o' tots

New Member
I would shorten the 22g wire to around 3" and extend with the 16g and try it. I hope you have a very good fanned heatsink on the hot side otherwise that peltier will run extremely hot and melt it's own soldered connections.

BTW, what solution did you go for? Could you use the chassis as the GND connection?

Mike.
i do have 2 large computer/fan heatsinks with copper pipes at the block on both sides held together with arctic silver 5 thermal paste and zip ties. It is quite incredible that if they are sized or oversized well, it does not get too hot, just slightly warm. I was careful to try and not insulate around the solder connections to not melt it. the insulation between the two heatsinks was a foam sheet i bought at the dollar store
I ended up cutting the 22gauge down to 5" or so and connecting a 12" 16gauge using a spade type crimp connector. The solution actually worked quite nicely and would consider doing it again in the future. I did not use the chassis as a ground. (can you even do that?)
 
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