Linear Movement

barneydog

Member
Hi all,

FINALLY!!! decided on a new project, taken long enough.

I'm deep in the stages of planning, selecting components and designing layouts. But I have come to a stop on one part and would like to ask your help.

For one part of it I need a linear upwards motion of about 10 cm, like an electric car aerial would be amazing.

Have looked into using linear servos but they are really expensive or do not move far enough at the cheaper end of the scale; also looked at lead screws connected to a stopped motor which would work brilliantly but take a large amount of space.

Telescopic would be an amazing way, but apart from a massive car aerial components, difficult to find a solution

anyone had this problem to over come before, or have ideas would be a massive help :)
 

barneydog

Member
thanks for the suggestion bear.

Sorry that was something else I looked into; decided against as it would take as much space as the lead screw. Lead screw looked the easier option to integrate and smaller space.

its going to push a small radar style dish up from inside a box
 

Buzby

Senior Member
A tightly coiled spring wire, like curtain wire, will self support vertically for a few cm. If you used the lead screw or gear rack idea horizontally you could push the spring though a 90' bend to get a vertical motion which is longer than the depth of the actuator.

Cheers,

Buzby
 

erco

Senior Member
A flat spring coiled up, like a tape measure being forced out between motorized rollers.
 

Jeremy Leach

Senior Member
Tiny electro magnets in a row that are activated in sequence by a Picaxe to push a rod. Rod has magnet and perhaps spring loaded. Theory and practice might not meet though :D
 

Buzby

Senior Member
An off-the-wall idea, a disk with the radar dish underneath.

Flip the disk, and the radar is on top.

( Got that one from Thunderbirds, via Wallace & Grommit. )
 

techElder

Well-known member
Or ...

A blow-up radar dish with a tiny air compressor in the base.

( Got that one from the "autopilot" from the movie Airplane.
 

premelec

Senior Member
With regard to linear actuation there is an interesting mechanical method used in opening and closing shop entry doors... A rotating rod with 3 wheels offset from perpendicular to the rod pressed on it with springs. Sort of virtual threads but no actual threads - if the wheels are perpendicular to the rod the rod does not move forward or backward. It is easy to limit force by spring tension on the wheels [so you don't crush anyone going through a shop door when the opener sense unit fails...].
 

Rick100

Senior Member
With regard to linear actuation there is an interesting mechanical method used in opening and closing shop entry doors... A rotating rod with 3 wheels offset from perpendicular to the rod pressed on it with springs. Sort of virtual threads but no actual threads - if the wheels are perpendicular to the rod the rod does not move forward or backward. It is easy to limit force by spring tension on the wheels [so you don't crush anyone going through a shop door when the opener sense unit fails...].
I've seen threadless linear actuators like this one to move small carriages on industrial equipment. If they overload they just slip instead of tearing something up. Very clever.

http://www.thingiverse.com/thing:112718
 

techElder

Well-known member
premelec, great idea! We used that method in a conveyor system for heavy pipe in our shop. It was amazing how much control one has on the pipe/"rod" motion by tilting/angling the rotating wheel assembly. You would have to make use of the spinning effect on the "rod"/radar dish though.

... A rotating rod with 3 wheels offset from perpendicular to the rod pressed on it with springs.
 

barneydog

Member
some very interesting ideas and some funny ones lol.

looking at sail winch servo. could attach the curtain wire to it and use that for its strength and flexibility.
 

JBrookes

Member
Hi all,

FINALLY!!! decided on a new project, taken long enough.

I'm deep in the stages of planning, selecting components and designing layouts. But I have come to a stop on one part and would like to ask your help.

For one part of it I need a linear upwards motion of about 10 cm, like an electric car aerial would be amazing.

----CUT.....

With mechanical means, your space, weight, force requirements are important, and I'm noty sure what they are, So...
Here is one idea:
I'd look at a threaded rod and nut. A stepper driven by picaxe pulses from Piocaxe can work. A regular nut will have backlash, but not a problem in unidirectional movement.
Another nut can provide guidance.

The problem of this is the threaded rod is it takes up space.
The advantage is it's easy to do.
 

barneydog

Member
finally everything arrived and i had time today to get it all setup and running.

the code is working up until the point of the actual stepper motor turning.

So when the input goes high to trigger the motor and the leds, the uln board flashes its leds as its trying to do something but the actual motor does not turn. when input goes low, uln board flashes leds go off but no motor turn.

I have tried different delays from 75, 100, 500 but no difference motor still will not turn. I have a second motor and board tried them; same results.

Included is the schematics and also the code, if you do not mind having a look for me :)

motor_schematics.png

'14m2 R2D2 Head Periscope
'For use 14m2, connected to
'Outputs B.1 - Servo, B.2 - White LED, B.3 - Red LED, B.4+B.5 - Stepper Motor
'Created 06-09-2015
'By James Ward
'Using Picaxe Editor 6.0.7.5(Beta)
'

symbol step_count = b0

main:
let dirsB = 255
let dirsC = 1
let step_count = 0
low B.0, B.1, B.2, B.3, B.4, B.5, B.2
servo B.1, 150

waiting_input:
if pinC.1=1 then
gosub periscope_motor_up
pause 1000
gosub periscope_led_turn
pause 1000
gosub periscope_motor_down
pause 1000
goto waiting_input
end if
goto waiting_input


periscope_motor_down:
if step_count > 0 then
toggle B.5
pause 75
toggle B.4
pause 75
dec step_count
goto periscope_motor_down
end if
low B.4, B.5
return

periscope_led_turn:
high B.2, B.3
if pinC.1=1 then
servopos B.1, 75
pause 500
servopos B.1, 224
pause 500
goto periscope_led_turn
end if
servopos B.1, 150
low B.2, B.3
return

periscope_motor_up:
inc step_count
toggle B.4
pause 75
toggle B.5
pause 75
if step_count = 10 then
low B.4, B.5
return
end if
goto periscope_motor_up


#no_data 'reduce download time
 

Circuit

Senior Member
You have components missing from your circuit diagram; see PICAXE Manual 3 page 16; you need outputs 7 and 8 of the ULN2003 fed back to pins 1 and 4 in order to activate all four coils in the correct order. In fact, the input order is wrong also. I am assuming that this is a unipolar motor; if you only have four wires then it is a bipolar motor and needs a rather different approach; four wires means two coils and these require a change in polarity to activate the motor. If this is the case then you need to look at the circuit on page 16 of manual 3 - this requires a different chip that can reverse the polarity on each coil in sequence.
 

barneydog

Member
Stepper Motor 28BYJ-48 + ULN2003 Driver Module Board is what im using.

I will check the manual again and have a rethink
 

barneydog

Member
having read through the manual. using the ULN2003 board provided, I will need the 4 outputs and cant join them together. is that correct or am I misunderstanding it again
 
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