Ideas for raising and lowering lightweight piece of ply using a motor

Hi all,

I need to regularly (daily) cover and uncover a space (in a chicken coop) about 300mm x 300mm using a piece of ply or masonite.

The coop only allows for the cover to be pivoted across the top of the space. (Think dog-door flap).

I have a 12VDC reversible motor (70RPM) which will do the trick. I was thinking of simply putting a spool on the shaft of the motor and pulley above the flap and rotating the motor to wind in (and wind out) some cable (yarn, fishing line, braided wire).

The distance to be wound in/out would be about 400mm. A spool of 10mm diameter at 70RPM would wind that in in about 12 seconds which is fine. I’d use microswitches as a trigger to stop the motor.

Does anyone have any thoughts on:

  1. What to use as a spool
  2. How to fix the spool to the motor shaft (4mm D-shaped)

Any other advice would be great.

Thanks,
Scott

ps. the purple door is what I need to raise/lower.

A simple way to make a spool is to cut a section from a dowel rod or brush handle and attach a thin ply disk at each end to prevent the string falling off. Another possibility is a cotton reel.

You will need bearings to take the force from lifting the lid so get some sort of steel rod that can be used as an axle through the spool. Then you need something to couple the steel rod to the motor. You can buy couplers - they are commonly used with 3D printers. Or you could make one from a piece of tube - metal is probably best if the torque is significant.

...R

Seriously, you need to beef up your metal-working shop, or find a friend with one. You won't find hobby shop stuff to do what you are asking.

Pau

PS: is it your intention to leave the motor powered in order to hold the door open?l

I'd suggest using a sealed actuator to pull a short piece of rope attached fairly close to the hinge.

A sealed actuator won't rust in weeks/months like a small hobby motor will when exposed to the elements
and moist outdoor air. The piece of rope prevents the actuator from forcing the door closed (safety
issue). You can omit the rope it this is not a concern.

Actuators already have limit switches, available in many sizes and powers, one common use is opening
windows and some may already have mounting hardware options for this use.

A winch system is quite complicated to design and make, and you may have teething troubles with it.

I've used a thread/craft spool hot glued to a servo horn like below for winding string. If you counter weight the door (paint sturing stick glued vertically to the outside of the door with a weight on the end), then very little force will be needed to operate the door. If the door is counter weighted, I'd look at just using a servo to operate the door with a wire linkage, somewhat like operating an elevator on an RC airplane. If you use the forum search feature in the upper right of this page and search for "coop", you will find many years of discussion on coop doors (weighing bee hives is also a popular topic).

servoblind3.jpg

servoblind3.jpg

Thanks for the suggestions. I guess it is a coop door, just an internal one. The chickens are sleeping in the laying box and that's what I need to seal overnight.

I do have a couple of linear actuators, and was actually using one to open/close my old coop's outer door. This was bolted directly to the door.

I do like the idea of an actuator simply pulling a string (to open) the door. I'll counterweight it such that it will close as the actuator extends. One advantage to this is that a chicken that may get trapped by the closed door can simply push the door to get out (which would be impossible with the actuator arm directly attached). Another advantage is that I won't require any sensors to limit the operation of the actuator as it doesn't matter if it lets out too much string during closing (it'll just go slack).

My maths tells me that with an actuator arm travel of 150mm, I would need to attached the string/wire at a point 95.5mm from the hinge to get a 90deg. rotation.

Cheers

You probably could hot glue a craft stick on a standard hobby servo horn similar to the below sail arm servo, and tie a string from the door to the stick end to lift and lower the door. Servos are very simple to work with.

https://www.towerhobbies.com/cgi-bin/wti0001p?I=HRCM3765

You need care with servos not to burn them out by having too much torque. They also burn power continuously, whereas actuators shutoff at the endstop and can't be back-driven.

When you say that servos

MarkT:
burn power continuously

do you mean because if their built-in control circuitry? I'm not overly familiar with servos.

Thanks

"do you mean because if their built-in control circuitry? I'm not overly familiar with servos."

I tested a typical TS-53 standard servo current draw while being supplied 5v and not being sent a control signal and it was 10.4 ma.

Interesting Not important for my installation which will be mains powered but for RC stuff that's quite an impact. Thanks.