New Periscope Lift Mech Prototype
I’ve been busy prototyping a new periscope lift mechanism for Artoo.
Some of you may remember my earlier posts and videos demonstrating a mechanism I’d purchased from Daniel, unfortunately I gave up on it a very long time ago. In my opinion the design was flawed from the start and I never did get it to work well, but not for the lack of trying on my part.
Now that I’ve finished adding servos to the dome I was anxious to get the periscope working. I remembered seeing photos of Wayne Orr’s lift mech and thought I’d try and do something similar. Rather than fabricate something new he uses a drawer slide as the basis for the design and a small motor to hoist the periscope up on a platform.
The only catch with Wayne’s implementation is that the periscope and life form scanner mechanisms extend deep into the droids body. I don’t have this luxury as I’ve left the top ring cross bar in place to support the slip ring. So anything I come up with would have to fit within the approximate 10″ height restriction of the dome. The periscope assembly itself is around 6″ tall, so that would be the minimum requirement but if I could get more height that would be a plus as I could add an additional riser or have room for a servo to rotate the periscope once extended.
I’d shopped around and bought a selection of drawer slides, but couldn’t find anything shorter than 16 inches locally. Once I had them on the workbench I realized that it really didn’t matter because whatever extended out would need to be hacked off anyway. In the end I picked a 20 inch slider made by KV because it’s two sliding components worked in lock step, which was important to my design.
I removed the stops and hacked it down to just over 10 inches and cut a small section of the inner slider that would run up and down on the sliding bearing, which itself ran inside main track.
This is the start point with the slider on the right
And it extended all the way to the left. Notice the two part slider has moved and not just one piece.
Unfortunately I have to jump a few steps as I didn’t take many photos of my late night tinkering with the lift platform and various iterations of how I tried to move it.
I’d originally added a roller to the top (similar to Wayne’s) which would guide the rope, but in the final design it wasn’t really needed – and currently acts as the end stop.
Right now I have a fixed motor on the lift platform that pulls itself up with a piece of string attached to the top of the slider. It uses gravity to lower itself back down as the motor unwinds the string.
I’m using a small Vex motor, but basically it’s a servo that can continuously rotate, so I can plug it directly into my receiver without the need for a speed controller.
It looks like the platform is sloping in this photo, but I’m hoping it’s just the angle of the shot 🙂
Here’s a short video of it in action
I have a lot more work to do on this and not sure how well it will work inside Artoo, especially at an angle. My short list of things to work are:
- Add support to help stop the drawer slide shaking.
- Extra weight to the platform to help it lower.
- Make sure it’s all level
- Limit switches to stop the motor
- Possibly automate with the PICAXE micro-controller, rather than control it manually via the Futaba transmitter.
In closing I also wanted to mention that I’d experimenting with having a spring loaded wheel on the motor (same position as it is now) that would run along the side of the drawer slide to pull the platform along. I still like the idea and may give it another try later. It definitely had a smoother action and having a wheel on the motor made the lift a little faster – Unfortunately I couldn’t get the spring mechanism to work right.
Posted by Chris on July 22nd, 2008 in Dome, Electronics | 10 Comments
Tags: Dome, gadgets, lift mech, lifter, periscope, servo, servos
Exavior remarks on July 23rd, 2008 at 6:26 pm
You can increase the speed at which the lift rises by increasing your spool diameter. That way each rotation of the motor will spool up more string. (But as the spool diameter increases, so does the demand for torque on the motor)
You’ll also want a riser that is about equal to the height of the drawer slider, so the resting/lowered position has the periscope top at the very top, above the roller. (flush with the dome) That should also give you the extra weight you wanted to increase the dropping speed.
Looking good!
/Chris
Chris remarks on July 23rd, 2008 at 6:29 pm
thanks for the tips, but i already figure this out a long time ago. don’t forget this is just a prototype and i’ll be adding the extra riser to the periscope assembly and fixing the position. i’m currently working on adding a small servo hidden in the riser 🙂
Exavior remarks on July 23rd, 2008 at 6:45 pm
Figured as much 😀
I’ve been working on plans for a system that uses a worm/screw drive and a hollow riser, stabilized with 2 drawer sliders.
As soon as I get the time, I’ll post some 3D models of it on the forums.
I love how everyone has their own approach to things like this. Can’t wait to see where this design takes you. You’re off to a great start!
/Chris
Chris remarks on July 23rd, 2008 at 9:26 pm
sounds good. i’d considered a worm gear as well as a rack and pinion, but i saw Wayne’s design and knew I had the parts handy or could get them locally for very cheap.
the advantage of the worm gear over a rack and pinion is that it will hold itself in position without power being applied. the ‘servo’ motor i’m using also locks itself in position so as long as i don’t overload it, i don’t think it will have problem holding the periscope up.
Paul Novak remarks on July 24th, 2008 at 3:01 am
Of course you’ll be bringing R2 down to the local swamp for a real test when this is installed, right? 😉
Chris remarks on July 24th, 2008 at 12:59 pm
Of course 🙂
Which reminds me, I’ve been trying to figure out how I can get him down onto the local beach for a photo shoot. It has some great sandy cliffs that would make for a good backdrop – but there’s no real access road.
Paul Novak remarks on July 24th, 2008 at 2:52 pm
At the rate you are going, you’ll be the first with the rockets in the legs. Problem solved!
Thomas remarks on July 28th, 2008 at 10:25 pm
Very impressive chris!!!! Your prototype has given me a few ideas. Not sure if I’ll have time to finish my periscope before my first (R2) Sci-fi Con, but will certainly try.
Ilya B. remarks on August 8th, 2008 at 11:05 am
Greetings!
But why don’t you try to put a rubber wheel on the end of servo shaft, just like you do in R2 dome? As I could see, the slider frame is stationary, so it could be a good rail for a wheel. Wheel should be in touch with slider frame, “ride” on it up and down, and pulls whole platform. When you put rubber ring on the end of servo shaft, you don’t need that piece of string any more and don’t need gravity at all! It should rise up much more faster than with that piece of string. Of course in case of good adhesion between the wheel and the slider.
Best wishes and sorry for my english =)
Chris remarks on August 10th, 2008 at 4:19 am
Hi Llya
Thanks for the suggestion – I’d mentioned this in the last paragraph of my write up on my tests. I’ve tried really hard to get a wheel to work and I think if I could lock the wheel when I get to the top that would be the ideal solution, but I can’t figure out how to do it easily. Without locking the wheel the periscope rolls back down. With the winch/string, it locks when it gets to the top due to tension in the string.
Chris