This is another cheap project, useful to those peoples too lazy to change backup tapes every night (If You said “What’s Backup?” please stop reading! :-) )
This project is less “art attack” than my homemade CNC. There is, indeed, a plan (well, sort of…) drawn with Google SketckUp (actually drawn BEFORE construction, and not AFTER, like I usually do :-) ).
Almost all mechanical components used can be salvaged parts, or can be bought in a hardware store.
The idea is simple and there will be no need to install drivers on the host computer: a group of optical sensors detects that a tape has been ejected (you obviously need a tape drive with motorized eject). Once the tape is ejected, the clamp takes the tape, slide it out of the tape drive and put it on the top of a tape stack hold into a sort of rack. After that, the tape at the bottom is slid out of the stack, lifted and inserted into the tape drive.
So, if the backup software can automatically eject each tape and detect a new tape, the DatBot is able to handle a backup job with any number of tapes up to the tape rack capacity with no human interaction.
MAIN CARRIAGE – Materials
These are the parts that compose the main carriage. The main carriage is the part that move vertically, raising and lowering the tape grabber carriage. It’s the gray part on the plan.
Parts are all pieces of regular aluminium bars that you can buy in any hardware store.
You can use other materials you have at hand.
MAIN CARRIAGE – Building
Parts are assembled with 3mm rivets, threaded bars and bolts/nuts
Here you can see she building sequence.
Pay attention to parallelism and swinging between the parts of the grabber carriage holder (you can see it in the 3rd picture) because the grabber carriage should be able to slide precisely into the holder but with little friction.
CARRIAGE – Tape Grabber
This is the part of the carriage that slides horizzontally to load/unload the tape into the drive and the various stacks of the tape rack.
As you can see in the first two photos, the grabber simply slides into the previously built guides. The tolerances are large enough to “forgive” small construction errors. Anyway you should make the holes a little larger, to be able to slightly change the alignment of the lower guides (second picture) before tightening nuts.
Some lubricant (grease or sewing machine oil) will help the grabber assembly sliding.
The motors used to move the grabber carriage and to close the grabber clamps are two standard RC model servos. Choose the cheaper you can find. Mine are two Futaba S3003.
Grabber clamps are just two pieces of plastic that I found somewhere. Any fragment of sufficiently elastic plastic will work.
… and before you notice: Yes. The leverages for the forward/back movement of grabber carriage are made with some scrap PCB slices. (I’m not happy if I can’t recycle something in every thing I build :-) )
CARRIAGE – Full view
Here you can see the main carriage fully assembled. The small wheels mounted to carriage side work as bearings for the vertical movement, and locks within two U-shaped aluminium rails.
This is the external support frame. It’s a simple wood frame. On the top and bottom parts, there are holes that holds aluminium rails in place. The bottom holes are blind, rails can be removed from the top holes.
The main carriage is moved vertically by a M8 threaded bar mounted on two 25mm ball bearings.
Two nuts are glued to short L-shaped aluminium pieces, that are tightly screwed to main carriage.
I’ve used a normal 12V DC motor took from an old laser printer. Motor is linked to threaded bar by a small timing belt.
As already said, tape rack contains actually a stack of tapes. The higher slot (the biggest one) in the rack is reserved to this purpose.
There are other two slots in the rack, useful if the system have to add/discard a tape or to sort tapes in the main stack.
A tray on top of the rack holds the tape drive by means of 4 small brackets.
MOVING PARTS TEST
At this point a test of moving parts can be done to check that all works as expected.
I’ve done the test driving manually motors, using switches to control lifting motor and a RC radio to drive the two servos.
Unfortunately the radio I used performed really bad on the servos movement range, so I had to do some movement in multiple steps.
No tape robot is complete without a “head” camera :-) so I put a wireless microcamera on the main carriage, and I’ve captured those shorts videos: