Obsessive Compulsive Design

Since I'm not pestering +Andrzej F to use the laser cutter at the moment I've applied myself to designing block lifter V0.2 (in addition to building garden beds and trying to satisfy an unsatisfiable client).  I think I'm getting a little lost in the design process...

Mortis and Tenon...

More technical activities have been superseded by building garden beds for the wife.  As opposed to doing it the easy way, which might have taken an hour, we opted to use a mortis and tenon joints.  Hailed as the strongest joints one can make with wood, the beds took me about 7 hours (half of which was spent figuring out the best way to do a mortis and tenon with the tools I had on hand).  A plunging router with a 1/2" chuck coupled with a mortising bit would have made life so much easier, alas I made do with my 3/8" chuck router coupled with a drill and a shitty Ryobi jigsaw (which couldn't cut a straight, vertical incision to save it's life).  Note: I have plenty of Ryobi power tools, they're cheap (I don't needs something a tradesman would, so I opt to pay 1/3 of the price for most of my tools) and generally get the job done, but not this damn things (it started out subpar and has continued to disappoint).  Anyway, here are the results of plenty of sweat, a few splinters and lots of wood chips:

(5'x3' bed)

(behold the strongest of joints)

UPDATE: Vivisection of a servo

Just spent an hour removing the physical stops from a variety of locations on the gear train, resulting in a broken pressure fit shaft socket.  The pressure fit shaft socket required some high precision grinding, too precise for my ham-fisted self, but only after the damn plastic piece cracked as I was clamping it in the vice.  Tried to reassemble the thing with it's broken socket (it still fit, but not as precisely as before breaking), no dice, the alignment is off and will never be right.  All this to say, my mechanical hacking skills are far below that of a remedial,  apprentice watch maker, and I have failed.  Even if I were successful with this hack it would still be too time consuming for mass production.  I'll just have to find some other small, inexpensive, bi-directional electric motor.

Vivisection of a servo

I'm redesigning the block lifting mechanism, version 0.1 (everything you've seen up till now) is too Rube Goldberg-ish (too many moving parts that rely upon the goodwill of the universe for alignment and proper functioning).  It'd probably work if I were a mechanical engineer, but I'm not, so discretion is the better part of valor.  That being said I plan on finishing 0.1 just to see it work (pictures and video will be taken and posted).  Anyway, I was struck by inspiration while I was daydreaming about a potential future project that involves a power screw to lift portions the sculpture.  Ugh, so blindingly obvious, use power screws to lift and lower the blocks.  Each block can be independently raised lowered with with power screws driven by small continuous rotation servos.  This solution would eliminate the need for a higher voltage power system just for the solenoids (to engage the rack and pinion), springs to counterbalance the solenoids (to disengage the rack and pinion) and the rack and pinion.

To this end, I've started looking at inexpensive continuous rotation servos.  One solution that +Jason Hoff suggested is modifying a Tower Pro MG90S servo (I have a couple laying around).  There are a number of tutorials claiming to modify this servo (they're usually not, people generally modify the TGY-90S which has nylon gears), so I disassembled one of the MG90S to see how difficult modding it would be for continuous rotation.  Here are some shots of the vivisected servo, I want my trusty EE to look at the circuitry before I start soldering in resistors and bypassing potentiometers (the MG90S looks a bit more complex than the TGY-90S).  So, once Jason has his ankle bolted back together and he's off heavy tranquilizers I'll see what he thinks.

(lovely, durable metal gears)

(stops that need to be ground down)

Block lifter V0.2 schematics will be forthcoming soon.  Once I've figured out how to mod this little beast I'll post a full and detailed tutorial (as opposed to a video of the the final result and vague instructions on what's needed and how to do it).

You get what you pay for...

(image included for visual interest)

For this project I purchased a drill press accessory for my trusty Dremel.  It's less accurate than I was hoping it would be, unfortunately the Dremel is light weight enough (and spins at between 5000 and 35,000 rpm) that the drill bit has a tendency to wobble and flop around.  This lead to some imprecise drilling today; in places where precision is important I'll have to fudge things with larger holes and some extra epoxy.  In light of these facts I'll be redesigning many of the parts to make the assembly process simpler and faster (with larger alignment dowels / rods).  Much of the design complexity was due to channels I made for screws and shafts, I'm now thinking life can be simplified (and made more accurate) with a drill template for each piece.  A real drill press would probably help as well. 

The Epoch of Epoxy...

The past couple of days have consisted of using a variety epoxy based adhesives to stick small bits of wood together.  Behold the result of JB weld, slow setting epoxy and fast setting epoxy...

In terms of adhesives I like the consistency and strength of JB weld, but it's ugly as sin where it oozes out on to the wood.  The fast setting epoxy (5 minutes) seems to set too quickly for the applications I am using it for.  The slow setting stuff is generally a nice compromise, but it's not tacky enough for some situations.

When the glue age comes to a close it'll be time to move on to drilling out the parts...

Think this design is intricate enough...

I have a feeling I'm going to need to redesign this particular part for the main prototype.  Laminating these parts is pretty time consuming.

Laser Cutter = AWESOME!!!

First of all, I'd like to thank the guys at the WiESEL group again for the use of their laser cutter, you guys rock.  +Andrzej F thanks for taking the time and lending your expertise to help me get the cutting done.  The cutting went really well (with the exception of me forgetting to include a part on the 1/8" sheet of wood, gotta go back an cut that part tomorrow).  Now the work of gluing and bolting it all together starts.  I loosened up the part tolerances (from what I've done in previous projects), it makes things easier to fit together, BUT in some cases I went too far and aligning the pieces while they're setting up (with glue) is going to be a pain.  Check out some of the videos and pictures of the cutting process and results.

(the first 1/4" sheet of plywood)

(the 1/8" sheet of ply wood, faster to cut)

(The outer portion of this prototype assembly)

(The rack and pinion, hope the hold together during testing)

(The block itself)

 

Parts, parts, parts...

Almost done with designing the parts to be cut by the laser cutter. Got time scheduled on Thursday.

Stalin, glorious steel...

Ran over to West Valley Hobbies today to pick up some metal rod and tube stock for the prototype block lifter.  Unusually enough, I found exactly what I was looking for, the right material, the right dimensions.  As far as I can tell, they have the best selection of thin rod and wire stock in the Salt Lake Valley.  The staff was courteous, friendly and helpful.  I have all (almost all, I forgot to buy one particular diameter rod) the necessary metal to make the bushings, alignment rods and position catches on the prototype. 

Block lifter schematic revision (again, no clever title)

I'm beginning to finalize the designs for the first prototype of the block lifting mechanism.  Here's a revised profile view.  The block has grown from a 63.5mm to 83mm, most of this expansion was caused by the solenoid's dimensions.  About half done generating files for the laser cutter.

 

Mr. Pigeon arrives and a shout out to my readers...

Mr. Pigeon arrived today, ahead of schedule.  I have to give itechcool credit, they stayed in touch and got the package here ahead of their predicted date.  I foresee trying to finagle a volume discount out of them in the future, for the moment I'll give them some positive feedback on eBay.  I have everything I need to prototype the block lifting mechanism (yay).  Now to finish the initial designs and swindle some laser cutter time out of my pals in the Weasel research group.  Here are some photos of the bearings:

A thanks to all the folks reading my blog.  I get a strange satisfaction out of going over the visiting stats for this blog.  Hello, to everyone reading in the lower 48.  Hi, to Luke up in Alaska.  Yo, to my sister and Jeremy in the Marianas islands.  Hello, to my mysterious reader in Deutschland (who do I know in Germany???).  Greetings, to my Chinese and Kazakh readers.  I promise this blog is headed far more interesting places than just servos, solenoids, linear bearings and hall effect sensors.

Block Lifter Model (no clever title)

A model of the block lifter, always a good way to better understand a design.  I'll do textures and more modeling later...

Weakness, solenoid be thy name...

I was curious how the solenoids we're going to perform in a situation resembling our intended application.  So I spent an hour or so constructing a very poorly designed test harness for a pair of them, I used springs from click pens to provide resistance.  This hastily assembled test yielded some interesting results, both good and bad.  The bad part is the solenoids when in their extended off position (the armature slug mostly hanging out of the end of the coil body) do not generate a strong enough field to begin compressing the springs.  Note, there's a lot of friction in the system due to poor design and no bearings, but I don't think this is enough to explain the solenoids behavior.  The good part, when I helped the solenoids compress the springs they were actually able to hold the springs in the compressed position.  Clearly friction needs to be eliminated from the system and shorter, slightly weaker springs need to be used for resistance.  We'll see if +Jason Hoff can come up with a circuit that provides an additional kick to strengthen armature's initial motion.

(behold my ugly-ass test harness)

Solenoid demo / test

Measured the resistance over the solenoids, 45 Ohms.  So, I was good to go for hooking up directly to my silly little power supply.  They work, yay, even better, the solenoids have a pretty strong throw (which means they'll actually work for this application).

Mr. Pigeon and the solenoids...

Not necessarily in that order.  The solenoids for our prototype of the block lifting mechanism have arrived.  They showed up damn fast too, three cheers for All Electronics (dot com).  So, at least on one front I can start designing in ernest (I've learned it's best to have materials on hand).  Here's some eye candy:

(10 little solenoids all in a row)

 (solenoid in the on position)

(solenoid in the off position)

 (the solenoid if you're not careful with the armature)

And now for Mr. Pigeon, itechcool you never seem to disappoint when you send me an email. 

Base on our radar system, our pigeon reported to us that he has already covered 50% of its journey of your item:

(Hmmm... maybe I should let military know that ebay sellers in China have access to radar systems that rival even NORAD's tracking system.  You guys can track a ladened pigeon in the middle of a trans-Pacific journey, you probably even know its air speed.) 

(150823864598 x2) 10 Pcs 8 mm LM8UU Linear Ball Bear Bearing Bush Bushing Linear Motion Machinery

to your address:

Ian King

------------------

Salt Lake City,UT

United States

(Glad we're both on the same page, you have my address and what I ordered down pat.  I just hope for both our sakes that's what's actually in the box.)

Should it not turn up on 2013-04-18, kindly give another 5 days, as occasional postal delay is possible.

(Not in America bub, in AMERICA the postman won't be held up.  "Through rain or shine ,snow or sleet, we deliver your mail", is the US Postal Service's motto.  He's also known to ring twice.  Though, these day's it seems like even Saturday will prevent mail delivery.)

And, if you still do not receive it by 2013-04-23, please let us know immediately, we will have to report to our Post Office and ensure you receive what you have paid for. Your patience is deeply appreciated.

(Once again, assuming I'm a patient person.  How deeply do you appreciate my patience?  Deeply enough to send another 50 bearing to me free of charge?)

(Notice: Since the air cargo capacity of China Post has been impacted due to a high volume of items, there might be a delayed shipment of some items.  So if unfortunately you haven't received the item within the expected time, please be patient and wait for some more days. Thanks for your kind understanding.)

(Again with blaming the Chinese post.  Tsk, tsk...)

If you have received your items: 

Kindly ignore this email, our pigeon must have worked really hard to get your products delivered.

(I must have gotten a lazy delivery pigeon.)

And it would be much appreciated if you could leave us Positive feedback for this transaction and we will do the same for your kindly supporting.

(I'll bet you'd appreciate positive feedback.)

Should you receive a survey in 'My Messages' on eBay with 'How do you rate your experience with this seller', it would be much appreciated if you rate us a 9 or 10 if you feel it is deserved. 

(I think a 9 or 10 is going to require free stuff, how 'bout a 7 or 8.)

Thank you so much in advance.

If unfortunately you receive defective or wrong product(s):

Take it easy, simply write to us via 'eBay Message' and we will be glad to help you. 

(Ah, so you're not absolutely sure about what's actually in the box.)

It would be much appreciated if you don't leave us any negative/neutral feedback or open a dispute on eBay/Paypal since we'll try the best to assist you to resolve the challenges.

(Simple, send me the bearings, you get paid and I give you a slightly better than OK rating.)

Once again, thank you for giving us the opportunity to share with you our products. We strongly believe that quality, blended with excellent service, is the foundation for successful business.

(This whole relationship is getting a bit needy.  The numerous messages, the cute reference to pigeon delivery... I think we need to start seeing other people.  Just make sure my bearings get here.) 

New & Improved!!!

+Jason Hoff  wants to replace the dinky little servos on the Eiffel tower piece with some slightly larger stepper motors (which will make the table's motion far, far smoother), which is awesome.  The  REALLY cool part is we're not going to have to cut the old servo bracket out (I had to glue them to the base of the sculpture since they were pulling themselves out of their sockets when I was first tested the design) and redesign them. 

(no really, I hand drew this on fancy paper)