;)
;)
;)
;)
« July 2005 | Main | November 2005 »
August 30, 2005
Cleaning-up a lo-res 3D printer part
1. The Back story
The Dimension BST is a great machine. It’s in the small-company price range and capable of producing functional prototypes with just a little post-build finishing and assembly. For exhibition or theatrical prop quality pieces, the surface finish is pretty crude. Curved surfaces are ribbed. Flat surfaces have thin patches where you can see the honeycomb subsurface. The limited build area often requires parts to be divided into multiple prints. The following is some step-by-step instruction in how Michelle and I clean-up the poor surface finish of simple FDM parts and seam two parts together.
This process is courtesy of FX artist and sculptor Brett Klisch.
The object we are demonstrating this process on is a replica 1/3 scale model of our living room table that Michelle is making for the
set of our current project.
2. The tools we use:
a. Rigid Putty Knife
b. Glazing Putty by Bondo
c. Sand paper (250 – 400 Grit, Wet-sanding pad)
d. Locking pliers
e. 5-Minute Epoxy
f. Dust Mask
g. Latex Gloves
h. White, Black or Grey Primer
i. Paint color of you choice
3. Putty
Apply the glazing putty directly to the surface of the piece. Squeeze out a small smear of putty on the part from the tube. Use the putty knife to spread it around. Try to spread a little bit of putty across as large a surface area as possible. You should be able to see the plastic surface through the translucent layer of putty. Remember to always close the tube between smear applications. The air will thicken the putty and it won’t spread around as well. Let the putty dry for 5 to 10 minutes.
4. Sand
Use 250 grit sand paper to sand the putty layer smooth. Sand in small circles until the surface is very smooth to the touch.
5. Repeat Steps 3 and 4 two or three more times depending on the roughness of the original surface.
6. Prime and sand
Once you have gotten a few layers of putty on the piece to fill in the crack, apply 3 or 4 coats of primer in whatever color you'd like. Between each coat sand the painted surface with 300 - 400 grit sandpaper. Let the paint dry for 15-20 minutes before you handle or sand the part.
7. Join
To join the two parts: mix up a batch of 5 minute epoxy. Apply a thin layer to both of the surfaces you want to join. We used the locking pliers to hold the parts in place. This is key when joining two parts. You have to find some way to preload the two surfaces together for 30-60 minutes. It is best to let it sit for a few hours to make sure the bond is strong.
7. Repeat Steps 3 - 6 three or four times until the seem between the two parts in nearly invisible.
8. Once the primer surface is dry, you can apply your top coat of paint. In our case we used glossy white since our table is metal with a white powder coat. We applied three layers of white gloss, sanding the surface with a 400 grit sandpaper between every layer but the last. Finish off with your final layer of top coat.
Be prepared for the inevitable scratch or chip. That is just life.
And don't be surprised if someone kicks you to the curb because of the fumes.
When we finish the table, I will upload some images of the completed project and you can see Michelle’s gilded table legs.
Posted by powderly at 01:52 AM | Comments (1)
August 12, 2005
Pocket Workshop
The following text gives step-by-step instructions how to make an LED circuit with conductive fabric, thread and epoxy embedded into a denim pocket. This was the topic of the workshop we presented at Eyebeam in July, 2005.
LessEMF - Source for conductive fabrics and velcro. For $10, they offer a fabric sampler to try out different materials.
Mood Fabrics - Our favorite fabric store. For our pockets, we used denim and regular pocketing. Sometimes you can find conductive silk organza at Mood, so bring your multimeter.
Botani - Botani only sells buttons. They sell traditional metal snaps in bulk.
Newark in One - Good source for conductive epoxy and electronics supplies. We used conductive epoxy to attach the snaps to the 3D printed LED holder.
L.C. LED and LSDiodes LED resources
Conductive thread - The conductive thread we used, did not work well in small amounts so we replaced it with fine gauge wire. There are some conductive threads and information available online:
Lamé saver
Intro to Wearable Technology
- Cut out pocket pieces from fabric and pocketing. To make a pattern, draw out the size and shape of the pocket, then add 5/8" around all edges for seam allowances. Press the 5/8" seam allowances down on all sides with an iron.
[pocket pattern] - Attach conductive velcro to both sides of the pocketing. This will be where the battery is attached later on. We recommend using the loop side of the velcro to the pocketing. We attached the velcro to the pocketing using regular thread on a sewing machine.
- Using conductive epoxy, attach velcro to both sides of a 3 volt battery. Make sure that the velcro does not touch the outer ring of the battery or it will short the battery. The photo shows a battery with loop side on the battery, but hook works better to minimize the chance of a short circuit.
- Next, we cut conductive fabric out for the front and back of the pocket on the laser cutter. The fabric can also be cut the traditional way, with scissors. The conductive fabric is going to be part of an electronic circuit so it has to be continuous. That is why all the letters in the graphic are attached to each other.
- Attach the conductive fabric to the pocket material, in our case denim, with regular thread. Both pocket pieces should have conductive fabric sewed to it. Make sure the fabric will overlap the velcro on the pocketing when it is all put together. Sew conductive thread creating continuity between the conductive fabric and the velcro on the inner pocketing for both sides.
- We made a plastic housing for the LED using the 3D printer. With regular 5 minute epoxy, we attached an LED to the housing. With conductive epoxy, we attached 2 female snaps to the housing. Afterwards, always check for continuity with a multimeter.
- Attach two male snaps to the front of the pocket for a place to snap the LED assembly to. First attach the snaps with regular thread and then go over it with conductive thread. One snap should sit on the field of conductive fabric and the second snap should sit on the denim. Make sure there is no continutiy between the two male snaps.
- On the pocketing material, attach a male snap that lines up on the inverse side of the denim snap on the front of the pocket. Attach it with regular thread first and then use conductive thread to create continuity between the male snap on the front on the pocket with the male snap on the inside of the pocket.
- On the pocketing for the back of the pocket, attach a female snap that meets up with male snap you just added to the front pocketing. After attaching the snap with regular thread to the pocketing, use conductive thread to create continuity between the snap and the conductive material on the back of the pocket.
- Sew the pocketing material to the pocket material and sew up the pocket around the outside edges.
Step-by-step pocket instructions:
Pockets from the workshop
LessEMF
Mood Fabrics
Botani
Newark in One
Posted by michelle at 10:22 PM | Comments (0)
August 08, 2005
How to build the robotic arm (wrist to shoulder)
This post is the step by step how-to instructions for building our first generation robotic arm (from the wrist to the shoulder). This entry includes zipped design files ready to be augmented or printed on a 3D printer, part pictures, assembly instructions and some general info on our progress...
In June we decided to take a new approach. Michelle is going to build a smaller, less expressive “michelle robot” and I am going to build a bigger and pretty expressive “james robot”. The james robot is going to be built around cheap available motors that can be augmented to provide for closed-loop control. Closed loop just means that our control system will have active feedback that will dynamically control the motor speed, acceleration, etc. When I say closed loop I don’t mean RC servo’s or DC servos with potentiometers. RC servos have a limited form of positional control but no user accessible feedback loop. And potentiometers aren’t very good positional feedback for our purposes as they are noisy, wear easily and are not reliably repeatable.
For the james robot, the first step was determining a size large enough to accommodate our motor assemblies, harnessing, etc., but small enough to remain very light and be considered miniature. So I shopped around for motors that would be cheap, small and enable closed loop control via encoders. At Honeybee we use Maxon and MicroMo motors. These are great motors and you can find them in small packages, but the cost was prohibitive for both our project and the low-cost DIY robot we want to make available.
So I decided I would try to find separate shaft encoders and motors and try to make an assembly (or a couple varieties of assemblies) that would couple them via gear pairs or pulleys or whatever. We tried out a number of different motors and finally decided we would use a few gearmotors from solarbotics. We chose the solarbotics motors because they had a range of reductions, sizes, shaft output orientation and were overall very light, very cheap and very available.
Check out solarbotics here
The GM3 224:1 gearmotor and the GM14 Sanyo 297.1:1 gearmotors have seen the most action so far in our arm assembly. The GM3 (and the GM2, GM8 and GM9) are all similar, use the RM3 DC brushed servo motor and have plastic gears and housing. They all also have an output D-through- shaft that can couple to an encoder shaft. The regular output shaft is also easy to couple to and the motor is pretty easy to mount with two built-in mounting through-holes. They are capable of 50 in*oz of torque, with a kludge clutch rated at 60 in*oz and a weight of 1.31ounces. They cost ~ $6.00 each.
The GM14 is smaller, lighter and has metal gears. This is a very small motor, small enough to universally make people say “cute” when they see it. It produces ~40 in*oz of torque and weighs .29 ounces. The output shaft has a flatted side, so it is easy to mount to, though there isn’t much shaft axially in general. Not particularly easy to mount but it does have some mounting holes and can be mounted by putting the whole motor in a rectangular recess. They cost ~ $25.00.
Both motors run on ~5VDC and draw current in the range of 100 ma to 600 ma.
I choose the U.S. Digital S4 miniature optical shaft encoder as the proprioceptive feedback device. This encoder is cheap, small, very accurate, comes in a number of resolutions, is easy to mount and can be purchased with a gear bearing shaft so the encoder can handle a substantial radial load. They cost ~ $45.00.
Check out U.S. Digital here.
So with these motors in mind I started trying to build an arm starting with the assembly for the elbow of the james robot. I picked the elbow for no particular reason, but it turns out biomedical engineers also use the elbow diameter as a figure of merit for human factors engineering. It looks like the smallest I can make the elbow joint is ~2" diameter. I could go smaller but it will actually cost more, as the gearmotors I would need are real cute and realy pricey. I decided to lock the size at ~52% scale to the 50 percentile man age 20-65 as documented by The Measurement of Man and Woman You can look at the overall arm dimensions in the Arm_Dimensions.xls in the Arm section of the DIY robot KIT.
The following design represents our first generation robotic arm. The current design has 3 DOF not including the wrist and up to the shoulder. This arm allows for motion approximating the motion of a human arm, including bending the elbow, forearm pronation/supination and gross supination/pronation.
The overall integration of the arm with its actuators can be accomplished in under ten minutes not counting soldering of leads, cabling and harnessing. The following numbered list describes and illustrates the basic assembly and integration of the arm.
1. Collect all 7 ABS parts, 3 S4 shaft encoders, 2 GM14 small metal gearmotors, 1 white plastic GM2 gearmotor, 3 plastic gears, 2 plastic hubs, 2 #2 socket head cap screws and nuts, and a heavy duty 6” rubber band.
2. Insert S4 encoder 1 shaft into the 0.372” hole in the upper arm motor/encoder mount (Part 1) until the encoder is flush. Lock it into place with the nut using a small wrench or pliers.
3. Insert S4 encoder 2 shaft into 0.372” hole in the upper arm mounting substrate (Part 2). Then begin to attach the encoder/motor mount (Part 1) to upper arm mounting substrate (Part 2) by lining up the two 0.115” mounting holes by inserting 1-1/2” #2 socket head cap screws through the upper arm mounting substrate and the encoder/motor mount.
4. Insert motor onto #2 screws until flush with encoder/motor mount. Tighten down nuts with socket set or wrench. Insert the hubs (Hub 1 & 2) onto the GM2 motor and the encoder shafts. Stretch the rubber band from hub to hub such that the movement of one shaft is mechanically coupled to the other. I am going replace this eventually with a v-shaped drive belt made of rubber.
5. Insert the shaft of the S4 encoder 2, while still mounted on the upper arm mounting substrate, into the 0.25 mounting hole on the gear feature at the bottom of the upper arm/shoulder rotational drum (Part 3).
6. Next, insert the small, thin pinion gear (Gear 1) onto the D-shaft of the GM14 motor 1. Insert the motor into the motor cavity in the upper arm substrate (Part 2). You will need to help rotate the upper arm/shoulder rotational drum so the teeth of the pinion and gear will mesh.
7. To finish the upper arm mate the other half of the upper arm substrate, the upper arm mating substrate (Part 4) to the upper arm mounting substrate. Use the motor and motor cavity as the alignment feature. I am going to add a latch to these parts very soon but for now fasten the two halves of the upper arm substrate together with rope, wire ties or rubber bands.
8. Next grab the forearm mounting substrate (Part 5) and place the large pinion gear (Gear 2) vertically in the slot on the mounting substrate so that it is parallel and co-linearly aligned with the 0.372” hole on the mounting substrate. Insert S4 encoder 3 into the 0.372” hole on the mounting substrate and the 0.25” hole on the large gear. Use needle nose pliers to tighten the nut on the encoder.
9. Insert the double flatted shaft of the GM2 motor 1 into the double flatted feature on the forearm mounting substrate.
10. Insert the GM14 motor 2 D-shaft into the small, thick pinion gear (Gear 3). Insert motor 2 into the motor cavity on the forearm mounting substrate so the gear and pinion are aligned. You may need to help rotate the large gear so the gear and pinion teeth can mesh.
11. Lay the Forearm rotational drum (Part 7) shaft and gear features so that the gear meshes with the thick pinion gear (Gear 3) and the shaft aligns and fits into the forearm mounting substrate shaft recess feature such that the forearm drum is secured in the X and Y planes.
12. Finally, mate the forearm mating substrate (Part 6) with the forearm mounting substrate using the motor and motor cavity and the shaft recess as alignment features. As before, I am going to make a latch for this so use rope, wire ties and rubber bands to secure these two forearm substrates.
In the next section I will illustrate and describe how to create and run the wiring harness for the arm, create service loops to accommodate rotational joints and how to properly solder the motor and encoder leads.
All the arm design files can be found in the arm design zip files in the Arm section of the DIY robot KIT. The zips include STLs for printing at service bureaus on FDM machines or ABS 3D printers, IGES part files, Autodesk Inventor part and assembly files, part DWF files and DXF files. All zip files are named according to file type and revision. Download the latest revision as we will be constantly upgrading. For more information on the design, fabrication and/or assembly of the 1ST generation arm please send me an email. The files are licensed under the creative capital non-commercial, attribution, share-alike contract. If you use or modify the design we would love to hear about it and we will be glad to host your new designs (and sing your praises) on the Lab Blog.
Download James Robot Arm Dimension Chart file
Download James Robot Arm IGES zipped files (parts only)
Download James Robot Arm Inventor zipped files (parts and assemblies)
Download James Robot Arm Part zipped pictures
Download James Robot Arm STEP zipped files (parts only)
Download James Robot Arm STL zipped files (parts only)
Posted by powderly at 02:20 AM | Comments (1)
