Mad Mare Studio's Medium-Duty Robot Gripper
by Miax, published
This gripper is designed with touch-sensitivity in-mind, with a specially-designed hand/paddle model combo that allows you to pancake an Adafruit Industries 1.5" x 1.5" Force Sensitive Resistor inside safely ; adafruit.com/products/1075 ; The paddle design ensures that the force is sensed regardless of where the paddles grip an object. :)
This model requires two Standard size servos, I have not completed the version in which both paddles are controlled by one servo, and a standard-size servo at regular torque might have problems just actuating the gripper as it is.
I recommend a high-torque metal gear servo for this! Servo City sells a Great waterproof servo (http://www.servocity.com/html/hs-5646wp_servo.html) and I have a servo-plate that fits them included. Or any standard-size servo, like the one's Adafruit sells: adafruit.com/products/1142
The models in this thing are oriented in the direction that I recommend you print them - with the proper face-down. To make a complete Medium-Duty Gripper, you will need to print some models multiple times while other models you will only need to print once. The instructions will detail this out.
I am modelling a more sophisticated version that will be able to grip much larger and heavier objects! Stay Tuned. :)
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First let me apologize for not reading this sooner!! I have been utterly consumed by a big work migration project and I wasn't even getting on the web for several weeks at a time. Now that its done, I'll be watching this again much more frequently.
Let me respond back to your question in-detail tonight when I get home from work.
After printing everything and ordering the parts you suggested, I have found several inconsistencies with the instructions and the reality of my printed parts. Heres the run down:
* The full-size servo from Adafruit does not fit the servo plate. The distance between the plate's top and bottom mounting holes are about 2mm too far apart . I guess the ServoCity full-size servo has a larger body. To resolve this, I adjusted the distance between the top and bottom mount holes. The bottom side (the side with 2 little legs) had it's mount holes and bottom corner of the serve cutout moved upward 2mm. I have not determined if this will cause any movement issues yet.
* The BOM says 1/4" aluminum spacers. (1/4" == 6.35mm). The Interface Links are 9.6mm tall. The photos show a flush mount between the interface links/spacers and the plates It would seem I'd need a 9.6mm spacer (at minimum) for this to work correctly. Additionally the servos don't allow the plates to touch both sides of a 1/4" spacer.
* Where's the code? :-) I'd be down for any sort of sample code you have. I know I can go write my own code, but since you used additional sensors, I'd like to see your full vision working.... at least before I hack it up to do my bidding. :-D
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I printed this with ABS plastic, but it should be printable in PLA as well. I use a MakerBot Replicator 1-dual for all of my printing, and set my heated platform to 115C (prevents warping, you can set it to whatever works for your printer and plastic combo).
You will need to print the following models to make a complete gripper:
1. One of DroidGripper-BackPlate
2. One of DroidGripper-SupportPlate
3. One of DroidGripper-GearPlate
4. One of DroidGripper-TopPlate
5. One of DroidGripper-ServoPlate
6. One of DroidGripper-LeftArm
7. One of DroidGripper-RightArm
8. One of DroidGripper-LeftDriveGear
9. One of DroidGripper-RightDriveGear
10. Two of DroidGripper-PressurePlate
11. Six of DroidGripper-InterfaceLinks
The numbered-images I uploaded in this thing will walk you through a typical installation process for the gripper, and I provide a number of installation tips below to aid you as well.
I'm using an Arduino Mega 2560 an Adafruit 16-Channel Servo Driver ; adafruit.com/products/815 to control the gripper and sensors, and I plan to add more sensors to the gripper in future releases.
TIP: I include my notes below on how to get the models off of a hot build platform without damaging them:
1. When each print is done, leave it on the build platform and let it sit there until the platform cools down to ~60C.
2. Then turn pre-heat ON and wait until the build platform gets back up to > 100C. Your object should pop off the platform with just finger pressure.
This works because at a molecular level the plastic will mold perfectly onto the platform and into every tiny crack, scratch, bump, and it's bonds to the klapton or surface. By first allowing the model to cool, and then re-heating the platform, you cause the platform to shrink and expand by a tiny fraction - it flexes - and this cooling/re-heating again will break that bond and allow the model to come off the surface with very little force. This does tend to bubble the klapton more than pulling a hot model off the build platform the moment it's done, but this method also prevents cooling-induced warping as well.
You'll need some #6 screws,bolts to secure the gripper arms together as shown in the photo's, I tried a number of ABS-plastic options but none could hold any weight or handle Medium-level duty applications. Here is the list of hardware I recommend if you want to make an exact replica of what I made:
1. Nine 1/4" tall, size #6 aluminum spacers: servocity.com/html/6-32_aluminum_standoffs__round.html
2. Eight 1 1/4" (one and one quarter) inch long, size #6 screws: servocity.com/html/6-32_truss_head_phillip_machin.html
3. Four 2" inch long, size #6 screws: servocity.com/html/6-32_truss_head_phillip_machin.html
4. Eight 5/8" inch long, size #6 screws: servocity.com/html/6-32_truss_head_phillip_machin.html
5. Fifteen+ #6-32 nuts: servocity.com/html/machine_screw_hex_nuts.html
6. Eight #6 screws: servocity.com/html/_6_flat_head_phillip_screws.html
That shouldn't cost more than $20-$25 total, and will secure all of the printed components together nicely, and you can get the parts anywhere. :) I'm going to work-up a Viseo diagram that describes how to bolt it all together.
Thanks for reading and printing the Mad Mare Medium-Duty Robot Gripper! =) All feedback is welcome!
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