Saturday, September 5, 2015

2015-09-04 (F) Weekly Summary

Getting this thing to move has been literally and figuratively difficult. Control and mechanisms have started to come together but there was not a ready-made solution to copy verbatim. Moving a four bar linkage in a parallelogram formation isn't particularly difficult in concept but attaching inexpensive servo motors to an oddly shaped keyboard and making it sit flush is far from a concept. It's possible.

Four straight levers were modeled and printed last week. Two of the levers were meant for acting as a hinge at each end while the other two were meant to attach to a servo at one end. Servo ends were revised from last week to attach in a more logical way. These simple parts were able to prove the desired motion was possible but the range range was not enough.

Screenshot of servo levers

Demonstration of parallelogram four bar linkage movement

To get the desired range a pair of servos were taken apart and converted to continuous rotation so they could reach a fully extended and a fully retracted position. Unfortunately the ability to sense position is lost during the process so limit switches will be necessary.

Servos in the process of being converted to continuous rotation

Trying to move something as oddly shaped as the keyboard would be easy if I just attached wide supports but that would be bulky and awkward to type on. Wide supports would also look awful and I would like this project to look cool. To make things work the shape of the levers was changed. Length was not changed since the hinges must still act like a parallelogram.

Offset servo levers

Making offset servo levers seems to be the right path although the first attempt had a few problems. The first problem was the offset size was way off in the x and y dimensions. The second problem was one end was supposed to attach to a servo. Thirdly, two levers were printed but only one was necessary. Lastly, there was unanticipated interference from a key pad.

This lever cannot reach the bolt

With all the previously mentioned problems a second lever was modeled and tested but this time it worked well. The lever was attached at the back of the thumbboard and all the clearances agreed with the model. All the printed parts were assembled with long #6 bolts. Although the servo controller has not been programmed and installed it was possible to manually move the parts and see the motion of the linkage which looked good. Making clearances for a fully retracted model may be difficult and more troublesome than worthwhile but a fully extended model which rests in the user's hand will be necessary.

Double offset servo lever


Partially assembled wrist mounted keyboard in the extended position

The retracted position hasn't been fully realized

Next week construction of the levers will continue. Limit switches and a controller need to be installed and a method of deploying the keys will be necessary. Enclosures still need to be made which will hold all the electronics. My dear hope is that next week there will come a moment when I hold this to my wrist and press a button causing these cobbled pieces of metal and plastic to move some switches into my palm. If this happens I will have such a smile.

Downloadable Files:
The rest of the weekly summaries have been arranged by date.





This disclaimer must be intact and whole. This disclaimer must be included if a project is distributed.

All information in this blog, or linked by this blog, are not to be taken as advice or solicitation. Anyone attempting to replicate, in whole or in part, is responsible for the outcome and procedure. Any loss of functionality, money, property or similar, is the responsibility of those involved in the replication.

All digital communication regarding the email address 24hourengineer@gmail.com becomes the intellectual property of Brian McEvoy. Any information contained within these messages may be distributed or retained at the discretion of Brian McEvoy. Any email sent to this address, or any email account owned by Brian McEvoy, cannot be used to claim property or assets.

Comments to the blog may be utilized or erased at the discretion of the owner. No one posting may claim claim property or assets based on their post.

This blog, including pictures and text, is copyright to Brian McEvoy.

Friday, September 4, 2015

2015-09-03 (Th) Wrist Mounted Chording Keyboard

Yesterday's recommendations were considered to develop a servo lever which can accommodate the shape of the keypad. Area under the lever was exaggerated to make the first fit easier and allow for measurements to be taken. Model changes were made but another revision may be necessary depending on performance. Corners on the model may need to be rounded (fillet) to keep from catching on clothing, scraping skin or becoming breaking points.

Rotating view of offset servo lever

A single copy of the offset servo lever was printed. Printed components were all assembled to make a makeshift keyboard. No controller had been installed so there was no motion but the levers and servos could be pushed by hand. When the pieces were assembled the offset servo arm fit well and didn't collide with other parts but it had to be placed on four washers so it wouldn't rub on wires connected to the thumb switches. This spacer could be built into the model or the wires could be routed differently.

 Keyboard in the fully deployed position

Keyboard in the transitioning position

When fully deployed, as though ready to type, the parts fit well without a thumbside lever arm which would have crossed the thumbboard if it was straight. Another offset lever arm will be modeled if necessary. When retracted the new offset lever arm had no trouble encompassing the parts but the straight lever attached to the opposite servo collided with the pulleys. Another offset servo arm will be modeled.

Keyboard in the retracted position

Example of where an offset servo arm might go

Servo arm colliding with pulley

Downloadable Files:
To do:
  • Wrist mount
    • Revise offset levers 
      • Shorten offset distance
      • Allow rear bolt hole to bend around
      • Replace far end of lever with servo end
      • Shrink hinge hole radius
      • Make holes in thumb board cylindrical instead of countersunk
      • Model servo arm to go around pulleys
      • Model hinge arm to go around thumbboard
      • Round corners?
    • Integrate:
      • Controller
      • Servos
      • Enclosure for each controller
      • Limit switches
    • Debug
    • Test
    • Refine
    • Repeat
    • Activation switch
    • Route wires
  • Write instructions
    • Make diagram with everything labeled
    • Schematic

The rest of the posts for this project have been arranged by date.

First time here?

Completed projects from year 1.
Completed projects from year 2



This disclaimer must be intact and whole. This disclaimer must be included if a project is distributed.

All information in this blog, or linked by this blog, are not to be taken as advice or solicitation. Anyone attempting to replicate, in whole or in part, is responsible for the outcome and procedure. Any loss of functionality, money, property or similar, is the responsibility of those involved in the replication.

All digital communication regarding the email address 24hourengineer@gmail.com becomes the intellectual property of Brian McEvoy. Any information contained within these messages may be distributed or retained at the discretion of Brian McEvoy. Any email sent to this address, or any email account owned by Brian McEvoy, cannot be used to claim property or assets.

Comments to the blog may be utilized or erased at the discretion of the owner. No one posting may claim claim property or assets based on their post.

This blog, including pictures and text, is copyright to Brian McEvoy.

2015-09-01 (Tu)

Thursday, September 3, 2015

2015-09-02 (W) Wrist Mounted Chording Keyboard

Lever arms were modified to accommodate the protrusions from the keypad. When the device folds back into the retracted position a straight bar would collide with the thumb switches or the folded keypads. It would be possible to extend beyond the switches and pads but the device would get unwieldy.

3D model of servo levers

3D models have been receiving frequent updates and since none of the models have been guaranteed the linked files at the bottom of the page will not be updated until the models have been decided upon. When the models get completed they will be stored as a single .zip file.

Printed pieces were held up to the keypad and tested for a fit. Several problems were noticed, none of which should have been difficult to fix. Measurements taken for the offset piece were exaggerated and should be tightened up. At the rear hinge point the hinge is below a keypad when it is folded and this will cause a collision when the device is retracted. Holes for the bolts to pass through are too large and should be shrunk. Since the rear hinge is being used it should have a servo style end on the back of the model instead of a simple hinge.

Extended position

Collision with folded keypad

Areas which need to be revised

Downloadable Files:
To do:
  • Wrist mount
    • Revise offset levers 
      • Shorten offset distance
      • Allow rear bolt hole to bend around
      • Replace far end of lever with servo end
      • Shrink hinge hole radius
      • Make holes in thumb board cylindrical instead of countersunk
    • Integrate:
      • Controller
      • Servos
      • Enclosure for each controller
      • Limit switches
    • Debug
    • Test
    • Refine
    • Repeat
    • Activation switch
    • Route wires
  • Write instructions
    • Schematic

The rest of the posts for this project have been arranged by date.

First time here?

Completed projects from year 1.
Completed projects from year 2



This disclaimer must be intact and whole. This disclaimer must be included if a project is distributed.

All information in this blog, or linked by this blog, are not to be taken as advice or solicitation. Anyone attempting to replicate, in whole or in part, is responsible for the outcome and procedure. Any loss of functionality, money, property or similar, is the responsibility of those involved in the replication.

All digital communication regarding the email address 24hourengineer@gmail.com becomes the intellectual property of Brian McEvoy. Any information contained within these messages may be distributed or retained at the discretion of Brian McEvoy. Any email sent to this address, or any email account owned by Brian McEvoy, cannot be used to claim property or assets.

Comments to the blog may be utilized or erased at the discretion of the owner. No one posting may claim claim property or assets based on their post.

This blog, including pictures and text, is copyright to Brian McEvoy.

2015-08-31 (M)

Wednesday, September 2, 2015

2015-09-01 (Tu) Wrist Mounted Chording Keyboard

Someone could make the point that when a servo is converted to continuous rotation it is little more than a gear motor. This is true for the most part. Gear motors, which usually reduce speed and increase torque, are expensive because they are larger than I want. It wasn't documented here but I also gave stepper motors a try because they would have been easy to mount and relatively easy to control. In the end I decided to use modified servo motors because they are inexpensive and they can be controlled with a single wire from a microcontroller.

Enough background.
----------

Two servos were selected to be turned into continuous rotation servos. Each was opened up and modified by the working techniques from 2015-08-23 (Su) including a 50kΩ potentiometer but this time the potentiometer was attached to the servo at the location where the wire exits the servo instead of the face opposite the top gear. In other words, the potentiometer is on the wire side instead of the bottom. One of the servos had trouble keeping the insulation over a wire so all three wires were replaced with salvaged 26AWG Ethernet wires. The larger Ethernet wires were more difficult to position due and the hole which normally only had to pass the power and signal wires was filed out to accommodate the large wires as well. When the regular potentiometer wires were run out the hole with the power and signal wires there was no need to expand the hole. PCB mounted potentiometers were used and had no protection on the back so moving parts were exposed. For this reason glue was not used to hold the potentiometers in place. Tuning the potentiometers was also difficult so they should be replaced with enclosed multi-turn potentiometers.

Opened servos with parts scattered

 50kΩ attached to outside of servo case

Edge filed down to allow larger wires to pass through case


Downloadable Files:
To do:
  • Modify two servos for continuous rotation
  • Wrist mount
    • Integrate:
      • Controller
      • Servos
      • Enclosure for each controller
      • Limit switches
    • Debug
    • Test
    • Refine
    • Repeat
    • Activation switch
    • Route wires
  • Write instructions
    • Schematic

The rest of the posts for this project have been arranged by date.

First time here?

Completed projects from year 1.
Completed projects from year 2



This disclaimer must be intact and whole. This disclaimer must be included if a project is distributed.

All information in this blog, or linked by this blog, are not to be taken as advice or solicitation. Anyone attempting to replicate, in whole or in part, is responsible for the outcome and procedure. Any loss of functionality, money, property or similar, is the responsibility of those involved in the replication.

All digital communication regarding the email address 24hourengineer@gmail.com becomes the intellectual property of Brian McEvoy. Any information contained within these messages may be distributed or retained at the discretion of Brian McEvoy. Any email sent to this address, or any email account owned by Brian McEvoy, cannot be used to claim property or assets.

Comments to the blog may be utilized or erased at the discretion of the owner. No one posting may claim claim property or assets based on their post.

This blog, including pictures and text, is copyright to Brian McEvoy.

2015-08-28 (F)

Tuesday, September 1, 2015

2015-08-31 (M) Wrist Mounted Chording Keyboard

Code was written to control two continuous rotation servos attached to a wrist mount. Rather than requiring one of the servos to have the motor leads reversed this code has outputs for two servos. While the servos should always turn synchronously it seemed more important that they can be easily hacked and many guides and tutorials already exist for converting servos to continuous rotation.

Outputs for this code have been written for Arduinos with more than six possible pins like an Arduino Pro Mini but comments were added for anyone wanting to use something smaller like a DigiSpark or one of the knockoffs. In the case of an ATTINY85 board the limit switches were put on pins 3 and 4, the data pins, so the USB programming will still work so long as the switches are both open.


Downloadable Files:
To do:
  • Modify two servos for continuous rotation.
  • Wrist mount
    • Program
    • Debug
    • Test
    • Refine
    • Repeat
    • Activation switch
    • Route wires
  • Write instructions
    • Schematic

The rest of the posts for this project have been arranged by date.

First time here?

Completed projects from year 1.
Completed projects from year 2



This disclaimer must be intact and whole. This disclaimer must be included if a project is distributed.

All information in this blog, or linked by this blog, are not to be taken as advice or solicitation. Anyone attempting to replicate, in whole or in part, is responsible for the outcome and procedure. Any loss of functionality, money, property or similar, is the responsibility of those involved in the replication.

All digital communication regarding the email address 24hourengineer@gmail.com becomes the intellectual property of Brian McEvoy. Any information contained within these messages may be distributed or retained at the discretion of Brian McEvoy. Any email sent to this address, or any email account owned by Brian McEvoy, cannot be used to claim property or assets.

Comments to the blog may be utilized or erased at the discretion of the owner. No one posting may claim claim property or assets based on their post.

This blog, including pictures and text, is copyright to Brian McEvoy.

2015-08-28 (F)

Monday, August 31, 2015

2015-08-30 (Su) Wrist Mounted Chording Keyboard

Printed servo lever arms were attached to ordinary servos. Coincidentally the thickness of the lever arm was very similar to the thickness of the servo horn hub thickness which made for a flush piece. A single screw was used to attach each servo horn to a lever while the old design would require two screws per servo. One servo was placed in the wrist mount piece but not screwed down. Two versions of the servo levers were printed, one attached to a servo while the other had ends meant to hinge on a bolt so they were simply open holes. Those holes needed to be drilled out in order to fit a #6 bolt.

Old style which attached to top of servo horn

New style which wraps around servo and attached to underside

Half of the levers and servo were assembled before animation and video were taken. Animations show the way the four bar linkage will move something from a forearm position to a palm position. As a simple demonstration the continuous rotation servo made on 2015-08-23 (Su) was also connected to the same servo signal to demonstrate how the two act differently despite getting the same signal. Video was shot which first demonstrated manual movement where the signal was changed according to the potentiometer which can be seen as it was turned. The second part, at 23 seconds, showed the neutral position where the continuous rotation servo is halted and the unmodified servo snaps to an odd angle. The final part of the video, at 27 seconds, shows automated movement where the shuttle moves back and forth and the continuous rotation swings around and around in both directions. This final movement was also captured as animation shown below.

Automated movement

Video showing Four Bar Linkage and the difference between servos
While watching YouTube videos it's possible to skip around by pressing numbers on the keyboard. For example, to go to the beginning press zero, 0. To go to the exact middle press five, 5.
To skip immediately to the second part of the video, where neutral position is demonstrated press six, 6. To skip right to the automated movement press seven, 7. Press zero, 0, to rewatch the whole thing.

Downloadable Files:
To do:
  • Modify two servos for continuous rotation.
  • Wrist mount
    • Build
    • Test
    • Refine
    • Repeat
    • Activation switch
    • Route wires
  • Write instructions
    • Schematic

The rest of the posts for this project have been arranged by date.

First time here?

Completed projects from year 1.
Completed projects from year 2



This disclaimer must be intact and whole. This disclaimer must be included if a project is distributed.

All information in this blog, or linked by this blog, are not to be taken as advice or solicitation. Anyone attempting to replicate, in whole or in part, is responsible for the outcome and procedure. Any loss of functionality, money, property or similar, is the responsibility of those involved in the replication.

All digital communication regarding the email address 24hourengineer@gmail.com becomes the intellectual property of Brian McEvoy. Any information contained within these messages may be distributed or retained at the discretion of Brian McEvoy. Any email sent to this address, or any email account owned by Brian McEvoy, cannot be used to claim property or assets.

Comments to the blog may be utilized or erased at the discretion of the owner. No one posting may claim claim property or assets based on their post.

This blog, including pictures and text, is copyright to Brian McEvoy.

2015-08-26 (W)

Sunday, August 30, 2015

2015-08-29 (Sa) Wrist Mounted Chording Keyboard

The modeling file from 2015-08-11 (Tu) was reopened and modified. Two different types of servo lever arms were needed to make the four bar linkage. One type of lever must attach to a servo horn and be hinged on the other side. The second type must have bolt holes on each end to act as a hinge in both places. Two of each piece should be printed for a full set. Each piece is the same length so the four bar linkage being constructed would be a parallelogram.

Rotating view of servo arms model

Full set of servo arms

Downloadable Files:
To do:
  • Modify two servos for continuous rotation.
  • Wrist mount
    • Model lever arms
    • Build
    • Test
    • Refine
    • Repeat
    • Activation switch
    • Route wires
  • Write instructions
    • Schematic

The rest of the posts for this project have been arranged by date.

First time here?

Completed projects from year 1.
Completed projects from year 2



This disclaimer must be intact and whole. This disclaimer must be included if a project is distributed.

All information in this blog, or linked by this blog, are not to be taken as advice or solicitation. Anyone attempting to replicate, in whole or in part, is responsible for the outcome and procedure. Any loss of functionality, money, property or similar, is the responsibility of those involved in the replication.

All digital communication regarding the email address 24hourengineer@gmail.com becomes the intellectual property of Brian McEvoy. Any information contained within these messages may be distributed or retained at the discretion of Brian McEvoy. Any email sent to this address, or any email account owned by Brian McEvoy, cannot be used to claim property or assets.

Comments to the blog may be utilized or erased at the discretion of the owner. No one posting may claim claim property or assets based on their post.

This blog, including pictures and text, is copyright to Brian McEvoy.

2015-08-26 (W)