The Robots are coming! Are you ready? Now is the time to build the (Totally Not Evil) Robot Army! This blog creates, builds, and explores the personal 'Making' of robots. Enjoy!
Showing posts with label Single Actuator. Show all posts
Showing posts with label Single Actuator. Show all posts
The skinny protype leg needs to be wider to support the robot. In general in needs to be more robust and handle the sideways transitional forces. To do this I am making the leg as wide as the 'pin' in my previously designed hinges. This pin is a 40mm finishing nail, which I have a box of. I have used them has hinge pins in the design of the wild weasel and Mojo4. This will provide some of the support needed for the sideways forces. The design must be carried forward down to the lower leg and foot.
Robot Running Leg Mechanism -v2
As the width of the robot increases, it is not possible to determine on which side the compliant link will go and the placement of the crank and crank gear. The back lifting linkage, does not need to be 'wide' as it is only projecting the motion, not the support.
Robot Running Leg Mechanism CAD (pins not shown)
Also in this step, I am starting to think of how to drive the crank gear with a motor. I have a 3D printed gear box from a previous design to reuse (Tilt! and 3D gearbox). This gearbox will allow the robot to be driven by a brushed motor from a recycled printer.
Here is a video of the current design step:
As you can see, there is a lot of movement generated by the motor. The leg is thrown around creating an oscillation and some unwanted impulse movement. This will need to be considered (dampened)in future design steps.
Milli - a Bio/Math inspired crawling single actuator robot millipede - now with teeth!
Milli - Millipede robot - now with teeth
From the last post, you may have noticed that I had tried to print some "nodes" as a possible improvement to Milli the millipede. Well, that thought was not as successful as I had hoped. There turned out to be no flexibility and too much tension on the helix. With this in mind, I reopened the milli design and set to work on some design updates:
Offset the motor
add a gear reduction to the motor
add a bearing to main helix mount - to remove force on the motor itself
try out a new power source
Add teeth - because we need to add more Nightmare Fuel!!
CAD Design - new Motor Mount and Gear
The new design is a new motor mount, with drive gear, a bearing mounted main gear, and new 12V "shore" power.
3D printing gears remains a dark art to me, but here you can see that they are functional. In this print, I have used a larger Modul of 1.5, this makes larger teeth. I believe for my quick 3D prints this is a more accommodating solution (more tolerance for rough prints!).
I applied a liberal amount of hot glue to attach the pre-existing helix mount to the newly printed main gear. That may qualify this for a frankenstein prototype, no doubt.
Sloppy gears? certainly room for improvement - on the next iteration. The thicker base layer print creates an uneven gear surface.
Another issue was the 'pede wheels' that I kept from the previous build. They function as wheels, however in the video you can see that the left wheel consistently unwinds and falls off, Doh!
Ready to Test! Let's get crawling!
Milli - Robot Millipede on a colorful background
For this round of testing, I am using "shore power". The robot is tethered to a 12V DC source. I reused a momentary switch - also from a printer - in order to easily turn on and off the robot.
Testing goes as expected. The motor gear hold, which is surprising. However the front left pede-wheel falls off frequently. The motion of the helix, continues to be smooth. I believe the addition of the bearing smooth this rotation off, taking load off the motor.
Video on YouTube:
Next Steps:
With this success, time to think of what would be in the next iteration.
Onboard 12V power supply
micro-controller with PWM output
Motor Driver board
remote or autonomous operation (Min1 project may come first)
Milli is a bio-inspired robot that uses a single actuator to create standing wave motion.
Where to go next on the design of the WildWorm drive and Milli?? As expected, the recycled printer motor that I am using (9-12v) powered by a 18v rechargeable drill battery, is too much for the little robot. (duh!) When testing, the rotational speed of the motor is too much for the directly driven helix spindle. After some testing this has lead to the helix base to be burnt out by the motor spendel.
Milli's WildWorm drive - burnt out helix mount separated from the motor.
What is needed is a gear reduction, to reduce the rotational speed, and increase the torque of the helix. This is very similar to the gear reduction used for the same motors on the Wild Weasel track. Here you can see the video of the gear reduction built into the track:
But Where to put this on the rather simple chassis of Milli?
Milli - Motor Mount
Actually, there is plenty of room. With the next iteration of design, I will:
Add a bearing to the chassis, creating the mount for the helix. this should reduce any load from the wildworm drive on the motor itself.
A shaft will connect the helix, through the bearing to a similar sized 3D printed gear.
The Gear train will consist of a small gear directly on the motor. This will drive a large gear with coaxial small gear. this small gear will drive the helix gear. (A quick estimate would have 18mm diameter to 40mm diameter gears. times 2 ~ 4.8:1 gear ratio)
If another gear set is needed, it can be added relatively easily.
Milli - Chassis with Recycled Printer Motor
Unfortunately, this is all conceptual at the moment. It is not even in the CAD system just yet. However - the thoughts have given me some new insight on Mojo3 - and there will be a new design blog post out shortly. Stay Healthy!
Milli is a bio-inspired robot that uses a single actuator to create standing wave motion. Update: I have been somewhat distracted (as we all have been with this virus), but here is some progress made. I have added a forward section of the frame to provide room for a steering mechanism. For the first prototypes, I will use a set of wheels that can be turned to steer the 'WildWorm' in a new direction. This may look like a traditional vehicle, but all of the motive force propelling the robot will still be from the oscillating standing wave motion. In order to keep the Millipede motif, the front wheels will be made of little feet! Here is a CAD view of the current design:
Milli in CAD - Single actuator bio-inspired robot 20MAR2020 (OpenSCAD)
and here is the current printed version:
Milli 3D Printed - Single actuator bio-inspired robot 20MAR2020
Milli now has many many new feet! Milli is a sinusoidal, bio-inspired Millipede Robot. It is completely 3D printed and is made of recycled printer parts and a metal cloth hanger. Apologies for the delay in posting, it has been a busy month working on my startup (non-robot) business. However, this weekend, I booted up the 3D printer and created a whole new set of golden feet for Milli. 81 new feet to be exact! (not quite a "milli" but getting closer)
Milli - millipede robot track - new feet
Mathematically, the new feet should provide more distance ground traveled with the twist of each tread. This will result in an even faster robot! The additional ground speed will also be enhanced by the additional grip (friction) with the ground surface, resulting in reduced slippage.
Milli Robot - Tread-Track with new feet 3D CAD design
Each tread now support either 3 or 4 feet. The 3 or 4 treads are interleaved, to prevent the feet from colliding when they are traversing the rotating helix. The resulting sinusoidal motion will spread the feet as it comes to ground contact. Then contract the feet when lifted. -- Video coming soon!
Milli Robot - close-up of the new track-tread-links
The result of the additional stretch between the expansion and contraction of the feet will result in a faster motion for the (standing wave) motion of the tread. Theoretically, the feet can be extended a bit further, this will be interesting to see in the future! I am currently working on the 'head' of the Milli Robot. The new version will support axle and wheel-feet (feet-wheels?) to provide steering. In addition, I need to create a place to stow the battery and controller. In other news... This TotallyNotEvilRobotArmy Blog has now had over 10,000 page hits!
The Prototyping of milli is moving - as well as Milli, its self!
The focus since the last post was to find and fix any binding parts of the tread tracks. I have located a specific tread that was not flexing properly, due to it being part of the v3 design and connecting to a v4 tread. I am using screws to act as 'pins' in the track to connect treads together. This is not a good practice as the tread of the screw can bind with the tread. however, if significantly bored out it ispermissible at this stage of development.
Milli OpenSCAD - for 3rd prototype test 16 Feb 2020
The other change was to adjust the design of the horizontal stabilizing arm. This arm converts the spinning helix motion to a moving sine wave. Thus it is essential to the design. Changes included shortening the arm by 8mm and increasing the opening by 4mm. I also noticed that the first tread was binding with the arm, and adjusted the tread to move more freely.
Milli - ready for static testing, full tread length, 18v battery, messy desk(!)
The result - the track moves freely! At least in the initial trials when I applied 18V to the motor it worked well. I then removed the frame holding the chassis and a quickly put together a simple axle and wheels. This was made by a thin rod and some plastic gears salvaged from a printer. I used alligator clips to hold the wheels in place. I put the robot drive on some carpet for friction and Viola! - the worm drive works!!
Next steps:
Find that nagging binding point seen in the video
Thinking on the chassis and covering. How the heck am I going to get a battery on it?
The Milli project is an effort to build a bio-inspired (math inspired?) robot capable of traversing surfaces that are problematic to other robots (such as loose gravel, shag carpet, and muddy bogs, etc). And to make it look really cool. ;) The results of the 2nd prototype are much improved, you can see from the video that the prototype has the correct motion and considerably less friction.
Currently, I have printed 23 links in the track tread. There is an additional load to rotate the helix, but applying additional voltage the motor resulted in enough torque to spin the helix. (at 18V it is very quick). Next steps will be to create a rear stabilizer to dampen the effects of the spinning helix.
Milli is a bio-inspired robot that uses a single actuator to create standing wave motion. The Frankenstein prototype was successful enough to indicate that the concept is feasible. The next step is to take the learnings and iterate on the next design as well as create new pieces to replace the Frankenstein parts. New in this build are:
a motor mount, with a frame to hold the Horizontal Stabilizer
a single piece Horizontal Stabilizer
upgraded tread-tracks (version 4)
new Helix mount for motor spendel
WildWorm Drive - iterative design (OpenSCAD)
The Frankenstein prototype was becoming 'stuck' due to two combining factors. An astute YouTube viewer pointed out that the Horizontal Stabilizer was twisting which caused the treads to bind on the helix. In addition, the pin in the Horizontal Stabilizer was crudely glued and would obstruct the rotating helix. The new design uses a single piece Horizontal Stabilizer, pictured above in light blue. In addition, the new motor mount will more tightly secure the stabilizer and position it in line with the centerline of Helix's rotation. The Tracks have been updated to use a screw as the henge pin between the treads. This design, I hope, will create more fluid motion. It will also be easier to assemble and reduce the failure rate the track becoming disconnected.
WildWorm - Underside view (OpenSCAD)
The underside view of the next design iteration shows the base of the motor mount. As you might be thinking, the helix will not be well exposed to ground contact with this design. This is true, it will be addressed in future iterations. For now, I need to verify the easy rotation of the helix. For this, I will need more track links and a smooth stabilizer.
WildWorm Drive - 3D printed, the new design works much better
[later today...] I have printed the new design and put it together. The single piece Horizontal Stabilizer was a significant improvement. With a some additional filing on the parts, the WildWorm drive rotates as planned. I will update with a video of the new design. Finally, for the Robot Lovers out there. Ninety-nine years ago, On January 25th, 1921 the Czech play Rossum's Universal Robots premiered, entering the word 'Robot' into the English Language.
Milli is a bio-inspired Millipeded Robot and today's blog entry is titled: FrankenWorm! Rapid Prototyping The best way to "learn quickly - fail quickly" is to using rapid prototyping techniques to test out ideas quickly and identify potential and real points of failure, design needs, and radical improvements. Three-D printers are great for taking ideas and making them solid. An even faster way of rapid prototyping is "Frankenstein Prototyping", where the initial prototypes are built by using parts from other projects. In many cases, you just grab the part that is close to what you need and fasten it to the build.
Frankworm! Franken-prototyping the WildWorm Drive
Today, I am Frankenstein prototyping the WildWorm with 3D parts left over from previous projects. I wanted to quickly see if the rotating helix is going to be able to move the track treads of the WildWorm drive. what is in the discarded print bin?
Motor frame - one of the chassis from the original Mojo
Battery holder - from an old RC car and RC Rover project
Motor holder - initial WildWeasle tests - holds a 'recycled' printer motor
Motor spindle adapter - from initial Centi tests
Helix Mount - Cam variation from the Mojo2 (he walks!) project
Horizontal Stabilizers - linkages from original Mojo project
Stabilizer linkage - v0 print of WildWorm track
...and this is why I don't throw away old 3D printed parts.
After finding the parts in the bin, I connected them all together to set up my initial tests. I just used quick fastening methods, tape, hot glue, twisted wire, and screws. It is meat only to learn what works, and what does not!
Can you identify the parts in the picture??
WildWorm prototype test - Franken Prototype
Test Results
I ran the first tests with a weak battery pack, just under 5V DC. This was attached to a recycled printer motor that is rated 9-12V (I believe). I thought the motor had plenty of torque to rotate the helix without beating the assembly to pieces. -which was important at this stage.
The video shows the results of my initial testing.
First of learnings, yes this worm drive concept is feasible. The underpowered motor is just barely turning the helix, but the rotation is consistent enough to move the treads. The stabilizer will need to be tightened up to keep the tracks in a steady horizontal position. and the helix will need to be smooth, as well as the inside of the treads, in order to reduce the internal friction and sticking.
This test only proved that the motor with stabilizer will move the track in the correct motion. There are a lot of design learnings available, now I can iterate on these ideas and go for the next set of testing.
Next in line for bio-inspired robots is the Millipede. (I know, I know, I am starting a new project without finishing the last ones. But, this one is interesting! ;) Millipede design that I am looking at is the concept of having many many feet on the ground for the robot. Similar to the Centi robot concept, I will use a mechanism to transfer the rotational motion of the motors to the feet in contact with the ground. For this robot build, i am focusing on the work of David Zarrouk. Zarrouk's SAW robot is a Single Actuator Wave-like robot. The design uses a single motor that is spinning a helix twisted rod. The rod moves a linked set of treads in a way to create an advancing standing wave.
SAW robot from David Zarrouk
This is best viewed in his video, from Zarrouk Labs:
For my build, I will start with the wave mechanism to provide the motion for the Millipede robot. There is a published paper which describes the math put into Zarrouk's robots. I am using this as a starting point in my design. Using this as inspiration, I will first try to replicate his work, then extending on it. I will attempt to use this wave motion, as the driving actuator on the robot. I am calling this my Worm-Drive, the WildWorm, for Milli the robot. Initial Design:
The Track - The most complicated part of the worm drive is the tread design. The tread is conceptually the same as a crawling tank caterpillar tread. The only exception to a tank tread is that these treads will not be moved by cog wheels. Each tread must have a pivot point so that it can be linked with the next tread. When linked together in must be very flexible. The joints must have low friction. Part of this design has the helix is spinning inside of it. The inside slot must have clear running path as the helix will actually slide along from side to side. But, as you will see it is not the helix that is moving, but the treads wrapped around the helix.
WildWorm Track design version 3
For this first set of designs, I am using nails to act at the connection axis. They will be positioned between two pin holes. the inside hole is small and will hold fast to the nail. The outside has a larger radius so that the part rotates around the metal nail. Finally I have extended a 'tread' to the track link, so that it can directly interact with the surface.
WildWorm 3D printed Tracks v1 - top left v2 - top right v3 - bottom
It might be obvious, the track linkages will need to frictionless. It occurs to me that low friction will need to be designed into the treads. The next iteration of the design will perhaps use a metal washer between the tracks to reduce the friction. Lubricant will also be helpful. Ultimately, the series of track will need to be nearly fluid when shaken.
WildWorm - Helix and Tracks - 1st prototypes
The Helix - The helix is the part in the middle of the assembly that drives the mechanism. There are not a lot of details about the construction of the helix. I have started by using a wire from a coat hanger. I have wrapped the wire around a metal pipe and adjusted to create a consistent helix. The helix should be smooth to reduce the friction of the track that slides around the helix. It may be possible to 3D print a helix, this would ensure the precision of the design and centering of the motor axis. However, a 3D printed helix may not have the strength needed to support the track linkages. First Prototype The first prototype assemblage of the WildWorm, has yielded a lot of insight. That is a nice way of saying, it did not go very smooth as I hoped. There will be a lot of tension between the helix and track. Perhaps this can be relieved by increasing the period of the helix. My first attempt was a 7.5 cm. I see that it should be much longer, maybe 10-12 cm.
WildWorm - 1st assembled prototype of the helix and track (5cm period)
Next steps will be to increase the length (period) of the helix. I will also design the motor housing, stabilizing arms, and a mount for the helix. The helix will be easier to test, once I can mechanically stabilize (hold horizontal) the tracks. [UPDATE] Extending the helix out to 10cm period, length of one full cycle, solves many issues. The track slide smoother, and there is significantly less binding.
