Robotic arm build: A fresh engineering adventure.

2 years in the mind, a week in the making

 The "Stringy bot" 

We saw a very repetitive production line, workers moving bricks off a conveyor belt onto pallets by hand. How could the sweat be spared? Of, course a set of robotic arms can do it. At that time still in high school and at least 4 years away from an engineering degree, we decided the only way to get something done sensibly sooner would be to design a small one from scratch and make it move- bit by byte, regardless of what we could be or might study to become. A couple of 3d printers, cnc machines and some education later...

The design objectives for Stringy Bot were:

-Cheap, competition was $900 'dobot'- naaaaaah dude! we want it free.

-Precise, 0.5mm repeatability fully extended.

-Versatile, ability to utilise different ends.

-Fast, therefore light in weight

-Larger than the average hobbyist size, arm lenth beyond 150mm.


To do it in a fasionably engineering style it needs to be in CAD form, and of course with a little bit of animation for inspiration!
 

 

Here are all the parts before laser cutting.

 Some free laser cutting after fixing the machine for the owners.

 Here is an unedited techincal run-down of all the parts fresh off the laser cutter.

At this point it took us quite a bit of time and cups of tea to make progress from here onwards.

The drive mechanism with some serious gear reduction was a challenge I had not completely solved yet. The options I was fairly determined(lazy, fussy, cheap) to avoid were:

-A planetary 9:1 reduction gearbox, too pricey and not available in all ratios!
- 3d printed or laser cut gears.. timeos to model and adjust by tolerances, and not scalably possible to a great enough resolution. 10mm gear on a 90mm...
- Toothed timing belt. More teeth to print or laser... same precision issue.

SOOOOOOO, now what? 

Disc and string.  

It sounds mad from a mechanical perspective but hey, its dirt cheap with almost infinite scalability in gear ratios not determined by any tooth modulus. 

After failing horribly using gravity as an advantage on a simplified version of our solution we resorted to using a trusty system found on many Delta style 3d printers.

Effectively two Dyneema/Spectra threads (think kitesurf line low stretch and tesile strength) run on two spools. Considering the drive spool, one line unwinds, while the other winches in the exact same amount of line in the other direction of the same drive spool- closed loop!  I need to mention that it is working satisfactory in this extent, for the current purpose, but there are some upgrades to better accomodate this system coming in V2.

The motor then drives a set of "parallelogram style actuators to separate the motors from the moving parts, therefore saving weight. More agility and better lifting capabilities. Try and make sense of it here, or check out the techincal run down for a basic demonstration.
 

And then for interest sake we drove the not-so-critical base axis using laser cut gears. 

 Mechanics are ready enough for electronics. Thats where the other guy in 'we' comes in, Ruan. Master(work in progress) of electronics and firmware! On the breadboard you can see an Arduino Uno compatible, and four stepstick stepper drivers. The basics, bare minimum at this time.Ladies, that is a four strand plait you see over there.


Usb and power into the nest of electrons, add some 1's and 0's, and we have a bot ready for action. With some basic code in the firmware , Stringy Bot does it's first movements!

 

Now to conclude, we have a cheap, fast, versatile, and strong robotic arm with an arm reach of 400mm! With the V2 we hope to complete our goals by bringing down our tolerances and making it a more precise and friendly bot to learn some new dimensions of mechatronic possibilities.

I just LOVE this stuff. I cant wait to see what the coders are capable of.

Five great reasons to come to the Red Bull King of the Air!

Since the Red Bull King of the Air has returned in 2013, I have been fortunate enough to witness both events, 2013 and 2014, in Big Bay, Cape Town. I can tell you this, the 2015 event will be the most extreme one to date. Spectators can see what the cameras miss. So here is a list of the most incredible things I witnessed in the KOTA Big Bay arena, which gives me reason to be there again.

Defiance of gravity:

 

The riders are not just jumping- they are Flappy Bird FLYING! The average height of a kiteboarder's big jump is around 8 meters. Last year the heights were recorded with a high tech GPS, Xensr, and the record height was 26 meters above the level they took off. That is jumping higher than an 8 stories, using no other force than the wind! 60% of the move's score is based on the height of the jump- so expect some massive aerial maneuvers.

Epic crash bail-fails from very dangerous tricks:

 

Megaloops do go wrong. Any move based on the Megaloop is undoubtedly extreme. The rider jumps high, really high, and then loops the kite in front of him so that the lines are horizontal at the peak of the jump. At this point the rider is exposed to free-fall with some serious down-wind speed. If the kite does not return to the top quick enough to "catch" him, the rider plummets like a stone.

One may think that the risk factor in kiteboarding is significantly less than that of other extreme sports, such as extreme motocross, but allow me to explain; an extreme sport should automatically progress to the level where the moves becomes life threatening in order to set the standard for competition. For example, a back-flip on a BMX is a fairly dangerous move, whereas a backflip with a kite not so dangerous. However, a kiteboarding move that can match the danger of a standard backflip would be a triple backroll in a high jump. What happens here is that kiteboarding moves are easily more impressive than any other extreme sport, regarding the extended air-time for flips, grabs, kiteloops and other acrobatic possibilities that a kite offers. A point to note here is that water nearly becomes rock solid from these crazy altitudes.

Never say die attitude:

 

Not only do the riders crash sometimes, but also their kites... Last year we saw a legend of the PKRA tour, Aaron Hadlow recover from nasty crash after one of his steering lines hooked some place it should not have, looping the kite a dozen times dragging him hundreds of meters downwind towards the rocks; the DEATH LOOP. Somehow, he miraculously regained control over his kite, tacked upwind and stomped one huge unhooked backroll megaloop with a handlepass in the dying minutes of the heat.

Sportsmanship:

When one rider has some problems with their kite or board during their heat, fellow competitors on the beach are quick to react to the rider's needs by lending their own personal board that they would need in the following heat. I have also seen competitors go and check with another rider after a hectic crash to see if he is okay, sacrificing their own time limit! Of course it is human to help another, but "every man for himself" does not necessarily apply in the battle for the crown.  There is definitely some fair play beyond the, "you got what you deserved" scheme among competitors of extreme sports.

 

Big surprises:

 

I remember back in 2013 Lewis Crathern playfully nudged another competitor with his kite in the middle of a loop- both riders were mid air. Imagine being hit by a kite... 

That is not all, Lewis is also a commentator at the event between his heats to provide the perspective from a rider; last year he called Billy Parker in his heat over the speakers and said, "Billy, I know you can hear me, I want to see a front-roll kiteloop with a nose grab." A few seconds later billy stomped that move "on demand"! 


Today's event might be held over two afternoon due to some anomalous weather patterns. Nonetheless, I'm expecting a great event with some astounding performances.

Come see what is radical in kiteboarding at the Red Bull King of the Air 2015, Big Bay, Cape Town.