Let's Make Robots!

Rotary walker entry for Rescue Robot Challenge

Navigates simulated disaster zone and picks up ping pong balls


            The premise of the Rescue Robot contest is to construct a remote controlled vehicle capable of navigating a playing field filled with obstacles in order to retrieve ping-pong balls.  The playing field is 18 feet by 10 feet and the obstacles that must be navigated include a 45-degree slope, an area filled with pea gravel, a 6-inch high wall, and a covered cave area.  Each contestant must collect four ping-pong balls from 4-inch tall pick pylons and place them all on a single drop pylon.  The contestant to move all four balls to the drop pylon first wins the round.     


Solution abstract

            My entry in this challenge has been scratch-built to meet all of the requirements in the most effective, yet inexpensive, way possible.  To traverse the difficult terrain my robot uses a versatile rotary walker locomotion method.  This allows my robot to have the same capabilities of a robot with treads without any added weight or worries about gravel jamming the treads.  The majority of the robot is made using strong, yet lightweight, PVC plastic, and this lightness also aids in getting over obstacles.  To navigate the “cave” my robot is fitted with a camera that transmits its image back to a real-time display.  This lets me fully control the robot even when visual contact is lost.  The final element of the robot is a versatile arm which allows the robot to easily pick up the ping pong balls yet still precisely set them down on the drop pylon.



            One key element to any robot is a versatile platform.  I have chosen not to buy a kit-based platform but instead build a custom one, which is incredibly powerful for its weight.  The construction is mostly PVC plastic, and in order to save weight the frame has holes cut out in areas not key to the structural integrity.  The platform uses a rotary walker mechanism for locomotion.  To my knowledge, there are no well documented robots that use this type of locomotion, and as a result a lot of work went into refining the basic idea before a working model could be built.  The advantages, however, were worth the time.  The rotary walker mechanism gives the robot a large surface area that has contact with the ground.  This spreads the robots weight evenly, allowing it to quickly cross shifting and unstable terrain such as the pea gravel in the playing field.  The extra contact area also aids in climbing up the steep incline on the course.  The robot also has a motorized “tail” which can lift the back of the robot up to help in climbing tall obstacles such as the 6-inch wall.  In addition to impressive capabilities, the platform is also simple and durable.  Because of the design, rocks and debris do not get jammed into the mechanism as they often do with treads.  Also, two motors drive each side, so if one experiences failure the other motor can still drive the mechanism without problems. 

            Mounted to the platform is an arm with an equal amount of innovative touches.  This arm can rotate a full 360 degrees, as well as raise and lower.  The servo that rotates the arm is geared down to allow for precise control, and the 4 joint mechanism which raises and lowers keeps the claw level with the ground at all heights.  To make the robot versatile, the rotating part of the arm contains mounting points that allow the existing claw to be easily swapped for a different one.  The claw for this robot is designed to be able to pick up a ping-pong ball easily without precise positioning, and yet still very precisely drop the ball on the place pylon.  It can do this because the claw opens in two ways.  One swings the claw wide open, which is ideal for picking up a ping-pong ball on a pick pylon because when it closes from this position any ball in the general area will be snatched.  The second way that the claw can open is a more gentle motion where each half of the claw opens slightly then swings up and out of the way.  This is ideal for placing the ball on the drop pylon without knocking all the other balls off.  The dual-opening mechanism is driven by two regular servos with just 90 degrees of rotation; it is a clever hinge mechanism that allows for a complex motion despite limited servo movement.               

            To control all of the robot’s functions a simple Play Station controller is used.  This is familiar to many people, meaning a complete novice can learn to accurately control the robot in a short time.  The real time camera allows the robot to be controlled out of sight and in tight places such as the “cave” where the robot is not visible to the operator.  The image from the camera is displayed on a portable color monitor.  A bright LED light allows the camera to still be useful when the area is dark, and a fish eye lens allows the operator to see more of the surroundings in the display.  To help make controlling the robot over the camera even easier a red colored LED shines on the area below the claw, so if a ping-pong ball is the correct distance away for retrieval the ball will be lit up red.  To power the robot a RC airplane lithium polymer battery is used, which is very lightweight.  One charge lasts about twenty minutes per battery, and because this robot uses a standard connector plug a higher capacity battery can easily by swapped in if more duration is required.  This robot is easy to operate, versatile, and costs under 300 dollars, which is significantly less then the competition.   

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Arty or techie, still it is very nice,great, amazing and others.

Nope- I did not invent this type of locomotion.  However, I have yet to find any documented robot that uses it, so when building mine I did have to start from scratch and try various angles (which I found to be very critical), wheel sizes, and slat numbers, before I found a design that goes straight and turns well.

Haha wow!  We've got some snow here, but I havent tried it outside in the damp.  I'm going to avoid risking the electronics and motors till after the contest, then I'll go try some fun off-road stuff- maybe even convert it to be amphibious.  

Anyway- I'd love to see other people's take on this idea.  Your right about adding tires (I considered this), but having all the traciton on the wheels when it's on a smooth surface may create too much "toe in"- where the wheels on the left and right drive against each other.  At least that was my reasioning, but I'm sure it could be made to work.  Goodluck!




I am really impressed by your innovation in building this robot. The drive arrangement is great and not just another one of the "same-old-same-old" propulsion set-ups. I am glad the drive system did not pick up gravel and get stuck behind the bars and the speed and power makes it climb right up that 6" barrier very well.

I have not yet seen the actual gripper /ball-grabber for the ping-pong balls yet, but I like the start you have in the rotating base for it.

I am still wondering about the covered cave part of the course.

I will keep watching your project with interest.  Hope you do well in the final challenge.

hey thanks!  I'll have a video covering the gripper up tomorrow hopefully.  And with the "cave" I'll be using the same camera setup as this robot: https://sites.google.com/site/botsfromscratch/robotics/remote-presence-robot  Appart from a light that wide angle video feed should work

That is looking very nice. That is, the picture at the top has an almost professional air to it.

Hmm, I was thinking...

They want you to navigate a simulated disaster zone and pickup ping-pong balls. I am trying to visualize what disaster would leave dangerous killer-ping-pong balls strewn all over.

There would not be, but I was considering what I heard about the nuclear disaster in Japan.  It is neither cleaned up nor even totally contained. It was much worse than they told the public. They have had to rotate through thousands of workers, because no worker can stay there more than 10 minutes.

Anyone visiting the site gets about a year's limit of radiation in about 10 minutes. Then they must leave and new workers come to take their places. They have used some robots, but only with limited success.

--While it may have nothing to do with it, maybe they are looking for a new design for a robot to aid in the cleanup.  They would need to build a much larger version of course, but they might use the winning design as a prototype.

------------Just a thought.

I relize this is slightly OT, but I think it's important to not shoot around information that is not strictly correct. so... here goes the rant - I'm unapologetic here, because I think too many people talk before thinking...

"Anyone visiting the site gets about a year's limit of radiation in about 10 minutes"
Quite frankly, this is unadulterated, and purely hysterical rubbish.

Firstly, radiation is measured in different ways, and the media (and therefore you) fail to make ANY distinction whatsoever:
Activity is measured in "bequerels" is "decays per second" and tell you absolutely nothing about how much radiation you get. your smoke detetector has about 30 000 Bq! and it's a LOT closer to you than fukushima! Why aren't you panicking? - because you're not seeing the full picture.
"rads" is how much radiation your body ACTUALLY absorbs.
As a good analogy: "Activity" is the rain, rads is how much rain hits you, sieverts is how wet you get (which depend on your raincoat, how big you are etc.). the media pick one unit, babble it, and pretend it all makes sense to the average reader which is most certainly does not.

 "anyone visiting the site....." is a bit like being astonished if you pour chlorine in your eyes and go blind. Firstly, as is the rule for ALL reactor sites and most power-generation facilities. not "anyone" can visit - and if you'd be far more than a fool to visit a damaged reactor site without knowing what you're doing. Secondly, in the case of fukushima, it always took a longer than "10 minutes" - often weeks. Not only could you calculate this yourself, additional facts bear it out:  The fukishima 50 (i.e. the workers), at worst, were limited to 15 minute sessions - that's per session, not in total. It's true that they were "expired" after SEVERAL of such sessions, and it's true also that some workers were evacuated after high instantaneous doses, but to make the claim that "anyone" visiting the site has to leave after only 10 minutes is a disingenuous and unsubstantiated lie.

Now, having ranted (and I deleted about 90% of what I originally wrote) at what was probably an innocent comment on your behalf, perhaps you can appreciate how passionately annoyed I am  -  (yes I HAVE complained to them to; with no effect of course, they love whipping up hysteria) and It REALLY gets my goat that people perpetuate these lies without even the slightest consideration of the harm you cause.

I live in japan. I live in tokyo. *I* am one of the people YOU affect by disseminating these careless  attitiudes and annoys me intensely. YOU might say "sheesh, I'd get out of there" - and then you'll get in your car and put yourself in more danger of dying in the road than I ever will from radiation sickness in Tokyo. If you say this, you'd be saying without having the slighest clue what you're talking about, yet, so many people do.

Just as additional information that unintentionally might come across as a pissing contest: my undergraduate was in radiation physics and radiation treatment planning for cancer therapy, I also worked (for a summer!) as an assistant saftey officer at Australias's nuclear reactor, I'm pretty familiar with at least the words the media uses, and how horribly they misuse them. Consequently, I'm routinely disgusted at the sucseptibility of the general public to soak up the horsesh*t perpetuated by the hysterical media and regurgitate it as if it means anything - IF you want to talk about Fukushima and be informed about it, I recommend the international atomic energy agency website. Like anywhere, they have bias, but they DO have transparent rules, regulations, information and systems - unlike Tepco, and unlike ANY nuclear reactor. The media is NOT a good place to get important information!! IF you don't want to read the proper information sources and get the correct information, PLEASE do not talk about these things in a public forum.

I'm ENTIRELY in support of building and desiging robots for rescue, it's one of the most perfect applications. I genuinely didn't mean to come across as condescending or arrogant, but I did mean to come across as rather angry - I really don't dig my mother phoning me up nearly in tears, telling me to come home because of some foolish comment written by a paranoid pretentious knowitall, she read on yahoo dot com, and having me explain the difference between bequerels and seiverts to her while she's hysterical. If you make a comment like this in a public forum - in ANY public forum, please, PLEASE consider what you're saying and who it affects.

Even though I said I was unapologetic, I really didn't mean to offend anyone - just shake them up a bit.. If you'd like to respond to this OT topic, please feel free to send me an email!!


Hi. I apologize if anything I said struck a nerve.  I may not have been perfectly precise in my wording. I have noticed that for people outside Japan, there are many who have not even heard about the problem. For example, even though (small amounts of) radiation from the explosions has even reached parts of this country (United States), were I to ask my adult son if he had heard of a reactor explosion in Japan, I would guess that he would say he had not. My message was more aimed at peaking people's interest into looking up information about it for themselves.

When I said "anyone visiting the site", I did not mean people well back from the center of the hot zone.  I know that people up to 30 km away were evacuated beginning 15 May 2011 (for example, Litate village and Kawamata town), but I do not mean that area, and I certainly do NOT mean Tokyo itself. By the "site" I am refering to the heart of the disaster (Fukishima Dai-Ichi [aka #1] and Dai-Ni [aka #2] reactors and even Tokai), the core of the radiation zone.  I understand there were varying amounts of damage at many reactors but that the worst of it, I believe, was at Fukishima Dai-Ichi. To keep things clear, I know that the radioactive cesium and iodine (Cs134, Cs137 and I131) levels are high close to where the series of reactor explosions occured, but for the most part have not exceeded the allowable governmental limits in the air, the sea water or the food supplies in other parts of Japan. (I believe samples have been taken in 18 prefectures and a few samples have been above the allowable limits, but most are not in the hazardous range, and the government does not want people to panic.)

To make things clear on my terms about radiation, when I was young (teen years) I was trained as a "radiological monitor" for the event of a nuclear war. (This was back in the Cold War era when we considered we could be in a nuclear war with the Soviet Union at any time, which could destroy all or most of life on Earth, and were trying to prepare for such a disaster to minimize the casualties.) Therefore, I do not think in terms of "decays per second". As you mentioned, this is useless or extraneous information. I refer to roentgens or rads (1 roentgen = 0.877 rad) of received radiation as shown using such methods as dosimeters and film badges, which darken as more and more radiation hits them. The theory being that the radiation hitting the dosimeters or the badges gives a reasonable indicator as to how much radiation has hit the person.

When I said that they received a year's amount of radiation, I was perhaps being a bit too colourful in my writing. What that means is that there are allowable limits as to how much radiation a person may receive without it being considered dangerous to their lives, their reproductive abilities or their unborn children. This limit can be expressed as instantaneous amounts, daily accumulations or even weekly, monthly or added up for an entire year. That was my point. If you go into the heart of the radiation area, you will easily receive enough to equate to the limit you should receive in a year's time. In order to utilize the knowledge of some of the core of professional workers familiar with the reactors, these limits have been (secretly) relaxed slightly, but for the most part the government wants the legal limits to be observed. 

You mentioned the fukishima 50. It is my understanding that this quantity is the number of workers there at any one time, whereas I refered to the total number of all workers who have worked there at different times since the beginning of the cleanup operation. Workers are regularly rotated out and replaced by other people. As you said, workers are "expired" (sent away from the site) after they receive too much radiation and new workers must be brought in to replace them.

I will accept that I may have been misinformed as to whether the general rule was 10 minutes or 15 minutes. You may be correct in this.  I would have to investigate further, but still, it is not a great difference.

I could go into more detail but I hope this clears up any questions that arose.

 Added Note:  I noticed you mentioned radiation sickness, and for those who do not know, it takes a LOT more than the governmental limit to cause radiation sickness. I have heard that some of those workers on site at the time of the tsunami who tried unsuccessfully to prevent a nuclear accident did have serious enough exposures to get radiation sickness.  They stayed on past what they knew was safe for themselves in order to cut down the danger to others.

After nuclear accidents like the 1954 accident in US "Operation Lighthouse" testing a hydrogen fusion bomb in the Bikini Islands, we found that humans are much resilient than previously thought. Wind change took the radioactive cloud right across the island of Ronjelap exposing the islanders to very high doses of radiation which caused severe sores and lesions as well as hair and tooth loss. However, twenty years later, it was expected that there would be high incidence of cancers, birth defects and so on, but the numbers were much lower than expected, only slightly higher than normal, proving the resiliance of the human anatomy.


I didn't intend to have a discussion about it. I'm TELLING you you are wrong. I'm also telling you that what you're doing is contributing to the already substantial panic and paranoia.

Quite frankly, that's all I intend to say on the matter - especially in this forum.

I see.

I should mention then that my information about the Fukishima disaster comes mainly from the International Atomic Energy Agency web site. If I have incorrect information, that is who you can talk with to correct their reports.



There is also this news item from the Associated Press: http://news.yahoo.com/probe-finds-japan-withheld-risks-nuke-disaster-100906893.html



You'd already conceeded your descriptions were "colourful" - moreover, the IAEA site certainly does not support your words that I objected to most strenuously. 

Nor does the yahoo mail. My point is validated. Pleae do this no longer - it's intellectually dishonest.