Friday, June 19, 2015

Robot Power Vyper ESC CAD Available

After coming back from Battlebots 2015, I am DEFINITELY feeling the big bot bug. I began playing with some concepts for robots but, as you know my design style, noticed a 3D model for the Robot Power Vyper ESC did not exist. So I made one off the physical item courtesy of Charles Guan and make it available here.



So here it is. The actual dimensions ARE larger than the advertised size online. My guess is the fan on top adds some height. I may have added a shameless plug on the bottom side, hehe (feel free to remove it).  Charles has more details on the internals. Here is a 3D printed version of the STL model. Not too bad?



The model can be downloaded as an:

Parasolid TBH is probably the easiest, but choose your own medicine. Warning, no weight has been input yet!

Cheers!
-Jamo

Sunday, March 1, 2015

Return the Victorious: Motorama 2015 Event Report

Motorama may very well be the toughest combat robotics competition in the entire Northeast. With that said, it is very difficult to place in any weight class. By chance and skill, I was able to place in two weight classes of three entrants! G3 Robotics was able to end with a respectable 10 wins and 4 losses. See the bot specific breakdown.



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Silent Spring
No place (3W - 2L)

Finally here Saturday morning and still no name for the beetleweight DDT clone. Despite the controls oriented suggestions given by other builders, my friends agreed to Silent Spring, the name that Nate Franklin had originally proposed. Once I explain the reference people think its clever >_>

Regardless of the name SS's day started out rougher than most. During safety, the drive motors would not shut off! I traced the issue back to the receiver, which does not appear to support failsafe protocol on the elevator and aileron channels. Broke a few wires swapping back to the reliable OrangeRx 6ch receiver but that was quickly handled by butchering a bind plug. SAFETY ALERT! THE 3CH S.BUS RX DOES NOT PASS FAILSAFE!

Silent Spring v Rmr
Soon we were ready to fight and SS pulled Rmr, a fellow MIT bot from MITERS. This bot featured an overhead spinning bar and an O-ring track system for drive. 


The fight was against his favor since my blade could reach under his blade to land hits on his body without hit myself. However, without ANY driving practice on SS, It would be very easy to over travel after a hit where Rmr could get my sides or even a wheel.


Because of that, I played on the cautious side and took smaller pokes. One of the first few glancing blows actually did result in him landing a body shot, but without critical damage I was able to continue the attack. Still, some nice scars there.



Silent Spring v Time Warp
Now hearing I would be fighting the modified Trilobite kit, I decided to take my time in repairing the drive belts which appeared to be loose in my first match. I would need every ounce of maneuverability to escape this bot. On top of the Trilobite base, Time Warp featured an angular plow from what appeared to be welded and treated steel. There was no way I could bite through that plow but as it would have it, I didn't need to.


I spun up to full and decided to focus on keeping the blade forward. Time Warp came to me with the plow first and after several big hits the pins keeping the shaft on gave up and the plow came off. If it didnt break at the collar, it might have broken at the beak. Small cracks were beginning to form.



However the blade had slowed significantly by the end. I had not received any visible damage but I could not spin up the weapon. This time dependent shortcoming would plague me for the rest of the tournament.

Silent Spring v Devastating Moment
Joey and I had once fought antweights in 2008. His Swamp Woman vs my DDT. DDT managed to get the better of that one but only because SW was an unweaponed bot. Now Joey had a Weta kit with a custom steel eggbeater. It sounded mean!

Unlike In the Margins (Weta Killer), SS has a thick blade which is better for big hits and less effective for chopping or grabbing. I would only be able to get good hits on hard surfaces and so instead of aiming for the feet, I aimed directly for the weapon bar.


I was essentially relying on the robustness of the robot mechanics since at this point I had not sorted out the weapon ESC issue. If I stopped spinning it could be over for me. I got lucky this time when he shut off unexpectedly  after two big hits and couldn't continue.

Speed Wedge 3 v Silent Spring
I met Ian this year when I spoke to him a bit in the pits. It didn't take long for me to realize a quality builder and solid competitor. When I pulled this match up, I predicted a loss immediately. With the spotty ESC and his driving skill, attrition would work against me. Well, I don't need to say much more do I? Loss by judges decision :P



In the Margins v Silent Spring
AHHHHHHHHHHHHHH WHY DID I HAVE TO LOSE. The most horrible match up pits friends against friends in the loser's bracket and its not even the finals! Last time Aaron and I had fought was actually last year where we went 1-1 against each other in the total annihilation of Dominant Mode.


This year we both built bots to last. Plastic construction, horizontal disks. It was shaping up to be a good match... but ended up pretty sad. Two soft hits in, my power switch opened up and SS turned off. Slim got a nibble on my wheels afterwards. Ah well, Aaron will have to carry the flag for the both of us (but ended up losing to Speed Wedge 3 also :/)!



Beetleweight Rumble
Immediately after the In the Margins match, I put SS into the rumble. Literally, re-tightened the fingertech switch and threw it into the box. I used this time to play with the throttle a bit and see if I could discern the cause of the ESC problems. It looks like if I keep the weapon at max the entire time it will power up quite alright.


That was it for Silent Spring. A solid robot with great potential, hampered by some bad electronics. Without another competition in the near future, I'll have plenty of time to figure this issue out. For the time being, Silent Spring has succeeded in its primary goal: Be entertaining and don't get destroyed :)
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Attrition
1st Place (4W - 0L)

Having started so far in advanced, Attrition's check-in was straight forward. For the rest of the competition, all I ever had to do was swap out batteries and decide whether to use the wedgelets or not. All these upgrades paid off and made Attrition a clear winner this time around.

Attrition v Maul
Maul was another bot that came out of MITERS but one I had not seen before. Partially because I don't frequent MITERS much anymore but also because I was led to believe the robot was still being completed at the event as it was safety checked immediately before the match. - _ -

It appeared to be some sort of thwack bot with cutting tools for wheels. The chassis was made from a rather thick steel pipe and there wasnt any chance of going through it. So, I opted to punt it around until he tapped out.



Attrition v Hyper Drive
When Cataclysm totaled Apollyon in 2013, part of me cheered just because I wouldnt have to face this legendary wedge bot in the future. However, Mike sold the bot to master craftsman Jerome Miles who then put the drive setup from his 60 lber into it and renamed it Hyper Drive. Oh dear.

Hyper Drive is an appropriate name. It has two massive inrunner brushless motors coupled to dewalt gearboxes for drive. It could move and spin fast enough to do reasonable damage in a thwacking mode. If it were more controllable, he could totally dominate this match.

I decided to play it safe. Start with low drum RPMs and gain maneuverability. I also put on the short wedgelets to help with his front wedge. Shortly into the match, HD lost one side of his drive (gearbox slid out) and I was able to flip him over using the wedgelets. How inverted and nearly immobile, I turned up the drum to full to try and lay on the killing blow. That hit took off the wheel on his good gearbox and Jerome tapped out.



Attrition v Isotelus Rex
Here we are! I finally get to fight my pushybot rival! I knew ahead of time that he would be using the snout again, so I best optimize for driving. Therefore I employed the same strategy as I had against Jerome in the match previous.

Things were going according to plan. I was able to dodge out direct attacks from the snout and lay some pecks on the Ti guard. A few flips went in my favor to added aggression points. Occasionally the drum would contact the snout and I actually noticed white plastic flaking off into the arena. At this RPM (and perhaps because my teeth were still sharp) I could bite into this snout instead of being deflected by it. I started going head on into whatever angle I could and was still able to toss him about.

For the last 30 or so seconds, I turned up the drum again like I did against HD. At this point there was enough damage to the plow to render the snout ineffective. Some showers of sparks and a few more tosses for good measure to start strong, end strong, and give Attrition a shot at 1st this year.



Attrition v Isotelus Rex (FINALS)
Isotelus Rex and Ripto fought a close match in the loser's bracket finals. Amazingly, Isotelus Rex came out the winner after 5 mins or so of judges arguing. I figured I would run the same strategy as the first time I fought him but it turns out it was not needed. He suffered damage to his gearmotors in the match previous and was unable to make the repairs in time. This left Isotelus with one drive, which severely handicapped his awesome driving power. After a few hits, he tapped out and Attrition was crowned the 12lb champion!



Motorama couldnt have gone any better for Attrition. Progressing from 3rd, to 2nd, and finally 1st was a hard battle through the years but taught me many things about robust designs. I am happy to say everything I learned about engineering was well worth it and demonstrated in this little robot. Next year I hope to fight against my other rivals in the division such as Ripto and Cataclysm. This will be the true test of this robot. 
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MegatRON
2nd Place (3W - 2L)

With a tightened clutch and new dustpan, I had hopes for Ron at least as a pushybot. It has been forever since I had driven a non weaponed robot and in particular my old old design from my childhood. We would see what the future holds this year at Motorama

MegatRON v Candy Paint and Gold Teeth
The first match was ALSO against an MIT folk! I felt like they were trying to phase us out from the start! Even worse, it was against my buddy Charles and his mean overhead bar spinner. He told me he was going to spin slow and have fun. I obliged but encouraged him to make it entertaining as well. I put on the abrasive saw to make sparks but not penetrate his aluminum frame.

He did not disappoint. At the speed he chose to spin, a slight pertubation from Ron's dustpan caused him to flip over. However, he had enough torque to Tornado-mer dance! What followed was nearly 3 minutes of watching CPGT try to self-right with the occasional Ron interjection with the saw blade. Eventually, Charles burnt out his motor and CPGT was counted out.



There was some damage after the match! CPGT was wailing around Ron so hard, that one of the cast aluminum pillow blocks actually shattered and left the arm in danger of a single supported system. I was quickly able to hack a solution together by taking my spare P60 gearbox face and using it as the far end pillow block.




A very expensive pillow block - _ -.

MegatRON v Whammy Bar
Whammy bar looked to be a deadly horizontal bar spinner. What made it scarier, is the fact that nobody has seen it hit anything yet! Alex tapped out early in his fight with WB before they could make contact so I will be the first to feel its teeth.

I went out to box rush him but missed! Argh! He was able to get up to near full speed when we made contact. The Ron took the hits like a champ but WB could not. Somewhere inside his robot, a component popped loose and WB stopped moving. Ron, and his ineffective saw, moves on :P



Damage pics! That penetration!


Whammy bar adds a nice dent on the inner of one pontoon


MegatRON v The Magnificient Poncho
I've always been impressed by Poncho. It is such a simple robot but with power and good driving it can conquer the toughest opponents. Earlier in the competition, Poncho defeated last year's champ Triggo. I will have to break out my best driving to stop him.

I used a lot of spin tactics to deflect his charges since I knew a head on collision would most likely be against my favor. I had a wide wedge and sloped sides that could be used to scoop around his pushing angle. This was effective for getting under him.

In the second half of the match, I was noticing a lot of over steering in my driving. I could see from my driver's stand that my one side of wheels were free spinning! Ah! the banebots keyway had stipped out! Luckily I could still drive a bit but I was definitely trying to just outlast poncho at the end. We got stuck together twice which helped in stalling for time. (normally I would able to spin him out of the tray if I had both drive sides...) The judges voted in my favor and MegatRON goes to the finals!



Some pictures of the wheel casualties.

4 old megatRON wheels. Since last year.

Banebots keyed wheel sheared section.


Thankfully, Jerome was nice to give me two replacement wheels. they didnt match the 40A's that I had as spares, but they would work for now. Thanks Jerome!

MegatRON v Triggo (FINALS 1)
Oh man, it is finally time. Many people would fear fighting Triggo but to be honest I wanted this fight to happen. As soon as Triggo was announced over Whammo, Charles and I had actually cheered.

I knew this fight would be among the hardest I've had in awhile. And to not drive a weaponed bot make it all the more exciting. There is some thrill in depending on skill. Being the robot that could be destroyed, trying to outlast the stronger robot. That is what I was looking forward to and that is what I got.

Starting out a bit tentative, I let him spin up a bit because I thought the dustpan was steep enough to deflect him. While that worked for a bit, he caught the right corner of the dustpan and spun the bot around catching another edge and flipping Ron. I had the clutch relatively loose to prevent stalling the motor but in this case it proved harmful as Ron could not invert. I had to tap out  to save the robot before Triggo's next attack.



MegatRON v Triggo (FINALS 2)
This time, I went as hard as I could. A solid box rush from the start slowed him but not enough to stop him. From there I had to stay on him as much as possible and keep him off his toes. A careful balance of poking with the wedge would tilt him and force him to spin down or lose control.

However, the two hits from the previous match took its toll on the dustpan; it was slightly tweaked on the right side and could actually go over the shell as he teetered out of control. During these times I was unable to control Triggo and wasted a lot of critical moments.

Finally I was able to herd him into a corner but... Ron stopped moving! ARGH!  He crapped out in front of my drivers corner so I could see that the powerlink (an XT60) was much much higher than it was supposed to be. Meanwhile Triggo was slamming himself into the pan and into the walls to push himself free. When he finally escaped, I tapped out to prevent a juicy juicy free hit on the arm.



People tell me I was winning that match but I didnt really care. it FELT EPIC! And that feeling alone was satisfaction enough. MegatRON would take 2md place to the 2014 champ Triggo. No shame in losing in the finals to a spectacular robot.

Triggo, the 2014 and 2015 Motorama 30lber champion


MegatRON after the 2nd triggo fight

Triggo nibbled at the wheels.

.. and did damage to the dustpan

The right side corner which was already raised was further chewed by Triggo. The left side is still pristine!

To conclude this post, I'd like to shout out to the many many people who made this event a great success, a great time, and overall made the experience of robot combat a wonderful idea. First is my bud Charles Guan, who I give credit to for the numerous resources and help used in building my bots. He also drove the group of us through the snow to get to Moto. None of this would be possible without you man! Then I'd like to mention the MIT and GT crew for a friendly competitive atmosphere and help in repair time. I find that things are most fun when you have your friends and robot fighting is no exception. Not to mention their unyielding support. Xo, Aaron, Gabe, Chad, Adam, Dane, Charles, Paige, Cynthia, Rebecca, Ciaran, Ian, and James here is to you! And I really really hope I didnt miss anyone. I would also like to note exceptional builders who made it a really great time. Zac, Mike, Alex, Kyle, and Jerome were kind enough to offer me parts and help in times of repair. And most important are the folks at NERC who kept the show running. That's Ed, Beth, Jon, James, Kyle, Rob, and Mike and many many more Im sure. Thanks for making Moto one heck of an event!.

Attrition, 12lber champion of Motorama 2015
MegatRON, 30lber runner-up of Motorama 2015



Friday, February 6, 2015

Attrition: Final Push for Motorama 2015

Last post you saw a glimpse of the tragic history of my first and only Hobbyweight (12) combat robot. At the end, I declared I would try my hardest to take the title this year and have implemented extensive upgrades to make it happen. It goes without saying that I did a complete teardown of the robot and its systems but here are the main points to remember moving forward.

Super-awesome new drums from Westar Bot Shop (Team Whyachi)

Last year the drum from 2008 finally gave up. Usually this is the point where builders will reevaluate their design and decide to build an entirely new bot all together. However seeing as how the chassis was nearly undamaged, there wasnt a point in rebuilding that so we will just build the drum again but better.



For this, I had the drums sent to a professional machine shop. Team Whyachi has been providing fabrication services for years and resulted in years of super happy customers. You can find their page hyperlinked numerous times above. I sent them some relatively simple drawings  and Clint Ewert immediately went to work. I started conversing with him maybe Dec 31 2014 and I had the drums back to me 1-2 week of January. Talk about quick turnaround!



The drum is still the same dimensions as the previous one (3" OD, 2.75" ID, 3.625" T-to-T) but the materials are now compatible. 4130 steel all around, hardened afterwards. I asked for 50-55 C Rockwell but some metals treatment literature say 4130 can only be hardened up to 45 C. I'll take the spare to the Rockwell tester to see how it actually came out.

BTW, I bought 2! Two drums for a total of $650 including shipping. Whyachi paid for materials, did machining and services, and a batch of heat treating which makes this a phenomenal deal! Plus, all dimensions are within 0.005" tolerance specification which is ABSURDLY GOOD for welding and HT. Would recommend again!

The bigger issue now is the fact that there was some internal damage to the motor components. While the Whyachi drums were on the way, I cracked open the drum to harvest the relevant components.



Oops. Isnt that supposed to be attached? This was the worst problem among the shattered bearings and dented races because that motor isnt cheap by far. I evaluated at this point if I should purchase a Turnigy equivalent to replace it.

What I ended up doing was JB welding the motor to the shaft. While this make it an incredibly permanent solution, I recognize that the state is fully encapsulated by the can and drum; It should be simple enough to salvage if things go completely bad. I think I am fortunate that none of my motor wires sheared. This gluing process was done with the guts in the frame. Because the center races are all in compression, it locates all the components securely.



I decided not to paint this drum. Partially because I was impatient but also because spraypaint would have fouled my tolerances inside the drum. I may consider painting the spare if the first drum gets damaged.

Revamped drive system

The majority of work was actually put into redoing the drive train. As mentioned previously, I lost a good majority of matches due to drive faults. The first modification to take place was the center double pulley. Last year the FDM pulley had far too much torque at the shaft and displaced the set screws threaded into the pulley.



This year, I borrowed some design concepts from Charles Guan. I started with some 5/8" aluminum hex and turned those into intermediate shafts. The hex would go over the nominal gearmotor shaft providing me a meaty aluminum interface for set screws and the like as well as a hex cross section for torque transfer. Snap rings on either end would prevent the pulley from sliding off the ends.



The pulleys themselves were selective laser sintered (SLS) nylon from Shapeways. They were my usual 20T XL pulleys but designed to go over the hex. I got them in black and red; the red set being the test set. I wasnt too certain about the durability of SLS parts so I got the red set to test part durability. If at any time during a test I saw red  powders on the bot I would determine they pulleys not combat grade. Black would have been much harder to spot.



The entire setup comes together like this:



Pretty neat eh? Initial test drives with the old motors were promising. No red flakes to be seen, nor belt slipping or tooth shearing. We'll run it later in the week with the weapon for some harder durability tests.



Next was the motor. Currently, I use "long can 400" motors or "480 sized" motors. I used to use Banebots 395 motors but they were too slow. See the difference between last year and the year prior. That shows nearly 4 mph of difference in speed! There are a number of 480 sized motors on the market but they are usually used for direct drive prop airplanes which means they are typically low voltage, hot wound, and timed. The trick for me would be to find something mid voltage, mild wind, and neutral timed. This search proved to be near impossible.



I ended up getting four of these 480 motors from RC parkflyers. But testing proved that they were actually 6V native motors and I quickly burned one out. Ugh.

A second option was to modify the mechanics of the gear reduction. The gearboxes are largely custom inside Attrition so this would not be easy. Essentially I needed a way to replace the existing stages with low reduction stages only. Some searching on Alibaba for 32mm planetary gearmotors turned up some interesting concepts. I found my 19:1 gearmotor model but the vendor actually sold a 14:1 and even a 11:1! What did this mean? This meant other stage combinations existed and this modification was in fact possible.



I did my research on gearmotors. Servo City sells 32mm gearmotors as well but their spec sheets are incomplete. Super Droid Robot Land provided the manufacturer's specification sheet which clearly indicated either 11T ot 17T sun gears. BINGO! That means there are only two types of reductions and they are either 3.7:1 or 5.2:1 as previously mentioned.










Then I combed through their standard reductions and factored their values by the two stage types. From this I can accurately tell what stages and how many will be inside each gearbox. I bought a 51:1, which is composed of three 3.7:1 stages.










Looks like the first stage is plastic. Not a problem since the other two were metal. Now I could use the slower but mild wind Banebots 395 motors to give me about 8.3 mph. It isnt as fast as last year but should accelerate faster. Plus, I can actually buy spares! While I was at it, I decided to replace the worn components in the gear motors. New shafts, new bearings, new steel shims!

Actual thought put into front attachments

Now this isnt a primary point of failure, but while I was putting my all into retrofitting the robot I might as well address this as well. Typically, I would run with or without wedgelets which were little slivers of titanium held on with stacks of UHMW shims that acted as spring loaded hinges. It was a neat idea for awhile but the ultimate lack of durability in the UHMW was a failure point in that they were easily sheared off.

After fighting designs like Thomas Kenny's "Shame Spiral" and Pete Smith's "Isotelus Rex", I realized there is a clear winning design to fight the "Solaris" drum bot design and that magical snout was the trick. To counter battle, I would play the arms race against their ramming plows.



I had these modeled in previous models but never took the time to make them. Now that I had "MegatRON" parts being made from Big Blue Saw, I decided to throw on some small parts for Attrition. Now I have a number of wedgelets in various lengths to handle general purpose wedges and specialty designs.

The one type of spinner Attrition has somehow managed to avoid are massive horizontal bars. For these designs, I have some additional defenses in the works, but no need to reveal them yet ;)

Loads and loads of spare parts

This time, I will not lose from lack of preparedness! I am bringing all this and more in case I have failures. These are the expected points of failure so it is possible other things can happen. However, should any of those parts take damage, the bot probably deserves to be retired. Lets hope I predicted correctly!



At this point, we are more/less ready to rock. I'll be running some durability tests with Charles between now and then so be sure to check out those vids when them come out. Cheers and bot on!


Saturday, January 17, 2015

Attrition: The Unspoken Hobbyweight

Before I get into this long long post, I want to mention the existence of my Facebook page. There, I make smaller posts on more incremental work (which is where I've been more recently).


So if you want to see more consistent updates, I suggest you go there and follow :P
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Prelude:
Long long ago, I built a hobbyweight with the help of fellow bot people like Brian Schwartz and Casey Kuhns. This was back in 2008 which for me was high school and my resources were limited so I would like to take yet another moment to thank those mentioned above. However, I did not blog about it because my blog did not yet exist. Later versions of the robot were also gone unmentioned (such as my Motorama '13 and Motorama '14 posts). I find it now necessary to log the development of this power-dense combat robot.

2008-2009:
This robot was a drum spinner (as was the flavor of the month) and was a wonderful blend of scavenged robot parts. It used a set of 5:1 'mabuchi' gearmotors I scored from ebay, a set of BB 12-45 escs I bought off a leaving bot member, and batteries given for doing a favor for another bot member. I bought a 40 mm copier stator to wind the brushless motor and had machining help as mentioned above. Furthermore, I had machining services donated by local companies to make my drum, an odd combination of 4130 for the drum body and A2 tool steel.



Please for heavens sake do not weld those steels together. EVER. Looked okay but was difficult to heat treat you might imagine...



Either way, this was my first big bot I made and it debut at Motorama 2008 where it went 3 wins and 2 losses to Igoo and Surgical Strike.




It had many notable flaws:

  • Banebots escs overtemp shutoff from the high current draw mabuchi gearmotors
  • poor detail mechanical design and material choices allowed for bent frame and lockup
  • weight distribution made for poor inverted driving (and poor ability to self-right)
  • additional precautions to secure connectors also required

 It was also the first robot I built featuring a custom made brushless-in-weapon system. I'll attribute the original idea to Corona and Skittlebaru but none have gone as far to put the esc inside. Will bales "Fluffy" came out later utilizing my old 5" drum idea having everything except the drive motors inside the drum. Lets just say there was a reason I didnt finish that version of Attrition. The things learned from this robot would carry in designs to come. Additional pictures from long long ago can be found here:


2012-2013:
By now I was in college at Georgia Tech. My activities at local events and Dragon Con had interested enough friends to justify the "Georgia Tech Fleet" to drive from Atlanta to Harrisburg for Motorama 2013. I dug Attrition out from storage and decided now was time to address its shortcomings.




I started from scratch. Time to apply new knowledge on mechanical design, materials, and even 3D modeling (since by then I had my SolidWorks professional certification). We would decrease the footprint to save weight and increase the durability of outer armor. For the same goal, we would also downgrade the weapon assembly. The gearmotors would have to go; Instead I picked up four higher reduction planetary units with 'long can 400' motors attached. This new version went by many names such as Tofu or War Machine but decided to keep it as Attrition to indicate its lineage.

Let's do some planetary gearbox math:
A single stage of a planetary gearbox can be calculated by:
(Ring + Center)/Center:1

Pinion :11 T
Sun: 17 T
Ring: 46 T

Stage 1: (46+17)/17:1
Stage 2: (46+11)/11:1

Overall: 19.24:1
This number was good according to my calculations should yield ~10 mph with my long can 400 motors.



To make everything compact, the keyword was 'integration'. I built the gearboxes into the frame rails to save space. The electronics were repackaged into a small cube to reduce wire space needed. I was able to find  the perfect battery to sneak into the remaining space.





Drive test showed the robot was fairly nimble. I dont remember if I had switched to Banebots RS395 motors yet or not. Either way this video showed that I could not use round belts like I usually favor. On high acceleration moves like direction changes, the belts would slip. This made driving with the drum impossible as I later discovered. Later i switched to waterjet machined XL timing pulleys.




The drum was simple; I cut the original drum from Attrition reducing its length from 8" to 5.625". The motor was a bit more challenging. To simplify the design I kept the esc out of the drum. This was a decision made based on 'Cake's matches where the drum would break free and eat its signal or power wires. I also decided to not route wires inside the shaft. This was so I could preload the inner race bearing assemblies in the shaft for higher rigidity and high frequency performance. As such, the wires would exit with a new concept I had involving a large ring bearing on the motor side.









The original concept was to build the internals from several stacks of waterjet material. However the drum was a bit warped so any precision machined parts would not readily fit inside. I ended up wrecking a motor in an initial test and remachined the entire assembly from a single round of aluminum. Some fully assembled pictures.



Now, time for the money shots! The LED vag was a nice touch too...




This version debut at Motorama 2013 where it faced a number of tough opponents including Zandor and the undefeated multi-time champion Cataclysm who won 2nd and 1st respectively. Attrition went 3 wins and 2 losses for 3rd place, going undefeated for 3 matches until he met Cataclysm on Sunday.





Somehow, Attrition came out in good shape. Aside from blemishes on the top and bottom plates, the majority components including the drum were fully operational. The source of my demise was actually lack of spares. After my match with Zandor in the quarter-finals, I was down one drive motor and went into the Semi-finals against cataclysm with only one drive side. This put me at a huge disadvantage and lost decisively. Shortly after, I lost the losers bracket finals to Zandor because of my lack of drive side. Originally the culprit was a broken magnet. The replacement given by another builder ended up failing also because of pinion slip.




2013-2014
Losses at Motorama 2013 were disappointing to say the least. This year's emphasis would be into the drivetrain. I wanted faster and more reliable. Now at MIT, I lost a valuable resource at the Georgia Tech Invention Studio. However my research afforded me new capabilities I would try and leverage when possible. In addition to remaking many outer armor plates, I also swapped the Banebots RS395 motors for the original long can 400 motors and remade the center timing pulleys from 3D printed material. I believed that high starting torque was the culprit for pinion slipping.




Another decal with lewd LED placement was needed.



As fate would have it, I was wrong. At Motorama 2014, Attrition went 3 wins and 1 loss in a round robin format for 2nd place. Agility was useful in my first match against the pneumatic flipper Jumbonator but I lost a drive side again after a win on Upchuck. This was a fatal blow against the strong drive of Isotelus Rex as I could not maneuver for a good hit. The FDM material actually split and rendered the center pulley useless. This was from the high stress concentrations near the 6mm drive shaft to the ~25mm center pulley. This could easily be fixed with a larger diameter intermediate made of metal.




However, another defect surfaced that I had not predicted. The A2 teeth, after years of battle, finally broke during the match against Isotelus. I suspect this was due to fatigue as nothing on Isotelus could have done that. However I note that points were given to him for 'damage' to my robot as the judges pointed out when Attrition had finally spun down after the match. Closer inspection of the welds show little to no penetration into the wall; it was no wonder they had broken.

Present Day:
No place in 2008. 3rd place in 2013. 2nd place in 2014. This year we pull out all the stops. At Motorama 2015 we will go for the prize!

I here conclude this post as a documentation of my first 12-pound combat robot. In another post, I will summarize the efforts to prepare Attrition for Motorama this year which includes professionally made drums and extensive drive modifications.

Video of all Attrition's matches can be found as a playlist on my Youtube. I have placed the direct link below.