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Keres, a pocket sized fighting robot.

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Picture of Keres, a pocket sized fighting robot.
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Keres is my latest combat robot project. This is my smallest robot to date, weighing in at just under 150g.

The main motivation for this build was to test out the prototype "Mini-Spark" gearmotors from FingerTech Robotics (http://www.fingertechrobotics.com/) that should be released in the very near future.

The attached .rar contains the drawings for the top plate, bottom plate and weapon bar as well as the .stl you would need to have the chassis printed. The chassis is also available on shapeways at http://www.shapeways.com/model/769811/kereschassisv3.html if you would prefer to just order it. I used White, Strong, & Flexible, which is laser sintered nylon.
 
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Step 1: Component Selection

Picture of Component Selection
Component selection for robots this small is fairly limited, but luckily there are still a decent number of quality parts available that aren't too large for the minuscule weight budget.

The radio system is a Spektrum dx6i, as that is what I already had and there was no point buying new radio equipment when my current gear can handle several more robots.

The receiver is a hobbyking R410 OrangeRX. It is one of the smallest receivers on the market that I am aware of with programmable failsafes that is also compatible with the dx6i. For a robot this small with the dx6i, it is one of the best receiver options. (http://www.hobbyking.com/hobbyking/store/__11972__OrangeRx_R410_Spektrum_DSM2_Compatible_4Ch_2_4Ghz_Receiver.html)

The battery is another hobbyking product, the Turnigy Nano-Tech 180mAh 2s lipo battery. I've run the larger cousin in my 30lb robot Nyx successfully, so it was an easy decision when I was looking for a small two cell battery. (http://www.hobbyking.com/hobbyking/store/__23135__Turnigy_nano_tech_180mah_2S_25_40C_Lipo_Pack.html)

The weapon motor controller is a Plush10 from hobbyking. These are a common brushless controller that appears to pair well with my weapon motor. (http://www.hobbyking.com/hobbyking/store/__4204__TURNIGY_Plush_10amp_9gram_Speed_Controller.html)

The weapon motor is an Emax GT Series 1560kv brushless outrunner. The original motor I was looking at went out of stock and instead of waiting and hoping that it would return to stock, I found this and have been happy with the performance. (http://www.himodel.com/electric/EMAX_GT_Series_1560KV_Outrunner_Brushless_Motors_Type_GT2203.html) One minor change I have made is the stock shaft has been replaced with one of the spare hardened 3mm shafts discussed in my instructable on my 1lb robot, Algos (http://www.instructables.com/id/One-Pound-Fighting-Robot-Algos/step5/Shaft-Replacement-and-Hardening/)

In addition to the weapon shaft, Keres uses the same weapon hub as my antweight Algos. The lightweight 3mm hub from ServoCity seems to work quite well in this application. (https://www.servocity.com/html/lightweight_set_screw_hub__3mm.html)

Drive motor controllers are FingerTech TinyESC's. I've used these in all of my small robots and they have proven to be a fantastic brushed motor controller. At this point, I use them in any application that they're appropriate for. (http://www.fingertechrobotics.com/proddetail.php?prod=ft-tinyESCv2)

The drive motors are 20:1 prototype Mini-Sparks which will be available soon at http://www.fingertechrobotics.com

O
ne additional component will be added shortly before the debut event for Keres. In addition to being used to test the Mini-Spark gearmotors it will be testing a prototype power switch also from FingerTech Robotics.

The chassis is held together via 3 7/16" long aluminum standoffs. The McMaster part number is 93330A515. These press into the printed nylon chassis.
01eggy108 months ago
I didn"t see it in the file. Is there any chance you still have it.
MikeNCR (author)  01eggy108 months ago
it's the .stl in the .rar (Keresinstructable.rar) on the first page.
01eggy108 months ago
Also what are the size of those wheels?
MikeNCR (author)  01eggy108 months ago
The wheels are 1.50" lectra lites that I turned down to around 1.375". The STL for the chassis is in the .rar file.
01eggy108 months ago
Thanks. Also would you have the CAD file of the plastic body part or is it in the rar file. And do you think the 120mah version of the battery would work okay.
MikeNCR (author)  01eggy108 months ago
120mAh will probably be fine if it can put out enough amps for the weapon motor. I've got the chassis available at http://www.shapeways.com/model/769811/kereschassisv3.html and it's priced as cheap as they'll make it, so if you're going to use them anyway, you can order right from that page. Also, I think this gearbox will fit the mount design- http://www.robotmarketplace.com/products/0-PL1093.html
01eggy108 months ago
Where did you get those motors. You said they were prototypes and I was wondering when they well become available.
MikeNCR (author)  01eggy108 months ago
There are a few things being sorted out, but eventually they will become available at http://www.fingertechrobotics.com/
Ibenos1 year ago
How does it stand in balanc whit only weels at the back?
yvesyuzo1 year ago
What are the width of the chassis walls? For waht I could see the rear is the only one thinner.

Do you pretend to compete at RoboGames this year?
MikeNCR (author)  yvesyuzo1 year ago
Rear is 1/16", sides are 1/8" with a few cutouts to allow motor mounting screws to sit flush with the side of the chassis.
yvesyuzo1 year ago
Thanks for all your of help so far, I'm basing a lot on your project.
I have a few more questions:
Did any robot heavily damage your nylon armor?
I'm also building a horizontal spinner, what's your opinion on these weapon motors?
http://www.hobbyking.com/hobbyking/store/__26482__2205C_1400Kv_Brushless_motor_USA_Warehouse_.html
http://www.robotmarketplace.com/products/0-EFLM1130.html
Does the price of RMP worth?
Thanks again!
MikeNCR (author)  yvesyuzo1 year ago
The nylon took a few good hits, but since it wasn't all that vital to the structure it didn't hurt me much.

The RMP motor is likely higher quality, but the shape makes it appear that mounting could be an issue. They're a great source if you need good parts quickly. The hobbyking motor you linked is a good bit heavier than the one I used, so torque will likely be better but you'll also have to find some more weight to fit it in the 150g limit.
yvesyuzo1 year ago
What's the receiver's weight? hobby king says 2.9g in the description, is that really truth?
Thank again for your help
MikeNCR (author)  yvesyuzo1 year ago
the one I have weighed in at 2.4g on the pocket scale I have, so I think assuming 2.9g for weight calculations would be fair and give some margin for error and part variations.
yvesyuzo1 year ago
Hi!
Do you think a 100:1 SRV Drive Motor would work fine insted of Mini-Spark motors??
MikeNCR (author)  yvesyuzo1 year ago
I think that would be far too slow. Of the alternatives, this: http://www.robotmarketplace.com/products/0-PL1093.html and this: http://www.botbitz.com/index.php?route=product/product&path=60&product_id=52 would be my suggestions.
Thank you!
Do you think fitting the wheels on the D shaped output shaft with FingerTech Lite Hubs would be difficult to stay balanced? I'm talking about the robot market place one.
Are you going to participate on any tournaments this year?
MikeNCR (author)  yvesyuzo1 year ago
Most of the shafts for that size gear motor are D shaped. So far I've never seen an issue with it.
yvesyuzo1 year ago
The ESCs you used does not have a H-bridge right? so your robot only goes foward? and if so the spinnings in your drive test video are done with only one active wheel?
MikeNCR (author)  yvesyuzo1 year ago
The drive controllers have fully proportional forward and reverse control, the weapon controller is single direction.

More detailed info on the motor controllers can be found here: http://www.fingertechrobotics.com/proddetail.php?prod=ft-tinyESCv2
yvesyuzo1 year ago
Sorry if I didn't see it, but how did you powered the receiver?
MikeNCR (author)  yvesyuzo1 year ago
the esc's have a battery elimination circuit, so once the power is turned on, the esc's are providing power to the receiver.
I was wondering how you pressed the motor shaft out and replaced it with the O2 shaft? once again thanks for all of your help and time.
MikeNCR (author)  mildlyimpolite1 year ago
Shaft removal was done by separating the can from the stator half of the motor, which exposed more of the fairly short shaft, then clamping the shaft in a vice. Once clamped, you then twist the can on the shaft while applying slight upward pressure to the can to work it up off of the old shaft. (be careful to not bend it in any other axis as that could bend the can) Once it's clear you can press the new shaft in using either a vice to squeeze horizontally or an arbor press to squeeze vertically. A mallet will work as well, but you have to be careful to avoid bending anything.

The trick to getting the shaft to fit just right is to sand it down by either clamping it in a drill chuck or a lathe and slowly turning it down till it just barely goes into the bearings in the stator half of the motor. For this, I suggest 3mm shaft that has a tolerance range above, but not below 3mm as that should allow you to size it for a tight slide fit in the bearings and a press fit into the can. Cut the shaft long at first, then trim to the final length after it has been installed and you know where it needs to sit to result in the robot resting horizontally.
Schmidty161 year ago
sharpen up the metal or put a saw blade on it lol
How much does all the stuff cost ?
MikeNCR (author)  Zaphod Beetlebrox1 year ago
Not counting the transmitter portion of the radio system (as it can be used on multiple projects) the parts for Keres would likely run around $180-200 plus cost of raw materials (titanium sheet via ebay and hardened O1 shaft) and waterjet cutting the titanium parts.
Thanks, I was hoping it would be less.
nice
germeten1 year ago
It's a great "weapons" design. May I suggest one additional feature? Imagine levers on both sides that would allow the robot to flip over 180 degrees. That would allow it to get out of jams and move the killer blade from horizontal to vertical plane and everywhere in between. It would be hard to stifle such a robot by anything but shear weight.
MikeNCR (author)  germeten1 year ago
There have been a few bots that have tried that with limited success. The main issue is building a reliable and light weight system because any weight you put into a tilt feature can't be put into the weapon, drive system or armor.
Have you seen Boston Dynamics' "Sand Flea?" A lever powered by such a piston would be a weapon in it's own right. You'd have an acrobatic buzz-saw ;)
MikeNCR (author)  germeten1 year ago
Yeah, it's a neat little machine. The mechanism could probably be re-purposed into a flipping weapon, but I don't exactly have their operating budget.
zxzxzxzx1 year ago
well done
It won't let me reply to comments... Anyway, I just wanted to say thank you for your time and ask one last question. I was going to ask about how much it would cost to get the parts cut? Thanks for your help and time.
MikeNCR (author)  mildlyimpolite1 year ago
From what I recall, cutting time was under 20 minutes, so depending on the shop you use, it will be whatever their setup fee is plus at most 20 minutes labor. In all probability the setup fee will be higher than the labor cost due to the short amount of time required to cut the parts. teamwhyachi.com is a good resource and will be able to source the material and cut the parts for you. bigbluesaw.com is another useful resource, however it becomes much more economical in larger part quantities or when multiple parts are nested on a single drawing.
Hi can u tell me were u got all the parts from
MikeNCR (author)  Imdaadghori ghori1 year ago
The links following part descriptions go directly to the sources I purchased most parts from. If there's anything you're having trouble finding, let me know.
Is there anything that I would need to add to the CAD drawings if I wanted to get them water jetted? Thank you for your time and the great instructable!
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