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Mechanics and Construction / Re: Free Rotation Wheel
« Last post by Ibaeni on June 10, 2015, 11:49:42 AM »
It's also very common to put some low friction piece of material as a third point of contact. Something like a bottle cap would even work.

If you want something a little nicer, you could get a ball caster. It is essentially a marble in a holder that can roll in any direction. They're relatively inexpensive on Sparkfun.
Mechanics and Construction / Re: Free Rotation Wheel
« Last post by mklrobo on June 09, 2015, 05:15:09 PM »
 ;D Hello!
In reference to your wheels selection, I would check out some of the vendors in this forum;
like ServoCity. Some of these vendors have some mind-blowing wheels,  :o that turn
in an unconventional way; and they are priced reasonably. Check them out!  8)
Mechanics and Construction / Free Rotation Wheel
« Last post by zizou244 on June 09, 2015, 03:40:07 PM »
Hello Guys !

I'm currently building a 4 wheeled car and I'm trying out a differential drive with the Two Rear wheels connected to DC motors, and two Free rotating front wheels.

I'm curious what kind of simple mechanism I could use to get the "free rotation" part. I only know about the bearing system you can find in this kind of wheel :

The wheel you can see in the picture has some kind of ball bearing.
Do you know of any other "simpler" way of ensuring the free rotation around the Z axis ?

PS : The car i'm building is a little big, and the wheels I'm using came from an old baby stroller (15 cm diameter and a 1cm hole in the middle)
Electronics / Spektrum AR6100e > Arduino Micro > Pololu DRV8833 > Tamiya RC260's
« Last post by bpolits on June 08, 2015, 03:37:34 PM »
Building a small 3 motor RC bot. How do I make the receiver -> Ardu Micro -> Pololu Controllers communicate?

Bought 3 x tamiya gear/motor units, 2 for the wheels and one for the "weapon". Further research suggested that the

Tamiya RC260's motors need low voltage 3 - 4.5v max. Very few speed controllers go this low but the:

Pololu DRV8833 does, but will not interface with the:

Spektrum AR6100e directly, so we needed a:

Arduino Micro to link the RX with the motor controllers.

My questions revolve around 1) how to power the various units 2) how to make the Arduino hear the PWM signals and transmit to the controllers, etc., 3) I heard a heat sink would be good for the (Ardu?Controllers?), etc.

A rank adult robotics beginner here with electric RC Airplane experience, just looking for advice on where to look for info, or a tip on where to find where people have handled this before with low-V motors.

You can find similar boards on ebay or other websites online, generally they will be less expensive than radioshack as well.
Thanks, but I have solved the board problem completely :) Now, I just need to find photoresistors!
;D Hello!
Programming the board will be a challenge in itself. It is supposed to be easy, as explained in the
tutorials. I have had problems with connecting to the Axon II, and producing the HEX file. You have to
download a some programs, and integrate them in your computer, in order to program the board. This is to
be expected, but the order and type of program to integrate is concerning. I have figured out all the tough spots, except for getting the Hex file. I bought a bootloader, and it can load the program to the Axon, but I do not have a Hex file to download.  :'(   Check out my posts in the miscellaneous section, Analyzing the Axon Series: Coding, Construction, and Contraptions.   ;D This may save you some headaches. (The information came from the Axon datasheet and instructions from the tutorials, that I tested.)  8) Good luck!!   8)

Ah man, you're scaring me  :-[ I'm definitely going to bookmark those posts of yours. I also don't understand must of the words you said lol. In the servo modifying article, it said I could do it mechanically (with less precision though). I'll resort to this if necessary, by making another post asking how to do with tools and my hands what the .hex code is doing :) Anyhow, if I have other problems programming, I guess I can resort to the forum :) One last thing, I think someone should tell Admin that it is a bit confusing for newbies like me how that part of the tutorial is written :) Do you think I can contact him?
Misc / HGR Industrial Surplus - Used Industrial Robots/Parts
« Last post by PTD on June 08, 2015, 10:04:31 AM »
We currently have in stock over 100 robotic items, from full industrial robots to parts, controllers, etc. that members of the forum may find useful.  You may follow this link for additional information: http://bit.ly/1CbzAen
Mechanics and Construction / Re: Drilling into a D-shaft
« Last post by bdeuell on June 08, 2015, 07:55:18 AM »
it would be helpful if you can explain the design intent as well as provide a picture of what you are planning to do. This will allow us to guide you based on factors such as drill bit diameter, material, required precision, etc.

Also not sure if you are just having trouble keeping the drill bit from wandering or getting it to cut the material at all. If you are unable to cut the material make sure it is not hardened, you can do this by running a file across an edge (if it cuts it isn't too hard if it skates across the material it is quite hard).

In general if you are trying to drill accurate holes there are some good techniques. First if you have a drill press use it but from the sounds of it im guessing you are using a hand drill. In either case fix your work with a vice or clamp. It is always a good idea to center punch your holes this will give the drill point somewhere to start. you can also use a center drill or spot drill to start the hole, both of these are short stubby drills that will resist walking and help get the hole started and then switch to the drill you want to use. you can also step up your drill sizes so that you start with a small bit and increase to your final size in a couple steps (don't go too crazy with this a small bit will bend easier). drill bits come in different lengths as well, with jobbers length being the most common (hardware store) but screw machine length bits are (very common in machining industry) are shorter and more sturdy. If you are trying to drill on a round surface you may want to file a small flat first (or make a guide fixture as suggested above).

Smith Lathes
I believe you are referring to a Swiss Lathe
Robot Videos / Re: DARPA robot competition videos (sped up) and other info
« Last post by mklrobo on June 08, 2015, 07:00:24 AM »
 8)   :o Awesome!
It was funny to see them fall down, even the CHIMP fell down. Still that is pretty
good for the robot, as the way of technology today.
IDEA!  :o Why don't we have an Axon challenge to build a robot to enter into the
DARPA contest! It could be an open source robot, that every one in this forum could
participate. Admin could set up the system expectations, and people in the forum could
build that particular interface for the robot. Would'nt it be cool to try to make a robot in the
forum to compete? The official participants would have to meet and complete the robot
in a specific place, debug it, then get ready for the actual competition.
The easiest way, (and cheapest) , is to make a model at home, then try that. The AVR studio
has simulators in the program, and, I wonder, could several simulations be running together
to make a whole robotic system? the PC would have to powerfull, and maybe have other
boards for higher processing power.  :-\ Just a thought.
Mechanics and Construction / Re: Project Advice
« Last post by scooji on June 08, 2015, 06:01:46 AM »
I am wondering the same i am building a robotic arm with 6 servos. can someone advise me on what kind of servos i should be looking to get. I am using an arduino r3 for control of the servos.
Robot Videos / DARPA robot competition videos (sped up) and other info
« Last post by Admin on June 07, 2015, 01:49:17 PM »
Most look as if power had failed before they fell, and not actually a programming or balance issue . . .

Hubo from Korea won the DARPA finals. CMU came in third . . .

CMU's Chimp at 20x

demo video from Italy's robot

report from day 1 of the challenge . . . and a video . . .

close up image poster of all the robots competing in the DARPA challenge finals:
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