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Mechanics and Construction / Working Transformer Costume
« Last post by scott111000 on November 04, 2014, 10:18:26 AM »
Hello,  New member here and first posting. It may be a stretch to call this a robotics project but here goes.  It's a working transformer costume, similar to this:


I need help sizing the motor. 

Wheel diameter is expected to be 10" so I estimate 50 to 90 rpm to achieve walking speed.  Total weight with costume between 170 and 190 lb. 

I'm looking to direct drive a single front wheel with a battery powered DC motor to accelerate from stopped position to walking speed on level asphalt.   How much torque would I need?  Can anyone recommend a vendor or even a specific motor? 
Mechanics and Construction / Difference Between A Cylindrical and Screw Joint
« Last post by arafatasghar on November 04, 2014, 09:54:34 AM »
Hi Everyone,

I am a new entrant into the field of robotics and familiarizing myself with some basic concepts about space configuration. While reading about joints and their associated degrees of freedom, I came across cylindrical and screw joints. Now both have rotational and translational motion yet the cylindrical joint has 2 DOF while screw joint is classed as having only 1 DOF. Why is this?

P.S I would really appreciate if someone referred some online educational resources that would help clarify the whole concept.
Mechanics and Construction / Re: Omni Wheel/Ball Transfer/Caster?
« Last post by bdeuell on November 04, 2014, 08:54:10 AM »
Your first robot looks great.

If you are looking for heavier duty ball transfers look here:http://www.mcmaster.com/#standard-caster-ball-transfers/=ug5l7x

I can think of a few advantages for both the omni wheel and the ball  transfer:

One advantage of the ball transfer is the wheel radius is the same regardless of which direction i.e. the ball will be able to roll over the same size object regardless of the direction it is traveling.

the omni wheel also has the disadvantage of being an uneven rolling surface. this can cause vibrations in the platform as the contact point of the wheel changes.

An advantage of a omni wheel is the internal bearing surfaces are separate from the ground contact surface. in a ball transfer when the surface of the pall gets damaged (from abrasive surfaces such as concrete) it will degrade the bearing surfaces inside the ball transfer.

The omni wheel is probably more optimized for forward movement given a certain mass. i.e. an omni wheel with the same mass as a ball caster would probably have a larger primary diameter making it able to roll over larger obstacles in forward movement. however the rollers would probably have a smaller diameter the the advantage would be lost during turning.
Electronics / Re: Filtering power supplies
« Last post by mstacho on November 04, 2014, 08:46:10 AM »
Hm...interesting.  I guess the question is: what happens if the cap is too large or small?  Is there a universal behaviour you'll see or is it just up to the circuit itself?
Electronics / Re: need brushless ESC/driver > 65V > 10A
« Last post by jkerns on November 03, 2014, 06:30:44 PM »
One of my students got one that apparently is for a washing machine - I think about 100 volts, and I think from E-Bay. I'll ask next time I see him.
Electronics / Re: need brushless ESC/driver > 65V > 10A
« Last post by sdk32285 on November 03, 2014, 06:04:06 PM »
Is this for a sensorless (back emf style) motor or one with hall sensors?
Mechanics and Construction / Re: Newbie needs help
« Last post by sdk32285 on November 03, 2014, 05:55:52 PM »
Welcome to the world of robotics.

This site has a $50 tutorial for building your first robot http://www.societyofrobots.com/step_by_step_robot.shtml
Mechanics and Construction / Newbie needs help
« Last post by Schnuchi on November 03, 2014, 03:50:07 PM »
Hey there. Robots have always been a passion of mine, and I've decided to give making 'em a try. The only problem here is that I don't know anything about it. I've decided I should start out with something really easy. As I am a fursuit maker, I want to blend in some robotica in my new fursuit. Everything would be cool : eyes closing, lips moving, nose sniffing. But I think my first project will be moving ears and a wagging tail. And I need your help! Because I have absolutely no clue how I will begin. I could guess I shall need some servo's (as much as 2 for each ear? Kind of depending on the movements I want from it, of course) , a board, processor.. But I really need feedback and advice please. Thank you for your time!
Electronics / need brushless ESC/driver > 65V > 10A
« Last post by Admin on November 03, 2014, 10:03:30 AM »
Trying to find an off the shelf brushless motor driver that can handle >65V (preferably > 85), and at least 10A.

Unidirectional is fine. Cost doesn't matter, but must be light weight.

Tried all the normal places but can't find one . . .
Electronics / SO.. i might have bitten off more than i can chew
« Last post by testsubject27 on November 03, 2014, 09:39:30 AM »
let me start off by saying hi to all as this is my first post.

Im currently studying a L3 btec in engineering and after getting top grades for my first year i have selected to make a Photovore for my last year project. to make my first robot more interesting i wanted to give it a memory recall system to prioritize high light locations and go there first.
and now that the first of my basic components are arriving i have found that i have no idea what i am doing with just the photovore, let alone the memory system.

so far i have 2x 5v motors, some 555 timers, lots of photo resistors, some zener diodes, 20 x NPN transistors, 25x in4001s, and 1 ultrasonic sensor unit for arduino, i already have an arduino Ono basic kit as well. i have also ordered the AEX001u picaxe board and chip to give options when it comes to programming.

I need so much help. any advice (and criticism served with help) is very welcome.
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