Let's Make Robots!

Mr. Slave

While waiting for my parts I used my free time to learn Google SketchUp (just realised it sounds like Ketchup).
It is really REALLY easy!!!

Anyways, my plan is to make a servant for me, that would fetch me drinks and other stuff once in a while.

As You can see from the photo below it has picaxe28x1, xbee module, sd21 servo controller (I was too lazy to make it 3d), SRF05, robotic arm and etc..


Got a few questions for You mates:

1. Are 4 AA rechargables enough for all these parts to work swiftly?

2. Do I still have to change the baud rates or invert signals or do anything similar for the xBee modules, if I am using Adafruit Adapter ?

3. Would this kind of robotic arm, in Your opinion, (made of the cheapest chineese micro servos) lift a can of soda (like this one)? I'll try to do the maths myself, but it looks very challenging.


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4 AA will give you 6V, that is good for the cheap servos, but I think you will want to upgrade to NiMH cells (7.2V) or a 2S LiPo (7.4V) (but NOT with the cheap servos, they burn over 6V). Use a second battery for the logic if you still decide for a 6V battery.

I would suggest to buy the HXT12K from HobbyKing: http://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=2&Product_Name=HXT_10kg_Servo_(metal_gear)_55g_/_10kg_/_.16sec At only $7.97, this servo has metal gears and 10kg*cm force.This servo works at 7.4V no problem. An arm built with these servos will have no problem lifting up a soda. But you need to design the arm accordingly. I suggest to use a one servo for each degree of freedom, except perhaps at the base and elbow. One servo for the gripper open/close, the one you designed tends to flip. 

Mount the driving wheels in the front of the robot and the caster at the back or the robot will tilt when lifting objects. Install the arm a little behind the wheels line, that will give it a good stability. Place the battery near or over the caster, try to balance the weight of the arm and battery so the center of weight falls in the center of the line between the wheels and the caster. Use a ball caster, not a swing wheel.

All this advice comes from building several versions of the robot and arm. Take a look at my big butler robot (see the versions) and at my mini prototyping version.



Here is the link you need for robot arms.

This is a off-the-shelf robot arm that one of the guys here put together. It is really a good post. If you google the model name of the arm (I can't remember it now --it's in the post) you can find a list of all the servos used. This will give you an idea of how strong of a servo gets you how big/strong of an arm. You can also see some of the geometry they used (the double servo positions). If you scroll down a bit, there is a photo stream with a picture of just about every part by itself. Between finding out what servos are used, the strength specs of the arm and studying the pictures, you should get a pretty good idea of what goes into one of these arms. I have been wanting to build something like this for a while myself, --can't ever seem to find enough money for all the heavy-duty servos!

Hope it helps, good luck.