Let's Make Robots!


When it's finished it should be able to get me a beer out of the fridge :) or make a mess for me to clean up :(

Updated, improvement to laser range finder. First test with picaxe 14M.


This is the base with the mid section attached. The mid section is driven by a 24V 100W scooter motor and uses an old car bottlejack as a gearbox/drive mechanism. I've added springs at the bottom to counter the weight of the scissor section so the motor doesn't work so hard when it rises. Fully extended, the top is a meter high. This is made from 25x25 and 25x38 aluminium box section.

Unfortunately the gears in the bottlejack are cheap diecast and don't mesh very smoothly. This is fine when turned slowly by hand when jacking up a car but is incredibly noisy when driven at 2500RPM. So that the robot can sense the height of the mid section I'm using a hall effect sensor and a small magnet. This gives me a simple analog 0-5V signal thats easy for the picaxe to read.















This is my cheap laser range finder (about $45). Doesn't work as well as the bought ones and I think it's short sighted as it only has a range of about 600mm at the moment. I wanted a sensor that could more accurately locate a table or chair leg. On the underside of the cpu fan is a small piece of a blank cd glued to the centre of the fan. This spinning mirror directs the laser (5mW red) around the room. The small black tube at the upper right is a phototransistor with a piece of heatshrink on it so it only detects light from in front of it. This signal is amplified by a couple of transistors and mixed with the tacho output from the fan to give me a pulse with a width that represents the angle of the mirror when the phototransistor was hit by the beam. The closer the object, the sharper the angle. The chip at the top is a "D" type flip flop that is used to mix the tacho signal and the pulse from the amplifier. The IC to the right of the laser is a stepper motor driver that is used to rotate the entire assembly and the chip at the bottom is a Picaxe 14M that controls the stepper motor and measures the width of the pulse. This is a slave device. It waits for a request from a master processor, aims in the requested direction, takes several readings that are averaged out and sends the result back to the master.


I've been trying to improve the range of the laser rangefinder.


The oscilloscope is measuring the output of the amplifier. I was using debug in the picaxe basic editor to monitor the distance of my hand but the white sceen in the background was messing with the camera.

As you can see, I'm extreemly jealous of Rik's new setup. The rangefinder with it's new monacle is balanced precariously on the front of the keyboard tray while the keyboard is hanging on for dear life at the back!

The picture that you can't make out is Leela from futurama drawn Tomb Raider style!








Anyway, enough of my jealousy and perverted taste, back to the laser rangefinder!

This was the first time I had the picaxe monitoring the output. Previously I had only tested it with the oscilloscope.

As you can see, I've got a 60mm magnifying glass taped to the front of a cardboard tube and mounted the phototransistor at the focal point. This does work better but I have to work on aligning all the optical components. I need to get the phototransistor / lens in line with the laser. At the moment moving the PCB up and down or tweaking the laser up and down affects the distance it can detect. I did get it to pick up a white object at about 2 meters but with some adjustments to both the optical alignment and the amplifier I think I can increase the range to a useful 3 or 4 meters.

If anyone wants to experiment with their own rangefinder I've attatched a simplified schematic to my blog on the rangefinder plus I'm looking at ways to reduce the size of it. The optical setup I've got here is probably bigger than I need but it was what I had laying about.














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I've posted a blog to try and answer your questions.

Awesome, I like it so far, especially the home built laser range finder. Did you come up with it yourself or find a schematic on the web somewhere?

My first thoughts about the lift mechanism would be to replace the jack with a heavy duty threaded rod and bolt laying horizontally.

I tried to find out how the commercial units worked but no luck so this was my solution to the problem. As for the threaded bar, that is what the bottle jack uses but it's driven by noisy gears and the reason it's vertical, not horizontal is so the load on the jack is constant (3x weight on top) otherwise the load is about 50x when the scissor lift is down and about 2x at the top.
how will you open up the fridge?
The main photo only shows the base, as soon as I work out how, I'll add photos of the scissor lift mid section and arms.