My next large scale robot based on an electric wheelchair
I have purchased, what I hope, will be a good base for my next robot. It is a Jazzy "Z" chair from Pride Mobility that I bought at auction for $27.50. This chair is smaller than the normal size chair and easily breaks down into 5 pieces for fitting in your trunk. It also runs on (2) 12 volt 12 AH gell cells instead of the huge heavy car batteries that most chairs require. Even though the chair is smaller and lighter weight, it is still rated to carry a 300# person at 8MPH.
This picture is with the chair removed and getting down to the basic chasis.
This picture shows how easily the base breaks into 2 pieces for easy transport. The first thing I need to do is disassemble the motors to remove the electric clutch. This will reduce the weight, size, and make the control electronics much easier to design.
I plan to document each step in the process so others can duplicate what I've done since these are a mass-produced item and easily obtainable.
Most electric wheelchairs have huge heavy motors and batteries making them quite unsuitable for robots. Since this unit is designed to operate off 2 small gell cell batteries, current draw on the motors should be more managable.
This patent application is for PAL who was the prototype for Johnny 5 and this robot will be loosly based on him. He appeared in an episode of "The Wizard" and was called Henri VIII
Here is the chassis with the body and electronics package removed.
This is a close-up view of the motor arrangement. As you can see, there's not much room to work with.
This is a close-up view of the electric brakes that normally have to be powered to release and let the chair move. My next step will be to remove these. Then I will power the motors up under load and see just how much current they draw, at that point I can start on the controller once I know the requirements.
Actual screen capture from the video. Notice the caster wheel is in the rear on the actual robot while it is in front on the patent.
Very intricate head but probably not very durable.
Nice shot of the mechanisms.
This is what the motor / brake assembly looks like removed from the chair. The brake comes off very easily with only 4 allen bolts to remove and the entire assembly comes off.
With the brake removed, you can see the hex head attachment that fits up inside the brake assembly to hold the motor in place with no power applied. A simple allen set screw holds it in place on the flatted shaft.
With the removal of the brake assembly, the motor can be checked for speed and current draw before it is re-attached to the chasis. This will provide a perfect mounting surface for a shaft encoder, which will be added a little later.
This shot is the motor reinstalled in the frame showing the space gained by removing the brakes. I did some testing of the motor while it was loose. Even though these chairs are designed to run on 24 volts, it runs quite well, (and fast), at 12 volts. No load current at 12 volts is about 1.5 amps. I could not stall the motor out on my workbench and current draw never went above 6 amps. I have a dual 10 amp ESC that I am temporarily hooking up to see what happens when I try running the bare frame around the yard. The next step will be to make the structual changes to the chassis and build up the base.
I've been working on the head but it took awhile to find just the right flashlights to use. These Ray-o-vacs were perfect. They are made of a very tough thick plastic that isn't brittle at all and they were the perfect size for my needs.
First order of business was to gut them.
After cutting off the handles, I put a bolt through where the handles used to be and used a standoff to support the rear.
I removed the reflectors and fashioned a piece of gold anodized aluminum for the top of his head.
I needed a easy method to mount the cameras so they could be removed easily to disassemble the head section when needed. I used the plastic spacers that come in stacks of CD's & DVD's. They already had a hole in the center and they are easy to cut with a nibbler. I trimmed them down to the same diameter as the front of the flashlight so when you screw on the front lens assembly, it is held tightly in place. Next step is to decide on the covering for the disk, (so you can't see through to the back of the flashlight), and to mount the blue LED's around the circumference so the eyes will blink, (like Loki). I have a ball & socket to support the front of the head, (to provide 360 movement), and will use 2 servos on the back of the head for up / down, and tilt.
I covered the plastic with adhesive backed gold foil / paper and mounted 18 blue 5mm LEDs. I built up a circuit board with a LED bar graph driver IC. LEDs opposite each other are wired together so the lights will attack & decay from the bottom to the top to give it the effect of blinking, (like LOKI), thanks for the idea Dave.
This is the rear showing the board for the video camera as well as the LED driver board. The LED board has an 8 volt regulator and some filtering to prevent problems with long lead power leads.
This picture was taken with a flash and LEDs full on.
This was taken without a flash and better shows the effect.
This is the controller I will be using, it's from www.EZ-Robot.com and has 20 digital channels, 8 analog and Bluetooth to communicate with the host computer. The software will do speech synthesis & recognition as well as video tracking & recognition. Their website has a ton of ready-to-go routines including speech files for all the popular TV / movie robots.
This is the E18-D80NK IR sensor that I will be using around the base for collision avoidance. They run on 5VDC and have an open-collector output, (pull-up required), and an adjustable sense range from 3-80CM. They are 17mm in diameter and are easy to interface. I got mine off Ebay for about $6.00 each with free shipping.