Let's Make Robots!

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.

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
anthonykevin's picture

That is a very nice and invention. Shows your hard work and efforts. I think such inventions deserve to be patented. go here and find out more.

birdmun's picture

are simply adjustable IR switches, and not, remotely comparable to typical Sharp sensors or their ilk?

Salvage's picture

I am aware what they are. You don't need distance data for collision avoidance, just go /no go.

birdmun's picture

Glad to see you still working on this. It looks like one of those long term projects.

Salvage's picture

Yes, it's been awhile, I had a lot of items on order and had to think about how best to do some of it but everything is finally coming together.

If you've never been to EZ-Robot.com, you need to check it out. This is the controller board I am using and it is awsome.

20 digital channels, 8 analog, built-in bluetooth, speech synthesis, speech recognition, and image recognition.

DigiSys's picture

I keep checking back on your progress as there don't seem to be many bigbot builders. Most seem to be doing the small ones. Even the ones I've found based on wheelchairs don't seem to get past the "remote control base" stage.

I need to snap pictures and start a page for my latest which is similar to yours. I stripped down a Pride Jazzy Select (big brother to the 'Z' chair I guess) and will convert it to an R/C lawnmower. I'm trying to do it without replacing the stock controller since finances are tight. I don't mind the built-in safety features for the mower and might look into reprogramming the controller if I need to tweak it some. I was going to make a full-size robot but, for reasons I'll go into on my own page, decided to make the mower with this and use the Drive Medical Cirrus Plus chair for the bigbot.

Yes, I got a deal on 2 'broken' power chairs. :-)

 

Salvage's picture

I've updated my progress if you're interested.

Salvage's picture

I also have the Jazzy Select, I got 3 chairs in the same auction, (Invacare also). I have run into a slight roadblock with mine, I can't find any way to make the chassis into what I want, so.......it looks like I'm going to buy some square tubular steel bar stock and learn to weld up a new frame. It's been over 40 years since I did any welding but this new wire-feed MIG looks a lot easier.

DigiSys's picture

Since you also have a Pride Select you'll see my problem which wouldn't exist if I had the Z Chair. I want to separate the motor section from the battery tray/rear swivel wheels. The Z Chair splits apart exactly how I want but the Select is solid heavy duty one piece frame. Basically I want to cut out the battery tray and mount the lawnmower deck in it's place. Since I don't have the tools or welding experience I put it all aside for now and started work on the bigbot project using the Drive Medical Cirrus Plus chair.

I need to get a page up for that build. I'm using 2 of those same proximity sensors for bump switches to detect obstacles too big to roll over but too low for the ultrasonic that will mount about head level (5 feet maybe). I might put a Sharp in the center watching the floor to keep from running off a stage/platform/stairs.

I like your head setup. Another area where I'm lacking is creativity. I had an old 13" terminal monitor I gutted for a head but it looked like crap and tossed it. I'll have to figure it out later after I get a body built up.

Salvage's picture

Another Jazzy Select just came up on auction and I don't know if I should bid on it, it's in nice shape and would be a shame to part it out but if cheap enough:-)

If you want a cheap and easy head for a large robot, the plastic dome off an old salon style hair dryer works well. I've used these on several robots and it's an easy build. A snap-ring holds the dome in place so all you have to do is use the base as a pattern and trace it onto a thin piece of metal. Set the dome on the metal base you just cut out and put the snap-ring around both the lip of the dome and the metal you just cut out and you're done. They generally come in a smoked plexiglas and have an opening where the dome is mounted and the air comes through. This works out nice to mount your speaker with a piece of perforated speaker grill.

I still have a couple sitting around waiting for another build.