Project Update 03-28-04

Goodies in the mail!

Got this stuff in the mail from surpluscenter.com. With these and other recently procured goodies, I started working on the wooden chassis mockup.

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Wooden Mockup Construction

If you want to save some time I suggest you just watch the vids. They pretty much cover everything here plus some more.

http://www.cp-tel.net/pasqualy/land...es/DTtest01.wmv ~7 megs

http://www.cp-tel.net/pasqualy/land...es/DTtest02.wmv ~4 megs


First off I had to do a ton of work on the wheels, spindles, rims, and hubs. The original hubs were designed to spin on the shaft. Im my case they needed to locked to the shaft. To do this, I drilled a hole though the hub and shaft and pinned it with a bolt.




Now that I had done this, the rims had to be modified so that the hubs would fit though with the bolt. Trying to stick the bolt in once the hub was in its socket was just out o f the question. This was a huge pain in the rear.





Here you can see the beginning stages of the body and spindles. Getting all this stuff to line up was pretty hard but I'm pretty satisfied with the way the work came out. I had to do very little adjusting.







Here you can get an idea of how things are gonna work with the motors and chain.






I mounted down the motors between wooden blocks to keep them from shifting.



This white bar you see is PVC pipe slipped over a 1/2in rod. It was supposed to provide chain tension but it didn't work so well.
One side ate into the PVC and the other side was a little too slack.


You can see how the chain winds its way between the sprockets etc. It goes over the motor sprocket and then under the PVC tension bar. I found out later that this doesnt make it bite nearly enough teeth for what I'm doing. But more on that later.



Here are some pics of the final deal. I aired up the tires and found I had two flats. I patched one and had to purchase a tube for another.



Here is a good view of how things are working in there.



Here are two pics to help you understand the size of this thing. Its freeking huge!!!
Remember, those are 14 inch tires!



I placed some of the other possible devices on the top deck just to get an idea of how much space I had. I realized that I just didn't have room for everything. So I decided to build a second deck. That would come later though. Looks pretty neat with all these goodies on it!





Here is the aftermath in my store. No worries though, it cleaned up ok. :)

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Problems Problems...
When it was all said and done it worked pretty well but for two major problems.
1. Chain popping.
The chain just wasn't gripping enough on the motor sprockets and the tension bar sucked. This will definetly have to have a major change done to it.
2. Skid turning requires lots of torque!
When you think about it, it makes sense, skid steering requires that your tires move off center to the direction that they want to turn. Rolling a wheel is easy. Pushing one sideways is not. The wider the wheelbase (left to right) the easier the turn because there off angle of movement is smaller. The Shorter the wheelbase (front to back) the easier the turn as well. I have about 5 inches or so in between wheel edges (front to back) that I can lose to help reduce torque needs but this won't be enough.
I can't go any wider either, she is just slim enough to fit though a doorway. So I have to add more power and also probably gear down the drive train.

If you want to know more about the problems of skid steering click here.

We also decided to try out only having a two wheel drive and caster setup. However this looked really lame and wasn't nearly as strong offroad as the 4wheel skid steering design was. Also it was really hard to drive this way so we gave up on that idea pretty quick. More on that and other solutions in the next update.


Here are the videos.
They Actually go into better detail than this page does and they include video of the caster test etc.

http://www.cp-tel.net/pasqualy/land...es/DTtest01.wmv ~7 megs

http://www.cp-tel.net/pasqualy/land...es/DTtest02.wmv ~4 megs

Project Update 03-13-04

ghhh, so much to update on. I'm not sure where to start. I'll try not to forget anything.

Even More Chassis Planning

First of all, I've done a little more design work on the chassis and drive train etc. I'm pretty much dead set on the motor in the middle design. I made a little video of the whole thing coming together and it makes things a little more clear.
drivetrain03-04.wmv about 1 meg



As you can see, I modeled the pillow blocks and flange bearings and made the tires a bit better than they were before. Its helping me decide on the actual demions of the frame itself. Right now its looking like the frame will be about 16-18 inches wide, with the tires that makes it about 30 inches max. Still pretty big.





Weapons Systems Work

Last update, I had just gotten my little BB gun. Will its been about two weeks and now my office is covered with little green plastic BB's. This thing is a BLAST!!. Big props to Z over at SomethingAwful.com for suggesting it to me. As I mentioned before, firing it with the SV203 board was just a simple matter of bypassing the trigger by soldering leads right onto the motor of the gun itself.


After that, I connected it to the 5V lines of an old AT Power supply from a junk computer I had laying around. It worked like a charm. Then I put a little reed relay between the gun and the power, the SV203 board controlled the reed relay via its on/off output capabilty. Perfect for the relay because it likes 20milliamps and the board puts out 25.
What wasn't so perfect was that the relay was only rated for 1 Amp throughput. I don't know how much the gun draws, but it was powered by AA batteries and those push 1.8 Amps. The relay tended to 'stick' in the on position alot. I fixed that by putting a power transister behind the relay. SV203 turns on the relay, relay turns on the transistor, gun goes shooty.

Mounting the thing on servos was a bigger pain in the rear. Our first attempt was just really really ugly, and crappy. But it worked. We screwed down one servo on the right side of the gun for verticle movement, chopped up an old power supply case to get a piece of angle iron and used that to mount one servo to another for horizontal movement. Then we just taped the hell out of that servo on a pole so the gun would have some clearance to move. It was really bad for the servos to be holding that weight, it hummed, it wobbled, it was ugly, but wooooo it was a blast!



Now, we still had problems with how to aim it and shoot it, and how to let other people over the net aim it and shoot it.
I tried a few pieces of software and 'Active Webcam' was the first one I got to work and work well. Though I'm not sure its the best for what I need. It is basically acting like a web server and a streaming camera. It serves out a single web page that contains the camera applet. However you can edit that web page to include what you want on it. That is where Serial Host comes into play.

Serial Host is a sweet little tool. Basically it converts incoming http requests to serial commands. "Hunh what?" you ask? Well its simple. I make a link on a web page, or email etc. When you click that link the request goes over to Serial Host and it then passes the command over to the serial port on your computer.
For example, if serial host was running at on my PC and I gave you the following link to use:

http://12.14.254.181:82/Pontech?SV203=MoveAbs(1,100)

Serial Host would take recieve that url request and then send the command over the serial port on my computer for the SV203 board to move Servo 1 to position 100.

If you still dont see how this would be useful, then just take a look at this:


Above is the final product of a toy gun, SV203 Servo Controller, servos, lots of electric tape, a webcam and software, and Serial Host.
There is my friend in Texas, shooting cups off of computers in my office in Louisiana.

I can't say enough good things about serial host. Steve McFarlin was very helpful when I had email questions as well. As soon as I have the money set aside I'll be sure to buy this piece of software because its just so darn useful.

Here is a video of the first version of our gun mount in action.
WeaponSystestFeb04.wmv about 7 megs

Trash vs Treasure

Over the weekend I visted my parents house and picked up a ton of goodies. I got some scrap lumber from the new house they are building, I'll be using it for a wooden mockup as soon as I have all my sprockets etc. I also found 3 or 4 sheets of 3/4in lexan or plexiglass. VERY useful stuff. It would have cost me probably $150-200 a sheet, but my parents were just going to toss it. I picked up some chain, a few sprockets, some old motors that are probably ruined, some old bearings and I got a chance to weld my sprockets to my hubs.

I had a chance to actually put together a quick mockup of one of the tires on a chain drive. I used a C clamp to hold the motor down, put the sprocket on, and ran a chain to the one wheel I had with a sprocket built on. The gear ratio was probably 3:1 so it was 3 times slower and stronger than what I will have at 1:1. I couldn't seem to stop the wheel using both hands. It was powered with a 12V car battery so I'm pretty pleased. These motors definatly have some umf to them.


I got my first donation to the cause as well. Tballz, a WWIIOL player sent me a box full of 'junk' that his company was going to throw away. Some fans, speakers, hardware, etc. The coolest was the handful of solor powered digital thermometers. Big thanks Tballz.


Weapon Systems II

I decided to redo the gun mount with my newfound materials. I picked up a router attchent for my dremel tool at Walmart along with a cutout bit. It works real well but you have to be very careful because once it gets hot its very easy to cut out too much. The Lexan sheets are a pleasure to drill too.

The base of the mount was made from an old power supply case (useful things to keep around!). We mounted a servo on the bottom and mounted a Lexan disk to the servo horn. 4 plastic 'bumpers' keep the disk from wobbeling too much.



Mounted on the disk are two upright pieces of Lexan. We used old computer expansion card slot covers as L brackets to mount them. Scrap is a wonderful thing.


I added a rod to the left side of the gun and kept the servo on the right side. The rod onthe left takes pressure off the servo and makes things more stable. However its not perfect, I may change it to a gear system so that the servo isnt directly connected to the gun, I'd also be able to limit the elevation with this method.


We tool the webcam out of its housing and used hot glue to stick it to the upper front of the gun. A much much better system. We had to move it later when we realized we put the wrong size arm on the servo horn and it kept slipping. So we glued the camera to a plastic tube that fits inside the gun and is screwed into place. That way we dont have to remelt the glue to get the gun apart in the future.




I also removed the handle, trigger, and clip from the gun. All of these were just spare plastic getting in the way. The clip was always there for show anyway, the BB's are kept in a hopper on top of the gun.


After we were all done, we turned on the web cam and the Serial Host server and let the guys over at WWIIOL and SA have at it. We had a blast letting them shoot old coke cans etc. We got hit a few times ourselves.
Here is a movie of the gun in action. At one point I had a pice of Lexan up as a shield and the sneaky boogers shot my fingers!
WeaponSystestIIMarch04.wmv