|
|
|
Forum Member
 
Last Login: 7/3/2010 7:09:18 PM
Posts: 126,
Visits: 643
|
|
Hey T-man,
It always goes slower than I like, haven't had much of a chance to work on it lately.
You called my bluff on the servo part 
They aren't servos YET...
They are heavy duty wiper motors with built-in gearing for more torque; a few bucks at the auto salvage. Great motors- they just need smarts.
I'm going to make servos out of them. I bought a couple of potentiometers and an arduino microcontroller. The "pots" will provide feedback to microcontroller so it will know which way and how far to turn the motors.
The microcontroller (very low current) needs a motor driver circuit to actually power the motors. The first one I ordered was discontinued. 
Found another reasonably priced one and ordered it yesterday.
Its a Sabertooth dual 10A motor driver.
In the "old days" this would have all been done in "analog hardware" without a microcontroller. I prefer the microcontroller approach- it gives a lot more flexibility. I'll also need the microcontoller to read the inputs from the Joystick for the "drive motor" controls. I haven't decided the details for the "brains" yet- it might have two microcontrollers before its all over. I might need them to incorporate some "secret bat features"... 
I haven't picked "drive motor" controllers yet- those will probably be the most expensive parts (those or perhaps the 12V batteries).
-Monta
|
|
|
|
|
Forum Member
Last Login: 7/3/2010 7:09:18 PM
Posts: 126,
Visits: 643
|
|
A very short video.
Test of the new motors turning the front wheels.
They aren't servos yet- I'm just touching the wires to a battery for a test.
-Monta
|
|
|
|
|
Forum Guru
Last Login: Today @ 2:55:37 PM
Posts: 637,
Visits: 2,318
|
|
|
|
|
|
Forum Member
Last Login: 7/3/2010 7:09:18 PM
Posts: 126,
Visits: 643
|
|
Standardization on an unstandard design.
What do you guys do about standardization?
I'm a little torn. I have this joystick that I'm going to use for steering and throttle. It comes wired like this
which IMHO is stupid.
So why did they wire it like that; joining the pots and not using the center tap?
I assume it was so they could save $.01 on pots and save one wire on the port.
So I open up this joystick for grins and what do I see?
Pots with a center tap, and TWO UNUSED WIRES....
The Dilemma
-----------
Solution 1:
Keep it the same.
The joy stick works but the response isn't linear. I can correct that in software, but I won't get the resolution I could otherwise. Besides is just feels 'dirty'.
Solution 2:
Spend half an hour and modify the joystick.
Get better, linear resolution and feel better about the setup.
The downside
------------
The only real downside is "standardization". I'm going have a standard looking device, connected to a standard looking plug; both of which have been "modified". If at some point in the future I decide to change the joystick- I'll have to modify a new. Not just unplug and replug a new one. More than that I'll have to remember I modified it (and how). Plugging a standard joystick in place will fry the microcontroller.
I'm sure you guys run into this all the time.
Any rules of thumb for what to keep standard and what to modifry (I mean modify).
-Monta
|
|
|
|
|
Forum Member
Last Login: 7/3/2010 7:09:18 PM
Posts: 126,
Visits: 643
|
|
Its ALIVE!
-----------
Couldn't find the 15 pin d sub connector I needed at Ratshack or the local computer store- Didn't want to order it from my regular electronics supplier and pay $15 shipping on a $.50 part. So I found a "cheap shipping" place and ordered it there. I grew anxious waiting for it to come in and remembered I had an old PC sound card in the junk bin. It has a game port on it (or did). Get out the "hair dryer" and desolder the thing. I'll use it 'til the correct parts come in.
Connect the (yet unmodified) Joystick to the microcontroller- write a little demo software. Spend an hour trying to factor a simple polynominal to make the output linear- give up and drop the equation in wolfram alpha, cool... It solves it, graphs it, and has a button to click to show HOW it solved it. Oh yeah, now I remember how to do that.... I could swear I heard that website call me a moron and snicker...
After I got the joystick input right- watching the numbers scroll by on the screen got old, so I grabbed a servo I had laying around for another project and hooked it up... The final steering will be just like this, except the servos will be (much) larger.
p.s. no you can't power a servo off the laptop USB through the arduino, too much current- it keeps resetting the microcontroller. I knew that. Really. Just had to prove it to myself again....
|
|
|
|
|
Forum Member
Last Login: 7/3/2010 7:09:18 PM
Posts: 126,
Visits: 643
|
|
Steering servo build.
I'm really happy with the PID (proportional integral derivative) controller for the steering servo. It gonna be great! The testing will all the pieces, (microcontroller, motor controller, motor, and feedback pot, and joystick) went great. Now it just needs a little cleanup. Then I'll have to build a real board for it (instead of the foamboard its installed on now). Here's the controller setup, the actual servo motor isn't shown in this picture. I'll get a video up in a few days.
Can't believe how cheap it is to build a couple of servos like this compared to commercial units. (Actually I don't think the commercial units I've seen are anywhere near this powerful). When I get the chance I'll measure its output in foot-pounds. (Most servos are measured in oz-inches). I'm excited because it has so many other applications too, anywhere I need precise positioning and high-torque. This might just be the coolest part of the build.
-Monta
|
|
|
|
|
Forum Member
Last Login: Today @ 1:04:31 PM
Posts: 359,
Visits: 1,983
|
|
Pretty cool! Any updates? 
|
|
|
|
|
Forum Member
Last Login: 7/3/2010 7:09:18 PM
Posts: 126,
Visits: 643
|
|
Ok. A few updates.
I fabbed motor brackets.
Installed motors sprockets and chains
And took my first ride across the garage! WooHoo!!!
O.K. It really wasn't much of a drive. Steering isn't operational. I travelled about 6 feet under what I'd call 1/4 impulse.... But I did ride on it.
-Monta
|
|
|
|
|
absolutely sucks at internet
Last Login: Today @ 2:35:33 PM
Posts: 2,059,
Visits: 5,377
|
|
whats the dimensions of it so far?
its not what you offer when you're dead, its what you offer while your alive that counts. ~the cow.
|
|
|
|
|
Forum Guru
Last Login: Today @ 2:55:37 PM
Posts: 637,
Visits: 2,318
|
|
hay Monta , that is looking pritty cool ...I'm with shaggy how big is it??
. . ( http://tmanskarts.com ) . .
|
|
|
|