Cart Project

1337 Rumfishian Knights R/C Cart R0X0RZ

Or at least it might if we ever finish it. However, progress so far seems promising. I don't have too long to talk at the moment so I will make this entery brief. The idea is to have a remote controlled cart capable of moving computer equipment in and out of the UofL Student Center where Lanwar is held so frequently. It would probably be much less hassal and work overall to simply carry the stuff or use a dolly but we Knights believe in a little time honored tradition of considering the "Coolness Factor". I mean everyone has got to know how freakishly awsome we are by now but thats why we have to put on a show because now everyone expects a certain degree of coolness and its a reputation we must uphold. Currently, the design plan will be a heavy duty steel frame and a differential drive system consisting of a left and right pair of power window motors with worm gear drive boxes for shit tons o' torque (I really hope its enough) powered by hopefully salvage lead acid batteries and will all be controlled by a tiny circuit board that I pulled out of a $10 R/C car from Walmart. Anyway, that is the overview and I have to go.

12:56PM 01/13/06

More Indepth (Technical Overview)

Ok, I started working on this bastard a couple of weeks ago but, for reasons I will reveal soon, I have not made any progress since then. Let's rewind, however, to the beggining. I was really bored one evening and I was contemplating how I had accomplished nothing with my break from college so I decided to see what headway I could make with this long planned project. I had most of the parts by my side so I sat at the bench and began to tinker around. First I tested my motor. Its a new power window motor with a worm gear box rated at 1.5A on 12VDC. It worked... that was good... So I needed to test my transistor which I had apparently not painstakingly enough selected from a catalog of thousands to be our motor driver. The TIP110 is an NPN based Darlington transistor which is rated to handle up to 60V at 2A with an hFE of 1000. That pretty much means it meets specs and was 3 for a dollar. I forgot to order its PNP counterpart for creating the H-bridge but I will discuss later. The problem with this transistor is it is wanting to over heat a lot. I now have the proper heat sinks and the PNP transistors but I will discuss all of that at another time.

So I have this transistor which is rated to run the motor directly. In the real project, the transistor itself will be driven by the $10 R/C car board from Walmart. This means that it will be part of the circuit and will need some way to run from the same power source as the motors. My power source for testing was an old 12V benchtop power supply that pushes 4A and has some kind of internal circuit breaker. I got a 7850 5V regulator chip to work (a minor feat in and of itself) which could convert the about 14.8V that the supply was pushing down to a nice and relativly clean 5.07V (close enough, Jesus). A zener diode knocked that down to about 4.7. Considering the R/C board ran off of three AAA batteries which each push 1.5V average and 1.6 or even 1.7 if fully charged, my crude power regulator with its many noise and EMF absobing caps should do well. I guess somewhere in there I tested the thing and it really worked for five seconds until something FUCKING EXPLODED!!! It was only a cap not rated for the higher voltage. Normally I work around 5V and these ratings are never a problem. After replacing this part, however, it worked very well.

I hooked up the transistor to sink the main power directly to the motor with its base driven by low current at the at 4.7V from my regulator. I switched on all the power and connected the base and much to my... not surprise?... the whole thing died. That was when I discovered the power supply had an internal circuit breaker (Thank Rumfish). Back EMF from the motor was throwing the breaker! I stuck in some more heavy duty caps and quickly remedied the problem. As for the transistor, it worked rather well to my delight.

So now I have tested power, motors, and driver transistor and it all works. Now was the moment of truth; should I press my luck? I clipped the R/C circuit from its battery terminals and plugged it into to my custom power regulator. I switched everything on and used the remote while measuring the voltage on the output lines... IT WORKED, OMFG IT DIDN'T SMOKE OR EXPLODE OR ANYTHING! Ok, now for the true moment of truth; to see if the output lines would drive the TIP110 and, essentially, the motor itself. As a precaution, I placed a 2n2222 transistor in between them as a step up assuming that if anything was going to fry, it would be that and not my precious $10 dollar R/C board from Walmart. I through the switch on the remote and... (suspense)... OMGWTFBBQ IT DROVE THE MOTOR... sort of. Now first imagine my ecstacy when all of my technical and theoretical work came together in one night and actually fucking worked without any big hang ups (I mean it took a while and there was a lot of adjusting but you get the idea) but there was one small problem with the circuit which I could not have forseen. The signal from the R/C board was driving the motor just as I had intended but the signal itself was not going to work. I will discuss this some other time but for now I must go.

12:55PM 01/20/06

Problem

The signal coming through the lines of the R/C circuit was pulsated. Some people have asked me WTF but there is a perfectly brilliant reason for why it was designed this way. Baring in mind that these output lines where meant to go directly to toy motors, the pulsation is a rather universal form of DC motor speed control. The toy motors, recieving full power, would probably spin well over 7000 RPMs. This is simply too fast to drive the wheels of a toy car directly. If you were the manufacturer, you could spend money on a gear system which would require more design, more parts, more assembly time, grease, and waste some energy and improve the chances of your already cheap ass car breaking after five minutes of play. Instead, they pulsated the voltage to the motor so that the motor would be recieving, over time, about half the power that it normally would. The momentum of the system carries the shaft of the motor over to the next pulse. Granted, these pulses are too fast to allow for gaps in motion so what you get is a low cost, low energy solution which PISSES ME OFF! I have a worm gear driven system which, if you know any mechanics at all, is a one directional system. Momentum will not carry such a system to the next pulse assuming the pulse was strong enough or long enough to begin with. My problem is I must remove or modify this pulsation.

12:40PM 01/30/06

Possible Solution?

I have been doing a lot of research lately. It would seem that I have stumbled on to a rather complicated but theoretically plausable solution to the pulsation. The 555 timer IC is a clock generator which can, by its design, be set up as a missing pulse detector. A pulsated signal enters this modulator circuit and a clean signal leaves. That's the simplest summary which doesn't tell you much in the ways of technical theory of operation but I don't have much time today.

12:44PM 01/30/06

I will have more info on this later