Unfortunatly I don't know where my camera is, so I won't be able to take too many photos at the moment. (August 2008 update- I am going back and fixing images where I can -Rob).
I want my 1/350 Tamiya USS Enterprise to have sound- and for a while now I have been fiddling with a sound box. Sitting there waiting for it to dry, I had an ingenious idea. I cut a book sock book cover in half and inserted the speaker into it. I pulled the material behind the speaker and used a hair tie to tie it back. BADA BING- I now have a speaker with a proper amplifier and baffle. She sounds great. I made a "control panel" for the speaker by drilling a hole into balsa and drum sanding the said hole. The Ipod sits to the right (attached with tape for the time being) and the entire setup sits snug into the Enterprise. Better yet- it is 2 inches off the bottom of the hull, meaning there is a smaller chance of something frying due to water intrusion if there is mild flooding.
Since super glue has been working so nicely for me, I super-glued the steering mechanism permanently to the Battery and electronics housing so the unit is one piece. I did this because fiddling with two seperate units is time consuming and annoying- the wires from the steering to the electronics are taped to the side of the battery housing, and not only that- the steering mechanism is centered perfectly (the rod is, anywhoo) for the rudder system. For the rudder system, I will implement my roommate's adjustment system for the push rod- adding even more customization and ease to the build- if something isn't turning correctly then I can simply adjust the rod to whatever length I want it to be at. I have a guide for it- I can just look in the Missouri and see what he did.
Here is the big cojone- I solved the prop shaft to motor shaft connection problem. Heat shrink tubing really wasn't working too well- so I looked into getting tube stuffing because it was recommended by R/C Naval Combat enthusiasts. Instead, I tried a what if, "what if I put the prop shaft into the square tubing?" and as I did I began to laugh maniacally and I used the spoonerism "WHO SAID I COULDN'T FIT A SQUARE PEG INTO A ROUND HOLE?" (it was the other way around). As luck would have it the motor shaft fit too. I got all excited and ran upstairs for a battery to test it out. I was on a fast paced course and I was getting near the last hurdle, then:
brickwall. ouch.
The entire system worked isolated from the body (hull, [ Gosh I sound like an engineer ]), but only for 10 seconds. The motor slowed down and called it caputs. I did a few more tests, this time with a half of another prop rod. The system worked perfectly isolated outside the hull. From this I can write the following equation:
[ LengthX=Torque1]
where X is proportional to the mass of the prop shaft material. The motor shaft is approximatly 1:10 the length of the prop shaft and it appears to be made out of aluminum or some steel alloy. I think the motor is trying to spin this thing, and it certainly isn't spinning inside the connector- it is stopping. I think I worked the horse too much and it got tired and called it caputs. The solution is to make X smaller or get a motor that will generate more torque to equal Torque 1.
where [Torque1=Torque2]
and
where [Ttotal=Iα]
where Torque 1=torque of the motor, Torque 2=torque of prop shaft, Ttoal= Torque 1+ Torque 2, I=moment of inertia, α= angular acceleration.
So now we are back to a Physics I problem.
Torque= (moment of inertia)(angular acceleration). From this equation, it can be assumed that the longer the distance (moment arm), the greater the Torque necessary has to be. When torque 1 was exerted, it attempted to spin the connector and the prop shaft, creating torque 2. However, torque is influenced by (moment arm)*(force). It will require a greater force to move a heavier object (the brass rod). The mass of the brass rod is directly proportional to the length of the rod- the shorter the rod, the less torque necessary to rotate it.
Thus, since the DC motor barely changes speeds on a Nicad battery source, the shorter the material means less mass- which in turn means that the prop will spin faster. So with this in mind, we can conclude that:
[The mass of the prop shaft is directly proportional to the torque and angular speed of the motor.]
There is a loophole here. Although length is a major factor, we can make it an insignificant factor. How? By using a different material. Aluminum (or an aluminum alloy) has been known to compete directly with many steels. The point here is that aluminum is MUCH lighter than brass- which is a combination of zinc (roughly 40% zinc) and copper. Copper has corrosive resistant properties, but the mass of bronze is too much for these motors to handle. Thus, I need to get my hands on some aluminum or a lighter material, somewhere. I am also thinking about trying tubing instead of solid rods- but tubing has a greater chance of corrosion and damage when I attempt to repair it. Tranes and Lanes along with Hobbytown USA should have a good selection of lightweight tubing and rods.
Aluminum is so light that it will make length negligible. I will update when I try some things out. Actually- I just thought of something. It could be that the motor is spinning inside the square connector, but it is slowing down due to the load because the motor is trying to turn inside the tubing- but the friction is too great for it to accomplish (that is why I chose it). I am going to get some of this tube stuffing stuff since the motor shaft has points of contacts all around the inside of the tubing, meaning that there is no mechanical energy lost in trying to rotate inside the tubing.
Hey, what I said above still applies though- but I thought that the brass could turn with the motor. Maybe I should do both!
No comments:
Post a Comment