Quote:
Originally Posted by Finnster
@ p4: Do you have a pic of your setup to show what you mean? I'm taking it you made basically a 1spd tranny? (sort of like the kershaw DD unit, but hopefully less craptacular lol) An idler gear would def help getting the ratio down a bit, lend flexbility to the geometry, but its a bit more complicated unit to get together and beyond was I was thinking of doing.
MM:
It is a better design. My first designs were to have the motor mount directly attach to the tranny mount holes, but I was having problems calculating exactly where those holes were. I actually went so far as to buy a used geometry textbook that was @ the library for $0.50 lol. I could measure all the lengths between the holes easy enuf w. a caliper, but what I was having a hard time determining was the angles between the holes. Its a pita to calc angles when you don't have a 90* angle, and its been forever since i've done geometry. I know there was something simple I was missing.
Ie, are the upper and lower holes directly underneath ea other and perpendicular to the ground, as well as parallel top line to bottom line? IOW, could you draw a big 90 between 3 sets of holes. It didn't seem like you could, but I really need to go back and look. I know the rear upper tranny mount is not perp to the lower mount, and I couldn't verify the front one.
The tranny mount is somewhat asymetrical, and I wouldn't want to assume they do run perp, then to create a mount and find out its pitched forward or backwards one way or the other. Also, What I was considering was reducing the number of mounts that need to be machined and designed. if the motor mount could be made in a dimension the same as a popular plastic mount (say a losi 8) then only one mount would need to be made, then use the plastic part for other side. Its a bit cheaty, but I didn't want to draw a whole other mount and worry about the geometry issues.
If I had a CNC or even a drill press to hand machine parts that would be one thing, but trying to draw up a CAD file on a cheap freeware SW, then send it to someone to build, then get it back to see I fragged up a measurement and it doesn't fit sucks.
Lastly, I wasn't sure this would leave enough room in back for batts as the tranny was pretty well centered. I would hope to move it up some, and maybe where I could use an OEM driveshaft. Less custom stuff to drive price and headaches higher.
I'll have to go home and look at my notes from a while back and see what I knew.
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http://www.rc-monster.com/forum/showthread.php?t=19259
BTW, you are right about e-machineshop being hideously expensive. I ended up just getting the parts waterjet cut (hence the raw finish) and having a local machinist counterbore for the bearing recesses. If i were to ever be in a production situation like Mike, the machined finish would be important for sales, but for functionality it does nothing. If you want, I can submit any drawing you want to my waterjet place when I have other work for them (cheapest I've found). If you want any dimensions on what worked for me as well, just ask.