R2 Reverse Gear Try No 3
Nov 11 2003
This is my third try at the reverse gear system. In the other two systems the torque of the Saturn motor would actually bend the bracket and pull the gear away from the second one. This caused the teeth to skip creating a lot of noise.
In the second try I reversed the location of the gear and chain. The chain was closer to the wheel and wheel bracket in hoping that this would make the assembly stiffer and the bracket would not pull away from the gear causing slipping. This required a new longer main drive shaft. Again I think the failure of this system was the fact that I made the bracket adjustable. Even though the screws holding the bracket were tightened the forces were so large that the bracket was being pulled away from the second gear every so often.
The next try I used a longer bracket for the gears. In this system I contained the drive shafts of both gears. This way there is no way for the gears to be pulled from each other. In the aluminum tube I drilled holes for the drive shafts to fit through. This means the drive shaft (steel) is rotating on the aluminum hole. Not an idea situation but cheap and it does appear to be working. With periodic lubricating hopefully there is no problems with wear. Time will tell.
On the down side to get the new bracket to fit in I had to move the motor out by about 0.25 inches. This meant drilling new holes into the foot mounting bracket to the motor bracket. As seen above I had to take a chunk out of the foot shell to get the bracket to fit. The opening isn't very noticeable
From the picture and comparing it to the previous attempt the new bracket is bigger. All the internals are the same as the second attempt. The right side of the motor hit the bottom left of the bracket. A little juggling may allow the motor to fit the original mounting holes. I just realized that my wheel axles were drilled too high and on our plans the holes were lower. This may be enough to get the bracket to miss the motor body.
End view
My foot assembly differs from the one offered to the group in that my clearance is lower. My drive shaft location is not as low as the one offered to the group. This meant my bracket bottoms can hit the ground every so often. To increase clearance the end of the brackets were cut off (with a jig saw that is why it looks rough) and replaced with the threaded rod and nuts. If people who bought the feet kit think they need more clearance they can do the same thing. There is an argument that this threaded rod might not even be needed. It is up to the builder to decide.
I did put quite a bit of lithium grease at the drive shafts to try and make the steel to aluminum rubbing surfaces as friction free as possible. I am not sure how the above pattern occurred.
Make sure set screws are tight. I had the ones in the gear loosen on me. Not something easy to reach to fix.
The weekend of Nov 7,8,9 I had R2 at a Hobby show and was running R2 around every so often. I could not run all the time or my batteries would quickly die. I had 2 sets of batteries so there was quite a bit of running around. I ran R2 so often that on several occasions the motors were too hot to the touch. So far everything seems good so far and I do not see any damage to components.
With both motors going forward at the same time the speed was good. I did notice that the left motor with the reverse gear was a bit slower than the right motor. I am wondering if this is the nature of the left motor or is the reverse gear system introducing a lot of frictional resistance. There is a possibility that the high heat loads and the fact that originally it was this motor driving in reverse all the time that the motor is damaged. All very possible and I should change the motor to a new one but maybe later.
I also thought would I get more speed if I reduced all the rolling friction in the drive shafts. The way to do it would be to use bearings instead of bushings. I don't know if there is room but I will look into it. A project for the future?
Nov 4 2004
Um as before this project is now obsolete with the 24V Saturn conversion but since I put so much effort into this project I am going to make sure everyone sees it.
Nov 11 is of course Remembrance day to honour those who fought in various wars so that we can live our lives in a free world. I will never forget.
If you want to build your own R2 go here --http://groups.yahoo.com/group/r2builders
or here --http://movies.groups.yahoo.com/group/astromechs
for an R7 go here --http://movies.groups.yahoo.com/group/r7droidbuilders
Email me ask@interlog.com