We were planning on using two Banebots Rs775 with a planetary gearbox reduction of 256:1 to power our single pivot arm. The arm is a little less than five feet long with a light weight manipulator on the end.
However, banebots is out of stock for this gearboxes and even if they had them, the lead time is dangerous.
Are there any alternatives that we could use? Either a different type of gearbox or the use of the other motors in the kit. Would two window motors be powerful enough?
Without more specific information, it is hard to give accurate advice. What is needed is: how far is the center of mass from the pivot point, what is the weight at that distance and how fast would you like to rotate the arm.
With these values, an accurate calculation and recommendations can be made.
That being said, the FP motor and gearbox is quite sturdy and powerful as long as it is implemented correctly. As you can see in this thread, it is capable of 34 Ft/Lb of usable torque.
Option 1: Hollow out this pinion (or a gear with the same specs) that mates to this AndyMark Planetary Gearbox, then modify the gearbox to add the mount holes for the RS775, then put that gearbox anywhere you can put a CIM. Read this, all of it. You will need some pretty decent machining capabilities.
Option 2: Use a CIM on the arm to test. Then wait for Banebots to get it together and replace it on the Thursday of competition.
At either of those points, however, it may be easier to use the FP motor if you’re only using 1 motor for the arm. Given that you need to gear anything down by quite a bit (1000:1 or more) in order to easily control the arm (2 seconds per 90 degrees), you could probably get away with that. With such a long arm, the manipulator will have to handle the forces of accelerating to and from over 10 feet/second at the tip.
If you look at the spec for the RS775-18, what else uses an 18V DC motor?
Try to find a cordless drill with a similar motor and then cannabalize it for its gearbox! Thats my contingency plan. You will find that the Banebot motors are very standard in their mounting and shaft configurations and I’d bet it’s pretty easy to match it up to an 18V drill with the same if not very similar motor. Just remember that a drill is not designed to take sideloads so you must isolate them using external bearings. Anyone who was around in 2000-2001 (?) possibly earlier can attest to the importance of this!
