Re: Minibot climb rate
 

You are correct... could be an "illegal" minibot.... I STILL envy that speed...Or maybe it's the Mythbuster-ish destruction that occurs when it slams into the top! COOL!

Steve

Re: Minibot climb rate
 

It is my assumption that "direct drive" in this thread refers to driving a wheel directly from the motor shaft. In other words, without the Tetrix gearbox attached. Is this correct?

My team is considering the idea of doing away with the tetrix gearbox. But I don't like the looks of that 2.5 mm motor shaft.

Re: Minibot climb rate
 

I believe when everyone says direct drive, they mean with the tetrix gearbox, considering you cannot alter the motors (which I assume means the gearbox connected also).

If I am wrong, please smite me. Thats what I meant whenever I said directly driven.

Re: Minibot climb rate
 

*smite*

http://forums.usfirst.org/showthread.php?t=16187

ye of little faith...:rolleyes:

Re: Minibot climb rate
 

I meant a direct drive off the stock gearmotor, not motor sans gearbox.

The latter could be done but for my team at least it's beyond our capabilities.

Re: Minibot climb rate
 

I propose that from here on in we specify what we mean when we say "direct drive."

My team is in the same boat regarding technical ability to use the motor shaft. On the other hand, I cracked open the tetrix gear box last night. With some moderate machining capability, one could signicantly modify the ratio of the gearbox. I took a couple of photos that I will try to put up this evening (CST).

I would love to use the internal gearbox alone for several reasons. Not the least of which is that two of our wheels and a driven tetrix gear came loose on our first climb test.

Re: Minibot climb rate
 

Here's an internal view of the Tetrix gearbox:



It looks possible to mate the brass helical gear to the 40T gear on the output shaft, with a little bit of machining. Sorry this post is a day late.

Re: Minibot climb rate
 

Or a just a case of skepticism with the treatment being a clearer video with close up? ;)

Re: Minibot climb rate
 

Thanks for the pic. How many teeth on the gear on the input shaft that mates to the 26 tooth gear?

Re: Minibot climb rate
 

Math would say 10. (40/10)*(25/15)*(30/10)*(26/10)=52:1

Re: Minibot climb rate
 

10 teeth on the helical gear on the motor shaft. This makes the ratio input 52:1 output for the gearbox and motor as assembled. Mating the 10 tooth element of the 26:10 brass gear to the 40 tooth output shaft gear would yield
input 10.4:1 output for the same assembly.

Re: Minibot climb rate
 

That is exactly what we did (using only an inexpensive mill and lathe and a dremel), and it works great.

Re: Minibot climb rate
 

Do the gains in efficiency offset the lower torque output of the motor, or is this an "experts only" mod for teams that make custom 2" wheels?

How dramatic is the speed gain? 1625-dramatic?

Re: Minibot climb rate
 

The dyno data showed a ~60% increase in output power. That makes it 1625 fast. You would definitely have to do some custom gearing and probably custom wheels (custom wheels will remove the necessity for some of the gear ratio). The big thing is to get the gear/wheel combo right so your reflected torque to the motor is ~50% of stall.

Re: Minibot climb rate
 

Here's a tip, whether or not you chose to modify the gearbox. We found in years past that cleaning the stock grease from our NBD gearboxes and using light lithium grease had a noticeable improvement in output (efficiency). It looks like this gearbox is pretty clean - don't know if it was that way when you opened it, but even if it was well lubed it might be a good idea to clean it out and put in lithium grease. (which per update 5 is an allowable material).