Urgent...Modifying this years drill motors
 

At first glance, this years motors are more than a little different than last years (which i knew inside out) So, i was wondering how vital the removal of the back-drive pins on this years motors would/will be.

Also, assuming i will be removing them, what would be the best way to open this years motors up to get to the pins?

any (speedy, please) help is greatly appreciated!

~Mimi

I have one gear box about 50% disassembled. These things are a lot tougher to take apart and not break than previous models.

So far...
On the first stage, there are two plastic tabs 180 degs apart. Pull them out and pull the first stage off.

The first stage shim and the first internal (ring) gear are pushed into the plastic grooves. You can pry the shim out and then get the internal gear out by tapping the stage on a hard surface.

The metal springs on the shifter can be pulled out with a pair of pliers and the shifter will slide off.

The second stage gears come out easily at this point.


The clutch shell (the thing with the numbers on it is retained by three double tabs at 120 degress apart. I put the shifter into its relaxed state. Then, I pushed in on one double tab with my fingernail and pushed up on the clutch shell. Rotated to the next tab and repeated, rotated to the next tab and repeated. Eventually by going around the circumference, I was able to push off the clutch shell.

I almost have the second stage off, although there is a non-obvious tab or something holding it together. I had to stop before I starting ripping tabs off (I do want to reassemble the thing later, after all).

Andrew, Team 356

Woohoo! Second stage is off.

The second stage comes off easily. You just have to twist it (I think clockwise) and pull. Once you have this stage off, the anti-back drive pins are right in front of you.

Still no luck with the clutch, but I'm going to try to get it from the back side.
Andrew
Team 356

We just figured that out too...one of our engineers had a "happy accident"...its also very easy to just do this from the start without disassembling anything else, which is how we did it. so...do you suggest removing the back drive pins?

From everything everyone has told me in the past, it is a good thing to remove the pins. I think there is a recommendation in the manual this year that you do it. Or maybe the recommendation is in a forum (can't remember).

I also recommend making a ring to disable the shifter and insert it into the gearbox. Unless you're planning on using the shifter that is.
Andrew
Team 356

If you don't remove the pins, every time you stop applying power to the motors, your bot will come to a very abrupt stop (assuming the drills are on your drive train). Its a lot like heading down the road at 10 mph, and slamming the breaks on. If your not wearing your seat belt, you keep moving at 10 mph into the dash. Now imagine doing that every time you had to stop at a light. There wouldn't be enough asprin in the world to cope with that headache, and your car would probably suffer to.

Same thing happens on a bot. Things will want to keep moving, the battery for example. Its a strain on the drive train espically.

So unless you are using the drills in some application that really needs to avoid back driving (some insanley powerful arm for example) or not using the gear box, its best to take them out. You will kill your drive train with them still in, and even if you don't it'd be real obnoxious to drive.

So ya, get the pins out. They make nice tropheys...

-Andy A.

Wouldnt that also cause a jump in the amperrage? i mean if you are going from a speed to an instant stop, you would have to experience that right?

Bad

Hold on
 

You may not have to remove these pins. Sure, the drill motor has more power, but our team has never really worried about removing the pins in order to save the gearbox from being ruined, like many other teams believe.

If a team drives their robot reasonably and mount the gearbox correctly, you may want to keep your pins in your gearboxes... don't just remove them because you think you have to in order to save the gearboxes.

We have used the old gearboxes during 4 or the past 5 years, while using metal treads (no slipping on carpet), and we only removed them for one of those years (2001). During those years, we blew a few gearboxes (2 in '99, 0 in '01).

Remember in 2000? If you wanted to stay on the ramp, then having these pins in place was a good thing... if you removed them, then you saw your robot coasting off of the ramp at the end of the match.

I'm just saying that don't simply remove these pins before you think it will benefit your team.

Andy B.

Re: Hold on
 

If you are on the top of the ramp you will want the pins in. That way a robot without pins trying to get up the ramp at the last second won't knock you off when they go coasting over the top.

Back at 2000, we put the pins back into the drill transmissions for the exact same reason... Our robot slipped down the ramp one match, and we never want that to happen that year again. During that year, those pins never break in the transmission.

However, if the pins do break, they could damage your tranmission so much that the failure will render it useless. So, every time those pins break, you may have to buy a new transmission.

Depending on your system, your pins might or might not break. My advice is, test your drive train hard before you ship the robot. Run it against walls, come to sudden stops, go on the ramp and down again, etc. Do different trails with the pins in, then take them out and see what happens. If the pins are ok even after a lot of testing, then I think it would be ok to keep them in during the competition.

This year is a little different than 2000, because the top of the ramp is flat instead of a peak, and to get the 25 points you got to stay on completely. So, if you are on top completely, you won't have to worry about sliding down. If you are fighting your way onto the top, your motor are moving anyway, so you won't need the pins to keep your robot on the ramp.

Heh...
 

One of our teachers picked it up and the thing decided to break into two pieces...the pins both fell out and all of us students were like "WHERE DID THOSE COME FROM?!"

Well...after about 1/2 hour, we got them back in using guess-and-check methods when our head teacher walks in and informs us that we probably don't even need them!

Oh well...at least we got to get a look inside it :)

Seems like that the ring to lock the motor tranny in high or low (after a quick disassembly and measuring session) should be roughly 1.520" OD, x 1.300" ID x 0.228" thick. You'll need to bore out part of it to clear the gear tooth molded into the inside of the stage 2 body.

I do not see a easy way to take out the clutch shell Last year's drill motor design the clutch can be locked out by removing the double-stack ball bearings and replacing with M6 set screws; however if you put the clutch into drill mode, 2 pieces of metal rises up out of the plastic shell to positively lock the clutch ring from slipping. All in all, this is one *MEAN* gearbox.

I love to engineer bigger and better toys, but aside from a lock-out ring, I don't know how much modding I am willing to try on this gearbox. Well, I also dont' want to break it, seeing how it's so new, replacements would be difficult to come by.

Anyone know what screw pitch the shaft is at? I don't have a set of thread gages handy.

-=- Terence

But if you don't make it up, you wouldn't want your robot to coast back into your scoring zone and knocking over your own scoring stack :)

I've seen a team that shot them out the side of the casing because of the way their drivetrain was. If you do leave them in, you should program the robot to decelerate or train your drivers to slow down.

would we be able to construct a high speed shaft onto the drill motor similar to the one designed by Dr. Joe on the white papers?

Yes, but why? The ones that come on the motor are pretty decent, I don't see how someone without good machining skills and a good mill and lathe can make something comparable. (You would need to hold good tolerances on the shafts, good surface finishes, and the flange on the other end ain't no picnic. On top of that, you have to get through the clutch housing, which I don't think anyone on here had been able to do.

The clutch mechanism that causes the clutch to slip out isn't in the shaft. If you look at the last planetary gear ring, it's not firmly attached to anything. There is a wave pattern running along the top, and what happens is some form of spring loaded pins press into the dimples. When the torque exceeds a certain amount, the pins / ball bearings / etc shifts and the planetary ring rotates (thus the tak-tak-tak-tak-tak sound)

-=- Terence

well we want to get a very high gear ratio from the motor for our transmission gearbox, well thanks for the advice, we'll try to think of something ;)

The new transmission looks pretty solid minus the shifter. It looks like the clutch could be locked by putting a few welds on the rings that Terence mentioned. The only part I'd worry about is the shifter. It is the only plastic in the transmission. Also if you look carefully there are some teeth inside the black casing.

-Ryan