pic: 2 Speed V.2

[sanddrag]

Originally Posted by sanddrag

I'm thinking you could drop that 60T gear down to something like a 45T. This would keep your high gear ratio the same but increase your low gear rpm (decreas the ratio) and decrease the ratio between them making for a 3:1 difference.

I'm fairly confident that you could even fit a 40T in between the CIMs if you wanted to as long as you keep the axes of rotation of the CIMs and the 40T gear all in the same plane. (my rough calculation shows you should still be left with about .080 between the CIMs).

This would give you a 2.67:1 difference between high and low which I think is pretty much optimal. This would bring your low speed up to around 4.5-4.8 fps which I think is much more useful.

Have you determined that you must be geared for a low 3fps before you can slip the tires without tripping breakers? I'm thinking you can gear a little higher than that and not trip breakers and still slip the wheels.

Oops, C-C distances totally skipped my mind when posting this. I'll come back with an edit and fix that problem.

EDIT: Okay, some of the things in my above post are largely inaccurate due to you need the same center to center distances for high gear.

BUT, I have gotten it all worked out. I think you should do this.

Keep the 12T gears on the CIMs
Those are both in mesh with a 45T gear
The 45 tooth gear meshes with the existing 30T gear

This concludes the high gear lineup and you now have a 3.75" c-c distance between the shafts provided these are 20DP gears. Now for low gear:

On the same shaft as the 45 tooth gear is 25 tooth gear (replaces the 30T non-dog gear you currently have).
In mesh with the 25T gear is a 50t gear (replacing the 60T dog gear)
and you still have a c-c of 3.75 so everything is in mesh.

And that concludes the gearbox. If it isn't clear, I can draw it.

This will get you a smaller lighter setup with the same high speed and a better (faster) low speed. You will have a 3:1 ratio between high and low.

Another option would be to run a 40T gear initially (instead of the 45T I mentioned above) mating with the 12T gears and instead of the 25T gear mentioned above, drop that to a 20T. This will give you a 3.5" c-c distance and a 3.33:1 ratio between high and low.

Or with the 40T gear initially you can go 25:45 for low which will give you a 2.4:1 difference between high and low.

It is all up to you. But the three options I listed are lighter and smaller than what you currently have. Also a bit cheaper money wise.

In any case, I think 4:1 difference between high and low is too much.

[Andy Baker]

Arefin,

You have come very far. This is stellar. You need to make a "portfolio", like an artist. Keep this up, and you will find yourself with a job of a designer for any number of companies. Someone should dig up the first design you posted on here and compare it with this. Talk about night and day.

Your gears look good. We've talked about the dogs over AIM. (I told him about allowing for some "play" between the dog and the pocket. Also, his pockets are overly deep at 0.3". They don't need to be more than 0.2" deep. Also, I would NOT use a chamfer - that would force the dog out of the pocket under load.)

At this point, there are plenty tweaks you can do. I prefer fastening screws into nuts as opposed to threading into aluminum, but that is just a preference. Put more creativity into your lightening holes, as your buddy Tytus does.

The point here is that Arefin has done a great job. This design could have detailed prints and could be made now. It may not be perfect, but it would be a working gearbox within 2 weeks.

I propose a toast, to Arefin Bari, a FIRST-rate gearbox designer.

Andy B.

[Cory]

Originally Posted by Gdeaver

As for the high speed gearing, 13 fps is fast. It takes a very good driver to control the bot at that speed and may be unusable in a crowded obstructed playing field. It's main use is a mad dash to the end zone at the end of the game.

13 fps is quite pedestrian compared to a lot of robots out there. The trend seems to be moving towards faster and faster robots. 15 fps is not uncommon, and robots have gone up to 18 or so before.

[sanddrag]

Originally Posted by Cory

robots have gone up to 18 or so before.

Haha, Travis (968) said 4th gear in that sucker is geared for like 22fps. LOL, now that is too fast. It would probably never get going that fast on an FRC field. Anyway, I've driven our robot which is geared for about 14.5 fps in high and I know I could still handle maybe one or two more fps, and this was without any software help.

Going this fast is a good idea though, especially in Triple Play when the far row can be stolen in a matter of seconds, and your home row can be stolen a few seconds later. If you have someone who can drive it (lots of practice and maybe some programming), I'd say definitely shoot for 14-15 fps. If you want to keep the whole field you're color, you need to be fast like the Cheesy Poofs. Just make sure the robot can still turn when you gear for these high speeds because it wouldn't make sense to race to the other side of the field and have to wast time downshifting because you cannot turn in high gear (turning in high gear - that's the part where the 5th and 6th motors come in ) or a well balance 6wd or omni wheels I guess.

[Arefin Bari]

There will be a lot of tweaking on this transmission and in the next few days V.3 will be up. V.3 has been always been my lucky version. I am taking a few things into consideration. The dog shifter pin needs to be changed. The depth for the pockets for the gears on the output shaft needs to be .2" depth instead of .3". I am going to also check if I can take more weights out (on the side plates). Mounting holes for the chassis (which can be added when a chassis design is complete). I am going to run a long bolt through the hex stands and use a locknut to attach both plates (easy to do). I am going to also bring up my low speed (will try to achieve 6 fps). For the pneumatics, it would be just fine with 2 bolts instead of 4, so I am going to change that too.

I would like to thank Andy for discussing this design with me to make it better, Also John, for being there whenever I had a question. Thank you David (Sanddrag) for posting about how I can make this transmission better. Thank you everyone else for posting here and keep on inspiring me.

There will be a time when you will finally realize why do you crave for more and more from FIRST.

Stay tuned... V.3 is yet to come....

[sanddrag]

Originally Posted by Arefin Bari

Thank you Sanddrag for posting about how I can make this transmission better.

Not at all a problem. We may have our differences but when it comes to transmissions, the world is united. Plus, transmission designing is a wonderful excuse to procrastinate on HW.

[NoodleKnight]

Originally Posted by sanddrag

Not at all a problem. We may have our differences but when it comes to transmissions, the world is united. Plus, transmission designing is a wonderful excuse to procrastinate on HW.

You know, I couldn't agree with you more...

[tiffany34990]

I agree w/ Andy now.. Arefin make sure you do keep everything organized. You need to have all your work in order...it'll help in the long run.. (lemme guess i should help you do that..b/c of yeah... )

keep on dreaming them up..like i've said the past few days...you keep dreaming and designing..i'll help you get into college..lol...

great job.. always proud of your achievements and work