transmission
 

OK, I was wondering if there were any draw backs to placing the shifting mechanisms on a robot right after the motor? Or advantages for that matter?

What do you mean "Right after the motor"? I am not understanding your question at all right now.

Cory

whats that mean dude?
_!_
--(0)--
specify....

As opposed to placeing the shifting mechanisms before the motor?!

(just kidding)

I assume you mean, you want to make a multi speed transmission, and you want to know if you should gear the motor down first, then put the multiple gears on the final output shaft (to the wheels)

or if you should put the multiple gears on the motor shaft, and then gear it down further after that stage?

is that the Q?

That's correct, Ken. This question came up at our meeting tonight and we couldn't think of an answer. Any help you or anyone else can provide would be appreciated.

George

The way I've usuallyseen shifting done is on the "last" shaft in the gearbox. Then there is one final reduction to the wheels. Like in the 2003 Technokats design.

If I'm not mistaken, team 45 actually used a chain reduction after their gearboxes...

I guess we also want to know *why* one would be better than the other.

Thanks again.

George

Did I ever say they didn't?

no chain for us in 2003....sorry...

refer to this picture

Technokat 2003 Drivetrain

I'd explain but its late and i've gotta get up early tommorrow....

My thought is probally flawed - I am really tired right now but...

Wouldn't this be a two-faced question?

If you where going from the motor to the tranny than REDUCING the gear ratio - that would be easier on the tranny.

If you went from the motor to the tranny than INCREASING the gear ratio - wouldn't that be putting more strain on it?

It will take power to move the robot - I realize that - but if you can avoid more stress than what is needed on the tranny - wouldn't that be better? :)

Agian - I am really tired and I am probally going to go to bed after this - but thoes are my thoughs. Hope this helps! (and I hope I'm right! :D)

We had this same debate.

Decision?
We decided to shift as early on in the gearbox as possible. (After all the motor combiner reductions and such). Basically, the reasoning behind this was, there is less torque applied to each shaft/gear at this end of the gearbox (higher speed = lesser torque). This means our shifter pins/dogs/whatever would be put under less load.

Problems with this?
We were worried that the high speed associated with this part of the box would cause our shifter to "grind" and not engage nicely. Some argued that perhaps at a slower speed, the dog/pin/whatever would engage "nicer".

Results?
She shifts beautifully from low to high, on the fly. She's not as fond of dropping from high to low while at full speed, but we're not worried about that as much.

She does make a nice little grinding noise as she jumps into gear, but, no damage or visible wear has occurred on our shifter dog, and the whole box seems to be functioning almost flawlessly.
*knock on wood*


Good luck to anyone attempting this. If you email me, or IM me, I'd be more than willing to share experiences, or help out with any drive design questions.


John

PS - The Technokitten Tranny shifts right after the motors combine (Andy has it shifting even earlier than mine does). They then go through another reduction afterward. In 2003, this additional reduction was mounted seperate from the main gearbox, and located on their tread assembly. The output from this secondary box turns their tread (direct drive). No chain.

Thank you, John. That's a great explaination, and it helped me to understand things a little bit more.

Sorry, sanddrag. I must have misread your post the first time... Lesson to all: pay closer attention to what saddrag says!

;-]

Of course, if anyone else has an opinion on the subject, I don't want to hear it. JVN is a god... Don't you dare disagree with him!

George

Bingo! John gets an "A" for the day.

When designing your shifter, do the shifting as close as you can to the motors. This means that you will be turning at a higher rpm, but more importantly, at a lower torque. This lower torque gives your dogs/teeth/hex shaft/etc. less stress and strain.

TechnoKitten... sheesh... no respect, I tell ya. :)

Additional reduction: *** this is BIG *** Last year, we had two gears which further reduced the rpms between our gearbox and our driven wheel. I over estimated our output speed and did not leave enough room to realistically gear down the robot. I placed the two gears at a center distance that was PAINFUL to deal with. I started out with a 32:20 gearset, thinking that if we had to slow it down, we could get a 36:16 set. We did this, and it was still too fast (no acceleration on the ramp). So, our final gearset was 40:11. There was way too much force at the gear teeth of the 11 tooth gear and we stripped that little guys a few times during the regionals.

My advice is this: the closer you get to your wheels, the more room you should leave for varying your speed. Be prepared to change your ratio so that you may have to speed up or slow down dramatically.

Andy B.

The democratic response:
If you use sprocket/chain for your final reduction, you can also greatly change speeds, relatively easily. (As long as you leave clearance everywhere to tweak your sprocket sizes).

Direct Drive can be scary stuff.
The thought of destroying a gear during competition leaves me... umm... scared. Not every team can bring spares for replacement! ;)

No disrespect intended, that technokitten drive sure is a beauty.

She purrs!!!

Everyone fear the mighty kitten-drive! Meeee-owwww.

Wow I live with god...I had no idea.....Oh the stories i could tell....


Yarr...


Chris C.