Was ist das?????.....tiny CVT!!!!!!
 

:D

Re: Was ist das?????.....tiny CVT!!!!!!
 

Okay. I'll take your word for it.

How does it work?

Re: Was ist das?????.....tiny CVT!!!!!!
 

nice...is that gear reduction?

Specs we need specs!
 

How does it work? What speeds and torques can it handle? What ratios does it span? Is it a home brew or an off the shelf item?

Do tell...

Joe J.

Re: Was ist das?????.....tiny CVT!!!!!!
 

The design is totally by us...the gears are off the shelf tho..... the outside parts were machined by us. The housings etc... are not shown here but that is basically everything other than motor mounts etc, but this piece by itself is 4" in diameter.

it can drive our robot from 2 ft/s to 15 ft/s .... that is w/ a 3.6 reduction at sprockets....i think...


haaaaaaaaaaaa...prrrrreeeeeeeeeeeeeeeaaaaassssssss ssssss....choooo!
:D

Re: Was ist das?????.....tiny CVT!!!!!!
 

WOWH!

that thing is Awesome . Looks Watterjetted i cant wait to se it in action
post Vids Please!

Re: Was ist das?????.....tiny CVT!!!!!!
 

Maybe I'm missing something, but it looks like a 2-speed planetary gearbox to me (although a nice and compact one). How is it continuously variable?

Re: Was ist das?????.....tiny CVT!!!!!!
 

....we'll post vids maybe when we get it working (there are a few more housing pieces we need) probably b4 end of the 4 day weekend.... it is not water jetted...not even CNC it is done on a regular "hand"(???) mill
oh if u r wondering how it works pay more attention to my oversensitive nose... ;)

btw... i think another team has done something like this.... but theirs had a worm gear which does not allow drift and has an efficiency loss...

here is a clearer pic...... i know...it looks like a planetary gear box but it changes speed w/ NO non rotationally moving parts

There are CVT's and there are CVT's.
 

It is relatively easy to make a continuously variable transmission if you are willing to turn a percentage of you powering into heat.

I am thinking that perhaps this will not do what you want it to do, but, I have been wrong before...

...though not very often ;-)

Joe J.

Re: Was ist das?????.....tiny CVT!!!!!!
 

I guess I'd just like to ask a quick question... why do teams go with this sort of varible speed gearbox?

I've read Paul's whitepaper, and his final equations yield that these sorts of transmissions are variable speed, but constant torque. This is because the torque is a function of the number of teeth, which remains constant in these sorts of designs.

I guess I just don't see an advantage of being able to push 150 lbs at either 2 ft/s or at 15 ft/s..

With the extra gears, you have some sort of an efficiency loss against your max torque (and max speed)... which means teams using the same motors coupled in a simple drivetrain will be able to push you around, and go faster than you...

Anyone care to explain to me, why you've decided to go with this sort of design? (Preferablely someone who's done some math, or had first hand experience with these?)

Thanks in advance,

Matt

Re: Was ist das?????.....tiny CVT!!!!!!
 

Matt,

All very good questions. IF we ever use the CCT again, we will ask ourselves one very simple two part question: Can we transfer weight to our robot? If so, how much? If the answer to those questions are "yes" & >100 lbs, then the CCT is in for us.

Here's why:

Lately, FIRST games require a pretty fast move in autonomous to get to the objects first, then the game changes slightly (depending on the type of game). I am a big fan of changing gears, in general, if you can transfer weight to the robot. If no weight transfer is available, then I am on the fence (we are NOT shifting this year). The CCT gives a very simple and robust way to get instantaneous gear shifting without going into neutral and using pneumatics. It is true that a drive train with the same motors as the CCT will have a bit more useable power, but if you also need to shift, then the CCT is a simpler solution with about the same results. Besides, it is really cool to see your robot instantly (almost) triple its speed while it's driving (like a 'vette doing 40, then punching it).

As to the design in the picture. Our CCT used the same principle you are trying to achieve with your transmission, but when our testing revealed some limitations we switched to the worm gear on the ring gear motor. All I have to say is watch out for backdriving.

-Paul

Re: Was ist das?????.....tiny CVT!!!!!!
 

I guess my question is this... since both ratios have the same torque output.. why would you ever shift out of the fast ratio?

I don't see the advantage of going slower with the same torque as you'd get if you were going faster.

Matt

Re: Was ist das?????.....tiny CVT!!!!!!
 

Ahhh? Battery power, motor life and controlability. During a pushing match, having a slow robot that has motors spinning fast can push forever. As you know, DC motors love spinning fast. The CCT allows the motors to spin fast while attaining a very high output tourqe.

Dual motor drives, in general, suck more battery power; although I do not think that is really a big issue.

Re: Was ist das?????.....tiny CVT!!!!!!
 

Ahhhhhhh. It clicks. You'll be turning at a constant torque but pulling much less current... this is indeed an advantage.

I guess the question is... how much of an advantage? I'd have to agree that in a two minute round with small spurts of pushing, the advantages are minimized since battery life shouldn't be too big of an issue.

Thanks for clearing this up, Paul! I really appreciate it.

Matt

Re: Was ist das?????.....tiny CVT!!!!!!
 

To control the backdriving we will monitor draw through current sensors and they automatically give more power to the motor being backdriven and less to the on that is doing the pushing until they even out....(thats what we hope ne wayz!!!! we have 2 program it in like 8 days), we don't want to use the worm gear because 1. it is has efficiency loss 2. the motor still kinda opposes it's just that the worm gear locks it ...thats inefficient...
a video should be here soon...maybe 2morrow...we got it running and tested tonight..... it works



we'll have a video soon ....