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

[Doug G]

[FotoPlasma]

Okay. I'll take your word for it.

How does it work?

[Rhs953]

nice...is that gear reduction?

[Joe Johnson]

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.

[Salik Syed]

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!

[Tytus Gerrish]

WOWH!

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

[Salik Syed]

....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

[Joe Johnson]

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.

[Matt Adams]

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

[alex.thomson]

Originally Posted by Joe Johnson

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

Or generate electricity to charge a battery - like the Toyota Prius. Incidently, it uses a planetary gear system not unlike the one shown to split the power coming from the gasoline engine and simulateously drive the wheels and charge the battery.

Bring on the hybrid robots...

-Alex

[Gadget470]

Hybrid robots? What's the hybrid part of it? Electical and Electrical?

First of all, I do not think you will actually be able to charge your battery by any significant amount, if at all.

Motor D: Drive Motor
Motor G: Generator Effect

Motor D has 2 places where it's torque is being used. Motor G and the wheel(s) it is powering. Each provides a different load on the motor. The motor can only provide x output, whereas power to G + Wheels = D output. Also, for D to power G, D must have an input power source (from the battery).

|BATT|--RES--[ M ]--***--[Wheel]
   |                 |
   ------RES-------[ G ]

The circuit would look something like this. RES being electrical resistances, *** is Resistance from friction within the gearbox (although relativly low). The loads upon M are outward from that. Anywho.. the turning of G is a load on M, so any electrical force created from G will be less than what is given to M. So the Net electricity used will be lower. BUT... to have equal output to the wheel, (as if G was not attached) more current must be supplied to M.

All in all.. we don't have the tools for perpetual motion.

In the hybrid cars, inertial force is used to generate electricity as well as the gas motor, which is not driven by the electrical motor.
Take a look at Toyata's Flash model of how the Hybrid Prius works:
http://www.toyota.com/vehicles/2004/...syn_drive.html

[Salik Syed]

yes...charging the battery we'll leave to the charger....the only time the chip motor would generate energy is when its being backdriven by the drill motor...but w/ current sensors that shouldn't happen...the second it starts to backdrive it will lower the drills speed and up the chips...we'll also keep the amt of power going to the chip a bit higher than drill (although we might not be able to go full speed from a stand still!)

[alex.thomson]

Originally Posted by Gadget470

Hybrid robots? What's the hybrid part of it? Electical and Electrical?

First of all, I do not think you will actually be able to charge your battery by any significant amount, if at all.

Neither do I...I don't think it would be an advantage at all.

Also, for a somewhat more detailed, but unofficial, explanation of the Prius hybrid system, go here. The hybrid system is a bit more sophisticated than the flash animation would imply. (The general idea is the same though)

-Alex

[ahecht]

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?

[Paul Copioli]

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