Re: What's a good transmission these days?
 

Now understand that I mean no disrespect to the ThunderChickens at all, or to their design team, but the 2002 ThunderChickens' CCT is not a CVT. IIRC, it is a clever way of combining two motors that run at different speeds that gives high torque when you need it and high speed when you need it. Toyota tried a similar trick on the original Prius, but was forced to change the name from "Planetary CVT" to "Hybrid Synergy Drive" when people discovered that it wasn't a CVT (there is in fact no such thing as a "planetary CVT").

The CCT, with all due respect to the ThunderChickens, was flawed in design because it required the use of a worm gear to prevent the high torque motor from backdriving the high speed motor. Since a worm gear only has about 70% efficiency (compared to 97% for a spur gear or sprocket), much of the extra torque gained was immediatly lost to heat and nosie.

Coming from a team that has build a CVT, I can tell you that it is very difficult. Although the 190 CVT worked perfectly mechanically (and never had any problems with slipping), programming it proved to be very difficult. Throughout the 2002 season, our CVT was run as a manual three speed transmission, and it wasn't until well into the 2003 season that we got it working. The CVT itself is quite difficult to dynamically model, especially since the shifting behavior is non-linear, and figuring out how to drive the thing with the right amount of dampening to prevent it from oscillating was a huge task.

If you want a CVT, more power to you. It is great to see teams innovate and try to improve on the past. However, I would definately make sure that you have a backup transmission, because your CVT might not perform as you want it to until the 2006 season.

Re: What's a good transmission these days?
 

With all due respect to 190... :rolleyes:
You speak of efficiencies, and mention your CVT "worked perfectly mechanically".

What efficiency did you achieve?
Have you ever dyno'd up that robot?

I was under the impression (correct me if I'm mistaken), that your CVT was of a toroidal style, which relied on friction (between 2 cast iron pieces) to transmit torque. How is this any more efficient?

You speak of energy loss to noise... well... I've heard the 190 CVT run.
To say it purrs like a kitten... would be a lie.


I fail to understand how the inefficiencies of 217's worm gear cause it to be "flawed in design".

As far as I know, by nationals in 2002, the CCT was a force to be reckoned with.
Though maybe Paul could more accurately answer your criticisms.


John

Re: What's a good transmission these days?
 

525 uses a very simple 4 motor single speed drive train. It uses the out of the box drill motor with the 2:1 right angle gearbox driving the 9" wheels at one end and a CIM with a double reduction spur gear set driving the 9" wheels at the other end. The number of teeth on the double reduction spur gear set are selected so the front & back wheels turn at the same no load speed. Then to make it easy to drive, there is a #35 chain connecting the front and back axles to force the front and back to turn the same speed.

The only precison machining needed is the gear centers for the CIM gear box.

We ran this drive train this year with zero problems.

Last year we used the same concept with the FP's instead of the CIM's. The only problem during 1 regional & nationals was one pair of burned out FP's.


Picture attached - note the chain connecting front and back is not visible.

Re: What's a good transmission these days?
 

Of course I was not speaking of efficiencies, I was talking about function (and I know the CCT worked perfectly in the same sense once they got their current issues worked out). I don't have the figures off hand for the CVT, but I know it was calculated by the group who designed it for their Major Qualifying Project.