Re: One speed vs Two speed gearboxes
 

Maybe "mostly" is a strong word, but I could have sworn I've read a bunch of posts about how batteries in FRC are used in a suboptimal fashion by us using them intensely for two minutes then immediately recharging them regardless of how much they had discharged. Probably not something I should regurgitate from memory without a strong understanding of the concept, though.

Re: One speed vs Two speed gearboxes
 

When I say "more efficient" in this case I am referring to the return of torque for the speed a CIM is going.

This is the chart I was basing it off of.https://www.google.com/url?sa=t&source=web&rct=j&ei=TfyeVLzwIIr5yQT4lIGwD A&url=http://www.chiefdelphi.com/media/papers/download/3511&ved=0CC0QFjAG&usg=AFQjCNFYBes4Az_jlxsofXC-Uv9SJspSsA&sig2=UuAzGda4w01JK0gZ632RnQ


If I miss interpreted this data I invite you to correct me. I would rather be wrong and learn from my mistake, than be wrong and keep thinking I am right.

Re: One speed vs Two speed gearboxes
 

The life of the FRC lead-acid batteries is a strong function of the number of deep-discharge cycles. There's a chart on the datasheet showing this.

These deep discharges can occur not only during competition, but especially during practice if the battery is allowed to "die" before being re-charged.

Deep-discharging and high currents are the main factors affecting FRC battery life, not charging a partially-discharged battery. Keeping the battery charged is better than allowing it to become deeply discharged.

Re: One speed vs Two speed gearboxes
 

OK, that's a reasonable metric...

OK, but be careful to compare apples to apples. Those charts definitely show a difference in linearity between the 884 and Talon. But to compare efficiency, you'd have to compare them at the same output PWM duty cycle, which is not shown in the graphs.

Re: One speed vs Two speed gearboxes
 

FRC use is serious abuse to the batteries but it is the deep discharge that causes the problems. Recharging the batteries as soon as practical is the best thing for a lead acid battery. A discharged battery will form sulfates at a higher rate than a charged battery, sulfates increase the internal resistance and lower the battery's output potential.

As Ether mentioned most of the data sheets show the expected battery life in cycles vs the depth of discharge. The lower the depth of discharge before recharging the greater the life expectancy. The curve is just that a curve.

From the Enersys data sheet.

30% depth of discharge 1200 cycle expectancy.
50% depth of discharge 550 cycle expectancy.
100% depth of discharge 250 cycle expectancy.

From MK's data sheet.

100% depth of discharge 200 cycle expectancy.
80% depth of discharge 225 cycle expectancy.
50% depth of discharge 500 cycle expectancy.

A 100% depth of discharge is when the open circuit voltage of the battery after a short rest period is 11.2~11.8v depending on which mfg you consult.

Re: One speed vs Two speed gearboxes
 

The information in my post was intended to be used as a guide, rather than a matter of fact. When all things are considered (specifically wheel type, robot weight, rotating mass weight, strategic intent) a drivetrains specifics should naturally fall into place.

That being said, history (2013 newton) tells me that 68 is no stranger to getting across the field quickly, so if the application is similar, there's no doubt in my mind that your data is spot on.

Going back to my original post, much of drive design beyond the basic 90-95% or so (essentially optimization of the system) is very application specific, and is best catered towards a robot and it's driver. So no matter what, much of this data should be taken as a starting point, and adjusted from there. Enough adjustment, and you might just attain perfection... If you've got the time.

Re: One speed vs Two speed gearboxes
 

Very fair. It's probably a good rule of thumb so you can push the envelope without getting burned.

That robot was really good at a couple things, one of them being getting across the field (the other was standing back up after we tipped it over :ahh: ), and it was a lot of fun to drive.

That also is some very good advice. The best I can give is this: One speed or two speed, if you've found a drive system that will work for you and meet your objectives on the field, that's usually pretty independent of game specifics. Stick to that system and get your last 5-10% out of it. That will serve you far more than starting over the next season with a "better" system. Once you've nailed that one down or decide it's not going to meet your goals any longer, look at something else (hopefully in the offseason) and consider it.