Re: Need general drive train expertise
 

Can you clarify a little bit more as to what you mean by this?

Re: Need general drive train expertise
 

A heavier robot would certainly incur more frictional losses in the drive, and thus would have a lower top speed. Can't say how big the effect is without any data, though.

Re: Need general drive train expertise
 

I'd qualify that by saying that there are plenty of commonly-available servos that can do the job, but they haven't historically been FRC-legal. Digital servos for giant-scale model aircraft would be great, for example. Saving the weight and annoyance of a pneumatic system could make it very worthwhile.

(I've tried shifting a DeWalt-based transmission with FRC-legal servos before. It was terrible.)

Re: Need general drive train expertise
 

Oh, certainly, I've worked with some beefy servos in other applications. I was only talking about FRC-legal hardware.

Unfortunately, FRC-legal servos are so weak that I've yet to actually find an application for them. I'm sure someone, somewhere has used them effectively on their robot, but I haven't.

Re: Need general drive train expertise
 

I know 67 has used a window motor configuration in the past because they did not have pneumatics. Using an opposing cam, it pushes or pulls into high or low gear.

Here is the link to their engineering notebook, I recommend any reads all of them anyways:)

-Ronnie

Re: Need general drive train expertise
 

After writing a front-end to Ether's sims and playing with it a bit, very large swings in weight will have an effect on acceleration from a theory perspective. Torque remains the same, but the mass is larger, thus acceleration is lower. For the same amount of time, it nets a shorter distance traveled. Small changes (5lbs here, 5lbs there) seem to have no discernible difference in acceleration on a FRC field since it's less than an inch or two of difference.

Preview here. Requires Java 8, Win7/CentOS 6+/Who knows what for a Mac. Probably works in Ubuntu 12.04+, but I can't tell what version of GTK it ships with at the moment. The preview is just the latest iteration of layout ideas I'm playing with. For example, I don't think it'll have a web viewer upon release, which is what the current preview has.

Re: Need general drive train expertise
 

Changing the weight will likely affect the rolling resistance of the bot, especially on carpet.

If you change the rolling resistance parameter(s) in the model accordingly, it will affect top speed as well.

Re: Need general drive train expertise
 

When I used to model in Excel, the resistance was modeled something like (1-0.995^n)*<weight> where n = # of loaded bearings. For most robots near the weight limit this falls between 5-6 lbs of resistance since only 4 wheels touch at a time.

This was really so I had some automated way to increase the resistance based upon weight and number of wheels hitting the floor rather than an accurate way to model it. It also provided a correlative model for what happened on our drive trains in 2008 & 2011, where the bearings had some binding due to improper mounting (thus the 0.995 was lower).

Re: Need general drive train expertise
 

FRC0330, back in '05 and I think in '00.

Both were used as latches, and as I recall the one from '00 had some assistance from a spring. (Used to lock a winch with a pin--might have been replaced by a short-throw cylinder.) The one in '05 was rigged to drop a thin sheet of Lexan. Why a thin sheet of Lexan, you ask? It's really nice to be able to deny someone who is trying to jam you against a goal half of their traction. There was no retract mechanism, though.

Re: Need general drive train expertise
 

We used them to make our scale model of Dozer look left or right with his eyes when steering, other than that I've got nothing.

Re: Need general drive train expertise
 

Servos controlled the pan/tilt of our camera in 2007. Tracking the green light over the rack was vital to the robot's success in scoring during autonomous.

2005's camera also had a pan servo, but a combination of factors led to our abandoning vision tracking that year.

There was a servo-controlled release on our 2004 fabric ball-collecting funnel, but we decided to leave the funnel off after our first couple of practice matches. We wanted to focus on knocking the 10-point yellow ball off its pedestal to drop the 5-point balls early.