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-   -   How slow is too slow? (http://www.chiefdelphi.com/forums/showthread.php?t=30694)

George1902 11-10-2004 22:33

Re: How slow is too slow?
 
Quote:

Originally Posted by Stephen Kowski
No I wasn't....George1083 and I have had debates on this topic many times into the wee hours of the night/next morning.

I do think anything over 8 to 10 fps is too fast.

I formed this opinion after years of watching drivers do their thing. When machines went faster than about 10 fps, the drivers got very sloppy; they just weren't able to accomplish their tasks consistantly. Many times, they didn't use their top speed at all!

A slower top speed helps to keep your motors cool and gives you a bit more pushing force in addition to helping your drivers out.

Steve W 11-10-2004 22:50

Re: How slow is too slow?
 
Being from the same team as Tristan, I may be a bit bias. I did see a lot of games in that I was an announcer for 4 Regionals, Championships and an observer at 1 regional. Speed is good and speed is bad. If you can't control the robot at any speed then it is not good.

What I do agree with is that having only a 2 ft/sec difference isn't really worth the time to build or the weight that is generated. If you added 4 (double) to 6 ft/sec then the advantages could be seem and measured. IMHO our robot was a bit too fast for our driver (sorry Jon) but if he had more time to practice maybe it wouldn't have been. I did see a few matches that the dash from 1 end to the other was the reason that they won the match.

Right speed with right driver = success

Karthik 11-10-2004 23:19

Re: How slow is too slow?
 
Designing a FIRST robot is all about trade-offs. Picture this pre-build season conversation, with a "Robot Dealer"...

RD: Hey you, strategy guy.
ME: Who me?
RD: Yeah you. Do you want a robot that can go 10+ ft/sec?
ME: Well yeah. Who doesn't? The extra speed can always come in handy. But wait a second, this is a FIRST robot. There must be a catch...
RD: Okay, maybe there's a catch. The one robot I had in mind has a one speed transmission.
ME: Hmm, no deal. I'd have to give up a lot of pushing power to be geared to go at that speed. Most FIRST games, require more torque than that gearbox would probably provide.
RD: HM, so you're one of those smart strategy guys. Okay, I'll give you a two speed gearbox. 10 ft/sec in high, 2 ft/sec in low...
ME: Wow, that'll let me be really fast and give me the ability to be a strong pusher I like that. But hold on. That sounds like a mighty big reduction. How much does that thing way?
RD: Fine. It weighs a lot. But I've got another one that weighs less and plays in the 4-10 ft/sec range.
ME: That sounds a lot better, but my drivers are pretty green. I don't know if they can handle that much speed.
...
This conversation could go on for a while...

The point is, speed is always an asset in FIRST game. You just can't give up too much to achieve it. I've seen many teams slave away in an effort to try and build the fastest robot. A lot of the time it's not worth it.

Remember, on a 48 ft field, there's not many times when you'll need to go much faster than 8 ft/sec. On the other hand, the ability move at 12 ft/sec, can be a huge asset. The decision you have to make, is whether or not it's worth the effort and weight to build in a function that may not be used very readily. This depends on your team's capabilities.

When it comes to the issue of control, I have seen some very fast robots which moved across the field with lots of precision. Team 25 in 2003 really sticks out in my mind. I've also seen some really fast robots slam into a lot of obstacles, and look like they've been driven by a drunk. More often than not, anything more than 8 ft/sec is uncontrollable. But with a nice PID algorithm and skilled, well practiced drivers, it is possible to control.

Would I build a robot that could only go 5 ft/sec? Probably not. I think it's very doable to build a simple two-speed tranny that puts you in the 4-10 range. This is a great range for most games. Remember, if your driver isn't comfortable with top speed, s/he can always pull back on the throttle. All that being said, there are many possible game designs that would cause me to go significantly faster or slower.

J Flex 188 11-10-2004 23:39

Re: How slow is too slow?
 
if there is sufficient practice among drivers, (usually by the time nationals rolls around..hehehe) a high top speed, if done within the limits of the team in question, done comfortably, the benefits are immense and immediately measurable. There was a direct happy finish for our team in Atlanta more than once due to our high gear.
Check out the final seconds of Match 53 at http://www.soap108.com/2004/movies/arc/index.cfm

where we streak across the field and prevent 1272 from capping.while that could have been done with 12 seconds left with a lower top speed, the fact is we spent another good 5 seconds manuvering with our grabbers, forcing the 2X ball to drop. Without that extra time, it is very likely that we wouldnt have succeeded. Thanks FEDS ;)


Quote:

Originally Posted by George1083
I do think anything over 8 to 10 fps is too fast.

I formed this opinion after years of watching drivers do their thing. When machines went faster than about 10 fps, the drivers got very sloppy; they just weren't able to accomplish their tasks consistantly. Many times, they didn't use their top speed at all!

A slower top speed helps to keep your motors cool and gives you a bit more pushing force in addition to helping your drivers out.


jonathan lall 12-10-2004 00:04

Re: How slow is too slow?
 
I agree, 16 fps (give or take) was too much for that game, especially with the configuration of that robot. Not tipping every match required great care on the part of the drive team, and hard turning manoeuvres and dime-stops with the arms up were perilous (we never tipped ourselves, by the way). It was quite hard to control. Mind you, the freakishly high speed was useful once in a while.

Archimedes Match 53.

That being said, what we needed last year was a smaller gap between gear speeds; 16 is too high and 4 is too low. The truth is that everything is changed by a shifting tranny; that is, George1083 is absolutely right (with regard to his last comment), but only in the case of single-speed gearboxes. The truth is, limiting yourself to 10 fps (well, 10 isn't that bad, but 8 for example) in your high gear ratio is a severe limitation of your ability to take control of the field and in its nature limits possible strategies.

In any case, as the bottom line has always been, you can't tack on a speed to shoot for. We've tried to many a time on CD. As was demonstrated in this thread already, 639 and 60 were both winning robots with different philosophies. Setting a 'magic number' is just plain silly, especially for teams with the means to build really advanced stuff.

Tristan Lall 12-10-2004 10:51

Re: How slow is too slow?
 
Quote:

Originally Posted by jonathan lall
George1083 is absolutely right (with regard to his last comment), but only in the case of single-speed gearboxes.

Quote:

Originally Posted by George1083
A slower top speed helps to keep your motors cool and gives you a bit more pushing force in addition to helping your drivers out.

In fact, this is totally a matter of gearing and the amount of throttle that your driver is using. If you've designed it right (suitable ratios), and are driving it right (full throttle as much as possible, pushing things as little as possible), the motors will be operating at a "happy" speed and temperature, no matter what your actual top speed is. Gearing it down (to increase torque) will not have any major effect on the operating temperature of the motors, unless the ratio was so unsuitable to begin with that you could hardly accelerate from a standing start--the driving conditions (mainly % throttle) are the primary concerns.


Quote:

Originally Posted by George1083
Many times, they didn't use their top speed at all!

This is the real sin. They won't save any battery life, and their motors will be operating out of their preferred range (contributing to excess heat, both because of the slow fan, and because of the higher current drawn due to lower voltage). This is also why it's nice to plan to change ratios, just in case your drivers don't like what they've got, and are unwilling (for strategic reasons) or unable (for human reaction time reasons) to alter their slow driving styles.

Swampdude 12-10-2004 11:10

Re: How slow is too slow?
 
Not to change subject, but depending on how you read this hint we may be looking at a sprint start again... ;)

Tytus Gerrish 12-10-2004 19:49

Re: How slow is too slow?
 
9' PS!!! Man! thats a big wheel Dan.

George 12-10-2004 20:23

Re: How slow is too slow?
 
Hi, I was just looking around and run across this thread,
The poof's (254) and Kingman (60--my team) run a 2 speed gear box with a high gear of about 15fps and a low of 5fps.
This seems to give the best of both worlds, low-end power, top end speed.
As for driving, practice, practice, practice
Think of it as a car or a bike it's better to have the speed and power and not
use it, then need it and not have it.

gotta go
have fun
Geo.


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