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Unread 08-12-2003, 23:08
Rickertsen2 Rickertsen2 is offline
Umm Errr...
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Re: Shifting Gears

<rant>
There is something that i feel every member of a FIRST team and anyone involved in engineering in general should read and take to heart:
http://www.seattlerobotics.org/encod.../classics.html

That said i agree with previous posts, which state that the benefits of shifting should be carefully weighed against its disadvantages. As hard as it may be, decisions should be made not on emotion, but rather objective analysis and common sense. One thing is see all to often is something which is done merely because it is cool.

The first step in determining whether a shifting transmission (or any feature) is right for your team is to ask why do we need one? Every good design should start by clearly stating what problem(s) it is meant to solve (not the inverse!).

Are you trying to achieve higher speeds? higher torque? faster accereration? A better balance between the three that does not involve compromising at least one of the others?

After assessing the need for a feature, one must then ask "do we have the resources to design, fabricate, test, and pay for this feature all within the set time constraints?"

If the above criterion are met then i would say go for it!... But remember a good bot, or anything else for that matter, is built just as much if not more by careful planning at the systems and functional level just as much as by engineering prowess. This is a lesson that our team learned the hard way last year, which could have easily been avoided.
</rant>


this thread seems to have forked off into a discussion of two discrete but related topics and thus i will address them induvidually.

>1 motor per side
If weight permits and current is not an issue, i see no reason not to use multiple motors on each side. There are 2 advantages i see in using multiple motors. First and most obvious, you get more power to work with. Depending on how your drivetrain is designed this can translate into more speed or greater acceleration and pushing power. Depending on the game this year speed and or torque may be of great advantage. Secondly, someone earlier mentioned redundancy. If One motor fails, your robot will still be able to move (to some extent) rather than being completely disabled. Given the high mortality rate of the drill motors redundancy is definately a good thing( the reasons for this are another topic). In the IT world, redundancy is pretty standard on "mission critical" servers etc. The disadvantages of multiple motors seem minimal. Yes there is added weight, but not much. <rant>Most of the gearboxes i have seen in FIRST are ridiculously overengineered and much heavier than need be. using 1/2" aluminum plates and gears capable of transmitting in excess of like 50hp under shock loads is just not necesary. Look at the gears in the drill gearboxes and the Technokats transmission. Have you ever seen one of these break?</rant> The weight added by multiple motors and gearboxes to couple them really isn't that much.

Shifting Transmissions
I think that most people would agree with me that a good shifting transmission has many benefits, for example your bot can have a normal gear for general driving and then a low gear for pushing matches and more delicate menuvers. There can also be big disadvantages associated with shifting. Shifting gearboxes are (generally) heavy, difficult to engineer and fabricate, and possibly unreliable. That said, if there is good reason to have a shifting and your team has the resources to implement such a design, i see no reason not to have one.
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