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Unread 26-11-2001, 23:04
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Andy Baker Andy Baker is offline
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Some Help

I'll try to help. You probably already know most of this stuff, but I'll post it anyway.

Variable speeds:
Many teams use variable speeds. There are a few ways to do this.

..Using the Bosch Gearbox gear switcher:
We've been switching gears by using the drill motor gearbox gear switch since '99, but team 73 used it before we did. Many teams use the "servo" provided in the kit to swtich gears, but team 71 used a small air cylinder to do it last year... that method is probably quicker than the servo. This is a easy way to switch gears that uses almost no robot weight, but your robot can only switch gears while standing still.

..Have a separate set of wheels turning at different rpms engage the carpet when you want to change speeds:
Teams 33 and 65 did this very successfully in 2000. This is VERY effective, since you can switch gears on the fly, but it takes alot of hardware and uses up valuable weight.

..Build your own transmission gearbox:
We built a CVT (continuously variable transmission) for our 2000 robot, but it didn't work too well and had too many losses in it. I hear that there are some other teams (Paul??) who may have some neat designs up their sleeves in this area.

The holy grail for changing speeds is to make something that lets you change speeds at full power and full speed, and it has to be simple, easy to maintain, and lightweight.

MOTORS USED IN DRIVE SYSTEMS:
Many teams have learned that the best motors to use for the drive system is the drill motors. Also, the fisher-price motors are pretty good. Some teams use all 4 of these motors in their drive system. If any FIRST team wants to be the fastest or most powerful, then they better use 2 Bosch drill motors and 2 Fisher-Price motors.... that is, of course, IF FIRST provides the same motors in next years' kits.

TYPES OF DRIVE SYSTEMS:
--Tank style systems are used by the majority of the FIRST teams. This is a simple systems that can be used for power and speed. All teams who switch gears use some sort of tank style system. Most of these systems have 4 driven wheels or treads, but some systems use only 2 driven wheels accompanied by 1-2 casters.
--Crab style (or swerve) drive systems provide better maneuverability than the tank drive system, but are more complicated to engineer and develop. Some very impressive drive systems have been developed over the years, led by teams 47 and 11 (and others). While highly maneuverable, there has not been a crab system which can mechanically switch gears yet. So, while agility is high with the crab style system, it is difficult to get both high power and high speed.

OTHER MOTORS:
--The van door motor is a good motor to use for the toughest job other than drive system. Many teams' arms are actuated by 1 or 2 van door motors. Be careful that these motors have plastic gears in them and can be stripped.
--The globe motors and window lift motors are also good for actuations. The rpms are low and manageable. Be careful to not put the mounting screws in too far on the globe motor... somehow these screws can suddenly grow and seize the gearbox of the motor.
--Seat motors are mainly used these days to collect balls (by driving a spinning roller) or to actuate something by driving a leadscrew. These motors have high rpms and have nice hardware which go with them in the kit.
--Torque motors were only used as triggers last year... if they were used at all.

Mounting a motor:

If you want your motor to last, take care of the shaft. Don't assume that the motor can take any side loads. Use ball or oillite bearings to support the exposed shaft of the motor so that the shaft is not cantelevered out into space.

Take care and good luck.

Andy B.
 


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