Broken Belt

[JesseK]

Mecanum drive puts added stresses on a belt because the wheels constantly change direction. It's not the acceleration or speed that's put on a belt that causes it to fatigue early -- usually it's repeated instantaneous direction changes. If you have robot-centric driving (i.e. the robot goes "forward" relative to its own direction) then the driver has direct control over how much stress it put on the belts. However, with field-centric driving (i.e. "forward" is always the same direction on the field, which is usually away from the driver's station) the computer calculates the vectors the wheels need and therefore the overall strategy and driving conditions control how much stress is put on the belts.

To help alleviate this in the future, you could make each toughbox transmission slidable so that sliding them with the belt in place will put tension on the belt. This eliminates the need for extra contact on the belt from external tensioners, thus improving the life of the belt. Or you could use a stackerbox setup that does the same thing (note that there have been many improvements made to that first design since its release).

[Daniel_LaFleur]

Originally Posted by JesseK

Mecanum drive puts added stresses on a belt because the wheels constantly change direction. It's not the acceleration or speed that's put on a belt that causes it to fatigue early -- usually it's repeated instantaneous direction changes. If you have robot-centric driving (i.e. the robot goes "forward" relative to its own direction) then the driver has direct control over how much stress it put on the belts. However, with field-centric driving (i.e. "forward" is always the same direction on the field, which is usually away from the driver's station) the computer calculates the vectors the wheels need and therefore the overall strategy and driving conditions control how much stress is put on the belts.

Mechanums, from what I've seen, put less stress, not more, on a drive train because they tend to have far less CoF. Skid steer with high traction tires (~1.3 CoF) tends to have far higher shock loads than Mechanums with a CoF (in most directions) less than .8 (consider a 120 lb robot moving full forward and being changed to full reverse without slippage in the wheels).

[Pat Roche]

This is a little advice for tensioning sprocketed belts. When you tension a belt you only want the belt to be taught. It should be a straight line between belt sprockets when under no load and when you push on it with your hands you want to be able to flex it a little. The amount of flex will be determined by the distance between the two belt sprockets. Over tightening it will cause the belt to stretch much faster and eventually lead to a shortened belt length. An under tightened belt will be tossed from sprockets much like chain would. The last thing is to make sure that the two sprockets the belt is running on are inline and parallel. Belts are perfectly feasible for drive applications but you should get all the information on them before using them in application. A good exercise is to set up a test platform using a motor and some belts and play with different tensions and measuring the displacement of the belts and find your most efficient and longest lasting belt tension to increase efficiency and increase your belt life.

Best of luck,

Pat

[m3ch4num470r]

Thanks for the advice, guys. We'll mull it over for a while, but we'll hopefully use belt or direct drive next year.