Can you mount the tires directly on the gear box?

[free_rider_151]

I'm from a rookie team so I haven't done this stuff before. I was wondering if you can mount the wheels directly to the gear box. I wasn't sure if it'll burn out the motor or ruin the gears and bearings in the gear box. Does anybody know?
~Olav Oksnevad
team 2039

[MrForbes]

The gear boxes are not designed to carry that much load, so it would not be a good idea.

[dfukuba]

Personally i think that the gearboxes will be able to handle such loads if you support the other end of the shaft. My team is mounting 6" colsons onto the gearbox, cutting the shaft a little bit shorter, and then using bushings to support the other end. These gearboxes were originally designed by team whyachi for combat robotics, they are pretty robust.
--Dan

[dtengineering]

The 12:1 banebots gearbox is quite capable of supporting a wheel, although it would be an extremely good idea to make (or buy... banebots has one for sale) a bearing block to support the outboard end of the gearbox shaft.

Supporting the wheel with bearings on both sides prevents you having a cantilevered load on the gearbox which can put a lot of torque (twisting force) on the bearings in the gearbox.

Something important to consider when looking at a direct mount of the wheel to the gearbox is whether it gives you a combination of speed and pushing power that matches your game strategy. With direct drive the larger the diameter of your wheel, the faster you will move (to a point), and the smaller the diameter of the wheel the more pushing force you will have (again, to a point). Most of the common FIRST wheels are in the 4" to 8" diameter range and should work reasonably well, although if you have the larger wheels you may wish to consider purchasing the conversion kit to take your gearbox to 16:1, giving you more torque (pushing) but at less speed.

Keep in mind when building and testing your robot that the playing surface is going to be carpet. This does not matter so much when it comes to going forwards and backwards, but when you are turning your wheels may need to skid to the side... there are several options discussed on several other threads that you may want to search for surrounding this topic.

Jason

[UlTiMaTeP]

Chances are it will but you really wouldnt want to do that, the speed would be too fast with no step down. The torque curve wouldnt match up to the speed and load.

[Jack Jones]

Originally Posted by UlTiMaTeP

Chances are it will but you really wouldnt want to do that, the speed would be too fast with no step down. The torque curve wouldnt match up to the speed and load.

No problem with speed if you use smaller wheels. With a CIM and that 12:1 transmission and five inch wheels, you'd go about 8fps.

[Donut]

Originally Posted by UlTiMaTeP

Chances are it will but you really wouldnt want to do that, the speed would be too fast with no step down. The torque curve wouldnt match up to the speed and load.

Really? I think with a careful driving strategy and the right type of wheels, speeds like that can have quite an advantage.

[Daru]

Originally Posted by Jack Jones

No problem with speed if you use smaller wheels. With a CIM and that 12:1 transmission and five inch wheels, you'd go about 8fps.

We calculated that we would go just under 9fps if we ran the kitbot wheels (6") on the 16:1 transmission with a CIM. We used the max RPM of 5342, which we got off the FIRST Wiki. Just another alternative

[Madison]

Originally Posted by Daru

We calculated that we would go just under 9fps if we ran the kitbot wheels (6") on the 16:1 transmission with a CIM. We used the max RPM of 5342, which we got off the FIRST Wiki. Just another alternative

Remember that the 5342 RPM number is the approximate free speed of the CIM motor. When placed under load, the motors will run quite a bit slower than their free speed.

[Daru]

Originally Posted by M. Krass

Remember that the 5342 RPM number is the approximate free speed of the CIM motor. When placed under load, the motors will run quite a bit slower than their free speed.

Interesting; I was under that suspicion but I assumed that the drop in RPM would be fairly small. In that case, my question becomes: How can you accurately calculate the FPS of the robot based on the loaded speed of the motor?