pic: This is our robot as of last night. Alot more should get done this week now that things are in place

Remember, the 72" limit is within the plane parallel to the floor, not the height. In any case, you’re right that it’s only a problem if your arm is straight out. I did some trig here that indicates that a widthless arm would be allowed to protrude up to 49.8 inches, minus rear bumpers, from the front of your robot. (Though that thread was speculative, my interpretation was upheld by the Q&A.) So, as long as they don’t have their arm straight out while fully extended, they should be perfect.

We did some tests with our 5lb. grabber on the end of an arm aprox. the same length as this.

One keyang motor was not able to lift it. After adding a spring, which took virtually all the load off the motor, the keyang could lift it with ease.

However, even without a load on the motor, a light tap on the end of the arm was capable of stripping the gear inside the keyang. Further investigation found that the plastic gears inside these motors have very small teeth and are easily damaged.

Just a warning…

The keyang motors aren’t that powerful when compared to the others in the kit.

A FP motor (or the BB RS540, which has less power) into the 256:1 42mm gearboxes from Banebots make an easy to integrate motor with lots of torque.

Or take a hint from 968/254 (60 too maybe?) and swap you FPs into the drive to free up two small CIMs to use on the arm.

Yeah I forgot to metion that we had a reduction off the keyang…

Unless you can make a worm gearbox FPs and CIMs are backdrivable.

Or take a hint from 968/254 (60 too maybe?) and swap you FPs into the drive to free up two small CIMs to use on the arm.

I specifically remember 254’s driver telling me after last year that they were NEVER going to use the FPs in the drive train again. The FPs caused them too much trouble.

You’re completely right. I remember 968 telling me the same thing…

Too many hours of robotics and too little sleep causes me to forget things…

I did not know that the gears were plastic. We will be using two of these on each side, with about a 1.75:1 reduction. I am hoping that this will be enough, in initial testing it seemed like it would work. But if we run into any big problems i may try to figure out a way to use the big Cim motors. Or get a gearbox for the FP motors. because it seems like we are so far ahead then we have been before, we will see if we can rebuild the whole superstructure after some real life testing.

Thank you for the heads up
–Dan

The 49.8 inches is assuming that your arm has no width to it. The wider your arm is, the shorter it can extend without breaking the 72" x 72" box.

Well, firstly’ the 49" is NOT taking bumpers in to account, and as lil lavery said, you have to take the width of the end of the arm into account.