Mathematics Update

We are indeed using some maths in our design. The servos provide 44 oz*in of torque. We are using three. One of them opens and closes the golf ball grabber. Because the golf ball will slide up a shallow ramp of card stock and the radius is quite small indeed between the servo and the golf ball, it is reasonable to simply assume that the servo will indeed lift the ball.

The second servo is positioned on the end of one of the grabber arms and actuates the draw bridge down which the balls will roll into the bucket. This draw bridge had a weight of 1.2 oz in the preliminary stages and its estimated current weight is 3 oz. Weight is distributed approximately evenly along the draw bridge and it has a total length of about 8 inches. It will be resting on the bucket while in operation so it is not necessary to include the weight of the golf ball in the torque calculations. Nor will the servo ever have to lift it entirely of its own power if all goes according to plan. However, assuming the worst case scenario, that the servo does in fact have to live the draw bridge, the torque on it would be 3 oz * 4 in (average length) = 12 oz*in, well under the rating of 42 at 6V.

The third servo is the problematic one. This one rotates the entire grabber assembly, which weighs quite a bit indeed. The unextended draw bridge is about 4 inches from this servo for a torque of 12 oz*in (when extended, it has an average distance of about 7 inches, but again, this servo will not have to hold that weight, for the extended draw bridge will rest on the bucket). The other two servos are placed at approximately 4 inches each from this third servo and at a 90 degree angle with each other, so the worst possible torque will occur when one is straight up and the other is straight out with a torque of 6.4 oz*in. The weight of a golf ball at 3 inches from the servo is 1.6*3 = 4.8 oz*in. The grabber assembly itself weighs about 6 oz and has a skewed weight distribution; the average distance of that thing from the servo is, according to the two-pencil method of finding the center of mass of an object, about 1 inch. The total torque we are putting on this thing so far is... 31.2 oz*in. Additionally, in order to get the 180 degrees of rotation that we need, we must gear the servo in a 3:2 ratio, giving it a torque of merely 28 oz*in. We will add more supports to the assembly, and the servo is clearly not powerful enough to lift it.

Therefore!!

To the servo that lifts the assembly, we attach a second rod in the opposite direction from the assembly with sufficient weight to offset the assembly and allow the servo to do its job.

The motors!

We need as much torque as we can get. When I built a gearbox in quarter 2 to help Mr. Podmers test stuff for this class, eyeballing the axle indicates that with such huge wheels as we are using, speed will not be problematic. Our design requires as much torque as possible, so we can not afford to engineer around speed in the first place. Knowing that the robot will move reasonably fast is quite sufficient for our purposes.

The previous torque calculations hold for the motors that drive the wheels, with the ratio of the radius with respect to the third servo to the radius with respect to the motors conservatively considered to be 8.5/6. Each small motor has a torque of 6.82 g*cm; conversion to oz*in, sending the torque through the gearbox, and multiplying by 2 (because we have 2 motors) gives us a total torque of 65 oz*in, more than enough to lift both the assembly and the counterweight.

2/22/10

Day Thirteen. Lucky day thirteen I guess, a hot glue gun exploded on our table right next to Mr. Podmers on Friday, forgot to mention that. But that was day twelve... huh. Anyway, we attached our motor-to-battery connector wires today, as well as put some finishing touches on our bridge and grabber. We also put on some axles to our wheels with massive amounts of hot glue.

2/19/10

Days Eleven and Twelve. Our grabber is finished! For the most part. We may have to tweak it every so often. Our bridge is nearly finished too! Everything is really coming together nicely.

2/17/10

Day Ten. The wheels on the robot go round and round! We learned how to calculate our motor's rpm today. We then turned around and went directly back to work on our grabber system. We couldn't get too much done with the half class left to us, even less so because the hot glue gun we selected first decided to start smoking. Still, it's coming along quite nicely.

2/16/10

Day Nine. Our robot still does not resemble a robot, but our components are starting to look like... components! We've very nearly completed our "cage" for our lift system, as well as the door through which the balls will fall. Also, our mascot, Herman the hot glue caterpillar, is coming along quite nicely. He's a big help, by the way.

2/11/10

Day Seven/Eight. The internet... has died! Until now that is. I was down from 2/11 till 2/15. That aside, we've been making progress. We started building our grabber, which we've strengthened with a lattice structure. We've even solved our weight problem with a counter weight on the opposite side of the robot. Our diligence is paying off!

2/9/10

Day Six. Our robot's wheels are cut, at least one of them is anyway. We've begun formal sketches, but it's really hard, since we're changing our minds every ten minutes. At this point though, it's better to brainstorm and continually scrap half-finished sketches than have a set sketch and go with it to the end, as it may block out even better ideas later. Like today, Jefferson revolutionized our grabber arm! It'll be incredibly long and house several balls at at time. We'll definitely win!.. I hope.

2/8/10

Day Five. We have completed the gear box! We've chosen configuration D, which has the most torque of all. Jefferson has marked off the wheels and wood components for the wheels. We're really seeing some progress!

2/5/10

Day Four. Our new robot design seems to be a ringer! We're planning on using huge wheels with a suspended body to not only get around fast, but to avoid all the inevitable flipping levers we've been hearing about. Jefferson will be posting formulas and such pretty soon.

2/4/10

Day Three. Mission... not accomplished. Although we got some clarification about routers and battery life, our bucket robot idea turned out to be far too difficult to build. The conveyor belt was the problem. Oh well. We'll sketch up some new ideas tomorrow.

2/3/10

Day Two. Norman was gone today... it's hard brainstorming group ideas alone! Though now we know that there's going to be a bucket, I'm sure we will be able to get some ideas through tomorrow.

2/2/10

Day 1,

We've begun brainstorming, but nothing definite yet. We're thinking of using high speed, lighter robot capable of making many goals very quickly. It'll also be easy to escape other robot's attacks (as we've heard most everyone talking about attack robots). Nothing's set in stone yet, tomorrow we hit the ground running!!