The End Draws Near!

3/30/10. Monday and Tuesday back from spring break! Now our robot's taking shape. We did something... odd with the grabber. We attached a sort of bridge to it, making it tilt down instead of being flat to the ground. Ingeniously enough, it lengthens our grabber's height enough for it to be able to score in the bucket!!! Now we just need to modify our bridge, now the actual grabbing surface, to be able to grab balls.

Oh joy of joys! I would like to be frank though, I'm not terribly upset by this. In the, oh say, 20 seconds it took for me to go in back and grab the game bucket, Norm somehow managed to destroy one of our motors and tear one of the wires off the other. I'm still confused as to how that happened.

Lastly, nervousness is setting in. In two critical days before competition, Thursday and Friday, Norm will be gone!!! Ahhh!!! This means that I will have the singular task of connecting all our servos, the speed controls, and the battery to the robot and make sure that they are all working properly, on top of securing our gearbox to the wheels. All I can say, is that Norm has a certain confidence in my skills, which is reassuring. I shall prevail!!!!!!

Another update of what we did from day to day

On Wednesday I modified the servos. That's about all we did. Chuck was not there. I started rebuilding the grabber, but there wasn't much time left. Oh, and I helped Alec and Rob's team with their servos, for theirs were malfunctioning.

On Thursday Chuck was back! We finished rebuilding the grabber. It looks a bit uglier than it did before and it doesn't glide perfectly smoothly as it did before, but our tests indicate that it will work well anyway. We also prepared our gearbox for mounting onto the grabber.

Friday was an exciting day. Raghav continued to bother us with questions about whether our car would actually even go anywhere, so we duct taped the wheels to the gear box and drove it around a bit for him to see. After that little adventure, we got our grabber out and started messing with it. Over the last couple days, when messing with the grabber, we had to twist it slightly in various directions so that the gears would mesh. On Friday, we glued hunks of wood to it such that it was permanently twisted properly. These same hunks of wood then proceeded to attach the grabber to the gearbox. We slid the wheels onto the gearbox for testing purposes. Chuck got out the ruler. The whole thing is under nine inches wide. Yay! We knew the grabber would be entirely inside the radius of the wheel (except for some protruding pieces of wood that we would stand off once the grabber was complete) because we checked it periodically as we were designing and building it. It therefore was no surprise when it did indeed fit entirely inside the radius of the wheel, except for some protruding pieces of wood. I took three trips to the sander, and the end result of this whole processes was that the grabber swung freely inside the radius of the wheel but remained close enough to the ground to pick up a golf ball. We tested each element of the grabber with the assembly hanging from the wheels and it all worked as expected. Yay!

I have two remaining worries with regard to this project. The first is that the grabber, though inside the radius of the wheels, is not far enough inside. When both wheels press against the bucket, the bucket will protrude inside that radius between the wheels. It's possible that the grabber will still get caught on that. If it does, we will push the grabber back. If it still does, the motors in the gearbox should have enough torque to push our car back a little bit and force the grabber up. I hope.... They do have a lot of torque with that gearbox after all. My second worry is that the axles will slip inside the coupler. If this happens, I suggest that we clamp the coupler onto the axles. I have several ideas. More on those if we find our axles slipping. We probably will.

It's high time we make another blog update

It's high time we add another picture too. I don't have one at the moment, but we will probably have more stuff to add by Thursday. I am calling just to talk about what we did on Monday and Tuesday. On Monday, I don't remember exactly what we did, but I strongly suspect that we worked on the counterweight design. Our work over the last few days, up to and including Monday, was making tweaks to get the whole grabber assembly to fit within the radius of the wheels. By shortening the grabber itself and rebuilding it once, we have succeeded. Getting the thing to fit within the wheel radius was likely to be the one damning factor in our design; if the grabber smashes into the side of the bucket and gets caught on the way up, it ain't going anywhere. Another thing that we had been working on up until and including Monday was periodically asking around about why the servos did not turn for their full 60 degrees in each direction; they turned only 60 degrees total, that is 30 degrees in each direction. This was quite problematic indeed, for our design depended on getting the full 120 degree rotation from the servos.

On Tuesday we learned that the wireless control system simply refuses to push the servos beyond 30 degrees in each direction. We spent that day ripping apart our grabber, extracting the servos (that we never intended to make removable, by the way) so we could get them modified for a full 360 degree rotation. Actually this will work better anyway because the servo that tilts the grabber (to specify a bit more, this is not the one that opens and closes the grabber or the one that raises and lowers the drawbridge) will be able to just rest on an outcropping (that we will take a picture of today) instead of wasting energy by exerting a constant, unnecessary force to keep the grabber tilted properly.

Just a lil update

Well we have finished building the dealybob that is going to lift and rotate the grabber. We have bent the copper rod running through the wheels so that the whole mess fits a bit better within the width limits. I have not checked the blog recently for updates by Chuck, but I expect that pictures either have been uploaded or shortly will be.

To quote Mr. Podmers and several other people, "It's never too late for a major redesign." Our redesign is not late, nor is it major, so we're in good shape. The grabber we had built before was originally meant as a prototype, but we decided to include it in the robot anyway and reinforce it as necessary. We now know that decision was flawed and we are correcting our design as necessary. The grabber prototype was fixing to be quite high off the ground indeed.It would be possible, though difficult to grab a golf ball. This is because the gears linking the grabber arms are placed under the grabber arms in our current design. The gears are not shown in the image below, but they would be approximately where the text "grabber arm" is on each side, meshing together behind the golf ball.

One way to remedy the problem of the high-off-the-ground grabber arms would have been to tilt them from this sort of doohickey:

To this sort of doohickey:

However that change would be cumbersome and flimsy. Neither design would likely be able to lift a golf ball anyway, as the gears slip on the copper rods pretty darn easily (this was before we started building keys). Oh, let me take a moment to explain what's going on with those. Gears often slip on copper rods. It's a fact of life and a fact of this engineering class. We have developed a solution to this problem. Ya sand down the copper rod and stick it through a small piece of wood. Then screw an eyelet into the wood so that it presses into the groove in the copper rod. This wood is now locked in place; it's going nowhere. Simply bang on the gear as usual, and to glue it to this piece of wood, as shown in the picture:

Additionally, in our old design the servo was placed high above the grabber like so:


The center of gravity for the old design was high, so the servo that was supposed to rotate the grabber would have a hard time doing what we needed it to, even with a counterweight. The grabber arms have to be close to the ground, so a counterweight that compensates for a high center of gravity would either need to be below the ground or really heavy and so close to the axle that it collides with the various gears hanging out about the dealybob.

Therefore we have decided to scrap our old grabber and build a new one. The new one will have a servo close to the ground, glued directly to the grabber arm, which is glued directly to the gear. There will be no copper rods involved, except for holding gears in place, and therefore no potential slippage in the first place. Keys are too bulky for this sort of work anyway. Additionally, the counterweight will be more practical because it will not have to balance out such a high center of gravity in addition to the weight of the grabber.

3/4/10

Day.... Infinity. It's been a long time since I last updated! I was sick for a long time and then... I sort of forgot. Well, here's what happened. We basically finished our scooping device, only to destroy it to gain a lower center of gravity. Though I must say I did a good job with the axles for our wheels. I also hooked up our motor, it works, but the reverse is tricky; it takes twice as long for it to shift backwards than it does going forwards. We were coming along nicely, but then everything went the way of the exploding stick. Oh goodness, the underlining won't go away!!!!