Robot is ship ready.
We completed everything that we are going to complete pre-ship today around 3:30. Then we headed over to RPI’s tech park, where every year some great people over there manage to put together a field. I don’t know exactly who is involved, but we are forever indebted to them. Anyways, here is a complete synopsis/overview of our robot and how it performed on the field.
Drivetrain: We FINALLY got our Banebots motors and cimulators to put on the robot, one of which ended up being bad. We need to take the gearboxes off one more time to adjust a spacer and add the pinion gears to complete our 6 motor drive. The belts didn’t sound good on the field today, and there was minor discussion about replacing them. I don’t foresee that happening before Thursday at WPI, and even still we may just run with the belts. However the robot did list significantly to the left and we aren’t sure why. Hopefully a good re-tensioning of the belts and a quick look to make sure all the CIMS are working will fix the problem. Hopefully it isn’t a code problem.
Arm: We ended up using a window motor because the bane bots motors took forever and it was too late to manufacture a FP gearbox. We may see the gearbox later in the season, depending on how our custom dog gear holds up. We have a custom dog gear held in place with a compression spring which solves the problem of getting the arm down that is attached to a nonbackdriveable (is that a word) motor. The counter balance is surgical tubing, and pneumatics are run on the outside. The sliding joint that locks with a piece of lexan for the entire match works perfectly.
Gripper: If our only problem with the whole bot is a split piece of wood on a gripper that is easily replaceable with aluminum, then we’re doing pretty good. The gripper is just 1/2″ hardwood cut out on the CNC machine. The piece that held the piston to the arm split today during some pretty heavy use. The claw is decently rigid and picks up and holds tubes in all sorts of orientations. We put a small piece of oil impregnated nylon on the bottom so the claw slides seamlessly across the floor.
Minibot: Even with an almost dead battery our minibot reached the top in about 5 seconds, and it looked to be going about 3/4 speed. We has the only working minibot at the pre-ship expo today which made us feel really good. We also have another design in our back pocket that may or may not be machined between now and WPI.
Even without our driver driving the bot, line up and scoring wasn’t difficult and the bot operated at about 80% of capability. We scored all three tubes at least once, and we completed a logo on the top two rows today. Doughnuts gave us a little difficulty because of the lag we were experiencing, but today was a refreshing look at how our work has paid off. A few tweaks here and there and we should be good to go for WPI. Look for a pre-ship video in the coming days, meanwhile I’m off to winter break in sunny California. Bother Chris with any questions or comments you have.
-Jack
Scouting 2011
In my absence from the team due to stupid things like “college” and “passing my classes”, I’ve been working on some things that Shaker may or may not use that could help the team out.
We’ve gone with KISS on our robot this year, as cliche as the term is, so why not extend that to scouting? Previously, we used an excellent Wii Remote based program for scouting. While it worked great, it wasn’t very easy to train people to use and it was a little less than easy to get data down to the pits for use by the strategists before matches. The software has ways to work around both things – mainly the ability to print prematch data out and simpler control methods – but I want to see if there’s a way things can be made simpler and less electronic.
So here’s what “I” came up with, the result of tons of causal research, conversation, and advice from people smarter than me. First: It’s all paper based. Data is inputted into a computer only for the Friday night pick list meeting. Paper is cheap, reliable, and intuitive. We’ll have a binder with sections for each team that includes scouting sheets from each match for easy organization and access. Forms are printed two per side on standard, three hole punched paper. Each team should only need about three full sheets of paper for data.
The forms are optimized to require taking as little data as possible. In this game, a lot of the “advanced” statistics you may want can be easily derived from a core set of general data. Rather than track a number of tubes scored on various positions of the rack and some other modifier for the right shapes in the right places, the scouting form just includes a 6×3 grid to copy the Rack onto. Rather than calculate minibot deploy and climb time, the form just asks scouts to read the arena clock when the minibot hits the top. Overall, only 5 points of data are asked of the scouts, which can later be derived into anything we could possibly need.
Here’s my rough draft scouting sheet and rough draft prematch form. Lemme know what you think!
Je suis retourné aux Etats-Unis.
Bonjour FIRST!
After a roughly 8 hour flight and 3 hour bus ride, I arrived about 11:30 Friday night. Even after being awake almost 24 hours, I got up Saturday after 6 hours of sleep, and went to robotics. While I was gone, we made progress on various components, but nothing was really finally decided or put together. The reason for that was drive train gearbox trouble, but I’ll get into that in a bit. Here is an update on each one of the subsystems on the robot.
Manipulator: We have not yet received our collaboration roller claw. While this is disappointing, we have an extremely solid pincher prototype that I am CADing the production version of now. Its too difficult to explain without a picture, and I will post the CAD ASAP, (as long as skiing doesn’t get in the way.) But, basically the bottom piece is going to be 1/4″ lexan with a vex wheel attached (3rd year in a row with a vex piece on our robot) and the pincher is going to be either 3/8″ or 1/2″ wood, and three different shaped pinchers will be laser cut for testing on the final version. Ideally the final one will be ideal for picking up off the ground, for picking up from the slot, and for reverse dunking.
Arm: With the banebots trannys on backorder, we have completely scrapped our first arm powering design because we can’t afford to wait any longer. After a telephone call with 1726 discussing the advantages and disadvantages they are finding with their use of the window motor for their arm, we decided to use an FP motor, with an am planetary, and a custom gearbox that uses tough box gears, with a final reduction with a 16 tooth sprocket on the gearbox shaft, and a 60 tooth on the arm. The final reduction comes out to 2507:1 and should turn at 45-50 degrees per second. If you would like, feel free to check our math. The arm will be two pieces of PVC with a sliding joint and a lexan latch that uses gravity to operate at the beginning of the match and is locked in place for the remainder of the match. The arm is then attached to a piece of 1/2 square wood that has been lathed into a rod to fit in the pipe. This design is relatively final, but almost nothing has been produced.
Drivetrain: The reason we are so behind is our custom trannys are giving us fits. We had the bot running around, and after awhile it didn’t work as it should have. We realized that the belts in the gearbox had stripped because they weren’t making enough contact with the pulley. It was too late tor make a tensioner to fix the problem, so the belt is being replaced with 25 chain. The remaining sprockets come in monday, and by the end of the day, we should be driving again.
Minibot: We have a really nifty deployment system, but the bot still doesn’t work that well. But the deployment system is kind of a lexan lazy susan, with surgical tubing holding it centered, but giving it some play. This way we have about 20 degrees of rotation, meaning we don’t have to hit the pole directly.
Bonne Journée!
Jack
As of Week 3..
So we’ve hit a bit of a quandary – both blog posters have been away from robotics for the last several days. I’ve been busy with the many things I have to do in college, while Jack is on an exchange trip to France. Hence… not many updates. Here’s where I’m guessing we’re at based on email correspondence and the single meeting I’ve been to. Between the massive snowstorm and college I have only been in the shop once – enough to film this video.
Drivetrain
This is more or less done. Our prototype drivetrain exposed a flaw in our design – after extensive use, the set screws holding on our drive pulleys slipped, sliding the pulleys out of alignment and snapping the flanges off of them. Since the prototype was meant to be quickly disassembled, the set screws were not held with Loctite. The quick fix was to simply Loctite the screws in the final version. No torque is being transferred through the set screws; a hex pattern has been milled (yes, milled – they look really funny but they hold) into the pulleys for this purpose. It’s not ideal, but it should work. Cotter pins are sitting at the ready if those fail. The shafts were found to have too much “play” between the snap ring grooves – they were then remachined I believe. It’s awesome how easy hex bearings make this kind of drive go together. We just have a ton of hex stock and turn down the ends to accept a snap ring. Anyone can do that in 5 minutes on a lathe. Thanks Andymark!
Some small modifications remain – we may need to cut down the end of a CIM shaft to make room for a belt, and the CIMulators have not arrived yet – but the drive is more or less done. I’m sure since I was last there it’s driven along the floor.
The chassis, with arm tower, is significantly lighter than Shaker’s 2010 bot. We shouldn’t have problems making weight.
Gripper
A wooden prototype pinch claw was mocked up. It seemed to work pretty well with surgical tubing for grip. Not the strongest thing in the world, though. With some refinement it would be a great system. Meanwhile, our friends from Team Number Removed have been working diligently on sending us their roller claw. It was designed as a test bed with an adjustable height top roller but we will probably use it as is. If not, our friends from Other Team Number Removed used some of the data we got in prototyping to develop their claw. They were VERY satisfied with the results. Their design is simple enough to construct that we have a backup just in case our sheet metal claw for whatever reason doesn’t work.
As of now I have no idea which claw the team has decided to use. We’re keeping our options open and hopefully designing our claw to be interchangeable. This way, we can put off the decision until as late as after our first event.
Arm
We made a stupid simple mockup of a one-time telescoping arm joint out of some PVC, a wedge-shaped piece of Delrin, and a piece of Polycarbonate. It worked perfectly. The PVC slides down via gravity, pushing the wedge under the polycarbonate. Once the arm is fully extended, the polycarbonate “snaps” behind the edge of the wedge piece, creating a simple one way latch. Vigourous tests with shaking the arm and repeatedly inverting it were unable to reset the system. If it needs more help, we’ve got tons of surgical tubing.
We have been waffling between a Banebots arm gearbox and a custom one I made in CAD. Originally Banebots was the way we were going, but now my arm gearbox appears to be favored. It has the advantages of not needing to be shipped from a supplier in addition to allowing the robot to self right.
Minibot
Waiting on new motors. We got a Vex based minibot to work just fine. If we had extra motors I would love to do transmission modifications, but it seems out of our reach at this point.
Lack of Updates
I want to apologize for the lack of updates all week – I have been attending college and actually showing up to my classes so I haven’t been to robotics since Thursday. A real update tonight! Probably!
We tested a pinch claw – looks good, and more importantly light.
We’re getting a roller claw soon. If it’s half as good as our pinch claw apparently is – I’m happy. Our concern is weight though – we want a LIGHT claw and roller claws aren’t really known for being light.
Chassis got welded – some parts had to be remachined due to CAD issues (wasn’t me, I promise). Arm gearbox… I dunno. I was going to redesign it but I haven’t had time and some people want to use BB gearboxes. I think the lead time is too high and we’ll just have to bite the bullet with 3/8 shaft.
End of week 2
It’s the end of week 2, and we’re gearing up for a long week 3. It’s midterm week and build hours have been extended from 2 hours a day to 6.5 hours.
A few updates from week 2 before we get into week 3 goals. We pulled apart our prototype of our WCD, and we realized the set screws on the inside belt sprocket had slipped. This caused the belt to get out of line and strip the side flange right off the sprocket. The set screws didn’t have any loctite holding them in, but we are currently debating on a few potential fixes anyways, including cotter pins and spacers. This week we also put together a pincher prototype, which works much better than I originally anticipated and it’s only the first iteration. We’ll see when the roller claw gets here how it compares, and we’ll make improvements and a final decision after that second iteration of each.
Next week we are getting the chassis back with arm supports welded as well. The arm is going to be finalized and machined along with the electronics box. While that is going on, we will put the chassis together and hopefully will be fully operating by Wednesday. At that point we’ll have a good estimate of weight and will be able to factor that into some of our prototyping. If everything goes to plan the manipulator should be done sometime during week 4 and week 5 and 6 will be practice time. Expect delays with more snow predicted in the northeast, it’s been extremely tough weather wise so far, so we hope to avoid too many more setbacks.
-Jack
