Let’s start building!

Apologies for not having reported back for some time. We made a lot of progress on the design front in the last two weeks. I’m always excited to visit Casti because the gals always have a new prototype to share when I get there. On Saturday, Jim talked about using the KerK lead screw and by Wednesday, the gals had finagled an 80-20 version of the arm with all the pivots and slides working!

The game plan for the next week: Build the chassis with Jim and reassemble the kit chassis so that programming can work in parallel. This means we have to:

* Go buy all the materials that we need for Jim to start putting stuff together with us. This means a trip to Alan Steel on Monday, January 28 @ 3:00 pm. Caroline is putting together a cut list for 1X1 and 1X2 6061T6 aluminum square tube stock.

* Getting together a list of stuff to buy from Mcmaster for delivery by Monday. This includes long axles, flanged bearings to fit into the meccanum wheels, extra master chain links, extra sprockets and any other fasteners we would need.

* Planning and getting any long lead items like the 24” Kerk Motion Lead Screw (BZ8050T) through Mcmaster. This should be arriving next Friday. Eeek.

* Taking off the new stuff from the kit chassis i.e. the gear boxes and putting on previous years stuff so that we can start building the new chassis. While waiting for the new chassis to be built, we can experiment with the meccanum wheels as well.

* Start building this year’s electronics board. We can put it on a piece of corrugated plastic again. We should have this ready to go to hook up to all the motors before the chassis is done!

* We gotta start looking at our weight! Check out photos of the motors and wheels on the scale on our picasa site.

Chassis: I think the gals have settled on building a four-wheel drive chassis with four meccanum wheels. This should be really exciting and interesting this year. We took a look at what the frame should look like this year given the stack up of the 3” thick meccanum wheels and the associated sprockets and fasteners.

Jessa and Doug did some serious thinking on the driving code on Wednesday which is cool. I think it’s time to start coding up driving.c and getting the interrupts working while the Ann, Nandini and the build team work together to get the meccanum wheels and the kit chassis assembled.



Arm: Looks like we can do a power screw drive on an arm (third class lever – effort between fulcrum and load), which should give us more precision and less backdriving than with the usual sprocket and chain. I am concerned that we’ll need to be able to fold the arm back up at the end of a match when we take the robot off the field. We’ll be using the Taigene van door motor, and likely doubling the output speed to 100 RPM (since we only travel 0.5 inches per revolution of the nut). The Kerk Motion products triangular nut limits us to a 150 lb load, which at an 80% efficiency leaves us with 120 lb. We can probably safely place the pivot point at ¼ the length of the arm (20 lb at tip X 4 = 80 lbs at pivot, not including all the inefficiencies).

Serious math this weekend going on with David and Tiffany. I think David taught an entire statics class in an afternoon to the kids with a foam core prototype of the linkage. And then Eric pitched in working with Tobi to figure out how much load the lead screw could support.





Gripper: A bunch of our initial prototypes out of PVC and foam core helped us to understand just how gianormous this part needs to be. We’re struggling to figure out how two or three pronged gripper is going to start inside the starting dimensions (28X38X60). It needs two extra layers of actuation just to do this (passive or active I do not know). I think our goal is to get the chassis and the arm up and running soon and then develop and attach the gripper separately at the end.



We have 26 days left (19 days in). I am definitely feeling the pressure to move towards building! Thanks to all the parents and mentors for their support!

Emily

The promise of variety

My favorite days mentoring are those that involve a little bit of everyone – something mechanical, something electrical and something involving programming. It reminds me of the complexity of the problem these girls are trying to solve and how much fun a multifaceted problem really is.

Jessa, Doug, David and I were there today. The teams have made some excellent progress on all accounts. Annie and Divya took my homework assignment seriously and actually built a small scale model of not only the overpass but of the mechanism they have been thinking about for lifting the ball out of popsicle sticks and a baseball to represent the game piece. These gals are smart. Real smart. I was also touched that Sherri and Caroline took it upon themselves to build a gripper out of PVC. I really do suspect that once we show them a way to prototype or a way to do things, the exposure is enough for them to take it and run with it. It’s getting over the hurdle of knowing what to do that is hard. I don’t think they suffer very much from what Bob Sutton calls the ‘knowing-doing’ gap.

For dinner entertainment, I pulled up a few sketches in Solidworks to try to explain four bar linkages to the kiddos as it applies to designing their lift. I emphasized that Solidworks is a tool to help them make decisions and I think that using the 2D sketching features would benefit them greatly in figuring out some of the geometries they are trying to build. Jimmy and I had a good working discussion today over lunch (as he was waiting to get through online to get burning man tickets nonetheless) and we’re interested in some sort of four-bar linkage or scissor lift. David brought up the extendable ladder mechanism which I think we can do easily with a winch. He also had a good point about those great drawer tracks you can get from home depot. Perhaps we can use drawer tracks along with one side of the scissor lift to give it some stability, especially near the load. More later on this.

While David coached Ann and Nandini on the prototype chassis assembly, Doug and I chatted with the gals about a few important electronics / programming topics including PWM and duty cycle, how moving the joystick translates to a motion in the chassis, and some ways to work around the over responsiveness of Scottie (last year’s robot). Driving Scottie, I suspect, is a bit like trying to fly a helicopter. Scottie was EXTREMELY sensitive because, to my awe and surprise, apparently the girls took the input signal from the joystick, CUBED it (took it to the power of 3 / talk about serious processing meltdown) and then divided it again by some number. Doug then had a great point about using a lookup table instead, so you are guaranteed with an output within your boundary conditions and a lot quicker processing. Doug and I also talked about using an accumulator and other time-based strategies to reduce noise in the signal.



We also sat down and wrote code on the board. Mentors who are interested in coding, please let me know and I will get you a copy of the compiler and default code. I can walk you through the default code (it is messy). Albeit the big family of c and h-files, the girls should only be concerned with modifying user_routines.c and user_routines_fast.c (for autonomous / hybrid period). In the context of programming an accumulator, we talked about global variables, constants and arrays. I actually think we should encourage them to work on categorizing their functions into library files like driving.c / driving.h, lift.c / lift.h and gripper.c / gripper.h so the components can be developed by separate coders and then incorporated into the program. Then default_routine (void) as a function can be kept very simple and clean. I would actually like one of us to strip user_routines.c down to the foundation so that all this extraneous code doesn’t overwhelm the kids.

This was definitely a good day. We have momentum. I know the kiddos are worried about not having designs locked down yet and feel behind, but heck, neither does my project at work! We’ll figure it out soon. I’ll be there Saturday. See everyone there!

End of Week One

This is really déjà-vu for me blogging again. We started up these blogs at the beginning of the 2006 season and they’ve morphed into and out of use and back into use again over the last two years. The purpose of these blogs are to keep the mounds of people who support this robotics teams either daily, weekly or monthly caught up on news so that we can all dive right in when we are together at Castilleja. Sherri has committed from the student team to blog regularly and I have committed from the mentor team to do the same.

After a tough first week, I think we’re on a roll. I do believe that the key to success mentoring this team is to get them hands on with problem solving and to let their intuition guide them once they start experimenting through this design phase. Fearless team leader Erin O’Malley just got back yesterday from a long journey to India, so give her a hug or high five when you see her! Here’s where we are . . .

OVERALL TEAM OPS: Running much more smoothly. It’s a really tough year because we have a lot of newbies and a lot of mentors. The girls who are leading want to get into the nitty gritty of designing but they have to manage us big kids AND the little kids and give us something to do. On Saturday afternoon, the mentors and the team leads had a meeting, and we decided that for the next two weeks, to try tackling the design with small teams focused on one part, rather than keeping everyone within their discipline (i.e. build, programming etc.).

CHASSIS / OPERATOR INTERFACE: (Caroline, Sherri, Allie, Anne, David (Mentor)) Lots of progress this weekend. The team is building a prototype chassis with the kit of parts with all the motors and electronics attached so that they can start working on the coding, which I think is a brilliant idea. They had a lot of driving issues with Scottie last year, a lot of which I think can be solved using smoothing algorithms (moving averages, PID controllers). Also, David mentioned that he’s used a yaw sensor to detect slipping so that we can also adjust for straight driving using electronics and code. We also have two gear tooth sensors that can be mounted to equalize the two sides of the chassis (Doug worked on this with interrupts two years ago and I still have the notes on flipping bits in the registers).

** We can also work on the input side – Jimmy and I have been chatting about tank drive (having two single axis inputs vs. one two axis input, which is really confusing). Karlin found that http://www.ifirobotics.com/ already has a USB board that makes it possible to connect all sorts of other input devices to the operator interface. The easiest way to do this right now is to take the two joysticks provided and to constrain their motion to only one axis (y-axis), read only that input and let a driver try using two of them at the same time. Fun problem.

** Goals for the week: The girls are planning to have the prototype chassis finished by sometime middle of this week. They are currently using wheels from two years ago and the same gear box and motors from two years ago. They had some issues finding bolts long enough today and are going to have to move their electronics board out of the way to the back in order to screw the gear boxes to the frame, but their close. The electronics look like they are all hooked up and can turn on (please note they are using the robot controller from 2005, which means when they compile, they need to make sure they compile for the PIC18F8520 (pre-2006) and not the PIC18F8722 (post-2006). They will likely also need help with the chain and tensioning it. They are also working with Ms. Mourad to get these omnidirectional wheels (http://www.andymark.biz/am-0083.html) Really hot stuff.

I’m really looking forward to debugging system issues on this prototype chassis (get all the code and sensors hooked up) before the real chassis gets built!! Go team.



LIFT / CLAW: (Nandini, Erin, Anne, Emily (Mentor), Karlin (Mentor)) Good progress this week. I worked with newcomers Annie, Divya and Crystal to build a portion of the overpass field element today (see photo below). This really helped us to experience what it like to manipulate the ball (like put it on and push it off) its sitting position. We discovered that it’s actually pretty easy to push off from below by just running into it with some momentum using first, Annie’s forehead, and then pieces of 80-20 and PVC pipe.

** In the last week, we’ve been bouncing a number of ideas. Jimmy and I have talked about elevator lifts and four bar linkages which help us start within the 60” tall X 38” width boundary and still be able to reach up beyond 78” with a claw. Fundamentally I am pretty concerned about the center of mass of the 40” diameter trackball. I think the more time we can drive around and keep it above our CG the better.

** Nandini spent a lot of time with David on Saturday exploring a good number of options for the claw. They explored the option of the claw having three actuated prongs, and then three prongs with only one active to clasp it. Nandini also had an interesting idea based on a tarp and a draw string, and finally, she has some really good thoughts on using rollers at the ends of the arm / gripper to keep the ball in place once in possession and to also expel the ball when ready. Thanks to Nandini for catching us up over the phone today and to Crystal for calling her.

** Annie, Crystal, Divya and I, after discovering the power of pushing from below, took a look at a solution based on a windmill. The pivot point would be high up and the two windmill arms tucked within the starting volume would rotate out to push and catch the trackball coming off the overpass all in one motion of driving through under the overpass at a fast speed. (VIDEO: Click here) . Divya came up with the idea of having a second smaller scoop type mechanism at the base of the robot that can get the trackball off the ground and into a position that the big windmill can scoop up and drop onto the overpass in order to hurdle. I’m having them prototype the system with ¾” PVC (they have a stash in the science project room in the back, along with a PVC cutter) now.

** So, I think all solutions are still on the table, but I would encourage everyone to start moving to wood, PVC etc. in 1:1 scale. I also pulled up Solidworks and used sketches to demonstrate the path of a linkage / arm and have them guide me while sketching changes. We also, with Doug’s speedy help, managed to get the portion of the overpass that we built at the right height (it’s tall) and sturdy enough for now. You’ll have to put it together outside in the walkway since with the ball on it, it’s way higher than the classroom ceilings.

OTHER STUFF: Keep us posted on your schedule. Thanks to Karlin for putting up the Google Calendar. I’ll be there on Wednesday night by 5:30 pm. See everyone next week for more fun!

Em