Iterave design, 2011

[Hawiian Cadder]

it seems like every year i learn a lot by watching competitions and seeing what design methodologies and techniques work, and how they manage to build robust, light, effective robots. however i always forget what i learn by the next season. so this year i decided to completely re-design our robot every two weeks, after watching what other teams do well. the basic design remained similar through every iteration. the strategy my team decided on in the beginning, was a robot with a rolling gripper, with a elevator that could score on all 3 rungs. my main goal through the iteration was to do the same thing better with less weight. we are always overweight. below are some renders of the different versions.




this is the original CAD of the robot, specs:
4 cim drive, 14 feet per second. 6 wheel tank drive. the wheels on the ends are omni wheels.

lift powered by the fisher price in a dewalt gearbox with anti back-drive pins intact.

the wrist is a rs550 in a 81-1 gearbox with another 6-1 in sprocket reduction.

the roller is powered by another rs550 in an 81-1 gearbox

weight, 119.9, according to the CAD, it was 112



the second version was put together largely the same way.

the drive speed remained the same. the only difference is the conversion to 8 wheels instead of 6.

the frame was changed to 4*2 tubing, and the drive is now cantilevered.

the lift was changed from a rolling design to a telescoping channel lift with nylon sliders. the method to power it remained the same, the FP in a dewalt transmission.

the manipulator remained largely the same, the motor powering the roller and the motor powering the wrist were both moved, they are on the manipulator near the wrist axle, this makes it lighter and more compact. the torque on the wrist is much less. another change is the electronics box, it was changed to be tall and have a smaller footprint. this allows the minibot deployment to move from the top of the box to the side.

weight according to cad, 92 lbs, not including wire or chain.



the tough-boxes have been changed to modified AM shifters. the high ratio is 16 feet per second, and the lower one is around 6.5.

all the axles have been changed to hollow shafts, and the tubes in the frame have been changed from 2*4*.125 to 1.75*3*.125. this reduces weight, and removes the need to pocket the frame. the lift has been changed from pocketed .25 thick channel, to un-pocketed .125 thick channel. the manipulator has a less CNC dependent design, which uses bolts instead of rivets to hold together. the gearboxes on the wrist and roller have been changed to rs550's in am planetary, and gems.


weight. 83 lbs. not including wire, includes chain this time.

sorry about the color of the cims being wrong on the last render, my team likes to prank me by changing the appearance of things in the CAD.

[Alpha Beta]

How is the iteration coming on the actual robot? Have you been able to take advantage of some of these improvements with the 30 lb with holding allowance? We look forward to seeing you guys in person this coming weekend at the Colorado Regional. We haven't been up there since 2008, but from what we remember 159 has an excellent team.

[Hawiian Cadder]

thanks, we cant wait to compete with you this week.

the goal of this was to make things easier to change, and more flexible.

on the third version there are clever examples throughout the design. the lightning pattern on the members with the roller is set up such that the axle can be put in any of those holes, allowing for adjustment on the fly without much problem. the chain between the spools and the dewalt allows for the lift to operate in the highest gear on that transmission normaly, and if something is broken and getting jamed we would be able to power through the resistance with a lower gear.

we do not have any upgrades for the robot because our 30lbs allowance is 15lbs of fischer prices. our lift is binding somewhere and eating them. we probably wont fix it until we fry at least 1-3.

a secondary goal with these redo's is for me to be faster with the CAD. the original took 4 days to get worked out for the most part. the second one took 14 hours. and i did version 3 in just under 6 hours.

these are primarily to look at next year, and see what we can do to make the build season go faster. each iteration removed machining. and standardized parts.

[GearsOfFury]

Thanks for sharing, this is a neat idea.

You mention the FP motors. Just so your team is clear, if these motors are direct from the manufacturer (e.g. KOP or AndyMark) and have not been modified (pinion gears, etc.), they qualify as COTS, and are not FABRICATED ITEMS, and do not count against your 30 lbs:

FABRICATED ITEM – any COMPONENT or MECHANISM that has been altered, built, cast, constructed, concocted, created, cut, heat treated, machined, manufactured, modified, painted, produced, surface coated, or conjured partially or completely into the final form in which it will be used on the ROBOT.

<R33> Teams may bring a maximum of 30 pounds of custom FABRICATED ITEMS (SPARE PARTS, REPLACEMENT PARTS, and UPGRADE PARTS, plus all WITHHOLDING ALLOWANCE items) to each competition event to be used to repair and/or upgrade their ROBOT at the competition site.

[Jeffy]

How is that single roller claw working for you? We prototyped something like it and couldn't find a way to overcome the tubes turning upon entry.

[Hawiian Cadder]

the single roller works fairly well.

the roller is a polycarbonate tube, which is attached to the drive axle with rubber bands. this gives it 1.5 inches of tolerances where it moves to accept different sizes of tubes.

the "sensor" on the roller is only C-A-N, the free current of the roller is 2-4, as soon as it exceeds 14 amps, we know a tube is securely held.

we looked at a variety of materiel for the bottom of the roller. regolif, was very promising, however we found that polycarbonate coated in duct tape works nearly as well, and is significantly lighter. regolif is also not COTS as far as i know.

the width of the roller also helps it to not turn the tubes. it does turn them up a little at the beginning, but when they get sucked in far enough they are forced to line up with the bottom of the manipulator.

the fisher prices have had their gear pressed off, and a new one put on. we were not sure as to the legality of that. there is also not much that can be changed. the original CAD will work just as well as the other two, once we get the lift to stop binding. our withholding allowance has a couple of new sliders, as well as spare axles. our the COTS items we are taking are a lighter digital sidecar ribon cable. a new encoder for the lift. and a few other things to cut weight.

i think were good, but does anyone see a problem with continuously stalling a rs550 at 14 amps?

[Jeffy]

Originally Posted by Hawiian Cadder

i think were good, but does anyone see a problem with continuously stalling a rs550 at 14 amps?

Absolutely. The BB motors get their cooling from a fan attached to the armature, if the motor is stalled, no cooling. We had a deffective gearbox with a 550 for the arm on a 20 amp fuse. It got unbearblely hot within 30 seconds and thermal shut off in under a minute.

What have your tests shown?

[Hawiian Cadder]

we did not have a whole lot of time to test it. 14 amps is not too much. i will talk to the programmers and see if we can change it to test for a tube every second or something.

[Alan Anderson]

Originally Posted by Hawiian Cadder

14 amps is not too much.

14 amps at 12 volts is 168 watts. You'll fry the motor in short order if it isn't spinning and cooling itself.

[Alan Anderson]

Originally Posted by Hawiian Cadder

...our 30lbs allowance is 15lbs of fischer prices. our lift is binding somewhere and eating them. we probably wont fix it until we fry at least 1-3.

I don't understand what you're saying here. If you're bringing in a fabricated mechanism with that much weight in FP motors, you need to be reminded that the 2011 FRC rules permit only one FP motor on the robot. If you're bringing in spare FP motors, they don't count against your withholding allowance unless you've made some sort of modification to them. Leave off the pinion gear and don't solder wires to them, and then you can carry as many as you want without having them apply to your withholding allowance.

[Hawiian Cadder]

Originally Posted by Alan Anderson

I don't understand what you're saying here. If you're bringing in a fabricated mechanism with that much weight in FP motors, you need to be reminded that the 2011 FRC rules permit only one FP motor on the robot. If you're bringing in spare FP motors, they don't count against your withholding allowance unless you've made some sort of modification to them. Leave off the pinion gear and don't solder wires to them, and then you can carry as many as you want without having them apply to your withholding allowance.

we dont know if anyone will have a 2 ton press at competition. there is also not much else we need as far as fabbed parts. the fisher prices are spares, because we fried 3 on ship day accidentally due to lift binding issues. only one will be on the robot at a time.