I used to be the mentor of 1989 of Vernon Twp HS. Well that team is no more so when presented with that in october a couple of kids asked and we founded 9713 and built a plastic/3dp bot - just a skateboard in less than 3 weeks and entered in the Brunswick erruption - and the bot survived and we played “D”. AND we got the $$ together to sign up for the season and will compete in Hudson valley (long story - not important) we have a small team but great kids all tech savvy. So we spent some time designing and Cadding. Most cad is done and 3dp has started. So the scateboard section is 80 percent printed from experience it should take a meeting to assemble. The gears for the gearboxes are all printed some spacers still missing. Bot most likely will be tank drive. With 2 powered hi grip wheels and 2 omnis. Ground clearance 2.3 in to take in the notes under bumper
2 5 to 1 shots of a scale model of the bot with and without the intake/shooter
Intake under bumper and frame and intake leeds into shooter so can hold one note then speed up the shooter and turn the intake on full speed and so work as a stage one accelerator for the shooter. Rollers on top and 8mm/5/16 aluminum rods in 688 bearings on the bottom.
Climber initially was with a 25 :1 gearbox on each side on the bottom but kids want to do a rack and pinion (double rack to mitigate deflection) so It will be on the top.
This is the “Fit test” on the first corner module. 6:1 reduction with motor mounted at 90 degree. can be geared up to 5:1. We intend to go fast from pickup to drop off. Programmatically also make a low speed range. Should be possible acceleration wise as the whole bot - if calculations are correct including batt and bumpers and everything should be about 90ish lb. The scateboard bot at N. Brunswick weighed in at 35ish without batt and bumpers.
Cad of what printed successfully is posted there. We have more cad but it hasn’t fitted yet and in case someone follows along we don’t want to waste anyones filament. All stuff designed to fit on a K1 Max so 300x300x300 and most will fit on an ender. In the past we used HIPS but RN I got a lot of PETG so PETG it is. And no prior parts will be used so to make sure we dot all I’s and cross all Ts rule wise and yes some of the parts have been available on my grabcad above and posted as they were inherited from 1989 and I always had them on my grabcad as the school never got around to approve grabcad for school use. Now that workbench is dead we just use it as a “live” reposit and I guess its ok if someone wants to follow us down that rabit hole “live” during the season
Also above includes 3dp models of field elements in 5:1 scale at least for the most parts
All together with bevel pinion and motor and mount.
All clears by about a mm or more so nothing that is not supposed to touch touches and it spins freely with no noticeable backlash. (nominal designed backlash on each gear interaction .1 mm
Printed in PETG on a Creality K1 Max about 660 g of plastic plus the weight of about 5 in long aluminum axle and the wheel and the motor and there will be about .2lb of al. reinforcement allotted to that corner piece which will make 6x8 in of the frame so in line for the target weight
Using the 3dp hole to lign up the table top drill press lets us make a nice straight hole in the right place so it comes out at the hole in the bottom which is important as the bottom holes are countersunk so we don’t snag a note by accident
Battery holder. Plastic frame with 2 short pieces of 2in x1in 1/8in L aluminum extrusion tied to the 1/2 in square tube below it and the plastic solid 6mm PETG. on the frame part 12 mm part on the side pieces.
Full frame. done . The wheels and gearbox parts are not mounted as it is easier to keep the frame on the table without it rolling off and makes drilling easier.
The parts for the note intake and shooter are printed - at least the prototype (we will see how it works. Robot has about 2 1/4 ground clearance which with the bumpers should allow us a little pay of getting in within the bumper zone and clearing the notes picking them up off the floor. It also looks good to hit our light weight goal of making it around 80 lb. Going for being fast and light
One side of the prototype intake/shooter to be assembled this week hopefully. Will probably have a “dustpan” in the front to help with "eating the notes which will stop about 1/2 way through there is a motor in the front. The intake starts angled at 8 degrees and then the shooter part points up at 54 deg and my students swear that will be a good angle to shoot. So there is an intake motor and a shooter motor and a gate keeper motor (gear motor) to keep the note from entering the shooter before we have it spun up and are ready to “fire” Both intake and shooter sections are geared the rollers in the center are idlers. On the intake/shooter part using on the powered rollers 51mm 3dp TPU roolers on square tubing with 6805 bearings the others are 8mm rods on 688 and 608 bearings. The rods are actually 5/16 aluminum round stock - inexpensive strong enough, fit the bearings well and are light
Double rack so we don’t have skipping issues due to deflection and multiple 3dp sections can be strung together on a 1/2 in square aluminum tubing. So we intend to have 2 independent Rack and pinion climbers - one on each side of the robot - so we can balance out in case more than one robot climbs on the same chain.
Now IDK if we qualify as a rookie team. We are new. I have been training the kids multiple times a week since september. I am not a teacher but have been earning a living (before I retired) doing all kinds of engineering and have been coaching various FRC teams for 14 years now so I am definitely not a rookie. But rookie status or not we are shooting for building a nice bot.
In the end we expect to use about 20-30kg of PETG (so far we are 14kg into the adventure) so not too bad as I usually by it 50 -100 kg at a time for usually $8-12/kg. (depending on negotiations lol) Even though there will be less than 20kg on the bot (around 15-17) more is needed as not every design works out the first time. We “inherited” a lot of designs from 1989 which is defunct but the designs are still on grab cad. And to be safe we built on that so all designs inherited are redesigned to make them better printable. And everything is being posted “live” on my grabcad. Well usually saturdays or sundays. So once a week.
First iteration/fittest of rack and pinion climber. Input stage with motor and pinion of the bevel still missing. Overall effective ration a little over 20 to 1. also missing top plate and some guides for the rack
For now all known dimensional issues on the climber worked out is driven by a neo and the 2nd one is all printed ready for assembly. Which involves replacing the bolts with proper cut axles and cut/mount the square tubing
Overall the concept worked and we did a little of everything.
Our main problem was that due to the fact of only having 3 active kids who obviously were all newbies. We had a tough time finishing the robot. So we got to the competition with an inoperable code. Thanks to team Robot tigers we got that working. First the driving and eventually intake and shooting and Climbing.
The driving had one problem that somehow the wrong spacer was used and we ground up a bevel gear. We replaced that 3dp bevel gear and installed the bevel gear and no more mechanical drive problem (we had a sparkmax die but that was 3dp unrelated as one of the pins on the encoder cables disappeared.) So the drive and basic frame gets a check. We damaged a part on the battery holder due to not screwing the battery in but that was easily fixed to and no more problem there as we made sure the battery was tied down properly.
The shooter intake worked well after we put some duck tape on some of the rollers (5/15 aluminum rods) as they were about 3/16 to far away from the powered rollers. So a design flaw. Wish we could have detected that a week ago. But as I said we were finishing to bot in the pits. The shooter worked well shooting but missed the goals which we had fixed by day 3 - kinda - with fashioning a quick adjustment moung mainly made of zip ties. It was not reliable but the concept - using 3dp gears and frame - worked and lasted.
The climber was working after we got some software issues worked out. We bent/broke one of the aluminum mounts/supports as our driver crashed full speed with arms extended into the trusses.
So to assess from another angle.
3dp PETG gears run with no lube - work well as long as they are properly mounted. They were used for driving and for shooting and climbing. IDK how long they would last in general but there was no detectable wear and tear after 3 days of competition.
Frame which is 3dp with al. reinforcement worked very well.
The TPU 3dp rollers worked as designed and so did all the bearing pocket mounts
The rack and pinion climber worked well too when we got to use it. The major problem was the driver was sometimes late lining up to climb.
All in all if we would have had another week or 2 to practice and make mods or a couple of more kids to get it done sooner this could have been a very competitive robot. So with only one competition (district championship) we did not qualify for nationals but we also did not finish last. So plan for the future is to get more kids and $$.
Oh and weight wise - according to inspection the bot was 72 lb weighed without battery and bumpers at the inspection scale
And not counting motors and electronics so filament/aluminum fasteners and bearings we had about $400 on the bot and that includes all gear boxes and drives and frame parts and mounts. About $150 in filament (PETG about 15 kg) about 150 in aluminum and the rest fasteners and bearings. Mostly M5 and #8 and #12 sheet metal. We probably used another 8 kg to print parts that were rejected due to design and fit problems in the process so <$500 including design waste
