We had very high expectations for both our machines this year, but came up short. We made some incremental improvements to Launch-Ness which greatly improved our cocking process, but we neglected the most important part of developing a successful machine, testing. We spent much more time than we planned on the construction of Chunk Norris. It may have delayed our success for this year, but I think the lessons learned on the catapult will be invaluable. For most of Punkin Chunkin’s history the main challenge for the trebuchets has been developing power. The entire division has made huge improvements in recent years, but now we have new problems to deal with. A huge challenge on both our machines this year was getting a pumpkin to survive the throw. We have a lot of work to do over the coming year to perfect the art of sling design. At the competition this year we received a huge amount of help from other teams on how they design slings to address the issues we saw. Team Chucky offered a lot of really good tips. The catapult and torsion divisions have been throwing with significantly more power than the trebuchets for several years, and already have a big head start on sling design. Over the coming year we’re hoping to use Chunk Norris as a tool to address several different issues, including sling design. Launch-Ness Monster is very complicated machine to operate. We’ll have lots of testing to do with it, but having a small machine that can fire a shot every few minutes will be very helpful. Hopefully during the coming year we can finally complete enough testing to find the true capabilities of both machines.
World Championship Punkin Chunkin 2011 Lessons Learned
November 24th, 2011World Championship Punkin Chunkin 2011 Summary
November 6th, 2011Hopefully I’ll get time to write up each day, but for now here’s the quick summary of the 2011 championship.
Friday morning was an early start with the new firing order. In past year’s the mechanical line would fire in the afternoon, but for 2011 the order was reversed. The mechanical would start in the morning, with the trebuchets at the beginning of the line. We started setting up the machine just as the sun was starting to come up in a heavy fog. The line was scheduled to start firing at 8:00, but was delay until 9:00 so the fog could burn off. It’s very hard to find a pumpkin after the shot in good weather, it would be impossible finding it in fog. For the first shot we picked the third best of our pumpkins. It was a lumpy looking Lumina with a few questionable spots. Nothing that looked rotten, but certainly not the ideal pumpkin. We loaded the pumpkin, and tried to put the perfect amount of slack in the sling lines. When it was our turn to fire, we pulled the trigger, and were rewarded with pie. Apparently our pumpkin wasn’t as sturdy as we’d hoped. In retrospect we were hoping for a shot somewhere around 1800-2000 feet. Until just a year or two ago, this shot would have been unthinkable for a trebuchet. Now it’s become a mediocre shot, but still requires everything to be just right, including the pumpkin. Several other trebuchets had similar problems for their first shot. Between mechanical failures and pie, there were several zeroes on the scoreboard.
After Launch-Ness’s shot we quickly scrambled down to Chunk Norris to start preparing the catapult for its competition debut. The firing line was moving smoothly and we were soon up again. We stretched the bands, loaded the pumpkin, and pulled the trigger. More pie. This was starting to become a theme of the weekend.
For Saturday, we replaced the sling on Launch-Ness. We lengthened the sling a little to help slow the acceleration and switched to a larger sling with more material to help support the pumpkin. We maintained the same 2000 pounds of counterweight. We found some very sturdy pumpkins from team Inertia II. Whatever weather had affected everything in the East, apparently skipped Colorado. This time the pumpkin survived the throw, but the sling ring had failed to release on time, and finally let go very late. The shot very flat, but the line drive carried the pumpkin 1153 feet. Not a bad throw, but we’d hoped for better.
We tried another one of the magical Colorado pumpkins in Chunk Norris, but again pied. No pumpkin could survive a throw from that machine, even at half power.
For Sunday we loaded an additional 600 pounds of counterweight to Launch-Ness hoping to finally get the shot we needed to stay competitive. The winches strained to lift the weight, and we switched into low gear for the first time. The winches would have no trouble now, but it would be very slow to raise the weights. We didn’t have to wait long though. Right as the counterweight started to rise, one of the winch cables snapped. It had jumped out of the pulley sheave and was cut as it rubbed along the pulley’s mounting plate. Several trebuchets had already fired and we wouldn’t have a chance to replace the cable. We weren’t going to miss the opportunity to take a shot. We quickly got to work stringing spare rubber bands from the catapult onto the trebuchet to make a slingshot. The shot wouldn’t count, but it would be fun to try. We swapped or beautiful Calabasa pumpkin with our neighbors, NASAW. Considering how hot a commodity good pumpkins had become, there was no point in wasting the perfect pumpkin. We fired our shot straight into the ladder to the top link of Launch-Ness. It was a miracle the pumpkin even made it that far. It somehow avoided all the linkages on its way through the machine.
After our slingshot performance, we prepared Chunk Norris for its final shot. After consistent pie all weekend we decided to remove most of the bands, bringing the machine down to quarter power. We finally had a successful throw, with a distance of 950 feet. Not nearly as far as we hoped, but enough to put us in 4th place. Launch-Ness ended the weekend in 9th with our Saturday shot.
World Championship Punkin Chunkin 2011 Set Up
November 3rd, 2011We spent both Wednesday and Thursday finishing up the set up of the machines. We still had some work to do splicing ropes on Chunk Norris, and spent a good portion of both Wednesday and Thursday getting Launch-Ness ready to fire. We brought our new set of pulleys and brackets for Launch-Ness with hopes of welding them on at the field, but couldn’t find enough time to get them on. The new pulleys were much larger and stronger than the previous ones. They would also spin with much less friction, helping to reduce the load on our winches.
Both machines passed safety inspection, and were ready to fire. We started Chunk Norris with half of the bands attached. We figured that would be a good starting point, since at quarter power the machine had thrown around 1000 feet in testing. We cocked the machine, loaded a pumpkin, and pulled the trigger. Pie. The pumpkin disintegrated early in shot, mostly spraying out the back of the machine.
This was disappointing, but we knew the pumpkin was weak to begin with. 2011 had been a very bad year for pumpkins. During our testing in the fall, we were unable to find any decent lumina pumpkins in New Hampshire. We couldn’t find any La Estrella Calabasa either. Several farmers we talked to said they tried to grow them, but the weather hadn’t cooperated. We had tried to grow our own, but also came up empty handed. We’d hoped the farmers in Delaware would have better luck, but we hadn’t seen many good pumpkins down their either. The few better looking ones we found were safely set aside for later in the weekend, when we’d really need them.
We moved on to Launch-Ness to try a test fire with the trebuchet. During our testing in the fall we’d worked out most of the snags in our cocking process. It was still very time consuming, taking nearly an hour to get ready for a shot, but things had been going smoothly. The machine went up just as we planned. It was the first test of the new winches with counterweight on the machine, and they handled the load without trouble. We loaded in a slightly overweight lumina pumpkin, making sure to leave some slack in the sling lines. During testing we had a coupe of misfires on our first shots. After watching the high speed videos several times, we determined that the pumpkin was rolling out of the sling at the very beginning of the shot. Right as the machine started moving, the sling lines would tighten, pulling on the pumpkin, and rolling it forward on the pumpkin shelf. The sling lines would then briefly go slack, before finally tightening as the arm began to come around. This small jerk was enough to move the pumpkin out of position in the sling. When the final pull came, the sling would slide off the pumpkin, causing a very exciting dry fire. We found that by including a little slack in the sling lines, we could avoid the initial tug on the pumpkin, without affecting the shot.
Despite our best efforts to adjust the slack in the lines, once the trigger was pulled the pumpkin rolled out of the sling and fell to the ground below the pumpkin the shelf. The machine shook violently, but survived its first dry fire with couterweight without any damage. We were out of time for the day. They were closing the field to test fires to finish setting everything up for the competition. We’d have to wait until early Friday, during the competition, to get another shot.
By Thursday evening we still had a few splices left to make in the sling lines for both machines. We worked on those in the RV on our way to the Dogfish Head restaurant, where we spent our last night before the competition.
World Championship Punkin Chunkin 2011 Arrival
November 1st, 2011After a very short night’s rest at a truck stop in NJ, we prepared to hit the road again for Bridgeville, DE. We gave the trailers a quick check out, headed back on the road.
We were only a couple hours away. The remainder of the drive went quickly. We reached the field by mid-morning, our first time arriving in daylight, normally we’ve shown up in the middle of the night. We found our pit assignments and headed for the firing line. The field order had been shuffled around from previous years. The trebuchets were placed at the very end of the firing line, and would be firing first in the morning. After trebuchets came the torsion division and then the catapults. Launch-Ness Monster and Chunk Norris we located in pits 14 and 28 respectively. This worked out well. The machines were close enough to run tools back and forth, but had enough machines in between to give us time to prepare and cock for each shot.
We were still exhausted from the long day before, but got to work setting up Chunk Norris. That went fairly quickly, and we had the machine assembled in under an hour. We spent a good portion of the afternoon perfecting wheelies on the minibikes and ATV. We decided to put off setting up the trebuchet until Wednesday and went out to do grocery shopping and find a generator.
We had left our generator back at home, since there was no power. The plan was to purchase another generator once we reached Delaware. That wasn’t as easy as we’d hoped. The storm and subsequent power outage was much larger than we had anticipated, and people from Connecticut had traveled to Delaware and purchased all the remaining generators. We picked up groceries and headed back to the field to set up camp.
We parked the RV, pitched our tents, marked off our site with caution tape, and passed out shortly after 8.
World Championship Punkin Chunkin 2011 Departure
October 31st, 2011For 2011 we had to planned to leave for Delaware earlier than in past years to give ourselves some more time for set up. Especially with a second machine, the catapult Chunk Norris, we wanted to be on the field by Monday so we would have the rest of the week to put the machines together and test fire. In 2009 we left Wednesday night, putting us on the field Thursday with just enough time to assemble the machine and take two test shots before dark. In 2010 we hoped to leave on Tuesday, but were still building the machine and didn’t leave until Wednesday again. When we reached the field heavy rain had already begun. The field turned into a muddy mess, preventing us from setting up until late Thursday and leaving no time for test shots. For 2011 we had a new weather challenge.
On the Saturday night before our planned Monday departure we were hit with a snow storm. By Sunday morning we had a foot of heavy wet snow, trees down everywhere blocking the roads, and no electricity.
We still had packing to do, and got to work in the snow. We managed to pack up most of the machines and equipment by Sunday night. We took a 2 hour trip during the day to find diesel for the truck since most gas stations in the area were without power, fuel, or both. We finally found a station several towns over that had intermittent power and with enough tries were mostly able to fill the tank. The RV had been filled earlier in the week, and had most of a tank of gas. On Monday, we finished packing up tools. We found a gas station and were able to fill a few gas cans to leave at home with the generator. We brought some other cans with us to fill once we were on the road south of the snow.
We finally made it on the road around noon, pretty close to our original schedule despite the weather. The trailers stayed attached and both tow vehicles were driving well, a big relief given the loads they were carrying. Somewhere in Connecticut, Mike called to let us know the RV needed to stop for gas. We pulled off at the next exit and into the first station. No power. The station across the street also had no power. It had never occurred to us that the outage would extend so far South. We talked to several people as they drove through the stations and no one had seen any other stations open in any direction. We heard stories of traffic backing up for miles around stations that might be running, but that seemed out of the question with the trailers we were towing. We found a large truck stop back in the direction we’d come on the highway and headed there. They also were without power, but were hoping to find generators that night or the next day, three days after the outage had begun.
After some debate we dropped Launch-Ness of the truck and left the RV, Chunk Norris, and Launch-Ness at the truck stop. We’d heard that Hartford might have power and hoped there was enough diesel in the truck to make it there. As we drove closer more and more cars were stranded along the highway, presumably they’d run out of fuel. When we finally reached Hartford things weren’t any better. No street lights, and no fuel. We drove around for a couple hours until we finally found a gas station with power, but no fuel. A tanker truck had just pulled in, but it would be a while before they could refill the tanks. We pulled into a line with about 20 cars in front of us for the long wait. The station didn’t carry diesel, but we would at least be able to fill gas gas to bring back to the RV. The station remained orderly with only a few shouting matches when someone cut in line, or tried to sneak in. We filled our tanks, 11 gallons, and headed back to the highway. We made it back to the truck stop, but were now almost out of diesel.
While we debated what to do about fuel we went to reconnect the Launch-Ness Monster trailer. We backed the truck up to the trailer tongue, but something didn’t line up right. The hitch ball was missing! When we disconnected the trailer to leave for fuel some of the brake wiring was tangled on the cotter pin. We pulled out cotter pin, but never replaced it, leaving the hitch attached only by the clevis pin. Somewhere along the highway to Hartford was a very nice weight distributing hitch.
The truck stop didn’t carry any and still didn’t have any word on generators. We got a lead that a station back across the Massachusetts border still had fuel and decided to head for there. We left both trailers this time with a note kindly asking that they not be towed, despite the large sign that read “All dropped trailers will be towed.” The station in Mass was certainly not on the main road, and we had to weave around several down trees to reach it, but they did have gas and diesel. We filled both vehicles and found an auto parts store, and bought their only 2 5/16″ ball and mount. We returned to the truck stop to find both trailers still there. After only 8 hours, we were back on the road.
We set a goal to at least make it only the George Washington bridge, and made it there several hours later. We pulled into a New Jersey truck stop around 3AM to finally get some rest.
Pumpkins in a Wind Tunnel!
September 25th, 2011One of my life long dreams just came true! We finally had the opportunity to test the terminal velocity of several different pumpkins in a vertical wind tunnel. The amazing staff at SkyVenture NH made some very special exceptions to their rules, and allowed our test specimens in the chamber. SkyVenture operates a sky diving simulator. Their facility consists of a very large vertical wind tunnel capable of producing enough airspeed to “float” several people in any flying position. Typically people can fly in the tunnel with air speeds around 100 miles per hour, but they can control the air flow much slower and much faster than this, perfect for testing a pumpkin. Due to the danger involved with trying to navigate the airflow, while wrestling a pumpkin, we let their staff maintain each pumpkin in the airstream. By holding the pumpkin out into the air flow and slowly increasing the air speed we could tell when the pumpkins became weightless. Once they were close, the pumpkins were released and allowed to fly on their own so we could make fine adjustments to the speed. The pumpkins only required an occasional nudge to keep them from flying off into the walls. We tested five different pumpkins. They flew between 105 and 129 miles per hour, which lines up well with their expected terminal velocities. the pumpkins we tested were of several different shapes. We used three that were roughly spherical, one with a flattened shape, and one that was a long thin oval.
To calculate the coefficient of drag for each pumpkin we needed to know their weight, cross sectional area, and terminal velocity. The weight was easy to measure using a small digital scale. The cross sectional area was a little trickier. If pumpkins we nice and round we could measure the circumference and easily calculate the area. Unfortunately, real life pumpkins are all sorts of funny shapes. In order to measure the area accurately we placed each pumpkin on a large grid with evenly spaced dots. Each dot represented 1/4 sq. in. of surface area.
We could count how many dots were obscured by each pumpkin to find the area. We measured the area in three different axis for each pumpkin so we could compensate for the pumpkins orientation while flying. The terminal velocity of each pumpkin was recorded once the pumpkins were flying at a constant height in the wind tunnel.
The three spherical pumpkins would all rotate in the airflow, so calculations were performed on the average cross sectional area of the pumpkin. The flat pumpkin and the long oval pumpkin were big unknowns for us. The flat pumpkin turned out to fly very stable, always presenting the wide underside to the air flow. Regardless of the original orientation it would always flip over and fly with the bottom of the pumpkin facing down. The oval pumpkin had similar stability, but would always orient itself with the long side facing the airflow. Despite the seemingly aerodynamic shapes of both of these pumpkins, they both preferred to fly in the least aerodynamic orientation.
| Pumpkin | Weight (lb) | Area T (in2) | Area F (in2) | Area S (in2) | Air Speed (mph) | Cd T | Cd F | Cd S | Cd Avg | Orientation |
| 1 | 9.806 | 85.25 | 93 | 84.5 | 129 | 0.40 | 0.37 | 0.41 | 0.39 | all |
| 2 | 7.986 | 69.25 | 61.5 | 62.25 | 115 | 0.51 | 0.57 | 0.56 | 0.55 | all |
| 3 | 8.212 | 87.75 | 64.25 | 64.5 | 105 | 0.49 | 0.67 | 0.67 | 0.61 | top |
| 4 | 8.108 | 69.5 | 70.75 | 69.5 | 116 | 0.50 | 0.50 | 0.50 | 0.50 | all |
| 5 | 9.796 | 64.75 | 99.75 | 87 | 105 | 0.80 | 0.52 | 0.59 | 0.64 | front |
The table above shows the data we collected. The highlighted cells show the calculated coefficient of drag taking into account the orientation of each pumpkin.
| Pumpkin | Drag |
| 1 | 1.00 |
| 2 | 1.03 |
| 3 | 1.29 |
| 4 | 1.02 |
| 5 | 1.55 |
The table above shows the relative drag for each pumpkin, taking into account both area and the coefficient of drag.
Below is a summary of observations we took on each pumpkin:
Pumpkin #1:
Just a normal orange pumpkin with a fancy decorating job. This one was mostly spherical and fairly smooth.
Pumpkin #2:
A slightly orange pumpkin. I don’t know what variety this was. The top and the bottom had deeper indentations than the first pumpkin, but still spherical. The outside was fairly smooth.
Pumpkin #3:
Another unknown variety. Probably a Cinderella. Much flatter than the previous two. It was much wider than it was tall.
Pumpkin #4:
Probably a Cotton Candy. Mostly spherical.
Pumpkin #5:
Oval shaped. Tall and narrow.
In summary, if you’re shooting pumpkins for distance, and you want them to go far, use spheres. The spherical pumpkins we tested had much better aerodynamics. It may be possible to keep a non-spherical pumpkin oriented along a more aerodynamic axis during flight, but it would require significant spin, and very careful orientation at the beginning of the shot. At the competition we’ll be trying to find the smoothest, densest, most spherical pumpkin we can.
Aftermath
November 25th, 2010Tonight will be the airing of both the Road to Punkin Chunkin and Punkin Chunkin television shows. It’s been less than a month since the competition and we’re still recovering. The trebuchet is parked behind the barn under an enormous tarp, which is unlikely to survive the winter. Hopefully, the trebuchet fairs better than the tarp. We’re still thrilled with our performance at the competition this year, but the planning has already started for next year. The to-do list is growing with tasks to fix all the issues we had this year.
First on the list is a new sling. Our sling was the only part of the machine that failed this year. The sling ropes were new this year and made from extremely strong Spectra ropes. These ropes proved to have much higher breaking strength than our nylon pouch. The pouch was a carryover from the previous machine. It was never designed to hold our new forces, but was already made. In our rush to get ready for the competition sewing a new pouch fell off the to-do list. Next year we’ll make a pouch from the same material we are using for the sling ropes. We’ll also be adding better strain relief the end where the pouch attaches to the ropes.
Second on the list are stronger winches. Our current winches were designed to lift 2000 pounds with the cable doubled up through a pulley. We were planning on using two to lift the 4000 pound counterweight, but they proved inadequate. We didn’t account for friction in the cables as they weaved through all the pulleys. We also added nearly 100 feet of cable to each winch over the way they came from the factory. The extra cable increases the diameter of the cable spool, which reduced our lifting force. Our options for next year are either to use more pulleys to gain some mechanical advantage our find stronger winches. We already have several pulleys and added more will only complicate the design. We also may not have room to add the extra cable we’d need to the winches. Finding stronger winches is not a trivial task. The winches this year were powered by 120Vac and had a good duty cycle rating. Many stronger winches are available, but they are designed to pull vehicles. These winches can provide very high pulling forces, but are usually powered from 12V batteries. These winches are also not designed for continuous operation. Lifting several tons 35 feet into the air is much harder on a winch than providing a short tug to get a vehicle out of a ditch. We’ll be considering moving towards heavy duty hydraulic winches but they come with their own set of issues.
Next on the list is the arm. Our arm this year weighed about 500 pounds. Most of the weight is concentrated near the base, but we still have significant weight out to the tip. We used steel for the arm this year since it was available and we needed to save time. For next year we’d like to make a modular arm. We’ll keep a very strong steel base, but instead of steel towards the tip, we’ll use bolt on aluminum extensions. This should save considerable weight. The arm weight plays a huge role in the performance of the trebuchet, and reducing the weight should offer big performance gains.
We also need to implement some simple fixes to make cocking and loading more reliable. We had several snags this year. These could be easily avoided with better cable routing and some guides to keep things from getting tangled.
The most time consuming task for next year will be practicing. We performed very well this year for our first few shots, but we know the trebuchet has a lot more potential. We need to do some fine tuning and get more shots in to see what the machine is really capable of. By competition time next year, we plan to be consistently throwing record breaking shots.
Nashua Telegraph Follow Up Article
November 11th, 2010Area Hurlers Squash Competition
By JAKE BERRY and DAVID BROOKS
Staff Writers
Two Nashua-area pumpkin hurlers didn’t break any records this month at the World Championship Punkin Chunkin contest. But they did steal the show, the teams said, as they returned from the 25th annual competition, held in Bridgeville, Del.
The American Chunker, an air cannon from Nashua, placed fourth in the competition’s air cannon division, reaching 3,535 feet in its second attempt. But the company drew more attention for its sleek design and corporate sponsorship from the Shipyard Brewery in Portsmouth.
“If there was a category for best in show, we would have won that hands down,” said Brian Labrie, who oversaw development and construction of the $100,000 cannon.
And in the trebuchet division, the Launch-Ness Monster, built by a team from Merrimack, placed sixth after its best shot, of 1,618 feet, was disqualified due to a technical issue. But the 34-foot-tall, 11,000-pound machine garnered far more praise for its advanced, steel-framed design, said lead engineer Jay Goodell.
Goodell and his co-designer Michael Powers, both 27, incorporated several elements, including a rolling throwing arm and a curved weight track, that have never before been used in pumpkin chunking competition, they said.
“The machine was a huge hit down there,” Goodell said of the device, more mechanical than Medieval. “We got a lot of attention and respect from other teams just because the design was so unique … We really stood out on the line down there.”
Made of steel and concrete, the machine’s design held up better than the Delaware weather did, Goodell said Wednesday.
After arriving late Wednesday night, strong rains created a mud pit on the competition field, preventing Goodell and his team, about 30 friends and colleagues, from applying the finishing touches and conducting the test runs. So the first round of the competition, held Friday, proved to be the Monster’s first throw ever, landing at 1,097 feet.
“We got the safety inspection about an hour before the shot, and we just pulled the trigger,” Goodell said. “We didn’t have the entire weight on it. It worked pretty well.”
The following day, the team applied more weight, increasing its distance to 1,265 feet. But on Sunday, for the final throw, the team was forced to apply only half the available weight because of wind conditions.
At half weight, the shot reached the 1,618 feet mark – about 400 feet short of the world record of 2,034 feet, reached last year by Yankee Siege of Greenfield. But judges quickly disqualified the final shot because of a piece of the machine’s pouch that broke, projecting forward.
“Obviously it would have been nice if all those things worked out … but we should have a real good shot at the record next year,” Goodell said. “We came pretty close this time with a half-power shot and a bad angle. We think we’ll be right there next time.”
The American Chunker, the air cannon from Nashua, suffered no such technical difficulties, said Labrie, who traveled with nearly 40 people and his six-person team.
If the title had been calculated differently – based on the average of the three competitive shots instead of merely the longest of the three – then Nashua’s American Chunker would have taken the title.
Unofficially, the 10,000-pound cannon’s best shot traveled 3,535 feet, which is 220 feet less than the winning shot by an all-female team operating a cannon called Hormone Blaster. That put them fifth overall, out of 27 air cannons.
“Mechanically it was perfect … We had no pumpkin pie,” said Labrie, using the pumpkin-chucking slang for the common problem of pumpkins bursting in mid-air due to the pressures encountered leaving the barrel at several hundred mph.
The average of American Chunker’s three shots was higher than the average of any other competitor, partly because three of the four cannons that beat it had at least one “pumpkin pie” event.
American Chunker is powered by a 680-gallon air tank, thick enough to hold air pressurized to as much 300 pounds per square inch. A 100-foot-long barrel of irrigation pipe is attached to one end, with a breech near the tank into which a spherical gourd can be loaded.
As for next year, Labrie said the big issue will be to increase muzzle velocity without destroying the gourd.
“That’s what we’ll be working on,” he said.
New Hampshire had a third entry in the contest: Tired Iron, a full-sized trebuchet from Hancock, built by one of the men who helped build the record-holding Yankee Siege trebuchet in Greenfield. Unofficially, it came in fifth, just behind the Launch-Ness Monster.
Yankee Siege, which won the title several times, was retired this year by its owner, Steve Siegars.
Jake Berry can be reached at 594-6402 or jberry@nashuatelegraph.com. David Brooks can be reached at 594-5831 or dbrooks@nashuatelegraph.com.
Departure
November 8th, 2010After a long weekend of competition, it was hard to muster the effort to pack up and go home. We couldn’t stay there though. Bring the machine down and putting it all back on the trailers went quickly. We were on the road by the early afternoon and making our way back to NH.
World Championship Punkin Chunkin 2010 Sunday
November 7th, 2010For the final day of competition we had to go all out. We’d have a full year to repair anything that broke. Saturday we fired for the first time with counterweights. For Sunday we planned to load all the weight we had and nearly double our power. We were still disappointed with the distance from Saturday’s shot. We went back to the simulations and high speed videos to see where our energy was ending up. We discovered some interference with the arm and the fulcrum tower. We’d hoped to have a perfectly straight arm and delrin slides in the fulcrum tower to keep everything lined up laterally, but we didn’t have the time to get everything worked out. We’d be using some plastic furniture moving sliders we bought on clearance the day before we left, but nothing held them in place. When we cocked or fired the slides would shift out of place and fall out of the machine. For Sunday’s shot we decided to keep some of the sliders in place, but also cover the entire arm in grease. With a generous coating of grease down the sides of the arm, things seemed to be moving better. We spent the rest of the morning adding 24 concrete blocks to the counterweight. That brought our total counterweight up to around 4000 pounds. We’d be working with some serious power for our final shot. Each concrete block was cast as a solid foot wide square, six inches tall. We left a 3/4″ diameter hole in the center that would slide over threaded rods on the counterweight hanger. Getting the first blocks on was fairly easy, but as we started putting more on they began to interfere with each other.
We needed to make a lot of “adjustments” to the blocks with a hammer, to chip off parts to get everything to fit. The last of the air cannons had fired and we were still working to add more weight. We finally added the rest of the blocks and prepared to cock the trebuchet. Despite all the issues we’d had on the previous attempts, with hooks not releasing and cables getting stuck, we decided not to make any changes. We had already worked out a process for getting everything set up and didn’t want to introduce any new problems by making changes. We started pulling the counterweight up with both winches clearly straining under the increased load. As the counterweight hanger started to go vertical the winches stopped. Our borrow generator wasn’t keeping up. We quickly grabbed another from our other neighbors, Medieval Postal Service. We started going up, but again the winches stopped. The generators were still running but the winches weren’t going to go any further with all the weight. They were almost to the trebuchets by now. We quickly scrambled to remove some of the counterweights and lighten the load on the winches. We dropped off four of the blocks and gave the winches another chance. The cables tightened and the counterweight began to climb but again, the winches died. We still needed to drop more weight. Another four blocks were removed. This time, we had to cut the threaded rod completely off one side. The rod had been marred when the blocks were put on and backing the nuts off was going to take too long. A quick cut with the angle grinder was a much better option. We’d now removed a third of the extra counterweight we spent all morning putting on. We gave the winches another chance. Again, they stalled just as the counterweight hanger went vertical. We were running out of time and needed to get the machine cocked, since we knew we’d likely run into more snags during the process. We started pulling two of the larger rods from the counterweight hanger, to remove a total of 8 more blocks. These blocks were jammed by other blocks that had been added after and the rods wouldn’t budge. With time running out, we started smashing away the blocks with the sledge hammer. We had to shatter a few blocks, but the rods freed up, and we could remove the weights. We had now removed 16 blocks, most of the weight we’d spent so much time adding in the morning. This time the winches strained and whined, but kept moving. The counterweight was slowly climbing towards to the top of the machine. We’d taken off enough weight to bring us back down to less than 2200 pounds, only slightly more than on Saturday. The weight reached the top and gracefully transitioned onto the trigger cables, rocking the machine as they caught. We got to work releasing the hooks and lower the tower. We had the same issues as before, but now knew how to deal with them. Everything went into place and we were cocked. Even with the lightened counterweight we still had an advantage for this shot. The Pumpkin Hammer team had donated a perfect calabaza pumpkin to us. This pumpkin was still the same weight as we used on previous shots but much denser. It was also almost a perfect shape. The smaller diameter and shape would greatly cut down on our aerodynamic drag. The pumpkin was loaded with what seemed like only moments to spare but there was a hold-up on the line. Pumpkin Hammer’s final shot didn’t go well. The shot had gone shorter than their best shot on Friday, which still had the in first place. There was a crowd of officials discussing whether the final shot needed to be disqualified. Apparently, the firing pin an the tip of the arm had come free and flown forward from the machine. The rules state that no part of the machine, no matter how small, can cross the firing line. If the pin went forwards, the shot wouldn’t count. Eventually, they found the pin, in front of the machine. They continued down the line to Medieval Postal Service and we were on deck. Medieval Postal service had a great shot, over 1300 feet, jumping us in the standings.
It was finally our turn on the firing line. Despite the challenges getting cocked, we were ready. The trigger was pulled and the trebuchet went into action. Everything moved smoothly and fast, no crashing counterweights, no collapsing steel, no splattered pumpkins. The pumpkin left the machine and soared out of sight. I’d never lost sight of the pumpkin before, so we knew this shot was really moving.
Something had gone wrong though. The trajectory was way off. We threw much higher than the previous shots. The pumpkin went in the right direction, but all that extra height was robbing valuable distance. Then one of the sling ropes landed on the ground in front of the machine. We knew we were disqualified. Our best shot ever, wasn’t going to count. We looked back at the machine to see the pumpkin pouch, ripped and tattered, swinging from the end of the arm. The extra grease and counterweights had done their job, but all the extra speed had blown out the nylon webbing holding the pumpkin. When the pouch tore, our pumpkin released, explaining the high release angle. It also meant we hadn’t even gotten up to speed yet. The pumpkin finally landed 1618.42 feet from the machine, but our Saturday distance would be the official best for the competition. It was disappointing to have to ignore a great shot for the standings but we knew we had shown what we were capable of. With some time to test and tune the machine, we were confident we could shatter the current record. We just had to wait another year to prove we could do it.
The weekend was a huge success. We finished building and designing the machine on the field during the competition. We had our first shot ever, on a completely new trebuchet design, in front of a crowd, and it worked! Throughout the weekend, everyone we talked to loved the design. It was something different that hadn’t been tried before and it looked good. The common response from people was that they thought it was collapsing, then magically a pumpkin came out from the wreckage. The linkages were an elegant, although complicated, way to manage an enormous falling counterweight. The arm rolling over a wheel proved to be an effective way to extract huge amounts of energy from the falling weight. We’d also introduced a design that didn’t require dozens of test shots to dial in or require any tuning changes during the weekend, even with wildly varying counterweights and pumpkin masses.
