HyperDynamic.co.uk

Scrapheap Challenge

time dedicated:100s of hours

location: Luton & Hitchin, Uk

year: 2007

Scrapheap Challenge index

Build Diary

Competition Diary

Preparation Diary

4/5/7 See the advert on the scrapheap website

5/5/7 request info

8/5/7 receive info

16-18/5/7 create first CAD model

18/5/7     Fill in entry form. We struggle with the name but go for 'the leading edge. After spending 2 hours filling the form in, word crashes and I have to redo it. Dan had left work by then so I  had to guess all his details :-('

28/5/7 created energy model - ~10000J for 10s ET 40000 for 6s ET (1 bungee ~20000J)

8/6/7 Get the call & told mark. Serena of RDF says they don't like the name - not the right format. She'll be in regular contact and want to come to interview us.

12/6/7 Told Dan

20/6/7 Receive my paperwork. Mark's not arrived. Dan’s not arrived - probably something to do with putting the wrong address on the paperwork!

27/6/5 Arrange interview

First meeting. Mark suggests we do it for charity. We all agree and decide to do it for a cancer charity. Mark says he might be able to get hold of some aluminium ladders for the frame - great idea!

28/6/5 Mark says he can't get hold of free ladders. Discuss use of ali frame sat around at work. did roll tests in evening- 15mph gives 100m of roll but last 1/3 very slow

28 & 29/6/5 Send out emails for bungy. Mark finds out we can't use work for filming. - will have to be his workshop, but we can't use that till late.

30/6/7 added roll test results to energy model. Realised gear ratios are very high. Realised peddling is beneficial unless we have the power of full bungee cords. Realised we need 3 times as much bungee as we currently have just to make it 100m under stored energy alone (~90s)

1/7/7 Realised high gearing means we could make it shorter.

Trials & planning

Ideas Board

2/7/7 developed the cad model

Chassis made from an aluminium ladder

+ light, aerodynamic, quick and might give us some suspension.

-might be difficult to get hold of as scrap, not very stiff, not very strong, no roll protection

Adapted aluminium frame

+ very stiff, very strong, safe

-very heavy, needs modifiying, we need permission to 'borrow' it, high aerodrag

3/7/7 Stared at the sun for ½ hour. Did trials while they filmed + asked questions.

Did the white board thing. Started with facts. They liked the petrol energy comparison. They had to hurry us along because we got into it too much! Did loads of maths. I got one wrong by a factor of ten (100/2*100 /= 50000) and another 10% out L. If they spot it I’ll look like a right idiot.

They got me grinding and Dan welding and asked us questions like win or fun & expectations. We talked over each other a lot and probably spoilt it. Next we laid out the bits we’d got & I put a helmet on and held a steering wheel, mocking up the proposed layout. They also filmed me explaining the CAD model.

- other thoughts

                                -how much traction can we get out of the rear tyres.

                                -what DIA is bungee cord

                                - What load can we expect bike chains to be able to take?

                                - What are the actual dimensions of the ali frame.

                                -how do you calculate buckling loads?

1-8/7/7 Plan: collect most of the parts & polish design

Actual:

2/7/8 emailed lots of companies and got no replies.

5/7/8 Tim allowed us to use the ali frame. gave Dan contact numbers for bungee companies.

6/7/8 , Dan rings the numbers I gave him. He didn’t manage to actually talk to any bungee companies, only leisure centres – no luck getting bungee.

Did some buckling load and weight calcs on Marks steel tube and the ali frame. it looks like we need some sort of truss if we are going with a strong bungee.

6/7/7 Mark rang the Luton papers – they want an exclusive! They’re very excited and will send a photographer on Sunday. Mark M rang Hitchin comet – they will ring next week. Serena rang. Raising money ok. No logos. Tried to get some bungee for us from their suppliers – they couldn’t and it was very expensive. They will look on their scrapheap on Monday for us.

7/7/7 researched some questions

                                -how much traction can we get out of the rear tyres.

                                                Coefficient is 0.7 (dry) 0.4 (wet) so traction is ~32 - 56kg

                                -what DIA is bungee cord

                                                3 – 5 x 5/8”

                                - what strength can we expect bike chains to be able to take

                                                Rated at 200 kgf (guaranteed) should take 1000kgf

                                -how do you calculate buckling loads?

                                                Derived by my modeling – 3*EI/l^2

                                                From wikipedia – EI*PI^2/l^2

8/7/7 planned: assemble design. More trials

Actual: developed design. Got photos taken by the paper photographer. He suggested talking to somebody at Fenner drives to see if they can help. Mark built a model out of welding rod. Agreed to build the back section in steel and attach the main chassis when we know the loads/length. We made the driver sit behind the rear axle to simplify the chain routing. Elastic now attached straight to a drum on the axle – no freewheel. We struggled with the frame design and axle supports. Went scavenging for pipe clamps for the bearings but only found a plastic chair, some steel angle and some inner tubes. Dan fell in love with the front of a dirtbike/scrambler.

Things we still need:

                -elastic

                -4 bearing supports (50mm pipe clamps)

                -2 more bearings

Did some load tests on the inner tubes at home. Stretches ~ 5 times. Load stress  ~4Mpa (max (about the same as the bungee) The two inner tubes should consume 12kJ. Load measurements suggest ~85% energy release. Bounce test shows only ~50% after one bounce (elastic at least 80%). Also did wheeley calcs. Should be just about ok.

The rod model, assuming one heavy steel tube was the main frame member

proposed front wheel/fork/frame with 30m pink elastic in foreground (background: 2 bike frames we might use + the rear axle attached to the rear wheels)

Me & Dan's Haul after going for a scrounge round two of Luton's industrial estates - Two van tyre inner tubes, a car inner tube, some tyre liners, a plastic chair (background) and a steel frame made from angle Dan Also fell in love with the front fork from a scrambler bike we found but it was way too heavy to use. At one point on the scavenge we thought we were going to get nicked - there were a couple of security cameras on the industrial estate but none of them were pointing our way. we thought it would be ok 'cause we were only getting things out of skips. One of them started barking "YOU ARE BEING RECORDED ON CCTV AND THE POLICE HAVE BEEN ALERTED! YOU ARE BEING RE...." in an automated voice. We laughed to start with, then get worried, then worked out that it was coming from a completely different part of the estate, it was just so loud we thought it was coming from right next to us. The police still haven't caught up with us so I think we're ok :-)

HyperDynamic.co.uk