[python] Re: (No From: Jaculus <jaculusbent@xxxxxxxxx>
Being a bit into rope climbing I see some design flaws in your rope set up.
First of all your rope goes over some pretty sharp metal edges, and a
threaded bolt. Both of these increase wear and tear a lot (especialy
when there is a lot of movement on those spots as I assume there is,
judging from the photo’s).
Then there is the issue of weakening a rope with knots and alike. As a
rule of thumb you can say the tighter the bend of the rope in a knot
is the more it weakens the rope. This does also apply for places where
the is no knot, but only a bend or an angle, like at the metal edges
in your pictures.
An other point, two "150 kg lines" (I suppose you mean two 1500 N
lines) do not ad up to a "300 kg connection" it will still be a "150
kg connection", because the changing loads will be on just 1 of the
two lines in certain moments.
Then the knot used: please keep it simple, improvising in knots rarely
ever helps. There are plenty of good knots, but to avoiid confusion
stick to simple ones. I would advise you to keep to the following 4
knots:
- (Double)figure of eight knot. (to thicken rope or make loops at the
end of rope)
- Alpine butterfly. (for loops in the middle of rope)
- Double fishermans knot. (to join two ropes)
- Clove hitch combined with a figure of eight knot on the lose end.
(to attach rope to a piece of wood/metal etc.)
Never have a knot in another knot or in a bend of the rope. And
remember the rule: Keep It Simple Stupid!
Jaculus
2011/9/19 dirk@xxxxxxxxxx <dirk@xxxxxxxxxx>:
> Hi Patrick,
>
> unfortunately, i don't have a link i can point to, but paragliders have the
> "knot issue" as well. There are certains knots that introduce far less strain
> into the strings than others do. Some can be reopened while others cannot.
>
> Greetings,
> DirkS
>
>
> Patrick van Gompel <patrick_van_gompel@xxxxxxxxxxx> hat am 18. September 2011
> um
> 17:44 geschrieben:
>
>>
>> Wow Henry, that looks like a nasty slide...
>>
>> I did cycle quite a bit the last few days and although everything seemed to
>> go
>> fine, I must warn people for the big loads going from swing arm to rocker arm
>> for the jetrike. Today I snapped a double 150kg line! I did have the trailer
>> behind the trike, but it was only loaded for maybe 50kg and not really
>> pushing
>> much on the hook (balanced trailer). I drove into a hole on a dirt road
>> followed by a bump and the primary line and the safety line of the left side
>> snapped. The rear hit the ground and dug into the dirt. The bike is ok and so
>> am I, but I am glad that this didn't happen on the road with traffic behind
>> me. So, a 300kg strong link between rocker arm and swing arm is not enough
>> for
>> my setup. I think I need to go at least twice as high, but preferably up to 1
>> ton for safety margin. If I were to use quality rod ends, that would mean M12
>> for size. This size rod ends are quite big and heavy (I use them for the
>> pivot
>> point) and wouldn't like them for the links. I need to find some 500kg
>> strings.... I might try some 5mm hunting rope. Polypropylene is not as good
>> as
>> dyneema, but 5mm is quite a bit thicker than I have now.
>>
>> Anyway, before things broke down, I had a great 75km cycling trip. First, the
>> lines seemed to be damaged a bit by the nut when the rocker arm turned. I
>> fixed this provisionally with a loop under the attached line around the bolt.
>> See: http://cycle.free-creativity.com/images/string_rockerarm.jpg This seemed
>> to work fine.
>> The other end was durable enough and I left it the way it was:
>> http://cycle.free-creativity.com/images/string_swingarm.jpg
>> That setup was nearly wear free for 150km. So I think that pulleys or the
>> like
>> are not really needed. A simple bolt will do.
>> Last Friday I went for a garden job with the trailer (2x20km trip). Including
>> my garden tools the trailer weighs about 50kg and the trike seemed to benefit
>> from the extra load on the hook/rear. Though, the ride felt a bit more bumpy.
>> Handling was excellent, but a bit slower than without trailer. Going to the
>> dump site with garden waste of a total of about 100kg, the trike was still
>> stable and ok to handle, but tight cornering needed more leaning it seemed.
>> Braking with this load with only having a front brake, still felt safe. At
>> least, a test by pulling hard on the brake didn't do weird things to
>> steering/balance or anything.
>>
>>
>> Side note; I just read some stuff about strings/ropes on the internet.
>> Mentioned are safety margins of 5 times the applied load. That means at least
>> 1,5 tons for me! And a knot reduces the strenght to 50%. O dear... I'd better
>> take the 7mm hunting rope.
>>
>> Good hunting,
>> Patrick
>>
>>
>> From: whpthomas@xxxxxxxxx
>> To: python@xxxxxxxxxxxxx
>> Subject: [python] Re: Pythonjetrike
>> Date: Thu, 15 Sep 2011 12:57:01 +1000
>>
>> Hi Patrick,
>> I concur with your observations. A loss of traction from braking or cornering
>> too hard is a real hazard with tilting delta trikes. Having crashed my
>> Jetrike
>> on one such occasion, once the front wheel went down, I had no time to
>> recover. I took the bike back later and took this photo. You can see the
>> skid.
>> The wider area at the bottom is where my shin hit the ground and the painful
>> gravel rash began :(
>> Best regards to everyone.
>> -h
>> Henry Thomas
>> On 15/09/2011, at 3:46 AM, Patrick van Gompel wrote:I fixed the wheel today
>> and did some more testing.
>> With the fixed rocker arm and strings to the swing arms it works sweet. The
>> simple setup of bolts and nuts as pivot points for the strings is working
>> fine, although I probably need to adjust it a bit for better durability.
>> I did a bunch of heavy brake runs. If the pavement is ok and I brake hard,
>> the
>> bike stays stable, but it is hard to stay in the seat. If you go a bit
>> forward
>> out of the seat the back of the bike will come loose. If I manage to stay
>> put,
>> the front wheel did slip sometimes. But this is at maximum braking and is
>> quite a bit more than I can achieve on my mountainbike. The weak point of a
>> leaning delta trike is when the front wheel is really blocked by the brake
>> and
>> it slips for a longer time. When going straight over a field of grass while
>> slipping, makes the trike rather hard to handle (leaning and steering). When
>> going over dirt/gravel and going into a corner while braking, the front wheel
>> breaks out, which makes the rider fall into the corner. When this happens it
>> seems unlikely to recover from it, although you can put your feet down to
>> prevent falling to the ground. But, compared to a mountainbike when only
>> applying the front brake, the performance is likely the same. So for slippery
>> surfaces I do need rear brakes on my trike.
>> I tested how the trike reacted when leaning to the front. The trike becomes
>> unridable as soon as a shift in leaning to the right or left is needed. This
>> might be because you don't have the grip of the seat anymore to control the
>> leaning, but possibly the changed CoG has the most impact.
>> I changed the steering pivot angle: going up in degrees makes the trike more
>> relaxing to ride and going down makes it more aggressive. I think that the
>> wheelflop had the most impact on this. 65-70 degrees seems like a sweet spot
>> to me.
>> I tested the use of the handlebar for leaning. It is only usefull for
>> stopping
>> and keeping the feet on the pedals. Steering the leaning when cycling didn't
>> feel right and was even dangerous when really trying to.
>>
>> All in all I tested quite a few settings, but it's really hard to get an idea
>> what does what. There are so many variables and while you adjust one, a few
>> others might change too. So if I would make another trike, it would be hard
>> to
>> optimize the design without changing the feel of the ride.
>> For example, I am still puzzled how the steering interacts with the leaning.
>> It is a bit hard to see how the trike leans when riding on it, but with the
>> handle bar for leaning I could feel which way and how much is was going.
>> Steering and leaning seems to go together like a natural thing. Even when I
>> tried to stay in the same position on my seat, the bike still seemed to lean
>> with every corner. I can think about reasons to justify this, but honestly I
>> have no clue.
>>
>> Anyway, I proved it is possible to crash the delta trike, but the feel and
>> stability is really what I wished for when I started to think about a trike.
>> Thanks again to Jürgen and Henry for sharing those great ideas!
>> Now I need some durability tests and get a fully loaded trailer hooked...
>>
>> Happy cycling,
>> Patrick
>>
>>
>
> http://dirk.steuwer.de
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