Delta trike design - constraints and solutions ?

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Sorry to hear of the sphincter-factor-9 moment. :( That can't have been fun at all.
It does suggest that you need over 50% of the rider-weight somewhere ahead of the rear axle OR every bump the front hits will have you pitching backwards (especially when going up a steep slope and hitting a rock/rut).
yes my concerns also

I think your idea of the BB spar folding backwards for transport has merit for this situation because you can keep the short wheelbase but move your C-of-G more central to the 4 contact points of the wheels.
Maybe , need a new mock-up see below
Better weight distribution and traction all round perhaps?
I am only skating around this setback unless I get some figures ?
So first up put wheels back on front and shove some scales under each wheel in turn , not accurate however it will yeild some figures to start with.

If I resign myself to it sitting on the outside back of the shed I can go from 55" to 66" in length without a problem ?
Paul
 
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So measurements !

First off I measured each wheel not sat on it:-

Original seat position @ emptyFront10kgbathroom scales unknown accuracy
dittoback10kgsame
Original seat position with me sat on itfront11kgwe may have found
dittoback40kgthe problem Houston
Seat move 6" forward with me sat on itfront25kgdigital luggage scale
dittoback36kgdigital luggage scale

So I added 1kg to the weight on the front with the original seat position !
I took a flyer and decided to try 6" further forward [ I can always move it again , it is easy to do ]
Now the figures look better however are they ridable ?

It now looks like this :-


Still not as long as the Python so may still fit inside car with a little tweaking ?



Next up I need to find room for my feet , whilst the pedals now clear the cross beam [ which is actually much to high ] my feet don't as feet hang over the pedals approx 4" forward from pedal centre and 8" back from pedal centre.
Also looking at width ?
Working on the assumption we adopted the EU's 1m width in our terms 39" I really don't want to exceed 36" [ yes sentimentally 1yd ]


So this shows where 1/2 my yard is going
4" for hub width
5" between hub and frame
9" between frame and vehicle centre , the area I occupy.

As the wheel can turn and occupy the full 5" available I should be able to work out the turn angle and from that the turn radius for both a 16" wheel and a 20" wheel.

Talking of wheels I got a pair of 16" for playing around with , and took this picture:-



of course I also had my scales down stairs so it would be foolish not to ?
24" on left with SA hub brake hub = 2kg
20" with steel hub and poor heavy tyre = 1.79kg
16" with Schwalbe tyre steel hub but no inner tube 1.03kg

Food for thought ?
16" wheels if you could suspend all for wheels for less than 1kg per wheel they would be same weight as 24" with no suspension
16" wheels if you could suspend all 4 wheels for less than 0.7kg per wheel they would weigh the same as the 20" wheels with no suspension

Paul
 
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The rear is easy to suspend but the front isn't. You generally add a lot of extra metal to form swing arms or wishbones before you add the suspension units. I'm not saying don't suspend it, just that it'll not likely be just 1 kg a corner extra. About the only time I've seen a front suspended and being both useful and light is using grp leaf springs. The only other system I can think of that's not adding a lot of metal is a coil on the bottom of the uprights which doesn't give much suspension but may give a sloppy kingpin feel. Old Morgans used a sliding kingpin. Swing arms would keep the weight down but will pay havoc on the geometry as it moves. Wishbones are great but heavy. Even with the new seat position you're still nearer the back so front suspension is less useful than rear.

You may need more than 5"+ 2" to centre of hub for the fronts to swing even if you have perfect centre point steering. 55 degrees steering (quite achievable) on the inner wheel will require 8.2" for a 20" wheel. If you go 16" then 6.6" will do (again including the 2" in the hub). Your current setup will give 61 degrees with a 16" but only 44 degrees with 20". In other words you need more room for the wheels than you are allowing if using 20". If using 16" it's fine. These calculations assume the chassis meets the tyre at the furthest point of the tyre. If the chassis is higher or lower than that then extra steering is possible. The furthest point of a turned tyre is usually immediately below half it's diameter due to the effect of caster.
 
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You have 9" showing as half your space. Are you only 18" wide or are you allowing for the width of the frame? ie assuming 1.5" tubing you would have 21" of space in your drawing if you are entirely above the frame. If you are genuinely only needing 18" then you can reduce the width by the width of the chassis beams.
 
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The rear is easy to suspend but the front isn't. You generally add a lot of extra metal to form swing arms or wishbones before you add the suspension units. I'm not saying don't suspend it, just that it'll not likely be just 1 kg a corner extra. About the only time I've seen a front suspended and being both useful and light is using grp leaf springs. The only other system I can think of that's not adding a lot of metal is a coil on the bottom of the uprights which doesn't give much suspension but may give a sloppy kingpin feel. Old Morgans used a sliding kingpin. Swing arms would keep the weight down but will pay havoc on the geometry as it moves. Wishbones are great but heavy. Even with the new seat position you're still nearer the back so front suspension is less useful than rear.
Yes only looking at something very simple like this ?



You may need more than 5"+ 2" to centre of hub for the fronts to swing even if you have perfect centre point steering. 55 degrees steering (quite achievable) on the inner wheel will require 8.2" for a 20" wheel. If you go 16" then 6.6" will do (again including the 2" in the hub). Your current setup will give 61 degrees with a 16" but only 44 degrees with 20". In other words you need more room for the wheels than you are allowing if using 20".
Yes it is all very tight at the moment :D

If using 16" it's fine. These calculations assume the chassis meets the tyre at the furthest point of the tyre. If the chassis is higher or lower than that then extra steering is possible. The furthest point of a turned tyre is usually immediately below half it's diameter due to the effect of caster.
A mono boom should be able to do that , however a peripheral frame maybe not ?

Paul
 
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You have 9" showing as half your space. Are you only 18" wide or are you allowing for the width of the frame? ie assuming 1.5" tubing you would have 21" of space in your drawing if you are entirely above the frame. If you are genuinely only needing 18" then you can reduce the width by the width of the chassis beams.
Always asking awkward questions :D keep them coming
I have not yet though of the frame , a mono boom at this point would be better , however for bodywork fastening a peripheral frame could be better.



This should clear the legs and give maximum steering , however will it be enough ?


Have some way to go yet ....

Paul
 
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The sliding kingpin design in the picture must have the lower rod end below the nut of the kingpin or it won't slide. This can mean that slop I mentioned as the rod end is not bolted hard to the bolt. Neither is the top one for that matter. The slop won't be much and may be acceptable. Probably one of the better sliding kingpin designs though that particular one has ignored centre point. Will need a regular grease as it's open to the elements and rod ends aren't ideal linear bearings.
 
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Found a kids bike last night whilst dog walking , confirmed it was out for the scrap man and hurried home with it .......

GUTTED to find it had 18" wheels !!!

why oh why do we need all these not standard sizes ?
  • 12in wheels – ages 2+ These are the small push-along bikes that were made popular in Scandinavia. ...
  • 14in/16in wheels – ages 3+ Once they've mastered a balance bike, it's time for your child to move onto a bike with proper pedals. ...
  • 20in wheels – ages 6+ ...
  • 24in wheels – ages 8+ ...
  • 26in wheels – ages 10+ ...
They don't even list in this table I found on the net !!!

Also to add insult to injury as with a lot of these it looks unused/abused just been sat in a garage I reckon for a couple of years.

Paul
 
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So thinking that although the wooden mock-up had taught me a lot it was never going to be pedalled I wondered if there was another way of getting a very quick quad to try the idea out ?
Whilst there are some examples of quads built from 2 bicycles on the net I could not find a recumbent one ?

I remembered DaleRider had kindly given me a kids 20" wheeled bike that had the same w/b as the proposed quad @ 30" , up in the garage loft were 3 NOS BMX frames and matching forks could they be pressed into service ?

They are posed @ approx 31" tyre centres.
Now it's a real bummer as these are 38" wheel base , maybe to big for the job ?


If they were to be joined in 3 places :-
Head tubes - BB [ front seat mount seat mount ] - rear axle area [ rear seat mount ]
Would I have 1/3 of a quad the other 2/3rds being steering and propulsion ?
[ I would probably add a 4th join coming out of the seat tubes and curving behind the seat ]



There certainly seems a lot less work than starting from scratch , however would I ride it much ?
Suppose that depends whether it get's through the barriers or not ? back to the annoying 38" w/b again !!! grrrrrrr

Paul
 
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So I pressed on with the BMX folly...

I built a rectangular inner frame and clamped the wheels to that , the head tubes were @ about 89' so close enough for rock and roll.
I then joined the 2 frames with a piece of timber with the corners planed off that was a hammered fit inside the BB then added 2 brackets to the rear axle nuts and joined them with a piece of floor boarding. The previous quad main frame was rescued as if I lined it up with the rear wheel axles it had fixing holes for the seat putting it in the right place [ well for a 30" w/b the place was right ]


I was then able to gingerly sit on it , all seemed well till I tried to pedal it !
The frames would have to be joined by replacing the wood with steel and also welding a piece across the head tubes , that would occupy the same space as was swept by my knees DOH.
Yes of course I could make it curve forward to miss the knees , I would also need a piece coming down from that to hold the BB in place and a quick build unravelled before my eyes.
So next up is to measure the available steering angle to predict the turning radius and if I brace the head tubes it may stand being pushed outside ?
Then it is back to thinking.....
Paul
 
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Almost dismantled it when I remember I was to measure the steering angle , almost just going through the motions I drew a line under the main boom and got out the angle finder.
very difficult to get it at right angles to the wheel ....

But hey look at the angle !


Strewth it's over 40' !!! according to DannyC's spreadsheet for a 38" w/b 40' equals a radius of 45" un-flipping believable so there must be a catch ?
No leg clearance maybe ?


Nope clearance both sides , and looks like quite a bit despite not having tyres on ?
Current tyre centres are at 31" so next I want to shave off 3" to make that 28" and see if it is still as impressive.
What a roller coaster ....
Paul
 
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OK so onto Mock-up Quad #3 [ the last [ I hope !!!]]


Just got the rear half done so far , wood has been cut to 1.5" [ 40mm ] sq to better represent frame tubing and for the time being left long at the back.
I aimed for 30" track , however failed to measure it , blame the cold !


Made some attempt to raise pedals they are at least at seat base height , main boom is 10.75" from ground @ centre of 20" wheels .


plenty of room for mechanics and/or luggage , red rear seat stays will actually be as close to seat as possible to remove them from this area.


If I chose a forward jackshaft [ for simplicity/neatness ] there is plenty of room for two chains to run either side of the seat ?

This passed the first test , I sat on it feet forward and attempted to tip myself over backwards as in post #117 and failed miserably so least I have the seat in the right place.:D

Next up
Better kingpins with centre point steering
Front cross member
turning circle

Paul
 
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Ok so mock-up front cross member clamped with 5" between ground and it's underside ?


2 lines on frame are roughly were cross member was on last mock-up , I tried cross member at rear line [ marked 1 ] and found plenty of clearance for heels [ wearing clip in shoes and cleated pedals ] so this is rear limit for cross member.
So moved cross member forward to position 2 , heels miss it by a whisper so I have now found the front limit of it's mounting points.



Now I guessed I wanted 1" - 1.5" clearance [ cross member this much further back ] and so propped up a wheel @ 30" wheel base and would you believe it is only about 1.5" rear of far forward position of cross member !!!



The wheel axle is also only about 3" above cross member , just enough room for a kingpin me thinks [ hopes :D]
So next up we want some kingpin mock-up that works much better than last one !

Paul
 
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Ok impossible to cobble up a kingpin and get the contact patch angle correct just using softwoods wood screws and bolts !
So next best thing ?



get pivot vertical and as close to wheel hub as possible ?
White wood represents cross boom plywood plate pivots on M8 bolt in foreground and takes the 2 x hardwood blocks with it.
Wheel will screw into M14 hole to be drilled in red circle and spaced to just rotate, M8 pivot will be done up tight and plywood forced to turn till wheel almost brushes legs then locked to white beam with a wood screw.

Should hold enough for pushing around the garden testing me thinks ?

Paul
 
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Nearly there , however identified a shopping bag full of ' issues ' that need remedial action ?


Just dragged it out and applied some lock to both wheels , they are not connected [ well yet anyway ]
fault 1 ) You can see the back is sagging , one of the things that needs attention.
fault 2 ) I found I was unable to push it as there was no clearance between the white soft wood cross bar and the wheels spokes DOH !!


left and right clearance as picture above [ still plenty ] so decided to measure the angles , best I could do were some chalk lines ...


Strewth that is a lot of degree's ! and that was not at the limit , wonder if I can achieve this once I have figured out a linkage ?


Obligatory comparison , seats lined up Python wheel base 10" greater than quad's at about 31" in above picture , quad pedals a little lower.

Dan's spread sheet predicts the following turning radius:-

wheel anglew/b 31"w/b 32"w/b 33"w/b 34"w/b 35"
30'54"55"57"59"61"
40'37"38"39"41"42"
At the current 31" w/b I think it will fit in my car , especially if the BB can swivel up over the boom.
Now I can get more wheel base by extending the ends of the boom forward to reach the kingpin , to stop the trike being longer in the car I could turn the wheels once in to 45' of turning which has the potential to shorten the trike by 5" meaning the w/b could be extended out to at least 34"-36" whilst only losing a little turning radius.
I wonder if this would increase the ride quality ?

Paul
 
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Dan's spread sheet predicts the following turning radius:-
But this spreadsheet is only operating an established/published formula and needs testing with a real (mock-up) trike to get a Plan-Vs.-Actual comparison. :)
 
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But this spreadsheet is only operating an established/published formula and needs testing with a real (mock-up) trike to get a Plan-Vs.-Actual comparison. :)
Well I did use the word ' predict ' and am working towards a test bed ?
Can we calculate the different radius needed for ackerman if we know one wheel's turning ability ?
i.e if I established that the inner wheel could turn through 45' without hitting me what would be the angle needed by the outer wheel ?

Paul
 
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Would need the track and wheelbase to model it.
Popshot

thanks for the offer , in the picture it is w/b 31" track 31" [ well as near as I can get ! ]
I was hoping to nudge DannyC to make a spreadsheet [ he really likes that :) ]

Paul
 
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