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PostPosted: March 20, 2018, 5:29 am 
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Joined: March 15, 2018, 6:03 am
Posts: 83
Gentlemen and Ladies (hopefully this isn’t an all-male preserve) I would like to solicit a little basic help, please.

I am designing a ‘reverse-trike’ (which I hope won’t be frowned upon by you 4w guys) and hope to start building this summer - I am currently trying to source some basic items which seem to be in very poor supply in my neck of the jungle... Uprights, especially...!

I enclose two graphics of my vehicle which I hope will clarify my immediate concern.
Attachment:
mangpong-a.jpg
mangpong-a.jpg [ 82.16 KiB | Viewed 1206 times ]

‘mangpong-a’ shows the basic layout, and ‘mangpong-b’ shows the front suspension in more detail. Like most designs the chassis sides converge towards the front, and I have always intended to connect the ‘wishbones’/control arms in line with the chassis sides i.e. at an angle of 8º to the longitudinal axis of the car... This will give a sort of ‘leading’ feature to the wishbones...
Now... although there seems to be nothing fundamentally ‘wrong’ with this layout (perhaps a little harsher reaction to potholes...) I have recently come across a couple of comments online asserting that wishbone mounting brackets should be mounted parallel to the central axis - but I have never seen anybody explain, Why...?

As it is possible to have semi-trailing arms, which immediately contradicts this ‘theory’, maybe it is not completely impossible to have leading arms - especially as they are only at 8º.

I should add that I am hoping to build a car that is aesthetically smooth and smart. Thus I do not want to have any suspension brackets visible outside the bodywork - just the control arms (with the ball-joints hidden), the pushrod (with the suspension inboard and also hidden), and the steering arms.

If I have to have the wishbone connections parallel I will endeavour to position the rearward mounts further inside the bodywork - but this would (I think) create a little extra complication, structurally. It would also then require two little internal ‘bumps’ (covers), the upper, rearward, one of which would be level with my knee, and the other level with my ankle - and there isn’t too much space in this area as it is...
Attachment:
MangPong-b.jpg
MangPong-b.jpg [ 113.49 KiB | Viewed 1206 times ]

So, simple question (but please make your answers as complex as you like): Is it really essential to have the mounting points parallel to the car’s central axis...? and if I don’t do this, what can I expect to go wrong...?
_____

Part 2: I would also appreciate some assistance in deciding the diameter of the wishbone struts. Again, for aesthetics, I would like to have these as small as possible. Each individual arm will be straight. Also, am I best to use solid bar and drill & tap to take the ball-joints, or use thick-wall tubing and tap that, or insert a threaded section. I imagine 1/2” OD would be too small but 1” would be too ugly, to my eye... The perpendicular arm length is about 11”, and the lower trailing arm is about 17”... Any comments would be appreciated.
_____

I will probably have other questions but, for the moment - That’s All Folks...

mangpong.


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PostPosted: March 20, 2018, 7:10 am 
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Joined: October 19, 2010, 11:57 am
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Location: Waterloo, WI
First, let me say welcome! Trikes (and pretty much any kind of build) are certainly welcome here. I'm assuming you have already discovered robbovius' B-3? My own project is aiming to be a reverse trike as well.

Second, regarding the suspension layout, I might point you one of my favorite trikes, the sub3wheeler. It looks like their original page has finally gone dead but you can still find plenty of pictures around. Slim tubes and pivots not parallel to the main axis of the vehicle.

Third, just because I think it is another well done trike that might be similar to what you're thinking, check out the Spartan trike on the reversetrike boards.

Finally, it looks like you've posted the same inquiry in multiple areas. I'd suggest pick one subsection and stick with it. If you start each day with the "view active topics" all the lively stuff floats to the top anyway! :cheers:

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PostPosted: March 20, 2018, 8:01 am 
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Joined: March 15, 2018, 6:03 am
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Hello Keith
Many thanks for your speedy response, and generous welcome.
I have just this moment finished three days of working through the ‘B-3’ YouTube vlogs... (Dragging the body out of the cellar... very Draculanian... lol.)

I will certainly check out the others you mention. I'm very new at posting on web fora and probably made a mistake with the first post. I think here is probably the better option but I cannot find a way to delete the other one...

As an incidental, as you’ve been here for a while, do you have any idea why some builds take so long to first test-drive...? Some guys seem to be at it for five or even ten years. As an ‘old-timer’ I'm slightly worried that I might not be around to enjoy the fruits of my labours... lol.

My theory is that many builders work alone (which is not efficient) and most have a ‘day-job’ (which can’t be helped) - being long since retired I am in a position to spend every day on the build so, to be realistic, if I manage 5-6 days/week, 40-50 hours/week, and utilise some local labour as and when (especially for electrics - my weak point...), can I seriously consider one year - give or take...
No, don’t laugh... ’Tis wicked to mock the afflicted...

I have access to some junior (apprentice-type) technicians locally who might be keen, especially with a little reimbursement...

Many thanks, Mangpong.


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PostPosted: March 20, 2018, 9:13 am 
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Joined: June 5, 2016, 7:03 am
Posts: 215
Location: ontario
mangpong.[/quote]

To your question about parallel wishbone mounting brackets:

I am one of those who departed from Champion's Book and built a chassis that would provide four parallel tubes at the front end of the car. I did this for the sake of simplifying the suspension construction (it was then the first time that I was building a car). Four parallel pin suspensions are an easier design for a beginner. Or one that would minimize chances of making serious mistakes. You may be an experienced engineer, in that case ignore my comment. If not, one word of wisdom: there are many things that you can produce in CAD that will be more difficult to materialize in the real world of metal.


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PostPosted: March 20, 2018, 9:37 am 
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Joined: December 17, 2010, 1:24 pm
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Location: Gainesville, Mo.
Once again, I am compelled to reach out to a fellow "Duffer" as regards the length of build time. Aside from the usual stuff of jobs, family, etc, there is frequently the problem of finances (this is one of mine) so for retired people like us, sometimes the $$$ goes out for the mundane necessities of life almost as fast as it comes in, leaving little surplus for timely car construction. Another problem is just that "Life Gets In The Way"! This is another one of mine. In the past few years, I've gone under the surgeons knife for a hernia. My dear Wife has had several strokes putting me in the position of caretaker during her lengthy recovery. About this time last year, we had a flood that ran us out of our home, and took several month to rebuild and repair. Last Autumn, I broke my leg which put me out of action for almost 4 months and caused a reversal of rolls with the Wife now my caretaker. At the moment things are coming back to normal, and I hope to be starting my build soon, after a wait of almost 50 years! Life is good! :D

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PostPosted: March 20, 2018, 9:48 am 
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Location: Cornholio OR "Where the magic happens"
MangPong wrote:
As an ‘old-timer’ I'm slightly worried that I might not be around to enjoy the fruits of my labours... lol.



The reward lies in the journey not the destination.

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PostPosted: March 20, 2018, 11:07 am 
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Location: Massachusetts
Quote:
I have recently come across a couple of comments online asserting that wishbone mounting brackets should be mounted parallel to the central axis - but I have never seen anybody explain, Why...?


Here is a simple way to look at this issue. You can find diagrams which involve projecting lines and intersections and heights etc., but they tend to be confusing and don't always explain well. I think it's because the writers often don't completely understand...

Mounting the wishbones directly to the angle sides of the frame introduces tendencies for anti-dive or pro-dive. In you drawing I think you would have anti-dive.

The reason is as follows. Consider the motion of the axle pin as the wheel moves up and down. If the motion of the pin is to also move forward or backward compared to the car as it moves upward and downward that introduces additional forces. When you put the brakes on the front will start to dive a bit. As it does so, the axle pin will try to move forward. In order for it to move forward, it must basically "lift" the cars weight backwards a bit.

A similar way to look at it is to imagine a surface in front of the car, like a sheet of plywood, at the angle the axle pin moves. Then imagine a ball between the front of your car and the plywood. If you push the car towards the plywood the ball will try to roll either up or down the tilt of the plywood.

As a practical matter I don't think you will notice this very much on your car. On my car I arranged the frame to allow the rear mounts of the front wishbones to be inboard a couple of inches. On your car the wishbones could be arranged like the upper wishbone in your drawing and the frame could go straight forward at that part of the car. The body work can hide that and just look like a straight taper in that area.

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PostPosted: March 20, 2018, 2:35 pm 
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Joined: March 15, 2018, 6:03 am
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You guys on this site are amazing - I cannot think of a similar situation I've ever been in where ‘so many have been so helpful for so long...’

phil
Wise words. I'm not really an experienced engineer - I had an engineering-biased education (I was taught to ‘design’ from the age of 11...) but I changed careers a couple of times. I have also renovated several old houses, and designed and built my own, so I also have some understanding of project control. And I was taught that you shouldn’t just design things to work but also able to be made - e.g. as the design stands I already know which two chassis members will be cut and welded first, to simplify the construction and assist the old alignment/distortion problems. That’s not to say I'm expecting it to be a breeze but I'm not afraid to try... I should also add it’s 50 years since I used an oxy-acetylene torch, and I've never used an arc-welder, of any kind. I like a challenge. lol.

mike
Sorry to hear of your troubles - none of that could have been easy. I've been very lucky - only two accidents that required surgery... the last, eighteen years ago. Maybe the ‘age’ issues will soon be upon me... I have a slight financial concern in that it is so difficult to ever cost such a project. My house projects were all completed within 10-15% of the budget but they tended to take twice as long as expected. The latter was easily solved by doubling my expectations... lol.

Bent Wrench
“The reward lies in the journey not the destination.”
I hope this includes the journeys I envisage in the car itself...

horizenjob
Many thanks for your explicit comments. It is interesting that at one time I had built in ‘anti-dive’ (by lowering the upper/rear mounting point) but this seemed to slightly complicate the wishbone design... and then I read (here, somewhere) that these cars are usually too light to bother. So it was taken out.

If I understand you correctly the mounting points @ 8º are likely to reintroduce this ‘feature’ so I'm not inclined to worry at the moment. What I was hoping was that if the angled points are a complete no-no someone would cry: “Do not do this...!”

Unfortunately I'm not entirely clear on your last part, about having the bodywork hiding the straightened tubes... Any chance of a sketch. It might be my drawings aren’t too clear, but this drawing of the central part of the ‘tub’ might show the mounting points more clearly...
Attachment:
mangpong-dd.jpg
mangpong-dd.jpg [ 77.62 KiB | Viewed 1154 times ]

Many thanks, Mangpong.


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PostPosted: March 20, 2018, 11:58 pm 
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Joined: January 18, 2015, 2:34 am
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Location: Los Angeles
For what it is worth, on my Birkin, there is a slight taper toward the from of the frame but the a-arm mounting points are essentially above each other. The caster is basically determined by the outer ends of the a-arms as the attach to the uprights giving 9 ½ degrees. While this sounds like a lot and would normally suggest a strong centering tendency, this hasn't been much of a problem. Birkin suggests setting 1/32" of toe in front and rear as a starting point, This is about the width of a pencil mark but it seems to work pretty well. Now that I have about 1000 miles on the car, everything has loosened up a bit and it drives quite nicely. I would caution to pay attention to bump steer as it is easier to resolve at the design stage than as a later fix.


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PostPosted: March 21, 2018, 9:47 pm 
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Hi papak - thanks for your comment... I'm getting a tad worried about setting such small dimensions - the room for 'error' is massive...
After a quick search I've been unable to locate 'Birkin' - any chance of a link, please...?
'Bump steer'... does it ever end...? lol. :roll:


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PostPosted: March 22, 2018, 3:51 pm 
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Location: Novato, CA
I've seen more projects get completely locked up on suspension design, and so have most of the people on this forum. You can learn a lot from books and the Internet, but it takes more than that to design a suspension from scratch, it takes experience, and a lot of trial and error. Keep it as simple as possible, and if you can copy an existing, working suspension you'll be way ahead of the game.

One of the big advantages of a book frame, IMO, is that you don't have to make a lot of suspension decisions. Maybe only two. You can get on with your build and end up with a great handling car.


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PostPosted: March 22, 2018, 10:05 pm 
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Hello Nick
Many thanks for your kind comments. I fully agree, as this will be my first such build, to aim for simplicity. At the same time, if we accept there are three stages to these projects: design; build; test & enjoy; my preferred stages are the first and third. I've been designing stuff since I was eleven, often just to solve minor problems at home. Many of these ideas never got made - I was just happy to solve (maybe) the problem.

I started this design 14-15 years ago, when I remembered a childhood love - the Morgan 3-wheeler - but my circumstances changed and I had to put it to one side. For the last six months I've been in a position to resurrect it, not knowing that in the meantime Morgan had created their own replica... lol.

I am also now able to execute the design (which no longer emulates the Morgan) and I'm grateful for the advice I've been getting from kind souls at LocostUSA. However, I would, ultimately prefer to create my own car, and perhaps fail... than just copy an existing design...

I hope this, perhaps foolhardy venture won’t end in tears but I will always keep your comments in mind.

Many thanks, Mangpong


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PostPosted: March 23, 2018, 3:44 pm 
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Mangpong, you sound just like me. I love to design stuff, and always had a big supply of graph paper on hand when I was a kid (no computers then). I was always drawing up one design or another. Have at it, enjoy the process, and don't let me or anyone else tell you what to do.


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PostPosted: March 24, 2018, 12:41 am 
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Hello Nick
(no computers then)
I always wondered what ‘BC’ meant - I can even remember what it was like before graph-paper... lol.
What I always hoped by joining here was that you guys would be harder on me and tell me what NOT to do... i.e. not to say, ‘What lovely drawings...’ ‘Ooo, you’re so clever...’ but to say, ‘For god’s sake don’t do it like that...! You might kill yourself.’

So far that hasn’t happened, but I don’t know if (so far) I'm being safe, or people are being overly polite... lol. I also love the way someone might advise against a particular idea only to later discover several other people are following the same idea - I've never been polarised - there’s a whole world of experience in between. Many people quote, ‘Life’s too short.’ My feeling is, ‘The World’s too big.’

Thanks again, Mangpong


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PostPosted: March 24, 2018, 3:49 am 
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Location: ontario
[quote="MangPong"]Hello Nick
(no computers then)


Once again MangPong, not knowing much about the 3 wheeler design that is in your head I am bound to offer both wisdom and motherhood to you... altogether meaning well.
Thinking about your project it occurred to me that one should not discuss the front suspension of a Morgan 3 wheeler replica as if it were a Lotus seven . The 3 wheeler is a cycle car with its own engineering challenges. One of them was and is stability. In the front wheel suspension design Morgan for instance had to address bump-steer issues at an early age. I noticed that they started using the sliding post type of suspension (by which the wishbone arms are not moving up and down but the spindles are moving (as in some motorbike rear suspensions in the sixties).
If I were designing and building a three wheeler I would want to know down to the latest detail what worked and what did not and why. There is fortunately in this day and age a wealth of data on the internet available to us. :cheers:

https://www.youtube.com/watch?v=2xcITHevPrc

https://www.youtube.com/watch?v=2X71spAvmw4


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