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Sliding Hub Suspension - Part 2
Previously, I described how the pillar doesn’t need to be inclined rearward to produce caster.
This time, I will try to explain the ‘drawback’ of pillars that are inclined to the centreline of the trike. (below is a pic of recommendations for a 4 wheeler.)
The hubs slide up the pillars. If the pillars are...Sliding Hub Suspension - Part 2More
Previously, I described how the pillar doesn’t need to be inclined rearward to produce caster.
This time, I will try to explain the ‘drawback’ of pillars that are inclined to the centreline of the trike. (below is a pic of recommendations for a 4 wheeler.)
The hubs slide up the pillars. If the pillars are narrower at the top than the bottom this will produce Toe-in on bump and Toe-out on rebound, (assume steering arms at the rear). Bad enough for stability in a straight line, now consider the Bump Steer produced by only one wheel compressing on a bump. Even worse, the strange alignment caused by the trike rolling in a sharp or high-speed turn. Outside wheel compresses causing Toe-in, inside wheel extends and Toes-out. Even if they somehow manage to ‘balance each other out’ your Ackerman is shot and the vehicle is no longer pointing in the same direction as your input at the steering wheel.
But! But! What about the Scrub Radius?
Scrub Radius is the distance between the steering axis and the centre of the tyre contact patch. It can be +ve , -ve or zero.
Scrub ‘sounds’ Bad… so zero must be Best!!???
If you manage to produce zero, don’t cheer yet. You have now got SQUIRM.
As the tyre tries to turn around the centre point, one half of the contact patch is scrubbing forward and the other half is scrubbing backward. Tyre wear and instability result.
Negative is less than zero….. so -ve must be Best!!??
-ve has some advantages for modern cars, but not so much for Cyclekarts. In FWD cars -ve scrub is less affected by torque steer. Also brake inputs, helpful with ABS and failures in split systems or in the case of a flat front tyre.
So...+ve? Older cars had +ve scrub. It helped parking without power steering because the wheel could roll as it was steered. +ve scrub provides more “feel” to steering inputs because of leverage caused by the radius.
Conclusions: For me, Vertical pillars and some Positive scrub radius.
We have skinny motorcycle tyres, minimal weight, and no front brake issues to consider.
If I want to (or need to) reduce the scrub, I have another option. I can use stub axles that are not perpendicular to the pillars to create positive camber, this will bring the bottom of the wheels closer to the bottom of the pillars. It is a classic Morgan trike look and I might do it just for that!
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I scrounged a couple of used McPherson Struts for the Hard Chrome shafts to make my front suspension pillars.
I ordered 22mm id bushes to suit them.
Although I prefer and actually tried to source these locally in OZ, as so often happens, it was so much less involved, way easier and cheaper to get them from China, via eBay.
My initial...I scrounged a couple of used McPherson Struts for the Hard Chrome shafts to make my front suspension pillars.More
I ordered 22mm id bushes to suit them.
Although I prefer and actually tried to source these locally in OZ, as so often happens, it was so much less involved, way easier and cheaper to get them from China, via eBay.
My initial preference was to get DU type bushes which have a 25mm OD. Finding tube or pipe with a 25mm (or slightly smaller) ID proved quite difficult.
Closest I found, was some old bicycle frame tubing with a 1" (25.4 mm) id. I considered that the welding of the axle and steering arms (and the appropriate bracing, reinforcement and support might shrink the tube enough to retain the bearing. In my youth, I would have plowed right into this option, just to see if it could work.
Instead........the bushes I ordered have a 30mm OD. This allows many more options for heavy wall pipe etc. and plenty of meat to machine the OD to suit my final selection. pics to follow.
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First chassis member bent. Will use this to create a simple form or jig to shape the other three!Post is under moderationStream item published successfully. Item will now be visible on your stream.
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Here are some life size working plans for exploring layout issues and bending the main chassis members.
Chalk lines on form board, easy to adjust with a damp cloth
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I have been doing a lot of research on the Morgan sliding hub front suspension. A seemingly simple system, but with many subtle tricks.
They have been maintained, modified and raced for 100+ years. A lot of the available information on-line, is for 1950's plus 'four wheelers'.
Vintage trikes were different. Here is some of what I have learned...I have been doing a lot of research on the Morgan sliding hub front suspension. A seemingly simple system, but with many subtle tricks.More
They have been maintained, modified and raced for 100+ years. A lot of the available information on-line, is for 1950's plus 'four wheelers'.
Vintage trikes were different. Here is some of what I have learned to build into my cycle kart.
The pillars can be Vertical. A degree or two of rearward rake might be useful to reduce 'stiction' on the edges of the bushes due to the offset/angle of the suspension forces during compression. ( I imagine these would wear and round-off a sharp edge pretty quickly anyway).
What about caster and the need to have kingpin inclination for the tyre contact to be behind the swivel axis?
Vintage trikes had the axle spindle fitted behind the hub and the pillar. (see pic) This offset is the equivalent of having caster angle.
It helps to look at Morgan suspension like a motorcycle telescopic front end. Instead of caster, use the term 'trail'.
With 17" wheels, placing the centre of the axle (say 50mm) behind centre-line of the pillar is equivalent to a Fork Rake (or Caster) angle of around 9 degrees.
One more factor re: king pin inclination that might be useful for a CycleKart builder.
If I was building a 4 wheel Kart and wanted to use a locked rear axle, then king pin inclination is way more important.
With rearward inclination, turn left and the left hub rises, the right hub falls. this transfers weight to the right rear wheel and reduces it at the left rear.
This is how Go-karts get around corners without the need to power slide, basically 3 wheeling. I'm already building a Trike.
Next time: Camber angle and Kingpin Swivel angle.
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kjacml@yahoo.com.au reacted to this post about 3 weeks agoFirst chassis member bent. Will use this to create a simple form or jig to shape the other three!Post is under moderationStream item published successfully. Item will now be visible on your stream.
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Daryl Jones reacted to this post about 3 weeks agoHere are some life size working plans for exploring layout issues and bending the main chassis members.
Chalk lines on form board, easy to adjust with a damp cloth.Post is under moderationStream item published successfully. Item will now be visible on your stream. -
Today I ordered the 22mm id bushes for the sliding hub front suspension.
Although I prefer and actually tried to source these locally in OZ, as so often happens, it was so much less involved, way easier and cheaper to get them from China, via eBay.
My initial preference was to get DU type bushes which have a 25mm OD. Finding tube or pipe with...Today I ordered the 22mm id bushes for the sliding hub front suspension.More
Although I prefer and actually tried to source these locally in OZ, as so often happens, it was so much less involved, way easier and cheaper to get them from China, via eBay.
My initial preference was to get DU type bushes which have a 25mm OD. Finding tube or pipe with a 25mm (or slightly smaller) ID proved quite difficult.
Closest I found, was some old bicycle frame tubing with a 1" (25.4 mm) id. I considered that the welding of the axle and steering arms (and the appropriate bracing, reinforcement and support might shrink the tube enough to retain the bearing. In my youth, I would have plowed right into this option, just to see if it could work.
Instead........the bushes I ordered have a 30mm OD. This allows many more options for heavy wall pipe etc. and plenty of meat to machine the OD to suit my final selection.
cheers, Daryl.
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Daryl's "Vintage Morgan" Inspired 3 Wheeler. reacted to this post about 2 months agoScaled drawings....adjusted to CycleKart dimensions.
I use Paint.net which is great for manipulating photos, drawings, scaling etc.
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Daryl Jones commented on this post about 2 months agoHi Admin, Where can I discuss with the committee the details of the exemptions for the rear wheel of a 3 wheel (morgan style) Kart.
Cheers, DarylComments (6)-
I would like to use a 14" pit/minibike wheel. The shorter spokes will resist the side loads better. The economical tyre options, other than MXI would like to use a 14" pit/minibike wheel. The shorter spokes will resist the side loads better. The economical tyre options, other than MX knobbys, are scooter tyres of 90/90 or 90/100 profile, ie. slightly wider than 3.25 Overall diam is close to 17" postie and is not seen under the rear bodywork. More ...Reported
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Hi Daryl. It seems like a reasonable change. Let me look in to this and get back to you.Reported
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Hi Daryl.
Looking at other Morgan interpretations they generally use a 17" rear wheel. However, the guidelines are really there to ensure thatHi Daryl.
Looking at other Morgan interpretations they generally use a 17" rear wheel. However, the guidelines are really there to ensure that (apart from safety) the overall aesthetics are consistent across all builds. The use of a common wheel diameter, wheelbase and track, is partially used to ensure that the scale of all builds are visually similar. The use of similar dimensions for wheel base and track also ensure similar handling characteristics.
The use of a smaller diameter rear wheel in this case should not impact the overall aesthetics, because as you state, the rear wheel is mostly hidden. The additional stated benefits are also noted with the additional comment that the reduction in tyre contact area due to the smaller wheel diameter, is offset by the use of a wider tyre. An exemption for the use of a smaller wheel with a larger tyre in this case is therefore granted.
Track and wheelbase rules still apply unless there is a specific reason to change them for the case of a three wheeler. Happy to discuss that further should the need arise.
Thank you for reaching out. I will email you out a formal exemption for your records. More ...Reported -
Thank you, Track and wheel base rules are fine for me. Onward and Upward! Cheers, Daryl.Reported
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Disassembling Scrap MacPherson struts for the Sliding hub pillars. (22mm hard-chrome rod)Post is under moderationStream item published successfully. Item will now be visible on your stream.
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