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 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!

Cheers, Daryl.

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 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.

Cheers Daryl.

Bonnet louvres
In order to achieve the look of the inspiration car, we needed to work out how to create louvres in the side panels of the bonnet. Some research online suggested a few potential methods. In the end we opted to use a punch and die set in a manual press. The punch is made of aluminium plate which we welded together to get the required thickness. The punch was shaped by hand to give the inside profile of the louvre. The die is a piece of steel with a long 'D' shaped hole in it. The die ha about 3mm of clearance around the punch (when the end of the punch is about 4mm below the top surface of the die). We rounded the top edge of the die somewhat and polished out and surface roughness so it didn't transfer to the aluminium sheet. To press a louvre we needed to cut the sheet for the opening of the louvre with a thin cut off disk in a grinder. Trail and error showed us that the length of the cut was key to getting the louvre to press cleanly. We also discovered that the radius of the ends of the punch needed to be enlarged as a tight radius resulted in the aluminium tearing. A larger radius on the ends stretches the sheet less. We found that it was useful to fix wooden blocks each side of the punch to hold the sheet flat when the punch was at maximum travel. This helps produce a more defined bend at the edges of the louvres. Once we were happy with the set up, we set a fence that we could run the panel along to ensure all the louvres were a consistent distance from the edge and at the same angle. Once we were set up it didn't take long to press the actual panels. 90% of the work is required to make the first louvre.

Chassis finishing
With the bodywork getting close and having decided there aren't any serious changes required to the running gear, it was time to disassemble the kart so the chassis and floor pan can be finished. Steelwork was finished in black enamel and the wooden floor pan got a coat of tinted varnish. After finishing, the kart is looking nice and clean. Ready for body work.

Transportation
Before the bodywork is progressed too far, we thought it would be a good idea to run the kart and test it out. We decided that the best approach would be to fit a frame into the trailer that will locate the kart wheels and also provide tie down points. The frame was built out of angle iron with some fittings built in so the frame can be clamped onto the trailer without the trailer needing to be modified. We are probably using too many tie down straps, but the kart does not move when being trailered.

Radiator
The bodywork around the 'radiator' is probably the most complex panel on the kart. A mock up of the surround was made from MDF so the shape can be tested on the kart. From that a paper template for the alloy sheet was made. This involved a lot of guess work as we don't have a lot of experience with forming aluminium sheet. Nik worked the sheet on the english wheel while comparing the sheet to the shape of the mock up. There is still some fine tuning of the shape to be done but it's really coming along. We found it is useful to anneal the alloy as it work hardens whilst shaping. It's a tricky business as it's very easy to overheat the aluminium.

Spent today working through getting the Cyclekart rolling. This included finishing the hubs for the wheels and the steering.

I had to drill the plates that I cut the other day along with the wheel hubs. I drilled these for M10 bolts. I will need to weld some bits of flat bar to locate the hubs into the wheel to stop the hub from spinning in the wheel under load, but I'll do that later. There's plenty of little bits to tidy up before final paint and assembly.

I also needed to clean up the rear axle as the fit of the bearing on one side was a bit too tight. With that done and the axle out of the car it gave me a chance to fit the brake disk. The disk dits nice and close to the cross member at the rear bulkhead, so it should be trivial to mount the calliper. I also have a seperate cable operated calliper as well, this will be operated by the handbrake lever. Handbrakes are a requirement for CCA events.

With the rear axle fitted up I turned my attention to the steering. I drafted up some arms to weld to the front hubs and cut them out on the plasma cutter. Then, literally just I was finished, right at that moment the Amazon delivery guy dropped off the two bearings that I had ordered to mount the steering column. It literally could not have been better timing.

So I made a quick mount for the lower bearing to sit on and a cross bar that I fitted to the dash hoop to mount the top bearing to. I intend to re-do the bottom mount as it is a bit ordinary, but for a proof of concept it does the job. I think I will keep the top mount, mostly as I plan to cover it with the dashboard so it will not be seen. There's plenty of room to slide underneath when getting into and out of the cockpit.

With the steering done and the final position of the dash hoop decided, I tidied up sone other bits and bobs and also fitted the hand brake lever. This sits in line with the dash hoop and will be slightly forwards of the cockpit opening. The cowl will extend past the dash hoop and will curve upwards slightly at the top of the cowl.

I also tacked the rear tail together and tacked it to the rear bulkhead hoop. The tail will be removable, but as I did not get the chance to fabricate the locking mechanism to hold the tail in place, I figured I'd temporarily weld it in position for the show tomorrow.

And so with that done there was only one thing left to do; see if it fitted into the trailer. The trailer is just a 6x4, but fortunately, with the front gate folded down the Cyclekart fits perfectly. The rear chassis member is just higher than the tail gate. Currently the tail section sits above the tailgate but once finished will sit a lot lower. This isn't an issue as It can simply be removed for transport. The trailer was original purchased for transporting the Cyclekart and the fold down front gate was a major plus, so good to see that it fits. One more job ticked off of the list.

So today was a non-build day as I had other commitments but I did manage to snatch an hour this morning to weld up the steering wheel.

I'm using the typical generic quick release go-kart steering hub to attach it to the steering column. This is an aluminium hub with a steel adaptor that you can weld onto the end of the shaft.

One thing that annoys me about these is the three bolts that hold it on, especially on a steering wheel with four spokes. There's a distinct lack of symmetry to it. So in a bid to make it a little more aesthetically acceptable I decided to add three more mounting bolts. On reflection, perhaps I should have just re-drilled it for four fixings as the original holes would be obscured, and it would have matched the spokes, but foresight appears to be in short supply today. At least with six mounting bolts it has some symmetry to it. I'm not overly keen on the socket head bolts as they seem too modern, but were evidently invented in 1910, so are contemporary with the era. I did have a go at filing a slot in one to turn it into a faux slotted head. But not too sure on what looks best. If I can find some M8 slotted countersunk bolts I'll swap them out.

I also received a delivery for some of the parts I reordered due to not being able to find the ones I already bought. Specifically the brake disk hub and extended hydraulic brake line. Got to hand it to Amazon, I ordered them two days ago and here they are already. Of course. Now that I have the replacements I am almost certain that I will now find the original parts. This being the Law of Sod.

One more day of CK suff before the event on Sunday. Don't expect I'll get anything major done. Lots of shits and bits to finish off tho.

Today was one of those two steps forwards one step backwards kinda days. I started off with a plan to pick up some more steel to get a start on the bodywork and make a steering wheel so that I could get the steering sorted out. My plan was to roll a hoop from 1" steel tube and use that to make the steering wheel. However, when trying to roll the hoop I found that the rolling machine made a right hash of it. The rollers are too far apart, so trying to roll smaller diameters is a bit of an issue

Defeated I decided that I would simply resort to buying a steering wheel. Surely has to be something i could pick up locally eh. Turns out that is a no. Next I decided that I would try and find something with a suitable metal rolled hoop that I could repurpose. Surely there's something in Bunnings that I could use? Unfortunately also a no.

Then I turned to one of my suppliers - a specialist tube benders. Surely they could roll me a simple hoop. Shit, I might even be able to call in a favour. As it happens they could not, but gave me the details of someone who can. I decided to park that as a last resort

So having wasted a few hours I finally decided to reduce the diameter of the tube from 1" to 3/4" and use the secondary rollers on the rolling machine. These are generally used for round bar but go up to 20mm. So I stole the tube I had set aside for the steering column and gave it a test. I managed to roll a reasonable looking hoop. Unfortunately I then needed to go get some more tube to roll another hoop and replace the steering column.

The steering wheel was made from the two hoops welded together. The machine cannot roll a perfect circle. it leaves flat bits on the ends, so to make a completely circular hoop you need to use two hoops and weld them together. Pretty straightforwards. Next I drafted up a basic cross shape for the wheel centre.There seems to be two main styles. One fabricated similar to this and one made from aluminium, so I tried to replicate the profile of the fabricated style of wheel. I also cut out some plates for the bottom of the steering column.

Unfortunately I did not get any further than this as I ended up having to deal with some other non CK stuff which frustratingly turned out to be a massive waste of time. Just the way it goes sometimes.