H: Hubs, Wheels and Tyres Hydraulic Steering Damper

macvette

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The rotation of the damper body with respect to the bike is less but what is more important is it's rotation with respect to the steering. If you compare this with Vincent's photos, you can see that the damper body remains almost parallel to the steering stem so is more efficient in translating the rotation of the steering into the linear motion required to operate the damper rod.
The length and offset of the damper actuating levers used on Vincent's, mine and Norman's version is determined by the damper stroke in order to get equal travel lock to lock and have the steering stops prevent movement before the damper stroke is used up. This is evident from the picture showing the damper stop in the side car mount where a "static"lever is applied to the damper rod.
When I decided to source a centre body pivot, I found many damper mounting kits for a wide range of modern bikes using these dampers. The mounting details vary but all had actuating levers on the damper rod with the damper body pivoted on the frame so I decided not to re invent the wheel.
I have noticed that with the damper, the steering is lighter than with the friction damper especially at low speed so I wouldn't use the original damper with the new one. I shortened the original damper rod so I could put the original back for appearance and kept all the original bits for a future owner when I join great VOC in the sky.
Mac
 

bmetcalf

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To keep my damper knob, at TT's suggestion, I removed the damper rod and everything attached to it at the bottom and inserted a short bolt through the underside of the FF25.
 

oexing

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Norman,
I do not see any clash with fork components, will post more photos. If ever required you could set the lot an inch deeper but I don´t see the need. Did you click on the Youtube link ??
I have certainly kept safety gaps for the rod with fork on its stops left and right and so most of the damper stroke is used. But what is more important: In centered position you get maximal motion at the rod for best effectivity to stop wobble right at the beginning, does not help much when effective damping is only achieved with more deflection from neutral, maybe you post a youtube clip about the earlier damper setup. Mac, do you refer to my setup when describing the almost parallel damper cylinder in all positions ? This is not the case with the very long lever in the known design. I´d be especially interested in the effetive stroke around the critical neutral position with the older idea, so a video clip could clarify this . Another benefit of my idea: No drilling of fork components required, you use the old friction clamping plates and knob, all parts of old system still mounted, only a simple alu shear pin may be a good idea for assembling later without thinking, but not really essential.
I do not see any snag with exchanging places for cylinder and rod at their respective mounting places, just see my youtube link above !!

Vic

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timetraveller

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VOC Member
If this shows up there should be a graph of the linear movement of the steering damper rod versus angle of the steering head. The straight line with the blue dots is the distance of one end of the damper rod from the damper body as the steering head is rotated. The lower curved line through the brown dots is the differences along the straight line to show up any non linearity of the movement against angle. Ideally these brown dots should be in between each of the upper blue dots. The line fitted to the brown dots is a third order polynomial, but you probably don't want to know that. Look at the lower curve and you will see that there is very little departure from linearity. Actual smallest value between the measurements is 9 and the largest, in the centre of the movement is 13.
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Yes Vic, I did look at your Youtube video. It was from that that I thought that some of the parts might stick out and interfere with the legs of the Bramptons but you would have to assemble it to be sure that there is no problem. I hope that you can see from the graph that although there is a difference between the ratio of angular movement to damper rod movement it works in the correct way. That is in the centre of the movement, the fourth point in the linear graph, there is most movement of the damper rod. 13 versus 9, about 40% more movement in the centre of the travel.
 

macvette

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Hi Vic,
I did look at your U tube video. I have slow broadband so posting videos is a pain. Here are 3 pictures, one straight ahead, one full right lock and one full left. The damper body stays almost but not quite parallel to the axis of the Girdraulic concentrics and Vincent's on his Bramptons is similar. What determines the damper stroke is the distance the damper pivot is behind the centre of rotation of the steering. The further aft it is the more damper stroke is used. The length and offset of the actuating arm is a bit of a red herring. The length is set by where the damper is at mid stroke and this is true of your design as well as the "old" versions. The offset (on mine at least) was chosen to minimise lost motion in rotating the damper body with respect to the rotation of the steering so that the damper gives maximum resitance to the motion of the steering ie there is minimum side thrust on the damper. Its not perfect but the best I can do with a hacksaw, drill and files.
Norman has done the math so I can't add any more. Anyway, as they say, there are more opinions in the club as there were bikes made so have fun. Regards Mac
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timetraveller

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Just so there is no misunderstanding; no, or very little maths was involved. All I did was measure the distance from the damper body to the holder for the rose joint on the damper rod and rotated the steering head from fully right to fully left. To get some idea of angular measure I fastened (temporarily) a dynamo drive sprocket to the top of the steering head where the damper knob normally fits. The dynamo sprocket has 28 teeth which means that there is 12.8571 degrees between each tooth. A pointer was made up to allow visual indexing of the teeth. Clearly that is not as accurate as, say, a dividing head but was good enough to find out what was happening. The straight-ish line in the graph above is just the seven measurements from lock to lock, giving a total angular movement of about 77 degrees (call it 80). By taking the difference from one point to the next one gets the amount of movement on the damper rod between equal angles over the whole range. I have enlarged the lower graph and moved the angular movement to the values they should have in between the measured points. The graph and fitted curve are shown below. The centre of the movement, dead ahead, is at about 40 on the horizontal scale. Although there is some scatter about the curve due to the crude angular measurement is should be clear that one gets about 13 mm of damper rod movement for each 12 ish degreed of steering head movement in the dead ahead position and this reduces to about 9 to 10 mm near to the limits of the movement. I cannot guarantee that either Vincent's or Macvette's will be identical as they use slightly different geometry but I guess they will be near enough the same.
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Cyborg

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Perhaps perception of "no or little math" is relative to the amount of poetry one reads?
Interesting thread. I thought I was just going to grab a damper from the dumpster and bolt it on the Comet Mongrel without any fuss. Figuring out the mounting points for the progressive rear shock absorber linkage is causing me to foam at the mouth.

This dingy photo will help illustrate the clearance between the fork girders and the damper. At first glance I thought it might be a concern, but after looking at a set, all the monkey motion takes place forward of the steering stem.
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oexing

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Norman, when looking into your last diagram, am I right in thinking that when 40 degrees is straight ahead, a deflection of 5 degrees to the left or to the right produces only very moderate stroke on the damper rod ? That was my very first impression when some pictures were posted of your setup on Girdraulics. But I must admit I could not fully figure out what all these components do or behave in real action, my main interest is definitely the range around zero degree. Any flutter or wobble HAS to be prevented right from the start at straight ahead, zero degrees. at maximum effectivity.
It is obvious from my photos that this is the case when the cylinder is mounted on my type of alu lever and the rod gets its anchor from the sidecar lug beam resp. a bracket on a crash bar. The lever is at 90 degrees to the rod at zero degrees deflection so spot on. Another plus is the bracket that comes with the Chinese set, that places the cylinder ca. 20 mm towards the engine so you gain precious space at full left or right lock. The whole affair is easy to copy , 57 mm distance between centres on the lever leaves almost 5mm safety on both steering locks.
Then no drilling of fork components is required, the lever is locked with knob , same as with friction discs - which can stay there - and no cracking of levers is to be expected as friction discs will slip. I´d say, try it, I don´t have an interest in producing sets or get patents, just hope it will be a lot easier to fabricate at home with little head scratching .
When Girdraulics are to be added with a damper, I cannot say much, maybe the eccentrics require a bit more space at full lock, but you will no doubt see for yourself when trying the cylinder on my type of alu lever. The anchor bolt for the rod could be adjusted a bit in that case I guess.

Vic
 

greg brillus

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Seems like an awful lot of trouble for forks that tend to behave themselves. Brampton's only misbehave when the bike is way too heavy at the rear unloading the front wheel/forks too much...........when the Brampton tries to become like the Girdraulic.
 
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