H: Hubs, Wheels and Tyres Hydraulic Steering Damper

[timetraveller]

Hi Vic, thank you for your posting #48 with the videos of various bikes having the dampers fitted to them. I looked at all four of them and was interested just how careful people had to be with extra 'O' rings or rotating fork legs to ensure clearance. I think those of us who have done this alone have done quite well to come up with systems which work and clear other bits of the bike.
When I was researching dampers for my design I saw these pictures but all were still pictures, not videos, so I was unaware that the damper bodies hardly rotate. I did try to design something similar for the Vincent but could not find anything useful to act as an anchor. I thought that the ability to adjust while riding might be useful but gave up in the end and users seem to find the system adequate with the damper below the steering head with no possibility of adjusting while on the move. At the moment I am not minded to change my design, remember specifically for the JE steering head. However, I can imagine a system similar to yours which does not use the original friction damper system as one end of the operating system and will think about that at some stage. Right now I still have over ten of my systems on the shelf to supply to JE steering head users and will continue to supply those to people who are interested.

 

[Oldhaven]

Vic,

I really appreciate your efforts and those of Vincent since I have been scratching my head about how to use a damper on my Brampton equipped Rapide. While I understand that Brampton's are less likely to shake, I figure a hydraulic damper will do no harm if it doesn't cause the weaving I asked about. I do wonder a bit about not fixing the mounting plate more securely in the damper position. You do mention using an aluminum shear pin. Vincent's work shows at least two studs or bolts. If the damper is supposed to stop or slow down a shake that may be strong enough to break wrists, I can't imagine that friction alone would keep it in place. If the bracket is displaced who knows where the damper body could end up, rotating to positions that could interfere with the forks. While it involves some hole drilling, I would probably use something like Vincent's mounting fixing even with your bracket. Am I missing something?

Ron

 

[BigEd]

Vic,

I really appreciate your efforts and those of Vincent since I have been scratching my head about how to use a damper on my Brampton equipped Rapide. While I understand that Brampton's are less likely to shake, I figure a hydraulic damper will do no harm if it doesn't cause the weaving I asked about. I do wonder a bit about not fixing the mounting plate more securely in the damper position. You do mention using an aluminum shear pin. Vincent's work shows at least two studs or bolts. If the damper is supposed to stop or slow down a shake that may be strong enough to break wrists, I can't imagine that friction alone would keep it in place. If the bracket is displaced who knows where the damper body could end up, rotating to positions that could interfere with the forks. While it involves some hole drilling, I would probably use something like Vincent's mounting fixing even with your bracket. Am I missing something?

Ron

One would hope that if you have a steering damper fitted and functioning correctly any shaking would be damped out well before it got to "wrist breaking" proportions.

 

[oexing]

Ron,
you could add some screws to bolt the alu lever onto the stem disc - same with the new timetraveller steering stem so my idea can be used there as well. That will ease your mind but in reality I do not think this will ever have to be done. The olde friction system was mostly effective enough with only minimal force applied as any more force would cause stiction and unprecise lines on the road. So thinking of that I am inclined to add that China damper onto most of my classics that have just the friction. The big bonus with hydraulics is you can have a heavy setting to prevent all flutter from first start but still keep the smooth steering not to spoil your lines. I only guess a fully nipped up alu lever of the China set via the old friction knob will easily apply sufficient gripping force to never slip as it prevents all fierce motion from the start and broken ankles may have been not the result of extreme force but from the fast motion that slaps arms when resonance has built up so much. I have thought about adding an indexing item to the alu lever: The Brampton has a slot in the bottom diameter of the stem about 3.4mm wide. I filed that to exact 4mm and the alu plate could be slot milled or filed for 4mm and a key added, so no drilling to be done. But drilling is much easier. I did a file job - remember myself retired toolmaker, that´s why . . . Yes, a counter sunk screw or two would be allright instead, certainly, for feeling better anyway. And in case of the new steering stem only fixing screws were suitable, just same with the present long alu lever, believing that costs and hassle would come down a bit in cases of minimal space for that kind of add-ons. The small o-rings shown in the video clips are just there to stabilize the assembly a bit from wobbling about the mounting bolts, not essential otherwise.
As to changing settings while riding, I think most people will keep their setting all year once a decent setting is made. I have the BMW damper on all of the 46 years I got the bike, but it is only a weak damper, non adjustible, on or off. I would no way want to have the damper on top of the fork for spoiling the looks on a classic !!
Anyway, I hope my idea was easier to copy in one´s home shed than the trickier long lever of the present design with its not so clearly to understand motions from lock to lock.

Vic

 

[macvette]

I decided to analyse the different set ups from basic principles. That is,we are trying convert rotational movement into linear movement. Sound familiar? Think crankshaft, conrod and piston.
The displacement of the damper rod is a function of the sine of the angle by which the steering is rotated and the distance the damper pivot is behind the centre of rotation of the steering regardless of which version is considered. This distance is limited by the useable damper stoke.
With the damper body pivoted on its centreline and on the centreline of the centre of rotation of the steering at mid stroke, this is a straight forward function of the sine of the angle of rotation of the steering from straight ahead.
This is not the case when the offset damper mounting bracket is used. At first sight this is not obvious. The displacement is still a sine function of steering angle but the offset bracket introduces a second lever between the driving bracket and the centreline of the damper reducing damper stroke for a given steering rotation.This is coincidentally compensated by the damper body ending up further away from centre of rotation of the steering. This equally true of both Norman's and Vic's set up using the offset damper pivot.
To get back to basics I dug out my fifty year old Theory of Machines text book from my university days and derived the algebraic relationship from there.
My conclusion is that centre line mounting of the damper body is the most efficient way to mount it regardless of which of the different approaches used.
If you want to mount a hydraulic damper on a C or D, use the old damper stop position with a centreline body pivot. Measure the distance from the centre of rotation of the steering to the centre of the damper. This is the distance your actuating lever needs to be behind the steering centreline. Mount the damper with its stroke and body on the bike centre line measure the distance to the centre of the rose joint on the damper rod. This is how long the actuating arm needs to be.
Regards Mac

 

[davidd]

I used a stock GSXR damper on this Egli frame:

The damper body rotates on the bolt. This is an electronic damper (note the lump on the bottom). I used it for the mock up, but changed it to the manual model. I could not find the Vincent's ECU.

David

 

[timetraveller]

It seems damper design is just like buses; one waits for ages for one to come along and then four, or more, arrive all at once. Mac is it possible for you to do the same measurements as me? You need something on top of the steering head, probably a protractor of some sort held in place by the damper knob, and an indexing system so that you know how far you have rotated the steering. Then all that is required is a digital vernier to measure the distance of the damper body from the casting that holds the rose joint on the end of the damper rod. A measurement every five degrees is enough and it would be interesting to see whether your design gives more travel per degree than mine. I was trying to save the £30 extra required to buy the kit which contains the on-axis damper support. It would be instructive to know whether it would have been advantageous to spend the extra money.

 

[vibrac]

Who has ever broken a wrist on a Brampton bike? come to that who ever had a tank slapper?
I am willing to accept it may of happened during the last 50 years my eye and ear has been on the subject but its never come to my attention.......
unless you know different.

 

[Oldhaven]

I added too many variables here causing confusion, sorry. Davidd had a slapper that tossed him off despite having a hydraulic damper. Thus my comment on the need for a locating pin. I am sure I remember someone relating wrist damage from a bad tank slapper. I am also nearly 100% positive that these were with girdraulics, or perhaps tele's because I can't remember hearing about anyone having a serious incident with Brampton forks. I changed the spring on my Brampton forks to a Thornton spring over so they no longer have the spring countering overextension, and instead are pre loaded so go to the full length of the damper stroke when the front is unloaded. That change makes me wonder if a hydraulic damper is good insurance. I also would like to explore the difference that a hydraulic damper would make compared to a tightly wound friction damper. Now that my machining time is spent on the Comet special I won't be adding a damper to the Rapide anytime soon, but now I have an idea how to do it.

 

[macvette]

Hi Norman ,
Just to make it clear I did this analysis to get to the bottom of the motion involved, not to get into" this is better than that" kind of discussion. In the real world they will all work. When I made my final version, I did it intuitively so my actuating arm has 60mm of offset to the back of the bike. Yesterday, I measured the distance from the centre of the steering stem to the centre of the old damper stop. It is about 57mm. I "eyeballed" the offset of my actuating arm at 60mm. If I had done the analysis beforehand, I would have made it 57 mm not 60 as I did. The result is that my damper moves out of // with the forks by a small amount so there are a few degrees of rotation of the body. I went to the centre pivoted damper to get good clearance from the eccentrics and spring boxes.
I could do the measurements you ask with some difficulty but I dont think its necessary.
The reason is that with 60mm rearwards offset on my actuating arm, I get the stroke required. With the offset pivot the damper there is approx an addition 15mm rearwards for the same stroke.
Regards Mac