Landracing Forum Home
December 12, 2017, 10:24:00 PM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with username, password and session length
News:
BACK TO LANDRACING.COM HOMEPAGE
 
   Home   Help Search Calendar Login Register  


(Note: Donations are not tax deductible)







Live Audio Streaming and Archives of Past Events
Next Live Event: TBD
Pages: 1 [2] 3   Go Down
  Print  
Author Topic: Rigid rear conversion to single shock swingarm APS-PG bike  (Read 1201 times)
0 Members and 1 Guest are viewing this topic.
Koncretekid
Hero Member
*****
Offline Offline

Age: 70
Location: Yarmouth, Nova Scotia & Lafayette, Co.
Posts: 1012





Ignore
« Reply #15 on: December 03, 2017, 04:31:11 PM »

Good work Tom! I think if I were building that I would incorporate plate gussets top and bottom on both sides. Twice the wall thickness of the tube, with tapered width on front and rear to carry the stress through the butt welded joints better. Maybe a  better description is they would look like lightening bolts.  cheers
Ed,
I thought as you did about adding reinforcing to the top and bottom of the swingarm over the welded connections, but after an analysis of the stresses, they do not appear to exceed 12,600 psi even at the maximum force generated by the spring-shock.   That's less than 25% of the yield value of mild steel, so I shouldn't have to worry - - unless my welding is faulty! Under normal conditions, the forces will only be about 3/4 of that value. But since Pete says my welds look good and he wouldn't hesitate to ride my bike, I think I should let him have a go at it.  Luckily, the chain force stress occurs in the horizontal plane while the shock action is in the vertical direction so they are not directly additive (it gets complicated).  The other comforting thing is that with the suspension, the impact loading is nearly eliminated resulting is less stress on other members (hopefully including me.)
Tom
Logged

We get too soon oldt, and too late schmart!
Life's uncertain - eat dessert first!
WhizzbangK.C.
Full Member
***
Offline Offline

Age: 56
Location: Kansas City, MO
Posts: 205


Ed Bennett, Speed Team Doo Kansas City fab shop.




Ignore
« Reply #16 on: December 03, 2017, 07:21:40 PM »

Good work Tom! I think if I were building that I would incorporate plate gussets top and bottom on both sides. Twice the wall thickness of the tube, with tapered width on front and rear to carry the stress through the butt welded joints better. Maybe a  better description is they would look like lightening bolts.  cheers
Ed,
I thought as you did about adding reinforcing to the top and bottom of the swingarm over the welded connections, but after an analysis of the stresses, they do not appear to exceed 12,600 psi even at the maximum force generated by the spring-shock.   That's less than 25% of the yield value of mild steel, so I shouldn't have to worry - - unless my welding is faulty! Under normal conditions, the forces will only be about 3/4 of that value. But since Pete says my welds look good and he wouldn't hesitate to ride my bike, I think I should let him have a go at it.  Luckily, the chain force stress occurs in the horizontal plane while the shock action is in the vertical direction so they are not directly additive (it gets complicated).  The other comforting thing is that with the suspension, the impact loading is nearly eliminated resulting is less stress on other members (hopefully including me.)
Tom

I was mainly thinking about it from the perspective of rigidity. I'm sure that your structural yield strength is good, but the gussets would have the effect of eliminating a lot of potential flex by passing the stresses through the joggled sections.
Logged

Ah, this is obviously some strange usage of the word 'safe' that I wasn't previously aware of.  Douglas Adams
Koncretekid
Hero Member
*****
Offline Offline

Age: 70
Location: Yarmouth, Nova Scotia & Lafayette, Co.
Posts: 1012





Ignore
« Reply #17 on: December 04, 2017, 12:01:18 PM »

Here is a new drawing with revised chain pull and stress calculations.  I have also shown some small gussets in the area of the welded joints to improve stiffness as well as reinforcing my welded connections.

Feel free to comment.  I have yet to add another crossmember just ahead of the swingarm and another tube on each side to stiffen up the fairing tailpiece connection.

Tom

I just noticed that I typed in "/1.2" which should read /2.1" on my drawing in the calculations area and I can't seem to post the corrected drawing.


* swingarm 12-4-17 top.jpg (186.45 KB, 1503x889 - viewed 32 times.)
« Last Edit: December 04, 2017, 12:18:49 PM by Koncretekid » Logged

We get too soon oldt, and too late schmart!
Life's uncertain - eat dessert first!
Peter Jack
Hero Member
*****
Offline Offline

Age: 74
Location: Calgary, Alberta
Posts: 3450





Ignore
« Reply #18 on: December 04, 2017, 01:32:01 PM »

Tom, if those gussets on the zig zag are pieces of 1" x 2" tubing you're going to create a sealed chamber when you weld them up. Drill a small hole in the swing arm so the space you've formed vents. That will prevent the expanding air from blowing the weld metal back onto the tungsten. You don't need the extra practice resharpening the tungsten.  grin grin grin

Pete
Logged
WhizzbangK.C.
Full Member
***
Offline Offline

Age: 56
Location: Kansas City, MO
Posts: 205


Ed Bennett, Speed Team Doo Kansas City fab shop.




Ignore
« Reply #19 on: December 04, 2017, 02:03:12 PM »

Tom,
What I'm looking at is the vertical stresses from hitting bumps as speed causing the sides of the swing arm to flex. With the left side having 1/2 inch more offset than the right, it looks like it will have more flex. Experience from riding choppers with worn out (and poorly designed to begin with) plunger suspensions tells me that this is not good if it happens, even in a straight line.
Logged

Ah, this is obviously some strange usage of the word 'safe' that I wasn't previously aware of.  Douglas Adams
Koncretekid
Hero Member
*****
Offline Offline

Age: 70
Location: Yarmouth, Nova Scotia & Lafayette, Co.
Posts: 1012





Ignore
« Reply #20 on: December 04, 2017, 07:22:43 PM »

Pete,
Thanks for the reminder - - I would have forgotten to drill them.

Ed,
Your point is well taken.  The entire swingarm has to twist in order for that to happen.  But there is only so much that can be done to stiffen up a long swing arm.  The rear axle passes thru holes in the internal solid blocks of 3/4" aluminum which makes what are called "moment" connections.  This ensures that one side cannot twist without twisting the other side (as long as the connections are tight).  If you look at older swing arms, usually round, they terminate in flat plates that have less resistance to twisting than the rectangular tubing with the internal solid pieces, especially if they are not extremely tight.  The only way I know of checking this is to physically grab the rear wheel, top and bottom and try to twist it.  On this design, when I try this even with the front end tied down, the whole bike frame twists simultaneously, so I feel that it is very good.  Luckily, I'm not planning to run any more slalom courses at Bonneville, at least not intentionally!
Tom
Logged

We get too soon oldt, and too late schmart!
Life's uncertain - eat dessert first!
wobblywalrus
Hero Member
*****
Online Online

Age: 64
Location: backwoods Oregon
Posts: 4470





Ignore
« Reply #21 on: December 04, 2017, 09:20:41 PM »

Tom, if in doubt, using double shocks like a normal bike will take a lot of load off of the swing arm.  Another advantage is the dual shocks act like struts if they are bottomed out and this takes huge loads away from the swing arm.
Logged
Koncretekid
Hero Member
*****
Offline Offline

Age: 70
Location: Yarmouth, Nova Scotia & Lafayette, Co.
Posts: 1012





Ignore
« Reply #22 on: December 05, 2017, 06:27:50 AM »

Tom, if in doubt, using double shocks like a normal bike will take a lot of load off of the swing arm.  Another advantage is the dual shocks act like struts if they are bottomed out and this takes huge loads away from the swing arm.

Bo,
I'm probably not normal and neither is my bike!  And I don't plan on running the Baja 1000, so the possibility of the shocks "bottoming out" is hopefully not going to happen.  Besides that, who wants to read a topic about adding normal twin shocks to a normal swingarm?
Tom
« Last Edit: December 05, 2017, 06:34:02 AM by Koncretekid » Logged

We get too soon oldt, and too late schmart!
Life's uncertain - eat dessert first!
Seldom Seen Slim
Administrator
Hero Member
***
Offline Offline

Age: 69
Location: Skandia, Michigan
Posts: 11824


Nancy -- 201.913 mph record on a production ZX15!


WWW
« Reply #23 on: December 05, 2017, 10:44:05 AM »

How would shocks bottom out on the salt?

Back about ten years ago (when the salt was a tad smoother than today)  we hadn't properly set the compression rebound on the shocks on the ZX12.  It was too slow - so the bumps kept slowly compressing the shocks more and more -- and pretty soon we would get handling issues as the suspension geometry changed/shocks got "shorter".

Don't say it can't happen!! evil
Logged

Jon E. Wennerberg
 a/k/a Seldom Seen Slim
 Skandia, Michigan
 (that's way up north)
2 Club member x2
Owner of landracing.com
Koncretekid
Hero Member
*****
Offline Offline

Age: 70
Location: Yarmouth, Nova Scotia & Lafayette, Co.
Posts: 1012





Ignore
« Reply #24 on: December 05, 2017, 11:39:55 AM »

How would shocks bottom out on the salt?

Back about ten years ago (when the salt was a tad smoother than today)  we hadn't properly set the compression rebound on the shocks on the ZX12.  It was too slow - so the bumps kept slowly compressing the shocks more and more -- and pretty soon we would get handling issues as the suspension geometry changed/shocks got "shorter".

Don't say it can't happen!! evil

I certainly hope not.  But the dampening could be an issue.  You state that you had to ease off the rebound adjustment on the shocks to prevent their jacking down or whatever it is called.  These Chinese pit bike shocks don't have any dampening adjustment, but they don't seem to have much, if any, anyway.

And Bo, I hope I didn't offend you with my offhand comments about the twin shocks, but truly I'm surprised nobody came up with "Why didn't you just add twin shocks?" earlier.  The reason is that I was afraid that they might interfere with the fairing, and the subframe on my bike wasn't designed to handle the load at the rear extremity.  And I guess I wanted to figure out how the single shock would work and now I've learned something.  We get too soon oldt, and too late schmart!

Tom
« Last Edit: December 05, 2017, 11:42:04 AM by Koncretekid » Logged

We get too soon oldt, and too late schmart!
Life's uncertain - eat dessert first!
Rex Schimmer
Hero Member
*****
Offline Offline

Age: 74
Location: Fulton, CA
Posts: 2125


Only time and money prevent completion!




Ignore
« Reply #25 on: December 05, 2017, 02:53:18 PM »

Tom,
Love what you have done to your bike! One comment, that goes along with several others, is that the fit between the swing arm bushings and the shaft need to be very close especially as the distance between the bushings is somewhat narrower than normal. I would also suggest using 1144 ground and polished rod for the swing arm bolt. It is strong, over 100,000 psi tensile, very easy to machine and the tolerance on the ground and polished items is +0 -.001. One other thing that I have found works of resisting corrosion is to soak the item in Gibbs oil after you are done. Let is set for a couple of weeks, what ever it does it seems to work.

Nice job!

Rex
Logged

Rex

Not much matters and the rest doesn't matter at all.
wobblywalrus
Hero Member
*****
Online Online

Age: 64
Location: backwoods Oregon
Posts: 4470





Ignore
« Reply #26 on: December 05, 2017, 08:22:19 PM »

The spring/shock system absorbs and dissipates impact loads.  It needs to allow controlled wheel movement so it can do its job.  The front and rear spring rates are set so the suspension bottoms out occasionally on a rough track.  So, adequate strength in the swing arm assembly during botttom-out is a concern.

Last year the suspension travel was used up a few times during the pass I made.  The track was real rough and the suspension was working very well.  Lots of impact was dispersed and dissipated before it upset the chassis.     
Logged
Koncretekid
Hero Member
*****
Offline Offline

Age: 70
Location: Yarmouth, Nova Scotia & Lafayette, Co.
Posts: 1012





Ignore
« Reply #27 on: December 06, 2017, 12:28:30 PM »

The spring/shock system absorbs and dissipates impact loads.  It needs to allow controlled wheel movement so it can do its job.  The front and rear spring rates are set so the suspension bottoms out occasionally on a rough track.  So, adequate strength in the swing arm assembly during botttom-out is a concern.

Last year the suspension travel was used up a few times during the pass I made.  The track was real rough and the suspension was working very well.  Lots of impact was dispersed and dissipated before it upset the chassis.    
Bo,
I didn't realize that you experienced full compression in your suspension last year.  What is the load on your rear axle at the shocks at rest with you aboard?  And what is the maximum travel of the shocks?  Do you know the spring rates and especially the spring force at full compression?  Knowing those numbers would help me in setting up my suspension as I can adjust the rate/travel and the initial sag to compensate.  As you know, we can't determine the load on the swingarm when it bottoms out because it is an unknown impact load, and that is what will bend or break a swingarm with the single shock at the front.


Love what you have done to your bike! One comment, that goes along with several others, is that the fit between the swing arm bushings and the shaft need to be very close especially as the distance between the bushings is somewhat narrower than normal. I would also suggest using 1144 ground and polished rod for the swing arm bolt. It is strong, over 100,000 psi tensile, very easy to machine and the tolerance on the ground and polished items is +0 -.001. One other thing that I have found works of resisting corrosion is to soak the item in Gibbs oil after you are done. Let is set for a couple of weeks, what ever it does it seems to work.

Nice job!

Rex

Thanks Rex, and I will look for such a shaft and the important align boring necessary to ensure a good fit next time I'm in Colorado.  For the time being, I've had a shaft made of cold rolled.  Unfortunately, reaming the bronze bushings is only as good as the machinist doing the job, and when you don't have the tools to align bore/ream the bushings, they end up with too much slack.  I'm guessing something like .005", but the machinists around here, both of them, normally only work on tree farmers, bulldozers, and fishing boats which apparently live well with that kind of tolerance.

Tom
« Last Edit: December 06, 2017, 12:35:56 PM by Koncretekid » Logged

We get too soon oldt, and too late schmart!
Life's uncertain - eat dessert first!
WhizzbangK.C.
Full Member
***
Offline Offline

Age: 56
Location: Kansas City, MO
Posts: 205


Ed Bennett, Speed Team Doo Kansas City fab shop.




Ignore
« Reply #28 on: December 06, 2017, 09:10:17 PM »

The spring/shock system absorbs and dissipates impact loads.  It needs to allow controlled wheel movement so it can do its job.  The front and rear spring rates are set so the suspension bottoms out occasionally on a rough track.  So, adequate strength in the swing arm assembly during botttom-out is a concern.

Last year the suspension travel was used up a few times during the pass I made.  The track was real rough and the suspension was working very well.  Lots of impact was dispersed and dissipated before it upset the chassis.    
Bo,
I didn't realize that you experienced full compression in your suspension last year.  What is the load on your rear axle at the shocks at rest with you aboard?  And what is the maximum travel of the shocks?  Do you know the spring rates and especially the spring force at full compression?  Knowing those numbers would help me in setting up my suspension as I can adjust the rate/travel and the initial sag to compensate.  As you know, we can't determine the load on the swingarm when it bottoms out because it is an unknown impact load, and that is what will bend or break a swingarm with the single shock at the front.


Love what you have done to your bike! One comment, that goes along with several others, is that the fit between the swing arm bushings and the shaft need to be very close especially as the distance between the bushings is somewhat narrower than normal. I would also suggest using 1144 ground and polished rod for the swing arm bolt. It is strong, over 100,000 psi tensile, very easy to machine and the tolerance on the ground and polished items is +0 -.001. One other thing that I have found works of resisting corrosion is to soak the item in Gibbs oil after you are done. Let is set for a couple of weeks, what ever it does it seems to work.

Nice job!

Rex

Thanks Rex, and I will look for such a shaft and the important align boring necessary to ensure a good fit next time I'm in Colorado.  For the time being, I've had a shaft made of cold rolled.  Unfortunately, reaming the bronze bushings is only as good as the machinist doing the job, and when you don't have the tools to align bore/ream the bushings, they end up with too much slack.  I'm guessing something like .005", but the machinists around here, both of them, normally only work on tree farmers, bulldozers, and fishing boats which apparently live well with that kind of tolerance.

Tom

Once upon a time, in a land far away, I was building a custom off road machine and fabricating the suspension system myself. I lacked the means of creating a close tolerance fit at the pivot points, much like you now. At the time there was a a product on the market that was sold to "repair" worn out ball joints. It was an epoxy material that was mixed and injected into the joint through the grease fitting. (Was not anything like a permanent repair and used primarily by shady used car salesmen.) I found this perfect for my needs. I put a grease zerk on the joint, smeared grease on the pivot bolts, and injected the material into the joint and let it cure. Like I said, it didn't last forever, but was perfect for the limited use I needed, and would work well for your purposes here too. I don't know if it's actually still available anywhere and don't remember the brand name, but you could probably come up with something to work the same way.
Logged

Ah, this is obviously some strange usage of the word 'safe' that I wasn't previously aware of.  Douglas Adams
Podunk
Full Member
***
Offline Offline

Age: 73
Location: Hebron, IN
Posts: 174




Ignore
« Reply #29 on: December 07, 2017, 12:20:31 PM »

PM sent
Logged
Pages: 1 [2] 3   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Simple Audio Video Embedder
Valid XHTML 1.0! Valid CSS!


Google visited last this page December 07, 2017, 03:44:58 PM