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Rishabh View Drop Down
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    Posted: Jul/29/2012 at 8:30am
I need some help regarding suspension travel. I am using lotus suspension analyzer v5.01 for suspension kinematics. I have some confusion regarding bump and rebound values.
Values:
Bump travel:6in
Rebound travel:3in
GC:12in
Spring Constant:
Front:8.7 N/mm
Rear: 27.5 N/mm
C.O.G: 26in
Front roll center height:12.32in
Rear roll center height:16.67in
A-arms config. in front and rear.

Bump travel is the vertical movement of the spring when the vehicle encounters a full bump. I intend to use the given travel to the front suspension and not in the rear suspension. Clearly rear suspension doesn't need that much travel because of the constraint of the movement of the CV joint. The software shows the values of camber roll center etc considering that both suspensions have the same travel. Due to that the camber variation is very high in Rear Tyre( I have tried to keep the roll center close C.O.G. for the rear suspension). I am not able to figure out what should be the travel of rear suspension and I am not able to change the bump and rebound setting of rear suspension.
Front suspension:image 1
Rear suspension: image 2


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Rivera Quote  Post ReplyReply Direct Link To This Post Posted: Jul/30/2012 at 1:47pm
So, what is the actual question?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote devvrat Quote  Post ReplyReply Direct Link To This Post Posted: Jul/30/2012 at 1:59pm
analyz rear sepreatly . Lotus anyways doesn't consider effects of front on back or vise versa .u'll get the same results even if you analyz front and rear in different files ....( kinamatic analysis)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rishabh Quote  Post ReplyReply Direct Link To This Post Posted: Jul/31/2012 at 12:38am
Question is what should be the suspension travel of the rear suspension?? polaris ATV's have a suspension travels ranging from 8-10in for both front or rear suspension. Do they have CV joints with better movement when suspension travel is high as 8in. Last baja we had the problem of our axle getting out of the gear box and my team reasoned out that travel was high of the rear suspension. 
 


Edited by Rishabh - Jul/31/2012 at 12:59am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rishabh Quote  Post ReplyReply Direct Link To This Post Posted: Jul/31/2012 at 12:39am
So even If I analyze front and rear suspension separately and keep the bump and rebound setting different,I wouldn't get a different result??? Anyways I'll try it and see what happens.Thnx for the advice!!



Edited by Rishabh - Jul/31/2012 at 12:51am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Soccerdan7 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/31/2012 at 12:50am
It sounds like your problem is with axle plunge rather than joint angle limitation. You need to carefully select your final drive location to minimize plunge and then you can keep the rear suspension travel. For reference, we are able to get away with 12 inches both front and rear and I would recommend 10 or more for all teams if they can do it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rishabh Quote  Post ReplyReply Direct Link To This Post Posted: Jul/31/2012 at 12:57am
Exactly,our axle used to plunge out of the gearbox!! so the positioning of the final drive train would solve the problem, and then we can extend the travel of the rear suspension?? But camber variation is very high with this much travel in the rear suspension(A-arms). And minimizing the camber variation  positions my roll center away from the C.O.G causing significant roll. Do you think the geometry of my A-Arms is incorrect according to the variations that I am getting????
Rear roll centre position w.r.t C.O.G:9.in
 


Edited by Rishabh - Jul/31/2012 at 1:56am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/31/2012 at 8:49am
There is no correct geometry.  You need to define goals for your system, and then prioritize the compromises you'll have to make. 
 
What Danny was referring to by axle plunge was not the movement of the stub portion of the shaft that enters the gearbox, but the plunge of the shaft between the CV joints.  If your geometry requires a shaft to stroke more than your actual shafts can accommodate, your shaft will pull out of the gearbox. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote devvrat Quote  Post ReplyReply Direct Link To This Post Posted: Jul/31/2012 at 9:39am
if u are taking part in baja india 6 inch in bump and 4 in rebound is enough..but the track requires good roll properties...and watch out for the stiffness of springs..prefrably d-zin ur own springs.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Soccerdan7 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/31/2012 at 2:49pm
What is the track like for baja India? I highly doubt you need to design your own springs
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Post Options Post Options   Thanks (0) Thanks(0)   Quote devvrat Quote  Post ReplyReply Direct Link To This Post Posted: Jul/31/2012 at 4:23pm
the track has a crazy straight line down hill stretch with sharp downhill curv at the end . cars have rolled over in the past..and the curves at most places are banked in wrong direction or can say damaged...with limitation in atv tires available here it becomes a bit tough to have full independence in suspension design ..the manuverability track is quite narrow and quite challenging but it needs more driving technique than a good suspension, the hill climbs are near to 37 deg..and use of cvts are limited, 10 percent of the teams run on cvts as the difficulty of getting spares is a huge problem..
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rishabh Quote  Post ReplyReply Direct Link To This Post Posted: Aug/01/2012 at 12:19pm
Ok,so according to you my priority should be to design the suspension with roll stiffness high enough to prevent roll, and 6in 4in bump and rebound setting comply for rear suspension too for indian baja??? we used a mahindra alfa gearbox and I think the problem was that gearbox was not designed for that much travel because maybe it's not meant for off-roading, perhaps that was the reason the axle was coming out!! I was adviced by the members that proper positioning of the drive train would solve the problem,but even then can a alfa gearbox give a travel(10in) without the axle being plunged out?? 

Edited by Rishabh - Aug/01/2012 at 12:24pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ErikHardy Quote  Post ReplyReply Direct Link To This Post Posted: Aug/01/2012 at 12:37pm
You're first priority should be making your drivetrain work mechanically. Until that gets figured out, vehicle dynamics mean absolutely nothing. Once you can confidently make things work mechanically then jump into vehicle dynamics theory and see if you can massage some of your mechanical points to better suit the vehicle setup preferred.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: Aug/01/2012 at 2:07pm
Originally posted by Rishabh Rishabh wrote:

Ok,so according to you my priority should be to design the suspension with roll stiffness high enough to prevent roll, and 6in 4in bump and rebound setting comply for rear suspension too for indian baja??? we used a mahindra alfa gearbox and I think the problem was that gearbox was not designed for that much travel because maybe it's not meant for off-roading, perhaps that was the reason the axle was coming out!! I was adviced by the members that proper positioning of the drive train would solve the problem,but even then can a alfa gearbox give a travel(10in) without the axle being plunged out?? 

A gearbox is NOT designed for travel. It sits, spins, and sometimes looks pretty. The box should not travel/move.

What you were being advised of was the placement of the output shaft of the gearbox that would allow the CV shaft to remain connected to the hub and output shaft through the full range of suspension travel.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rishabh Quote  Post ReplyReply Direct Link To This Post Posted: Aug/01/2012 at 11:59pm
Well I know that gearbox doesn't travel. What I meant was the portion of the gearbox in which the axle is inserted and I got your point.According to you a travel of 8-10 in rear suspension is possible so I'll work according to that.
  


Edited by Rishabh - Aug/01/2012 at 11:59pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Purduebaja Quote  Post ReplyReply Direct Link To This Post Posted: Aug/02/2012 at 1:20pm
If you bring your inner suspension points closer to the centerline of the car you can use longer cv shafts and get less cv angle change per inch of travel. The rear of your chassis (between suspension points) is rather wide and you are either going to hit the limit of the cvs maximum articulation or their maximum plunge. By tuning where the cv joints are in space you can minimize plunge, but that still isn't going to help with the articulation. Otherwise you would have to lower your static ride height at least in the rear to still get high travel while being within the limits of the cvs. I understand you may be contrained by an oem gearbox for your inner cv spacing, but longer links and shorter chassis is usually a good rule of thumb to follow when trying to design for high amounts of travel. Less cv angle will also help a little with drivetrain efficiency. Do you guys have a number of degrees that's the cv joint can handle? We had this problem two years ago in which the rear suspension was fine at ride height but at full droop it destroyed the cvs. We ended up having to run limit straps to bandaid the problem
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: Aug/02/2012 at 5:42pm

 

Originally posted by Rishabh Rishabh wrote:

Ok,so according to you my priority should be to design the suspension with roll stiffness high enough to prevent roll.

?

The formula for rollover takes in account track width, lateral acceleration (the speed you have and the radius of the corner), and the CG height. Change those things and you wouldn't have a problem anymore.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rishabh Quote  Post ReplyReply Direct Link To This Post Posted: Aug/03/2012 at 2:17pm
Calculated Maximum Cornering speed:
32.2 kmph. 
22in C.O.G. 
Turning radius :6.7m.
track width :54in


Edited by Rishabh - Aug/03/2012 at 2:26pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rishabh Quote  Post ReplyReply Direct Link To This Post Posted: Aug/03/2012 at 2:43pm
Thanks for your valuable points and I think lower the ride height is a good option !!! Plus the roll cage was constrained of having powertrain within 25in so accordingly I made those suspension mounting points. But we'll try to make changes accordingly either by changing the mounting points or increasing the track width.
No,we didn't have the data of the number degrees the CV joint can handle.
Is it more for an ATV's axle as compared to a normal passenger???  
   


Edited by Rishabh - Aug/03/2012 at 3:02pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Purduebaja Quote  Post ReplyReply Direct Link To This Post Posted: Aug/05/2012 at 5:09pm
It depends on the atv, but many FWD passenger vehicles don't have all that much articulation on the inner cvs but have alot more on the outers since they need to be able to travel vertically and turn. We used honda foreman CV joints which only have articulations in the low 20s on the inners depending on what plunge you are running. There are companies such as gorilla axle who provide high articulation CV joints but you can avoid this problem by making your shafts longer. Keep in mind that increasing your rear track width in relation to your front track width will have a tendency to increase understeer.

Edited by Purduebaja - Aug/05/2012 at 5:09pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bajasid Quote  Post ReplyReply Direct Link To This Post Posted: Jun/14/2013 at 10:38am
Our team is facing a similar problem this year.
I've oversized the tire dia, dropped the ground clearance by 2 inches AND pretty much maxed out vehicle track. And still, my half-shaft angles at ride and droop are higher than they should be.
Plunge seems to be fine, though.
Is there any other approach that I can use? Using polaris RZR rear axles.
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Yes, design your car properly, respecting the angles and travels.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lingesh Quote  Post ReplyReply Direct Link To This Post Posted: Jul/20/2014 at 1:15am
where can i get the software&how to activate the software? plz help
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Andy.R Quote  Post ReplyReply Direct Link To This Post Posted: Feb/23/2015 at 12:12am
The cv is only as limiting as the length of your trailing arm, I have played with the model of having 20 inches of travel in the rear, granted it did not meet spec, but I was still within the CV limits of 20deg. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richie_Dagger Quote  Post ReplyReply Direct Link To This Post Posted: Feb/23/2015 at 1:42am
Originally posted by Andy.R Andy.R wrote:

The cv is only as limiting as the length of your trailing arm, I have played with the model of having 20 inches of travel in the rear, granted it did not meet spec, but I was still within the CV limits of 20deg. 
How'd you manage that? Even with a 32" axle that's barely possible. It's hard to push 16" of travel with 30* CV angle limit and a long (for SAE Baja) 22" axle.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FelixB Quote  Post ReplyReply Direct Link To This Post Posted: Feb/23/2015 at 9:46am
With 20 inches of travel, i hope you had good ground clearance :P
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Andy.R Quote  Post ReplyReply Direct Link To This Post Posted: Feb/23/2015 at 9:54pm
I spoke to soon, went back and modeled it. I was wrong I had 16.3 inches of travel with .2 inches of plunge.  and that was within 21deg of cv travel.  My bad. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Andy.R Quote  Post ReplyReply Direct Link To This Post Posted: Feb/23/2015 at 9:57pm
you could achieve 20 inches with a solid axle and a long drive shaft with a mid mounted engine. Might workTongue
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FelixB Quote  Post ReplyReply Direct Link To This Post Posted: Feb/23/2015 at 10:14pm
he he he, still that's pretty good suspension travel! I assume that it's at the wheel?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerin Quote  Post ReplyReply Direct Link To This Post Posted: Dec/01/2015 at 9:34am
can anyone tell me how to control output shaft without being plunged out frm tripod joint while using trailing arm!

Edited by Jerin - Dec/01/2015 at 10:05am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kcooper273 Quote  Post ReplyReply Direct Link To This Post Posted: Dec/01/2015 at 11:23am
If you have that much travel, try using a limiter strap on the trailing arm.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerin Quote  Post ReplyReply Direct Link To This Post Posted: Dec/01/2015 at 12:12pm
Is there any proper design methodoloy to restrict its motion? Without usingstrap
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FelixB Quote  Post ReplyReply Direct Link To This Post Posted: Dec/01/2015 at 12:51pm
you could try this
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerin Quote  Post ReplyReply Direct Link To This Post Posted: Dec/01/2015 at 12:56pm
is there anyother way to lock the half shaft while using cv and tripod only??

Edited by Jerin - Dec/01/2015 at 1:02pm
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lots of worm-clamps and gorilla tape
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerin Quote  Post ReplyReply Direct Link To This Post Posted: Dec/01/2015 at 1:07pm
So how did u used those
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RLM Quote  Post ReplyReply Direct Link To This Post Posted: Dec/01/2015 at 5:08pm
using Adams software, you can play with your suspension geometry and simulate its cyclical motion. with a member to act as the drive shaft, you can measure the plunge over the travel. from this you can proceed one of two ways:
1) attain an axle which can handle the plunge (we have used one in the past that did 3" plunge by plunging at both the inner and outer CV
2) move your suspension points or gearbox output shaft relative to each other and reduce the amount of plunge. HINT: if you lower the output shaft of the gearbox relative to the suspension points, you can decrease the plunge required, however you may run into clearance issues with regard to other components

Hope this helps

also point of information a tripod joint is a type of CV joint so it would be ideal to refer to them as inner and outer CV joints.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerin Quote  Post ReplyReply Direct Link To This Post Posted: Jan/22/2016 at 11:12pm
Can anyone help me for how i can change schrader valve or air valve of fox float 3 coz we jzt broken it and all the air is leaking out!!
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I would assume it just unscrews with a valve tool just like the one in a tire. the tool is cheap and can be found at all major auto parts chains. you can often get a small box of new valves in a box with the tool.
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how did u set the COG to 26 in ?
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In lotus you just type in the coordinates (x,y,z) of the COG. This can be obtained through various methods which include but are not exclusive to weighing+math, or from a complete car CAD model. 
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See that is okay.. but what if I have just started my design. I am making my geometry for the first time so I wont know or u cant derive it from any models where my new car will have its cg.
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Joined: Nov/15/2012
Location: Hamilton, ON
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Points: 1258
Post Options Post Options   Thanks (0) Thanks(0)   Quote RLM Quote  Post ReplyReply Direct Link To This Post Posted: Apr/28/2016 at 12:59pm
you'll have to set a goal of where you want it to be and then use old cars as a validation of you goal. 
McMaster Baja Racing (09-Dec 2015)
Team Captain 2012-2015
Suspension Lead 2015-2016
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Double Secret Probation
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Joined: Apr/27/2016
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Post Options Post Options   Thanks (0) Thanks(0)   Quote orc_7 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/28/2016 at 1:35pm
so if i consider a cg and then work on the design.. then after assembly of my whole buggy if i do not get the same cg my geometry is useless and wont behave the same.?
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Baja Godfather
Baja Godfather
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Joined: Nov/15/2012
Location: Hamilton, ON
Status: Offline
Points: 1258
Post Options Post Options   Thanks (0) Thanks(0)   Quote RLM Quote  Post ReplyReply Direct Link To This Post Posted: Apr/28/2016 at 9:50pm
if you estimation is done well, and you use previous knowledge of COG of other cars, it should be close. 
no matter what the car will not behave exactly as designed because as soon as the terrain changes (i.e. constantly) the sim will not be identical to real world. 
McMaster Baja Racing (09-Dec 2015)
Team Captain 2012-2015
Suspension Lead 2015-2016
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Joined: Apr/27/2016
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Post Options Post Options   Thanks (0) Thanks(0)   Quote orc_7 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/29/2016 at 9:45am
Ok thank you..
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