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Post by mtntech on Dec 21, 2013 0:40:39 GMT -5
Are rod ends ever acceptable in this application? If so, how is the proper size calculated? Shear load Rating? Good question you pose. I would answer that by saying that they were not originally designed to be used in a situation where shear forces are the primary stress. If you're going to use them so, use quality parts and err on the side of caution in terms of sizing. I would be going with a 3/4" rod end. |
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Post by captainamerica on Dec 24, 2013 18:31:22 GMT -5
This has street/track use in mind, off road trucks tend to use 3/4-1" rod ends on their suspension. The only place where larger might be needed is the lower fronts because of the push road point putting the a-arm in shear. In the future, once I have finalized a suspension setup that makes me happy I plan to put spherical bearings on all ends of the a-arms. Either that or standard car joints, can't think of what they are called, but those have their own design quirks including being in single shear when mounted (which means the upright has to be designed to handle that joint).
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Post by darrel on Dec 24, 2013 20:40:04 GMT -5
Sounds as though you have a handle on it Captain.
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Post by mtntech on Dec 25, 2013 15:06:12 GMT -5
This has street/track use in mind, off road trucks tend to use 3/4-1" rod ends on their suspension. The only place where larger might be needed is the lower fronts because of the push road point putting the a-arm in shear. In the future, once I have finalized a suspension setup that makes me happy I plan to put spherical bearings on all ends of the a-arms. Either that or standard car joints, can't think of what they are called, but those have their own design quirks including being in single shear when mounted (which means the upright has to be designed to handle that joint). Your rod ends are fine in every position with the exception of the one that connects your lower A arm to your upright. That rod end (heim joint) is bearing the entire weight of the vehicle at that corner, not to mention road impacts etc. Those loads are all shear loads,which you're asking a 1/2" threaded shaft to bear. An auto motive ball joint is mounted differently so its main load is not a shear load, rather a tensile one. |
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Post by captainamerica on Dec 29, 2013 19:54:15 GMT -5
This is basically what I just said. In the future I will have a stronger joint, probably at all ends of the a-arms.
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Post by Guest on Dec 30, 2013 2:12:53 GMT -5
Do you know the rating for loading your rod ends axially?
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Post by captainamerica on Jan 1, 2014 17:23:17 GMT -5
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Post by captainamerica on Jan 1, 2014 22:24:56 GMT -5
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Post by captainamerica on Jan 2, 2014 16:01:49 GMT -5
I understand what your saying Joker, but I would tend to think the opposite, that the force to remove the ball in the perpendicular direction is far less then the axial strength down the threads. Also from experience, you will bend the threads before you lose the ball. Basically in terms of failure on a rod end, shear at the threads is number one, then ball failure, then axial failure down the threads. www.fkrodends.com/PMXTPMXLT27.htmlI'm thinking the half inch version here will suit me fine for testing before I move to non alterable joint type. |
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Post by captainamerica on Jan 3, 2014 23:35:03 GMT -5
So he basically said exactly what I am saying at the end of the article, build adjustable setups for testing and then build a final set with spherical joints once the proper suspension setup has been decided on. I agree with what you are saying, but if you read what I wrote I am calling out specific load types, I am not talking about the manufacturer numbers or whether they are saying axial or radial or whatever. The rod end in bending is the number one failure mode, this is caused by shear force at the threads, whether from the brakes or the weight of the vehicle coming through the push rods.
Side note here, when I had a chance to drive a three wheeler down in Florida the company allowed me to drive their test vehicle which had rod ends at the lower upright joint, before I got into the car I made them change both sides because it was bent and they were running a ~900lb car with driver, they also beat this car up all the time so that probably didn't help. So even though we are all light, we are not light enough. To all those out there building and reading this forum take note of this conversation between Joker and myself, its important to the safety of your vehicles.
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Post by Liteway on Jan 4, 2014 1:09:54 GMT -5
Terrific discussion. Well reasoned, with sources supplied and informative. Sorry I have nothing to contribute, but I thought I might take advantage of the knowledge base here. I have only one set of rod ends in the front, those being on the inboard end of the steering links, normally the joints at the ends of the steering box. I installed them with the rod end ball positioned vertically instead of the usual horizontal mount, to avoid any possible angle limitations. This results in the ball's primary movement spinning in the race rather than wobbling side to side. I must admit to not seeing them used this way on the forum and wonder why. More friction perhaps? Is this ok?
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Post by captainamerica on Jan 4, 2014 21:19:43 GMT -5
Need some pictures on this one, I think I know what your talking about but I am not sure, and I can't find your thread where you have pictures of the steering system.
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Post by jim99 on Jan 5, 2014 10:41:32 GMT -5
Hi All, The 6,700 lbs rated rod end is commonly known as an economy rod end, it is not a good choice for a lower ball joint. It will bend under normal operation and break in a crash. How do I know this? Twenty years of racing formula cars and using rod ends as lower ball joints. For the lower ball joint I use a 1/2”chrom moly rod end rated at 16,500lbs, at all other attachment points I use the 6,700 lb rated rod end. Excellent source for rod ends and information is www.rodendsupply.com/ They have been around for a long time and they are racers that use their products. I put about 10,000 miles on my first trike with no problems using the same configuration of rod ends. Trike weighed 1,050 lbs empty and seated two people. My current trike has over 15K on it with no problems with this set up, seats four and weights in at 1,230 empty. I have autocrossed both trikes and tend to abuse them when out joy riding and have not had any problems with rod ends bending or failing. Jim |
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Post by Liteway on Jan 5, 2014 11:07:59 GMT -5
Actually, as I look at some of the chassis pictures of your trike I do see rod ends used, as I tried to describe, on the ends of the links that take motion from the lower A-arms to the rockers and coilovers. Why are they turned 90 degrees on the outboard ends of the A-arms? Probably no functional difference as long as off road type suspension travel is not needed, and ball angle limit in the race is not exceeded. Just curious.
If, as Joker says, pushing the ball out of the race is a possibility, using the mounting method you have on the coilover links would seem to address that. But as you say, the threaded ends would probably be the failure point anyway, so no help there.
The thread on my steering system was deleted for reasons unknown. Inquires to staff have not been answered. Do you know anything about it Jim?
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Post by captainamerica on Jan 7, 2014 15:47:35 GMT -5
If I am reading you correctly the rod ends are put that way so that their normal direction of rotation is in plane with the rotation of what they are attached to such as the rockers. On the uprights they are done that way to allow for maximum steering angle. Future designs on uprights may allow for the rod end/spherical joint to be rotated so the bolt axis is parallel to the direction of travel but structurally I don't think it makes much difference.
I agree with Jim and his conclusions from experience, I just purchased 4 rod ends from FK with 23k static load rating for my test setup, a bit pricey at $44 a piece though. This does not negate the need to put correct joints where required but from a "do I feel safe" stand point think I will do just fine with my current design until the new setup is built and ready.
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Post by Liteway on Jan 7, 2014 17:06:11 GMT -5
44 bucks a piece. Yes I can see why Jim would only use them at the lower link. Nonetheless, Its a small amount to pay to avoid a reconfig for a ball joint. I would be tempted to go with the high strength rod end but maybe in a bit larger size; 5/8 or 3/4. Anyway, if you want to take a bit more effort to do it the safest way possible, can't argue with that.
Yes, you did understand my question, and I understand your explanation. Thanks,TT.
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Post by captainamerica on Jan 13, 2014 23:15:56 GMT -5
Mid January '14
Sunday I completed my first internal and external thread on my lathe, they were mock up test pieces for what I am going to make with the spindles. I used 14 threads per inch after testing 16 and 13 to see what seemed right. Its a nice feeling to have the two threads lock together for the first time and know you did it right. I will have a pic up for this next weekend. I also got around to installing the hydraulic clutch and started plumbing the clutch and the rear brake, both should be completed next weekend. I am looking into using even stronger lower rod ends on the front suspension which come in about 20% stronger then the ones I just bought and use a 1/2" bore with 5/8"-18 threads making the shank a lot stiffer. Still trying for a mid February first drive, well see if it happens with all the work travel I have been doing lately (currently in New Mexico).
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Post by captainamerica on Jan 24, 2014 0:54:31 GMT -5
Jan 14' Lots of things are happening quickly, I just accepted a new job and I am moving to Mooresville, NC so I will be leaving behind my newly finished shop and taking my trike with me. I have two and a half weeks to smash through all the little things I need to finish to get the trike out of the road. Anyway, the spindles are almost done, I have one last nut to make which is proving to be more difficult then I thought for some reason. I have bought thread cutting tools (vardex makes nice tools) and learned how to cut threads on my lathe and have been learning quite a lot at a rate slower then I am putting out bad parts. I do not like the way that the machinist hand book lays out thread dimensions, I understand why they did it the way they did but it should just be an OD or ID and a depth to cut with a tolerance. Mostly its just badly written in my opinion and so I am ranting about it because I cut some threads to deep. Regardless life will go on. I installed the hydraulic clutch from the race motor, but its missing a piece that attaches the speed sensor so I need to make that. The fenders are on order again after waiting two months for trailerpartsdepot.com to ship nothing apparently, canceled that order. Also another complaint...trailer fender dimensioning is really stupid (22-1/2" L x 7" W x 8-1/4" H), backing out the diameter of tire that will fit from this information is a pain without a CAD sketch. The fact that most places list the size of the rim the fender should fit makes no sense, and the weird thing is they all do it. After finishing the machining on my steering rack mounts I found out that waterjet cutting circles is not exactly a good way to do things. The mount holes for the rack are canted sideways by the draft of the jet and so we get what you see in the picture which needs to be fixed by the 1-1/2" end mill I bought yesterday. Basically the draft causes the circle to be cut at an angle because of the way the jet moves through the radius. Worse case I have the tools to make ones entirely on the mill now, just not the time. I also bought a new M4 systems slip on exhaust tip which has the bonus of sounding different and not requiring a secondary mount point off the bike tail like the stock muffler, well see how it works out when it shows up next week. I still need to bust ass and get the new A-arms, steering tie rods, and push rods made so that the suspension will actually work correctly and safely.       |
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Post by captainamerica on Jan 28, 2014 23:58:55 GMT -5
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etard
Junior Member
Posts: 11 
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Post by etard on Jan 29, 2014 21:48:22 GMT -5
Looks good from here man! Go Go Go!!!
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