Then I'm in good company
Caster and shock angles...am I overthinking this?
- Thread starter Zandoz
- Start date
choppedtop
Well-Known Member
I am too lazy to do a test. Anyone know how much the degree in caster would change from normal ride position, to axle traveling upwards a couple of inches? I know mine don't move more than that.
So your shocks are angled in at the top 10°...is the shock mount vertical, or is it angled out? It's looking like with the head of the shock mount directly over the outside of the frame, my shocks would be angled it at the top around 15°. It looks like you're shock mount is cut out of flat plate, and I see no gusseting. True? Have you noticed any deflecting of the shock mount? I'm thinking that at 15° I'll be needing some lateral support <shrug>
choppedtop
Well-Known Member
Ok, I got curious and did some testing. My hairpins are 33" long including front of axle. 7 degree caster. If the pivot point on the hairpin moves down 2"(on extreme rough surface bump) the caster changes to 10 degrees. If it moves down 1" it changes to 8 1/2 degrees. Figure this is for split seconds only, so I suspect it don't really matter. My shock mounts are the same as the ones in the attachment in your last post and at 15 degrees. No flexing.
ellis8500
Member
Zandoz.....my shock mounts are vertical; head is over inside of frame. Mounts are 3/8's steel plate fab'd by RPM. They do not deflect! Bolted to the frame with three through bolts. You could lift the car with them. Keep in mind that the shock puts very little load on the top mount since the shock moves under load. Even a 20 lb axial load from the shock would only put a 3.5 lb horizontal load at the top of the shock mount [20 x sin 10 deg = 3.5]. Not nearly enough to visually deflect an RPM mount.
Choppedtop...starting at 5 deg caster with 30" hairpins, a 2" rise would increase caster to 8.32 deg according to the layout I did on my CAD program.
Choppedtop...starting at 5 deg caster with 30" hairpins, a 2" rise would increase caster to 8.32 deg according to the layout I did on my CAD program.
choppedtop
Well-Known Member
Ellis, wish I knew how to run a real CAD. I checked my findings the ole fashioned way with a degree meter, some lengths of metal and my old eyes. Can you do the same thing using 33" from pivot to axle front for me? I would appreciate it.
Lee
Lee
choppedtop
Well-Known Member
Thanks Bill. I will check Turbo out. I have an old version, but I think I may need Turbo For Dummies.
Lee
Lee
fluidfloyd
Active Member
choppedtop
Here is a full blown "FREE" cad program that will run on a number of different systems. There are no gimmicks and it is fully functional. I have run Autocad for years but needed to upgrade a few years back and found this. It is a product of Solidworks and is almost identical to Autocad. There is also a manual that is a free download from their site. Well worth the time to download it. You do have to re-up once a year. They just send you a request to click on and you're good. They also send you tech upgrades and tips once in a while. There is a forum you can join to seek help or just see what others are doing. You sure can't go wrong with this program. Hope it works out for you. Good luck!
George
Note: It looks like they want to give you a 30 trial period then charge you. Pay no attention to that as it is for if you want the professional version. The cad program will be basically the same but the pro model has some features for web page use, graphics and other things that have no meaning to someone designing parts. You're still getting the powerhouse!
www.3ds.com/products-services/draftsight-cad-software/free-download/
Manual:
http://www.solidworks.com/sw/products/draftsight-getting-started-guide.htm
Here is a full blown "FREE" cad program that will run on a number of different systems. There are no gimmicks and it is fully functional. I have run Autocad for years but needed to upgrade a few years back and found this. It is a product of Solidworks and is almost identical to Autocad. There is also a manual that is a free download from their site. Well worth the time to download it. You do have to re-up once a year. They just send you a request to click on and you're good. They also send you tech upgrades and tips once in a while. There is a forum you can join to seek help or just see what others are doing. You sure can't go wrong with this program. Hope it works out for you. Good luck!
George
Note: It looks like they want to give you a 30 trial period then charge you. Pay no attention to that as it is for if you want the professional version. The cad program will be basically the same but the pro model has some features for web page use, graphics and other things that have no meaning to someone designing parts. You're still getting the powerhouse!
www.3ds.com/products-services/draftsight-cad-software/free-download/
Manual:
http://www.solidworks.com/sw/products/draftsight-getting-started-guide.htm
I did a bit of CAD testing to...using DraftSight (free and I love it). A 4-bar set-up with 21-1/2" bars configured for 7° caster, and the axle moving up 2-1/2", showed a 1° caster change. On the other hand, a mere 1/8" shortening of the lower bar decreases the caster to 5.42°. It also caused the top end of the shock to move about a 1/4".
Not really stuck...I've decided to take a stumble of faith (I've not leaped in decades) and just plan on laying out for 7° of caster built in...and hope for the best. Unfortunately I already have my shocks, or I probably would go with bearing shocks. If it turns out that the bushing shocks don't work well, then I'll change.
Did you use crush prevention tubes where they are bolted through the frame?
Dan Noecker
Member
I like the thought process going on with this issue. A nice bit of engineering.
2old2fast
Active Member
That would depend on how thick the frame rail is & what type of steel it is & how tight you tightened the bolts..... plus ,over time , my guess is the frame will deform & the thru bolt will be loose.... probably not enough to affect performance , but it will "crush"..
dave
dave
Excellent! With no welded in crush tubes, it's something I can do myself after the frame is built. But I am surprised that only 1/4" bolts are used. Did RPM custom make yours to get the right length and head angle? Do you see any reason that the mounts could be swapped side-to-side, to put the heads of the mounts over the outside of the frame rails? Over the inside, as yours are, would put the shocks at around a 25° angle...too much.
The bad news is that it looks like I'll have a set of forged F1 shock mounts to add to the pile of parts I won't be using...too tall.
ellis8500
Member
Just so we are on the same page here.....crush means permanent deformation as when one crushes a soda can. If the frame crushed then the bolt would never be tight. There is elastic deformation in the vicinity of the bolt head, about 0.007". The Spirit frames are 3/16 wall 2x3 tube. Very tough steel; I do not know the grade. It is not mild steel. It was difficult to drill and tap.
My frame will probably end up 2x3 3/16" wall...but I'd actually prefer 1/8" wall as a matter of lightness. Between the short span of the frame rails due to the short wheel base, and the light weight low power engine, the 3/16" wall seems overkill to me <shrug>
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