SAE Baja 08

[Weasel]

Okay new thread. And since SAE dropped the mini it's now SAE Baja. Post of pics and specs of what you guys have. I will be dropping by our shop sometime this week and grabbing some photos. Our rear uprights are pretty trick.

Frame

[Jeepermat]

We'll be at Peoria this year, taking 2 cars (hopefully).
I have a question for sac state, did they give you much crap about your muffler placement so close to your feet? What sort of gaurds did you need around it?

Ill get back with some pics a little later

[XJ_ranger]

Originally Posted by Jeepermat

We'll be at Peoria this year, taking 2 cars (hopefully).
I have a question for sac state, did they give you much crap about your muffler placement so close to your feet? What sort of gaurds did you need around it?

Ill get back with some pics a little later

we originally had it mounted to the motor, and then a post muffler exhaust pipe to route the fumes out the side... using some 3.5" exhaust tube - so no engine losses...
but tech Jason didnt like that, and said a remote mount muffler would be better... we had to search ALL OVER to find tube with an ID of 1.25 and ended up with some Inch and a Quarter SCHD 40 pipe weighing in at like 12lbs per foot to remote mount the muffler...

we had a sheild over it with the words 'caution - HOT' on it in red paint pen, to prevent someone from touching it, but other than that - it wasnt an issue...

their big concern was that the exhaust fumes were headed towards the driver... so dont do that


some stuff for CSUS this year -
our front knuckles -





rear link mounts -


rear suspension without shock hoops -




Frame -





full thread here:
http://www.rockhardxj.com/viewtopic....st=0&sk=t&sd=a

[Weasel]

any reason you guys are going with solid axles again? I like the knuckles and gussets, nice work.

[Jeepermat]

Originally Posted by Weasel

any reason you guys are going with solid axles again? I like the knuckles and gussets, nice work.

Looks solid in the rear and A-arms up front

[crewchief]

Solid axles are tough! Easy to link and mount. Way less moving parts then independent and stronger. Trophy truck=solid rear axle.

[ZJARCHER]

Originally Posted by crewchief

Trophy truck=solid rear axle.

Not for long... Pflueger and some others are going to be soon running IRS trucks. Keep an eye out for the new generation of TT to come. Its the start of a new trend, we'll see if it works as well... Pflueger is pretty confident it will be.

http://pfluegerracing.com/08_SF_Test.mov

[Weasel]

Originally Posted by crewchief

Solid axles are tough! Easy to link and mount. Way less moving parts then independent and stronger. Trophy truck=solid rear axle.

They only use them in the rear due to the problems with getting the IRS joint to survive the operating angle due to the large amounts of travel.

For our application (light weight underpowered cars) IRS handles everything better at speed. IRS can be swept back matching the direction of impact and makes you faster through the rough stuff. It's easier to tune to vary your understeer/oversteer behavior. Roll centers move in a straight line which keep the suspension response constant through out your travel and the shock rate is progressive.

[XJ_ranger]

Originally Posted by Weasel

any reason you guys are going with solid axles again? I like the knuckles and gussets, nice work.

the same reason we have power to all 4 corners -

because no one else does!

No one on our team knows a damn thing about A-Arms, or any other independent suspension system... The team members backgrounds are in 4x4 rock crawling, drag racing, tractor driving, and karting... We're taking a stab into the dark with the front end, and fully expect to have to re-do the front IFS geometry a few times in testing...

Solid rear axle is reliable, strong, and keeps our rock crawl prowess

[Weasel]

Originally Posted by XJ_ranger

the same reason we have power to all 4 corners -

because no one else does!

No one on our team knows a damn thing about A-Arms, or any other independent suspension system... The team members backgrounds are in 4x4 rock crawling, drag racing, tractor driving, and karting

Yeah thats cool. That were we started too. I think my first year the entire team was into rock crawling and we figured it all out eventually.

There are plenty of team still running swingamrs and a linked rear is leaps and bounds ahead of that. I like the 4 wheel drive theme, we though ahrd about it for two years (actually a light duty front partial drive system(open) but we have never had a course were it would have helped enough.

[badbbmaro]

Yea the effort, time, and over all weight penalty of 4 wheel drive has been a huge headache. We would have been driving the vehicle already but we really like how unique the car is. We also know for a fact that if we continue to develop 4wd we can make it fairly competitive and just as reliable as the 2wd cars. Due to our budget, and lack of team members it is not feasible to try and go for an over-all win so the next best thing is to pick an event and break everyone else's back, which is exactly what we did last year This year, we HOPE to win the rock crawl but would also like to be somewhat competitive in the other events. If we can attain that goal, then I say keep up the research and try an IRS and a better IFS as well next year. Besides, it wouldnt be fun this year if the tech inspectors didnt think "Jesus christ! Not again! WTF Is wrong with those guys!?" Anyways, hope this sheds some light on what we were thinking, and I hope to see you guys at comp again this year!

Ken M
CSUS Mini Baja - Treasurer

[Weasel]

Nope thats cool and I think you guys can do well in the direction you are going. The big thing in doing well is not completly changing your design but perfecting and optimizing it. I think even if you had some sort of way to maybe not tranmit full power but some to the front or maybe just open in the front would work well.

And yeah when one team blows away one event, like you guys did, it really effects the scores of everyone else as the spread grows quite a bit, which I think it good.

[badbbmaro]

A front driveshaft disconnect is in the works as we speak so as to minimize the losses during the endurance race where 4x4 can be considered a waste. Last year we had locking hubs which helped but we ended up staying in 4wd with locked rear and open front throughout the race.

[XJ_ranger]

made an A-arm...

[jarmumd]

Originally Posted by XJ_ranger

we originally had it mounted to the motor, and then a post muffler exhaust pipe to route the fumes out the side... using some 3.5" exhaust tube - so no engine losses...
but tech Jason didnt like that, and said a remote mount muffler would be better... we had to search ALL OVER to find tube with an ID of 1.25 and ended up with some Inch and a Quarter SCHD 40 pipe weighing in at like 12lbs per foot to remote mount the muffler...

we had a sheild over it with the words 'caution - HOT' on it in red paint pen, to prevent someone from touching it, but other than that - it wasnt an issue...

their big concern was that the exhaust fumes were headed towards the driver... so dont do that


some stuff for CSUS this year -
our front knuckles -

We did knuckles like that in the rear of the 05 auburn car, they worked well for a single race, but I would suggest welding plates to the back of them (fully box them). I've seen them crack right at the weld between the plates and the center bearing support (fatigue failure). Good luck!

[Weasel]

Originally Posted by XJ_ranger

made an A-arm...

Nice!

[Baja Driven]

I like those knuckles, too, but I have to say Jwitz is right about fully boxing them. We've used those knuckles in the last few years since he's been gone, and after making about 50 of the bastards, I've seen how touchy they can be at times. Your plate thickness is different then ours, though, so you might be able to get away with it, just keep checking them for deformation during testing.

I'll go ahead and throw up some pics of Auburn's 08 car. Nothing terribly special, the usual Auburn car; short, CVT, and as simple as possible -

Frame -



Our version of plate knuckles (on an older car) -



From testing last saturday -



Yours truly and my little brother (our second driver). This year's seating position is amazing compared to previous cars -




Jeremy

[Weasel]

ill have to get some pic of our car rolling, did some testing today, it's fast. faster then last year...

[Jeepermat]

We have been beating on ours for a while now, but we are still plagued by our CVT.
We are running a Comet 780 and the damn thing just will not work, when driving it trys to bog the engine all the time, typically taking it down to 2400 rpms. If we pull the rear end off the ground it will wind up to 3800 no problems. We have been changing the ramp angle in the rear and springs with little effect. As far as I know the front only controls engagement speed, so it shouldnt be our problem.
We should have gone to a different CVT this year, I am really sick of this stupid thing.
If anyone has any insight to this thing let me know.

[Weasel]

Originally Posted by Jeepermat

We have been beating on ours for a while now, but we are still plagued by our CVT.
We are running a Comet 780 and the damn thing just will not work, when driving it trys to bog the engine all the time, typically taking it down to 2400 rpms. If we pull the rear end off the ground it will wind up to 3800 no problems. We have been changing the ramp angle in the rear and springs with little effect. As far as I know the front only controls engagement speed, so it shouldnt be our problem.
We should have gone to a different CVT this year, I am really sick of this stupid thing.
If anyone has any insight to this thing let me know.

Keep playing with the spring in the rear, you can also change the preload on the spring as well. We have used them and done good.

[Baja Driven]

This is going to be long, sorry for the novel, but I've done a lot of writing on CVT tuning. Also, if any of your teams use this to help, and beat us at comp, you owe me a keg (this is basically 4 years of my research, boiled down to one page)-

I've never played with the 780, we use CVTech stuff, but I may be able to help. I've done some pretty extensive tuning programs with ours, and what I've found is that a) the most important clutch to tune is the drive clutch, and b) clutch balance is essential, of course, and tuning reactions should be handled much like you would handle FD tuning; that is, for major changes, tune the drive, for minor changes, tune the driven.

Generally, the primary weight choice controls engagement rpm and max rpm, along with shift rate and linearity (however this one is actually a balance with secondary spring rate/preload). Shift rate and linearity is also controlled by the slider/roller ramp angle. In the secondary [driven], spring rate controls the downshift rate, and the spring rate and roller/slider ramps are a balancing system with the primary to control shift rate and linearity.

For your issue, jeepermat, there could be several big factors. Because it's shifting down to 2400 rpm (almost right at max torque), that means the cvt is actually doing its job fairly well, it's trying to find the optimum torque/ratio balance to accelerate the vehicle. This doesn't mean it's tuned properly, just that it's not broken in any way.

I would look first at the FD ratio. For 22-26" tires, I've found the best initial ratio to be between 35:1 and 55:1, with the ratios in between those being a personal choice to balance accel. and top speed. Anything lower than ~30:1 and you'll have major accel issues, and the top speed side will show diminishing returns based on rolling resistance and aero (we ran a fairly complete hypothetical sim a few years back that showed that due to a baja cars rolling resistance and aero drag, the maximum top speed for a baja car, running a 100% efficient drivetrain, is 36 mph. Most teams that give top speed numbers higher than that mean that their maximum ratio can yield that high number, not the actual complete system). Anything higher than ~60:1 and you'll start to see serious deminishing returns on torque (due to both diminishing rotational acceleration rates, and wheel spin), meaning you're sacrificing top speed for almost nothing. Due to the differences in weight between our vehicle and the general baja population, I would say to err on the higher side of those ranges, so that you can maintain the acceleration rates needed for short events (don't worry, I'm not calling your car fat, I just don't know which school you're from, and so I don't know what your cars usual weigh)

Next, look at your total drivetrain efficiency. Add all your efficiency connections up, and see what your theoretical efficiency is around. A cvt is going to run generally at ~95% (I was told this by an old baja captain, I can't prove it myself yet), although I have heard of numbers as high as 98%. For each spur gear mesh, we take away another 2%, for each bearing, ~.5%-2.5%, depending on the bearing style, and each chain sprocket, another 1% (this one is entirely arbitrary, we don't have the instumentation to determine chain efficiency, so we just use half of a gear mesh). Your general efficiency is going to tell you a lot of what is going on.

Next, look at the CVT center distance. Different CDs are going to yield different effieciencys and ratio ranges (that one is tricky to realize, most companies give you a set range for that CVT, but it actually changes slightly with CD, and the range they say is for one single CD). Unfortunatly, both are entirely unique to individual CVT models, and belt choice can change them as well. A better thing to look at is CVT CD versus Belt CD. A 'too loose' belt won't yeild proper acceleration, due to slippage, and won't be able to reach full speed, because there is slack in the ratio. It will also cause belt slap (a cause of additional efficiency loss due to vibrational slippage). I would say this is not your problem, because a loose belt is going to allow the engine to run higher RPMs. A 'too tight' belt will give you excellent acceleration and will reach top speed, but unfortunatly will also yeild efficiency loss due to heat after a while, loads of sheeve wear, and a ton of belt stretch that can lead to belt slap and belt side angle deformation and wear (the side angle being the most important part of the belt; think of it like a tire contact patch). This one may be part of your problem, but I doubt it. It's just something good to look at.

Finally, start in on the CVT weights and springs. Lighter weights and springs, along with lower ramp angles, are going to give you higher engagement rpms [drive weights here], higher max rpms [both], decreased downshift rate [secondary springs here], and lower driven torque [drive]. The lighter stuff will also give you faster shift outs (due to decreased rotational mass, for the primary, and decreased required shift out force for the secondary) IF the shift force can overcome the vehicles rolling resistance, weight, and drivetrain effeciency properly. As a corollary to shift rate, the vehicle is likely to see very good initial accelerations (the first 75 ft.), however, slower acceleration on longer runs (150-225 ft.) These weights are generally used for cars with lower total weight or higher initial FD ratios (the higher ratio being in balance with the decreased driven torque). Lighter primary [drive] weights could lead to engine bog when the total shift force necessary exceeds that which those weights can produce (an example of this would be a low ratio car on acceleration, the torque multiplier just isn't there). This bog would be long and drawn out, and I have a feeling this one might be your issue. Lighter secondary springs can lead to slight engine bog, as the shift rate tries to exceed the vehicles speed, but you have to be pretty far off for this to happen, and generally you will actually see belt slip (i.e. increased rpms) over engine bog in this case. The bog is this case is slight and cyclical, meaning that as the overshift occurs, the engine bogs to catch up and balance necessary torque (50 rpms or so), and then it overshifts again.

Heavier wieghts/springs and higher ramp angles are going to give you lower engagement rpms [drive], lower max rpms [both], increased downshift rates [secondary, though ramp angle might not be a factor in this one, just spring rate], and higher driven torque [drive]. You will see slower shift out rates, due to increased rotational mass for the primary, and increased shift out requirement forces for the secondary. Again, and opposite of the lighter drive weights, you will see lower acceleration in low speed or short runs (to 75 ft), but higher acceleration rates on longer straights (150-225 ft). Higher weights can lead to engine bog, as higher primary weights force the engine to work harder to rotate the clutch, and higher secondary weights increase the necessary force required for shift out. The first case leads to long bog periods, but the car will still be accelerating quite well (although certainly not at maximum rate).

I'll go ahead and take a second to talk about shiftable boxes and their CVT tuning requirements. Last year, we had a 'ground' shiftable box. It started as a fly shiftable box, but I'll go ahead and save anyone the effort of designing a fly shiftable box around a CVT by saying - Don't try it, Things explode. When tuning our CVT around the 2 speed (which, btw, I am of the firm belief that CVT tuning should be done the long way, I don't bother with DOEs or simulations. My tuning book requires no less than 360 acceleration runs for our CVT alone. Last year we ran around 1100 before SDSMT, as I also tuned around different tire diameters, sprockets, and the 2 speed. That may seem like a lot, but with a proper set of photogates, it can be accomplished in 3 evenings)... anyways, while tuning the 2 speed, I found, surprisingly, that the setup we deemed proper for first gear, was also the setup we deemed proper for the second gear. We certainly saw differences in times and speeds, however the shift rates were remarkably similar. I haven't determined if it is due to the gap between gear ratios being too similar for shift rate differentiation, if the fact that the efficiency was the same for both gears (we used a dog setup), or if it's related to the vehicle weight (or a combination of all 3). If either of you test a shifting setup and find the same thing, let me know.

I hope that helps, let me know if you have any questions or issues. Oh, and if it does help, let me know what you specifically changed to better the problem so I can add that to my research data notes. Also, having written all of that, I'm gonna brag for a second, my ego is too large to pass it up - The other night, in the test trim seen above, we managed to run a photogated 5.198 in the 150', with a top speed of 33.2 mph at 300'. Anyone who looks at the accel results from SDSMT last year will be able to tell how excited I am about that.

Jeremy
Auburn Baja

[karman1970]

Why do you say a shift-on-the fly box won't work?

[Baja Driven]

Sorry, I should have clarified. A 'clutchless' gear box with a CVT will not work for fly shiftable (unless you have developed a new system that I hadn't considered).

The CVT downshift rate is not high enough to match to the new RPM rate inside the gearbox in the time it takes to shift. You would have to have sufficient throttle control to very carefully rev match the cvt, with a downshift time of about 2 seconds (if you got the rev match spot on). During that time, the car has slowed considerably, due to rolling resistance, so you end up chasing the rpms down to 0 speed. With a clutched system, you would see the same problem, however chasing the rpms would be considerably easier.

Basically, our system used a sequential gear set that could be shifted without the use of a clutch, and we were counting on belt slip to allow us to change the RPMs of the secondary quickly during a shift. What actually happened is that the RPM change caused the secondary inner sheeve to snap turn off the ramps, and then slam home again. It sounded like a small cannon, and after the 6th shift, it broke all the slider pucks off the CVT and we scraped it.

[karman1970]

Damn. We're using a Comet 40 (2.43:1 low, 1:1 high) driving a Honda Rancher 5-speed. We've run manual transmissions every year and I never use the clutch, just back off the gas and grab the next gear. If your timing is decent, it just pops right in. Same for all my motorcycles. I guess my question would be, what does a CVT do when you back off the gas? I figured you back off for a second and with no load you just grab the next gear, stomp on it, and the CVT sees a torque change and corrects. Were you guys backing off, or just slam shifting? None of us really understand CVTs (hence the use of sequentials for 3 years now). Thanks.

[Jeepermat]

Thanks for all that, we will definatley be putting all of that info to use.
We have a fairly light car at ~390 lbs, this was us last year at SDSM.


And here we are being denied cause of this damn CVT