Acceleration MPH |
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Unproductive
Milling Master Joined: Jul/11/2009 Location: Rochester NY Status: Offline Points: 66 |
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I was wondering what kind of mph you guys were seeing at the end of the accel test, or in the endurance for that matter.
We don't have the datalogger setup yet. Edited by Unproductive - Jul/17/2009 at 12:56am |
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-Bob
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adrive7
Baja Godfather Joined: Oct/19/2008 Location: Lancaster, CA Status: Offline Points: 711 |
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In CVT tuning sessions before I left, we were getting ~20mph through 100' gates, and a max around 32. Far slower than it should have been based on calcs, even with big loss factors. CVT still needs work.
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-Joe
Chief Organizer, Baja California 2016, 2017, 2019 Ohio State Baja 2005-2009 Co-Host, Science... Sort Of http://www.sciencesortof.com |
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Waffles
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Although CVT tuning is certainly the most important and most time consuming part of baja, don't forget that there are other factors which limit the top speed of a baja car. One of our alumni once did a back of the envelope calculation analyzing the amount of drag that a flat plate of equal area to the firewall makes at speed. You eat up that 10 HP in drag pretty quick, which is why it's important to make your firewall as small as possible and drivetrain as efficient as possible
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adrive7
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Yeah, but at 30mph you are only looking at 2HP. I just ran that calc. Thats with a big firewall. Our car should have been doing in the mid 40's, and you could see clearly the pulleys weren't spooling fully.
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-Joe
Chief Organizer, Baja California 2016, 2017, 2019 Ohio State Baja 2005-2009 Co-Host, Science... Sort Of http://www.sciencesortof.com |
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dillon_b12
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I've never seen a Baja car run mid 40s. ETS(or Sherbrooke) claims 43 in their design poster but who knows if it can actually do that. Also, top speed is not what makes a car win. We could probably change out final drive ratio and get in the 40s, but the car would ultimately suffer because it could never get fully wound out and would be short on power for hills, mud holes, and things like that. |
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adrive7
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I just ran it again. Theoretical top end aerodynamically speaking is about 50 with 10hp. Obviously there won't be much torque in the high 40's, but thats why you run a CVT or shifting box.
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-Joe
Chief Organizer, Baja California 2016, 2017, 2019 Ohio State Baja 2005-2009 Co-Host, Science... Sort Of http://www.sciencesortof.com |
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CLReedy21
Baja Godfather Joined: Nov/30/2008 Location: Marysville, OH Status: Offline Points: 736 |
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What about off road tire rolling resistance or the efficiency of a belt drive and subsequent friction losses of every moving part in the system? Fastest car that I've ever heard of was a gearbox car that could hit 38-39mph on flat ground. We geared for 36 this year and that was really stretching it and required a huge area to get topped out. If the pulleys aren't fully shifting, that means you're out of power and they won't shift farther. I'm not trying to call BS on your car, but that's way past what I've always considered possible.
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-Chris Reedy
TTU Alumni Fourwheeler Drawer "Quick with the hammer, slow with the brain." |
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rjwoods77
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Does anyone have any data from this year running the the accel events in each race?
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CLReedy21
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They were all 150' events, 2 on hard dirt, one on asphalt. As far as actual run data I don't have any since dataloggers have to be included in the cost report.
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-Chris Reedy
TTU Alumni Fourwheeler Drawer "Quick with the hammer, slow with the brain." |
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j-man
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Our 43.5 mph claim is reached on long downhill runs similar to what we had in Oregon (without the corners...) but on a level asphalt we can easily reach 37 mph (40 being a top speed on level road) depending on the wind, tire pressure, etc.
But obviously it takes a lot more than 150 ft. Air drag and tire rolling resistance are responsible for most of the losses as our biggest powertrain losses are, according to our tests, limited to the transient sequences of the CVT. If you eliminate the 43mph because you need to be a little gravity assisted, 40mph means a difference of 10,71% to our goal.
I know for sure FEI and probably OSU have similar data.
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Jean-Martin
Used to be Design leader and CNC abuser ETS Baja SAE 07-10 |
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blue2kss
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We have similar numbers to you also: Our theoretical was 43mph, but we ended up hitting a max of 38 mph for a brief second at Auburn on the slight downhill during the invitational last year according to the Race Tech. data system that we have |
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Dustin Bride
University of South Florida SAE Alumni/Consultant Mechanical Engineer - Naval Surface Warfare Center, Marine Corps. Counter IED Development |
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waylon
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When you guys are running your calculations are you using 10hp. A few years ago our team dyno'ed a stock briggs and were only seeing a peak of 8hp. This is quite a large difference and could be a significant source of error.
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CLReedy21
Baja Godfather Joined: Nov/30/2008 Location: Marysville, OH Status: Offline Points: 736 |
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When I say theoretical I mean the engine is at the rev limiter with the CVT shifted fully. It's a function of engine RPM, gear ratio, and cvt shift ratio.
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-Chris Reedy
TTU Alumni Fourwheeler Drawer "Quick with the hammer, slow with the brain." |
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johnpate01
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That's basically the same idea that we are using, but with some allowances for the CVT shift ratio never really reaching 100%. I think we shot for 95% of max in the overdrive mode.
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-John
Co-Captain, Team Tennessee 2008-2010 |
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Shocker Racer
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Does anybody have a speed that you could gear a car to, and be certain you will reach that speed. We have played around with the idea of gearing a car to 30,35, or 40 mph and know we can get there rather than gear higher and use gravity down hill.
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Wichita State University
Shocker Baja Racing |
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adrive7
Baja Godfather Joined: Oct/19/2008 Location: Lancaster, CA Status: Offline Points: 711 |
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I guarantee you can hit 20.
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-Joe
Chief Organizer, Baja California 2016, 2017, 2019 Ohio State Baja 2005-2009 Co-Host, Science... Sort Of http://www.sciencesortof.com |
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Shocker Racer
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LOL....you can get to 20 with a super high gear ratio. we currently have an old car that will theoretically do 55mph and it will do 21mph by 150ft. Much over that and you need miles to get the cvts to continue to shift.
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Unproductive
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Last year we geared the car for 45mph, it was a bad idea but we were pretty much forced to by packaging constraints.
This year we're building a 3 speed gearbox that will have a low gear, a running gear that we'll use most of the time, and a high speed gear that is mostly there because all we had to do was add a gearset. |
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-Bob
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adrive7
Baja Godfather Joined: Oct/19/2008 Location: Lancaster, CA Status: Offline Points: 711 |
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More seriously, our car last year was geared to about 44. GPS Top end was 32. 20mph through 100'.
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-Joe
Chief Organizer, Baja California 2016, 2017, 2019 Ohio State Baja 2005-2009 Co-Host, Science... Sort Of http://www.sciencesortof.com |
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jeiB
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We have our new car geared to 37mph with 23in tires but i think we are
going to switch to 25's and therefore reach a top speed of 40mph. We
hit 36mph in montreal downhill.
I ran the areodynamic calcs and i get a max speed of 40mph with the following parameters: rpm=3600 max power=9.5hp engine efficient=0.7 coefficient of drag=1.15 air density=1.2 kg/m^3 frontal area=1.2m^2 i think all those numbers are pretty conservative so maybe we can squeeze out a few more mph but anything above 40mph is unreasonable. Edited by jeiB - Nov/10/2009 at 1:33am |
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Jeremie B.
McGill Baja Racing 2009-2011 Captain minibaja.mcgill.ca |
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Shocker Racer
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40 seems reasonable to me, however i wouldnt be surprised if you get less HP than what you have accounted for. Also i dont like gearing for "downhill" as it seems you spend little time going down hill at most courses and the speed out of the corners and uphills seems more valuable to me. However, i dont think you are far off by gearing to 40. We geared this year for 37 as well.
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Wichita State University
Shocker Baja Racing |
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mu
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I was orignally shooting for 38 mph but the way the gearing worked out it'll be around 37mph. We'll see how it works out.
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CLReedy21
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We gear a little different than a lot of folks it seems. Our cars will actually run what we gear them for (maybe cause it's so low) so theoretical and actual are usually the same or 1mph off. '07 ran 27, '08 ran 28, '09 ran 33 and 35, and '10 is getting geared for 32-33.
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-Chris Reedy
TTU Alumni Fourwheeler Drawer "Quick with the hammer, slow with the brain." |
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jhu42
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I dont know, that seems a bit slow for Rochester.
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Adam Baumgartner
Social Media Director, #BajaMaryland Test Driver, Honda R&D Americas Inc Hopkins Baja, '07-'10 |
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CLReedy21
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'07 finished 3rd overall and 3rd in the endurance on the lead lap with a Comet cvt and a 27mph top end. Don't forget about all those hills, we like to go up them pretty quickly :)
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-Chris Reedy
TTU Alumni Fourwheeler Drawer "Quick with the hammer, slow with the brain." |
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jhu42
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hmmm... good point. I had forgotten :) |
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Adam Baumgartner
Social Media Director, #BajaMaryland Test Driver, Honda R&D Americas Inc Hopkins Baja, '07-'10 |
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well, if you look at the CVTech cvt for this year (same as last year), the shift range is close to 7:1. Setting your maximum speed at 40mph and a mininum torque sufficient enought to climb a 35deg incline, ideally, you would require a shift range of 6.15:1.
Thats the reason why ETS and Sherbrooke had larger than usual top speed last year, the shift range is soo big that trying to go a little faster wont hurt your torque. In montreal, our theoritical top speed was 38mph and we reached 36mph (albeit downhill) |
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Jeremie B.
McGill Baja Racing 2009-2011 Captain minibaja.mcgill.ca |
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povajax
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i know this depends on many factors but i would like to know how many rpms of the engine is the real value to calculate the real final speed
for example if i have a reduction of 10 to 1 and the cvt .76 in high tires= 22 inch vehicule weight:400 pounds top speed= 3800/(10x.76) x (22x.0000254x3.1416) x 60= 52.6656 km/hr but i dont now the real loses of the engine an cvt whats is the rpms 3200? 3600? Edited by povajax - Feb/07/2011 at 5:00pm |
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jeiB
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engine rpm is probably going to be around 3550-3600
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Jeremie B.
McGill Baja Racing 2009-2011 Captain minibaja.mcgill.ca |
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That car is not going to pass 45 km/h...
.76 maybe it's comet, maybe polaris, both cant use the whole range. in testing you'll see that neither it starts on the nominal reduction, or it ends...
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This isn't true, i tested in our test track and we reached almost 58 km/hr with our car that was 13th in acceleration in South Carolina
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Pedro
2009 team captain baja sae Uaem be wild Sara Juana Racing team |
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top speed= 3800/(10x.76) x (22x.0000254x3.1416) x 60= 52.6656 km/hr How is the top speed more then the maximum in theory? |
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How did you measure your top speed?
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Dustin Bride
University of South Florida SAE Alumni/Consultant Mechanical Engineer - Naval Surface Warfare Center, Marine Corps. Counter IED Development |
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i dont know if you read my first comment but the commentary said, for example mmmmmm ... I was just explaining my point not the ratio, weight or cvt that have our car. our car weights 370 lb it is unlikely that any team will tell you their exact ratio, and with all possible respect I do not want to fight just want some good team with experience in this area tell me what parameters used to measure the maximum speed of his ratio thats all |
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Pedro
2009 team captain baja sae Uaem be wild Sara Juana Racing team |
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I said that the example car wouldn't, and you did not explain...
anyway, that depends totally on the CVT, on it's shift point... so it depends on weights, ramps, helix, spring, reduction, belt tension....
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with a really simple method, our car was follow with a atv and the speedometer says 58 km hr our car is light (370 lb) small ans fast maybe we has the smallest car in south carolina 2010 but our suspension sucks just i think that we are fast because we have a really good power train (gearbox 11lb) and 20x7x10 tires reducing the moments of inertia but we need work a lot with suspension this is our 2010 car in south carolina |
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Pedro
2009 team captain baja sae Uaem be wild Sara Juana Racing team |
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CLReedy21
Baja Godfather Joined: Nov/30/2008 Location: Marysville, OH Status: Offline Points: 736 |
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I think this has gotten waaaay off topic. The OP wanted to know how many engine RPM teams are turning when the CVT is fully shifted. I don't have a precise answer without digging through old datalogs, which I'm honestly too lazy to do tonight.
So, any takers? |
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-Chris Reedy
TTU Alumni Fourwheeler Drawer "Quick with the hammer, slow with the brain." |
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Pedro UFPBaja
Baja Godfather Joined: Mar/03/2010 Location: Brazil Status: Offline Points: 886 |
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Funny words, man. Weight ,ratio, cvt model... mean nothing alone. What really makes it different is the setting of the cvt, if you curve it has adapted to the resistive forces which your car is subjected and keeping the engine running properly to each load situation. For example: This is our 2009 car And this is 2010 Both use the same ratio and same CVT, the 2010 is heavier but pretty much faster. PS the theorical speed serves to almost nothing, unless your car is moving on vacuum on a track with almost no friction on a straigth runway of 100 miles. Edited by Pedro UFPBaja - Feb/09/2011 at 1:53am |
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Akron 1998 to 2004
Welding Master Thread Hijack Champion Joined: Jan/20/2011 Location: WA Status: Offline Points: 327 |
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The engine governor is not digital, it's an analog device that starts to affect engine power about 300 rpm before the max RPM. Governed: 3800 RPM Peak Power: 3500 - 3600 RPM Special Note: If your car doesn't get to that speed in 100 to 150 feet on race day, IT DOESN"T REALLY MATTER! As far as I know, the last time they recorded top speed was 2005 with engines governors set to 3800 RPM. I believe this was in 100 feet.
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João Araujo
Milling Master Joined: Feb/07/2009 Location: Brazil Status: Offline Points: 61 |
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Actualli, in baja brazil, we still have a max speed test.. (but thats on 300 feet)
FEI reached 58,5, Poli-USP 55 and a lot of teams above 50. EDIT: That's in Km/h... not mph..
Edited by João Araujo - Feb/09/2011 at 2:21pm |
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UFPBaja Team - Brazil
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Akron 1998 to 2004
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FEI reached 58.5 km/h (36.4 mph), Poli-USP 55 km/h (34.17 mph)
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João Araujo
Milling Master Joined: Feb/07/2009 Location: Brazil Status: Offline Points: 61 |
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That's CVT tuning, they use a highly modded CVTech driver, and a Team performance modded secondary.
poli-usp weights 150 kg[330 lbs), FEI actually weights more (around 157 [345 lbs]). I'm From UFPBaja (same team as Pedro UFPBaja that posts in this forum also). We never could go to US, we finished 12 on baja brazil, only top 3 teams can go.. UFSC would go this year, but they were late for technical inspection, they got desqualified from the dynamic events. in 2008 UFPE reached 56 km/h, i don't believe that 2 km/h is that much more. Our new car is weighting 143 kg (314,6 lbs) now, it's not finished yet, when it does, it will weight around the same as Poli-USP.
Edited by João Araujo - Feb/09/2011 at 3:10pm |
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jeiB
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Careful Akron 1998 to 2004, you seemed to be accusing FEI of cheating. They are a VERY well established team and have no doubt a GREAT car every year. Top speed has nothing to do with weight.
Things that will help your top speed: Rolling resistance drag (they have a half firewall, thus reducing there drag coef,) drivetrain efficiency |
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Jeremie B.
McGill Baja Racing 2009-2011 Captain minibaja.mcgill.ca |
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Pedro UFPBaja
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In the Baja SAE Brazil some teams have the engine confiscated for inspection against illegal modifications after the endurace and all engines are sealed in the cage during the rotation inspection. The FEI's car was one that had the engine seized for detailed inspection by the briggs brazilian dealer (even UFSC, POLI USP and MAUA lost the engines). Well, the engines aren't really confiscated, they are traded for new ones.
Edited by Pedro UFPBaja - Feb/09/2011 at 4:31pm |
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Akron 1998 to 2004
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CVT tuning has nothing to do with ultimate top speed if you have a long enough distance (300 feet should be plenty) the CVT completely shifts or stops shifting. It might as well be a fixed gear ratio at that point. Anyway, if your argument is Poli-USP didn’t have a tuned CVT; that’s silly. Ultimate top speed is based on rolling resistance, air resistance, drive train efficiency, and engine power output. In a competitive competition the two fastest cars are going to have approximately the same rolling resistance, air resistance, drive train efficiency. That only leaves engine power output. 58.5 km/h requires 13% more horsepower than 55 km/h (the equation has velocity squared). Maybe they just got that nearly perfect motor from the factory with all the right tolerances. It's hard to say why if no one demands an inspection. But this is off topic so if you feel like disagreeing with me, I’m sure others would prefer you contact me directly. |
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Thanks Pedro UFPBaja
Good to know the engine was seized for detailed inspection by briggs and passed. I'd love to know how they got their car that fast.
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Pedro UFPBaja
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One more thing: FEI and POLI USP has a gearbox with two speeds in series with the cvt.
UFSC has a fully funcional cvt and a 6 speed gerbox at same time!!!! see FEI's sistem: |
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dillon_b12
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Which is it man?
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João Araujo
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CVT tuning has nothing to do with top speed on 300 feet?
You have no idea what you are talking about. if the cvt shfts to soon, it makes it not use the engine full power. Read the cvt tuning handbook... on 300 feet it's not the final speed yet, so that makes a difference, rolling resistance, inertia, all that makes difference, even the CG position, makes difference.. It's not our fault if you make a 60-70 lbs heavier car... or a giant firewall, or a chain misaligned reduction, or a bad tuned cvt. Poli-USP was using a old engine, in the US they had a new model, that seems to be better.
Edited by João Araujo - Feb/09/2011 at 5:13pm |
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UFPBaja Team - Brazil
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dillon_b12 At first glace those comments seem to contradict each other but the engines were seized and inspected by Briggs and nothing was found out of the ordinary. Thus my comments don’t contradict. I’m just disappointed that I didn’t have a 110% efficient gearbox. |
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