Hopkins Baja Design / Build Thread

talking about tire and rim carnage reminded me of this picture from Alabama where I was showing our endurance driver what he did to the tire for the first time. Needless to say we're not running those rims anymore. 

that's a 22x7x10, at the time of the picture 0 psi, prior to the picture and a run in with the railroad rails 8 psi. 

looks like we used the same rims...

this is the result after going down the rock crawl in illinois with a flat tire..


Edited by charles ulaval - 2010-Mar-15 at 10:03pm

Our problem was not the rim itself but the lack of steering blockers.. the wheel got stuck, the tire got off the rim and the rim got like the one on the picture!

Hi All !!!

Phew feels like forever since I last posted on this forum :)

Anyways, we just got back from the Greenville SC event on Monday and have been slowly getting our life minus baja back in order.

Anyways more importantly here's how we did.

Overall 28th place !!! Our teams best finish ever!!

Breakdown

Design
Report: 61.33/75  
Presentation: 71/125 
Design overall : 32nd place

Cost: 78.97/100 30th place

Dynamic:
Acceleration: 56.61/75    5.448 seconds  34th place
Manuveribility: 48.23/75   62.00 seconds 16th place
S & T : 60.81/75  34.59 seconds  26th place
Pull : 68.89/75   9.69 seconds 10th place

Endurance
28 laps 42nd place

It was a really good competition for us.  One thing that I think really helped us is our odd front track width rear track width arrangement.  We have a much narrower rear than front.  On the maneuverability course we were able to have it so that once the front wheels cleared, the rear tires would not impact a tree like the other teams were doing.  This allowed us to carry our speed through faster.

Also the 10th place sled pull did not hurt either, No idea how that happened, we did not design for it. 

Low endurance score did hurt us, we had a our Drive CVT melt (small plastic piece holding back the main drive spring) on us which cost us 40 mins for a fix.  Of course there is always stuff to improve :)

Going to fix this by lowering idle RPM significantly and possibly making the piece which melted out of aluminum

Had a great competition,  Big thanks to Robbie from SunyIT and Cornell University for those rod ends.  We used all of them !!! 

Thanks guys,
Adam

Originally posted by jhu42 Low endurance score did hurt us, we had a our Drive CVT melt (small plastic piece holding back the main drive spring) on us which cost us 40 mins for a fix.  Of course there is always stuff to improve :) Going to fix this by lowering idle RPM significantly and possibly making the piece which melted out of aluminum

Whoa! Been a while since I've been posting, sorry for the delay!

Anyways, Thanks p.lewis for the suggestion.  I think you're right about the Al piece not really fixing the problem.  Our alignment is perfect, but our CVT cover is holding in quite a bit of heat, When the piece melted the only escape for air was out of a hole only 2 cm^2.  Perhaps not the best of ideas considering that a CVT can get very hot.  I am going to get a lot more ventilation to the CVT.  We will have this fixed for Rochester.

Originally posted by RonGeorge Adam, Thanks for sharing the wealth of information and the story of your team. I really enjoyed this thread. Its interesting you had a melted component in the CVT. I can't see a plastic piece melt unless temperature rises over 250 degree F and over.  What were your CVT ratios in low and high and final gear ratios? Just curious, as you said you came 10th in sled pull unexpectedly. Were you engaging in the mid-range RPM...1900+ ?

Hi RonGeorge!

Sorry for the delay in my response!  Anyways, the ratio we are running is 12.46:1.  This is accomplished by two reductions,  the first is a 35 pitch 15 tooth to 54 tooth sprocket and the second is a 41 pitch 13 tooth to 45 tooth sprocket.  That'st just for the Chain box.  Our CVT has a low ratio of 3.0:1 and high ratio of 0.43:1 so the effective lowest ratio is (3x12.46) = 37.38:1.  The effective hightest ratio for our cvt is  (0.43x12.46)  5.35:1

Interestingly the low ratio allows you to look at some cool things.  I know that the engine will want to go to ~3400 rpm under full throttle (determined in testing empirically last fall).  Looking at the HP curve of the Briggs engine the higher the rpms the more powerful the engine.  so... if you calculate how fast the car is going using the lowest ratio of the CVT you can see at what point the car begins producing peak power.  For things like sled pull you would want to get to peak power as quickly as possible.  Using our setup we get to peak power at 5.95 mph.  The cool thing is that you can hear this in the sled pull video.



I think that's pretty cool :)

later,
Adam

Hi everbody,

Edited by jhu42 - 2010-Jun-06 at 7:43am

hmm, I hear what you are saying.

Thanks Joe.  I believe they will pass with little drama.  We ran a "worse" setup for flotation in 2008 with no problems in tech.  After being able to run off road on a track way worse than Rochester will be I'm pretty sold on this design. 

The key is that the attachments of the metal hooks of the rachet-straps are made into a 1"x.065 tube frame that runs all around the periphery of the flotation.  Its a proper chassis sub frame.  Its impossible to see this frame in the pictures.  This metal on metal attachment is much stronger than just hook on fiberglass.

Appreciate the spot!  We will be ready now to explain the design in detail in tech!!!

-Adam

We also used ratchet straps attached to a steel frame that is embedded in our molded 2 part foam. My only worry is that we have some studs welded to the subframe to locate it to the main chassis and there is no way to check to see if they are grade 5 because it's buried in 5" of 2 part foam on either side(and the head is welded to a piece of steel).

Originally posted by adrive7 Well, I guess there is some precedent, not that it always matters, but hopefully it won't be a problem. Straps are certainly a simple way to do it.

Yeah, precedent doesn't hold much weight with Jason.  This year we, as well as several other teams got hit with rule 31.1 item 1.  We brought a car that had been entered and passed tech in 2009, but even though the wording has not changed at all, this year they deemed the cage unsuitable because they changed what two points they measured from.

We also got hit for having a kill switch that wasn't perpendicular to the firewall (22.3.2 B) even though last year we mounted it the same way and it passed, with the same wording of the rule.  Jason was very adamant that "we did it that way last year" was not a valid argument.

Ratchet straps are one of the lightest options with least headache. You can try using cables if you wanted but why bother.

Adam,

Really interested to know how much power coating increased your frame weight by. Thanks.

I think the Velcro has two real reasons why it's not sound in this application:

Edited by p.lewis - 2010-Jun-08 at 12:45pm

Hi Guys,

Sorry for bringing this post back from the dead,( lost track of time I presume)  but I wanted to finish it so that when one is reading through it just does not stop all of a sudden after we did our testing for Rochester!

We did in fact go to Rochester and did pretty well!!



Here are some of the highlights

Here is our full hill climb on the Rochester "Wall"



As you can probably hear I was pretty excited, as a freshman in 2007, I was on the JHU Baja team and we were not able to ascend the hill.  Vengeance was mine this time though. 

Also the car did pretty well in maneuverability making the shortcut, despite almost rolling on the first turn.



But we really struggled in the Enduro.  We seemed to get all the bad luck we had avoided so well in Carolina!  We broke down a total of 4 times, all for broken sprockets in this race.  It was certainly a challenge, but it was a hard lesson about making sure you test for every possible scenario.  Our test course that we used did not have the same kind of hills that existed on the Rochester Course.  This low endurance score, combined with a very very unlucky S&T score put us much lower in the rankings than we were hoping. 

However, despite the low score I felt that the team really pulled together.  Even though everything was going wrong, nobody complained or moaned.  That focused team is now working on the upcomming 2011 car so watch out! 

I'm retired from being Baja Captain at JHU but man oh man was it fun!  I'm really glad to have had the chance to be Captain of a Baja team for 3 years! and to see it grow and mature!  Big thanks to all the teams that have helped us, a few off the top of my head I can remember right now, Eric of Cornell, Jean-Sebastian of Sherbrooke, Stick of USF, Steve of UMBC, Dr. Wilson and Tony Marble of TTU and many many more.

If you're reading this and have the chance to be Captain of a Baja team DO IT!!! Its the best experience you'll ever get to do in College.  I'm so glad I did it. 

Anyways this is the final entry in the Build Design Thread soooo

Currently I'm working at Honda R&D here in Raymond, Ohio!  I started June 14th, the day after the Rochester Event ended ( no joke! ) .  I drove straight from Rochester to Columbus.  I'm from Northern Virginia fyi.  Anyways the job!  I'm really enjoying it!  Its really exciting and stressful all at the same time.  Baja definetly gave me a leg up and I use the teamwork and other design skills that I got from the program everyday!



Anyways Good Luck to all the teams in 2011 (Especially JHU) !!!  I hope to be a judge at the events so if you recognize me say hi! 

See ya,
Adam










Edited by jhu42 - 2010-Nov-23 at 12:53am

Originally posted by jhu42 I hope to be a judge at the events so if you recognize me say hi!  See ya, Adam