View Full Version : Drivetrain - mini baja

07-13-2010, 03:24 AM

I am involved with a Mini-Baja team at AUT, Auckland, NZ. I am incharge of the drivetrain for our gen 2 racer. Our gen 1 used a CVT from a Suzuki Eiger and solid chain-sprocket drive.
For gen 2 I want to incorporate a diff to aid cornering abilities and design and build a gearbox inplace of the CVT OR use the CVT and make a F/N/R box.

We have a diff of unknown source, with a locker, but the outputs have male spline for half shafts. I am not looking forward to making the adaptions!

So, does anyone recommend a diff that they have had success with?

I have read many posts that utilise Polaris items, however, in NZ they are like hen's teeth - rare to find.

I also plan to use shafts rather than belts and chains except if I use the CVT of course. I had the idea to mount the diff and rest of the rear axle on a trailing platform. For gen 1 we used an independant setup but it was a real pain. Note that I have freedom on the rear section of the chassis, thus I have been given the resonsibility to design it accordingly. The gen 2 chassis design is planned for dramatic changes and won't be finalised until well after I am completed with my project - shame.

Anyway any info will be greatly appreciated.



p.s. our team site: www.autom8s.org.nz (http://www.autom8s.org.nz)

07-17-2010, 04:24 AM
Hi Boe, welcome aboard. I got a book somewhere titled "How to build motorcycle engined racing cars" Bought it from the UK over the net. There's a section in it about making your own dif. Haven't read it in a while and when I did I didn't take too much notice of that section. But I can remember the author describing something about getting the guts out of a Ford "Fiesta" diff, (which might be an Escort in our part of the world:confused:) and enclosing it in a custom housing. There was a photo of a finished in the book. Apparently its reasonably common in the UK hillclimb scene.

Good luck:)

07-18-2010, 04:48 AM
Thanks intfit, I will look into this.

07-19-2010, 02:56 AM
For those who's partners complain that you collect junk and hoard rubbish, well it does pay off.

In our scrap parts bin, I found the half shafts to accompany my diff. That means I'll save time and money not having to make adaptors for the splines, yay!

07-24-2010, 03:30 PM
Since this is a low power application have you ever considered using dog clutches as found on Hytrol type industrial chain driven conveyors?. Of course this would give you freewheel in the forward direction but it would be 1/8th the weight of a diff. Most of these are set up to go on a keyed shaft.. I just love Aukland. My mother is from Wellington.

07-25-2010, 03:24 AM
Hi Shrapnel,

Thanks for the info. The diff I have located isn't too bad, approx 8kg / 20lbs. The extra weight will help with traction, although 0 - 100kph would be low.

Having talked to my project supervisor, he has requested that I focus my time on mathematical principles governing the CVT control/operation. Man they crack the whip! I am more happy with grease under my finger nails than using MATLAB, no offence to MATLAB! :D

It's good to hear from someone who has links to NZ. My mum grew up in Wellington / Masterton too. The only thing I hate about Auckland is the traffic - my solution would be to build a monster truck and drive over all the other motorists, mind you, parking would be a problem :D

Take care

08-11-2010, 04:09 PM

im part of a baja team in montreal canada and we always attend the north american races.

we are currently looking into the detroit gearless locker. It is usually used to upgrade some ATV or some jeeps as well. Its a locking diff so thats pretty good for of road.

We usually run a cvt (CVTech, canadian company, they sponsor baja, u should chek it out, its more suited for our application) with a custom single speed gearbox reduction.

I dont know what motor you have been using but all bajas that enter the north american races must have the SAME briggs and stratton engine (10hp..). I doubt anyone can get 100kph out of it (well its impossible)

You should check out this forum as well, specially dedicated to baja sae, LOTS of info and smart people over there lol

BajaSAE Forums (http://forums.bajasae.net/forum/forums.html?SID=79185e9e8c9z961c34d47f78eb6ee137)

good luck

PS: i looked at ur website and your car doesnt look bad, how were the performance?

09-16-2010, 03:18 AM
Hi JeiB,

Thanks for the heads up.

Gen 1 isn't complete yet due to lack of student members this year and little staff support - so no performance spec's yet
Gen 1 uses a 10hp diesel and is not upto SAE spec. It will be used for marketing purposes for the university.

Gen 2 is being designed to race intentionally, to bring it over to the states and comply with the rules.

I should have said "acceleration time" not "0-100", just a force of habbit. More like "0-0.1" :D!!!

The main problem we face at AUT is the engineering content associated with projects - all of them, not just Baja. Example, to design a gearbox, with nessary ratios, material selection, FEA backed up with solid mechanics, dynamic anaylsis and construction, does not qualify enough "final year BE-level engineering content". We must boarder on post-grad research such as applying fuzzy control to determine the best ratio or verify the transient heat Bessel function and that it applies to modeling the heat transfer on the welded areas on our chassis. This is because AUT heavily weights our cirriculum on these projects - thus Baja in particular, suffers from delays and functionality as the physical constraints on the vehicle are independant of the projects conducted. I am trying to change this but it has been hard on my own. I have effectively be conducting two projects, designing and building a drivetrain for gen 2 AND verifying my control theory and experimental apparatus for our CVT. The only way I can see a positive change is to incorporte the "design and build" at a year 3 level of our cirriculum and the year 4 stuff delves into the research stuff. However the engineering school needs to think seriously about having Baja as a perminant fixture, which I hope happens, and thus we need 100% support, which we lack right now. What the school needs to realise is that baja is not just for the petrol heads, but project development as a whole, which is significant in engineering, don't you think?

Anyway, that's my rant.

Take care,


09-24-2010, 12:36 AM
this is my 4th year on the team already and i agree that its more a project managment than anything. Anyone can built a car, but not everyone can design, built, test and race a car in 8months. Its funny, according to your university, the engineers out of mine arent qualified enough :P. oh well, bureaucracy, its everywhere, we have our fair share of problems here as well, so just stick with it and good luck

09-24-2010, 03:00 AM
Yes, it's a tough one, however, 6 weeks left of being a student and it's all over, yay! I am fortunate enough to have patience.

Not much more to finish, just the steering mechanism and plumbing the brake lines. When the car is done I'll be sure to post up some pics and vids.

I don't know how you guys are placed but good luck with your car and studies too.