Resources for designing a transmission? |
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Elpwnage20
Welding Master Joined: Apr/12/2014 Status: Offline Points: 225 |
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Posted: Sep/16/2014 at 11:04pm |
Hi Guys! This is our first year starting a Baja team at our school and I have a team of three working on the drivetrain as a capstone project. I'm not very sure of how the various components in the drivetrain work on a baja car i.e the CVT, transmission, differential. What does the CVT do that the transmission can't do? Do I need a CVT? Do I need a differential?
Does anyone know of any resources that can help me with this? |
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Richie_Dagger
Baja Godfather Joined: Sep/25/2011 Location: Las Vegas, NV Status: Offline Points: 615 |
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I've uploaded two pictures of some transaxles that have been posted on the forums. The first has no neutral or reverse and has a Honda cam and pawl differential, while the second is a F-N-R with a spool. You can run an open diff, spool, or an LSD depending on your design philosophy. You just have to keep in mind that what you choose in a differential has to mesh well with the rest of the car. A spool is naturally going to want to understeer, so putting it in a rear heavy car that keeps both rear tires on the ground with little weight transfer would be an understeering disaster that would be troublesome in maneuverability. However OSU uses a rear weight bias and keeps their tires on the ground so they can utilize their open diff and cutting brakes effectively. You can find a lot of information on how a differential will effect your car's design on the forums and in race car books. If you're talking about a CVT vs a manual trans, a CVT can shift without a momentary pause that kills valuable momentum, and keep engine RPMs at a relatively constant speed as well. You don't need a CVT, but after trying a 6spd manual from a Yamaha Blaster last year we're going back to a CVT. For a first year team, the simplest setup would probably be a CVT with a double chain reduction to a spool. But since you're doing this as a capstone project maybe you want something a little more rigorous, it seems that at a lot of schools somebody makes a transaxle for their capstone project.
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krowx
Welding Master Joined: May/19/2012 Location: Norfolk, VA Status: Offline Points: 117 |
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Our chain drive utilizing Honda Cam Pawl. Easy, Cheap and very reliable.
https://www.facebook.com/ODUBaja/photos/pb.159882564108959.-2207520000.1410972219./616917131738831/?type=3&theater |
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Karson
ODU BAJA 2011 Kansas 2012 Wisconsin 2013 RIT 2014 Illinois |
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cozierad
Bolt Sorter Joined: Oct/03/2012 Location: United States Status: Offline Points: 27 |
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You can run just a manual transmission, skip the CVT/ gearbox combo all together if you really want. This is what we have done for several years. We like the manual gear box, ours last year was pnuematic/electric controlled(think paddle shifters).
The first picture is one of our old cars. Engine on top with a chain to the gear box(out of a honda bike) then a chain to a spool out back http://i815.photobucket.com/albums/zz76/cozierad/photo.jpg The second/third pictures is of our current system. A side by side configuration where the trans is bolted right to the engine. This is a custom machined case. http://i815.photobucket.com/albums/zz76/cozierad/trans.jpg http://i815.photobucket.com/albums/zz76/cozierad/photo1.jpg
Edited by cozierad - Sep/19/2014 at 9:51pm |
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Elpwnage20
Welding Master Joined: Apr/12/2014 Status: Offline Points: 225 |
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Wow that's pretty wicked! What about a clutch though? Did you guys buy one or make your own? MY problem is that I don't know how to start making a manual gearbox for the car. |
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Richie_Dagger
Baja Godfather Joined: Sep/25/2011 Location: Las Vegas, NV Status: Offline Points: 615 |
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We ran a manual last year by taking a Yamaha Blaster motor and ripping the whole top end out. We then pulled the crank out and machined an input shaft that ran from the B&S crank through the main bearings and crank seal to drive the clutch using the original crank gear. It was a pretty simple conversion. But we were disappointed with the performance and are going back to a CVT. Our untuned P90 primary/CVtech secondary hybrid is already quite a bit faster than the old setup both on top speed and a 100' timed run. You can kind of see it in the picture below.
Edited by Richie_Dagger - Sep/20/2014 at 11:49am |
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cozierad
Bolt Sorter Joined: Oct/03/2012 Location: United States Status: Offline Points: 27 |
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The internals for the case are from a Yamaha XT225, it includes a clutch. When i have pictures of the system I will post them up. A hydraulic clutch is used that is linked to a manual handle mounted next to the drivers right hand. This allows the driver the feather the clutch. The hydraulic clutch is also linked to an air cylinder that can throw the clutch on the push of a button. the clutch is only needed for stop and start, shifting up and down just require the driver to let go of the gas. In terms of making one, start with a CMM to get all of your shaft and bearing locations, clearances for gears/shifter mechanisms. Have a couple of people look at the model and verify it. Buy a $1200 7075-t6 chuck of aluminum and make a case. Sounds simple right?
Edited by cozierad - Sep/29/2014 at 11:18am |
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Miami University: RedHawk Racing
Oxford, Ohio Miami was a University when Florida belonged to Spain... |
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cozierad
Bolt Sorter Joined: Oct/03/2012 Location: United States Status: Offline Points: 27 |
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Northeastern ran the blaster internals in their custom case last year. It has a clear clutch cover that was one of the coolest things I've ever seen. They tend to do pretty well too.
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