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 Post subject: 250cc Gear Set & Average RPM - What were 2008 teams at?
 Post Posted: Fri Jan 09, 2009 1:28 pm 
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Joined: Tue Aug 19, 2008 8:30 am
Posts: 12
Location: Drexel University
Hi,

I'm one of the team members for Drexel's 2009 Formula Hybrid team. Last year we used a little 7 hp Briggs & Straton engine that was underpowered for our Perm generator setup. This year we're changing things around and using dual electric motors on the rear, and a 250cc Ninja ICE to spin our permanent magnet generator. We were trying to find out what average gearing other teams with 250cc's used though. The bike has a 6 speed trans, so we were just looking to see what gear most other teams were running theirs in then gearing to their generator accordingly, and also what RPM your ICE was usually ran at.

Thanks for the help, we appreciate it,



--Josh Verdieck


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 Post Posted: Fri Jan 09, 2009 7:17 pm 
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Joined: Fri Oct 31, 2008 1:46 am
Posts: 14
Location: NC State University
wow...we are doing the same sort of set up with a Perm generator and 250cc ninja. We have not yet decided on gearing. Which perm generator are you guys using? You will have to determine first what rpms you want your generator to rotate at and the required power/torque output, then go from there. If you are using it solely as a generator motor you just want it to consume the least amount of fuel to obtain a certain rpm during the normal load. Responsiveness does not matter since it is not driving the wheels.


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 Post Posted: Sat Jan 10, 2009 8:54 pm 
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Joined: Tue Oct 30, 2007 6:50 pm
Posts: 78
Location: Illinois Tech
We had two cars last year, a series and a parallel. The series never run at comp (inductor spikes can kill just about anything) but did use a ninja engine coupled with a 17kW generator. The generator delivered the voltage we were looking for around 6k rpm, which also happened to be its rated speed. So we put the ninja in top gear and then used a final drive of about 0.6 in order to get the 6k rpm needed, at around the 10.5k crankshaft rpm at which the ninja delivers its pick power. We used the pick power rpm as our target because our generator rated power was very close to our engine top power.

On our parallel system we used a YZ250F engine coupled with a pmg132 motor that was used as a generator and a motor. Again we put the engine in top gear and then we tried to match the rpm at which we got pick power from the engine to the rated rpm of our generator. This was done for two reasons: 1. If we used the pmg132 as a motor then both the ICE and the motor would be providing pick power at the same rpm and they would nicely complement our series wound traction motor, 2.If we wanted to use the pmg132 as a generator then we could extract the pick power while still having some power to help our traction motor. The car finished two of the events (autocross and endurance, we didn't pass all of tech until after the acceleration) without any left over gas but we still had about 85% SOC in our batteries. We run the last 1-2 laps of the endurance using just our electric drive. Oh and we had some acceptable lap times.

The way I see it if you are building a series system then all you have to do is find the rpm at which your engine provides a bit more power than your generator's top power and then match that rpm with the generators rated rpm. If you have a band of rpm that you can use, then use the rpm at which you get better fuel economy at the generator's rated power output. On the other hand if you are building a parallel system then you have a lot more options depending on how many electric machines you are going to be using, how they are interconnected etc. The one thing that you should keep in mind is that is worth having a controller for your generator no matter what kind of system you are using because it makes controlling the output voltage of your generator so much easier and thus the whole system easier to manage.(Exception to this would be the case in which both your motor controller and your generator controller are running on the same bus and your accumulator and generator do not have enough juice to feed the motor. Then your motor controller might destabilize your generator controller and that causes all kinds of problems depending on how the controllers were build and how they work.)

Ant
Illinois Institute of Technology
Formula Hybrid Racing


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 Post Posted: Wed Jan 14, 2009 2:36 pm 
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Joined: Tue Aug 19, 2008 8:30 am
Posts: 12
Location: Drexel University
Thanks for the info.

I'm on the EE team, but our ME team was just concerned with a couple things. One was just running the ICE at 8-9-10K RPM's for such a continuous amount of time. Also we still need to review the RPM/Power dyno charts a bit more, but it looked like we'd need to be in 5th or 6th gear to reach the output shaft RPM we need on our generator to get our 72V output. And with that, I was just wondering if there'd be issues with trying to start the ICE with it locked into 5th or 6th gear and connected to the generator.

Here's the specs on our generator/motors we're using:

Power: 8 cont-- 19 pk hp
Voltage: 72 Volt rated
Speed: 3700 rpm @ 72V unloaded


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 Post Posted: Sat Jan 17, 2009 8:06 am 
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Joined: Tue Oct 30, 2007 6:50 pm
Posts: 78
Location: Illinois Tech
As long as the generator does not have a load on it when you start the engine you shouldn't have a problem. How are you planning to control the power from the generator to your high voltage bus?


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