# Need some advice on gearing a D&D sepex 72v



## todayican (Jul 31, 2008)

I am choosing sprockets for a "ground up" build I am doing, and need some input...

its a aerodynamic trike (2 front 1 rear) with the D&D 72v sepex (425amp sevcon controller) and a 10hp diesel to make a paralell hybrid.

I need the electric motor to be responsible for speeds from 0mph to 45mph

AND...

hopefully give the diesel a helping hand in say passing speeds from 60 to 75 (if possible)

I understand that most of the torque is at the bottom of the electric motors range.

the rear sprocket is installed and I would rather monkey with the fronts if possible, it is 60 teeth.

question 1) is there any hope at all of the electric making a noticable difference between 60 and 80 in addition to the diesel?

question 2, what would the best gear ratio be if the diesel wasnt a factor (as long as the "80 mph" number diddnt exceed 5000 rpms (redline) for the electric?

I was guestimating about 2000 rpms for the electric at 60mph?

Thanks
Tom


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## eao (Mar 6, 2009)

I just joined this forum and saw your post, and was wondering how your project was coming along, because I'm planning a similar trike without diesel hybrid, using a 72V D&D es 15 6 motor (10hp continuous, 40 peak).
I'm not familiar with the specifics of your motor, but 72V x 425A = 30,600W / 746(W per hp) = 41hp, peak, minus motor/controller/etc inefficiencies. Depending on vehicle weight, you might be able to use the diesel strictly as a generator, and let the motor be the sole drive? 
Looking on evdl.org, it seems like similar vehicles use around 4:1 gearing. I haven't done my own math on that yet, though.
Eric


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## major (Apr 4, 2008)

todayican said:


> question 2, what would the best gear ratio be if the diesel wasnt a factor (as long as the "80 mph" number diddnt exceed 5000 rpms (redline) for the electric?


Hi Tom,

You need to figure the power required from the motor to get your top speed. Then check the motor performance curve to see what the top RPM for that power is. Then set the ratio such that you get top speed in mph equal to that RPM at the motor. You'll want to gear a little higher or it will take forever to reach top speed if you don't have a little extra torque to use.

Ideally you want to use the highest numerical ratio possible to solve the equation above because that will give you the most torque multiplication, meaning faster acceleration. 

Or to avoid the math, just get a bunch of sprockets and chains and play around with it until you get what you like the best. Worked for me when I did my lawn tractor. Had a set pulley on the axel. Unknown motor as far as RPM/torq curve. So I got 3 or 4 different size pulleys for the motor shaft and a couple lengths of V belts. Third try, I was golden. Been that way for the past 13 years. Yeah, I have a couple of $4 pulleys on the shelf. Big deal.

Regards,

major


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## john818 (Aug 1, 2008)

eao said:


> I just joined this forum and saw your post, and was wondering how your project was coming along


For more info on his projects, his website is http://tshtrikes.com/


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