Quote:
Originally Posted by WCRiot
What gear ratio do most of you use? I need to go 30-40mph, and move an 800lbs (without batteries and other electric drivetrain parts) buggy.
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Quote:
Originally Posted by WCRiot
So i need to decide on gear ratio. then electric motor/controller combo. Tires are 24inch. Gear ratio of differentials is 4:1 with these tires. So the gear ratio at the motor probably needs to be close to 10:1
It sounds like most golf carts are running around 15:1
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Hi WCRiot,
It sounds like you have an interesting project going on.
I have a fairly heavy Cushman work cart (1620 lb operating weight / 1200 lb capacity) which is rear wheel drive (other cart specs are in my footer below). As a comparison, the gear ratio on my cart is 15.875 to 1 and is certainly geared for higher torque. My GPS measured maximum speed on a level section of gravel road is 17.4 mph on 23" tires (72" tire circumference measurement). At a 17.4 mph maximum speed, my motor would be rotating at 4050 RPM.
I mention the above Cushman specs since your original requirements stated that you "need to go 30-40mph" which is about twice as fast as my maximum speed. To get that speed, you will have to have a gear ratio that will support that speed, as well as a motor that will provide enough torque to meet the physical requirement of your cart. From what I read on BGW, an upper speed limit of up to 25 mph is achievable on most carts, but going above 25 mph is going to need better braking, suspension, steering and tires... plus the obvious improvements to the battery and motor. The MOT A1 motor you have ordered is rated for a 22 mph maximum, so perhaps you have reduced your maximum speed requirements or you may need to shop for a higher speed motor.
When talking about gear ratios, you mention the motor to driveshaft of 10:1 and the differential (driveshaft to axle) at 4:1 ... which will result in a 40:1 ratio from the motor to the axle. To achieve a motor to axle ration of 15:1, with your 4:1 differential, your motor to driveshaft ration will need to be 3.75:1 (i.e. 15 divided by 4).
Are you planning to have the cart operating on full time four wheel drive? If so, you may want to confirm that you will have sufficient motor torque available. I understand that full time 4WD carts use considerable more power and your battery, solenoids, controller, motor and etc. will need to be sized appropriately. You may have researched this already, but understanding how other existing electric 4WD carts are powered may help you "right size" your components in advance.
Good luck with your build ... I look forward to following your thread.
Regards, 3CW