# Building EV bike, motor question



## azninferno (Nov 12, 2008)

Would this motor be sufficient? my goal is 65+ mph with a 15mile range. Donor possibly coming this week (87 VFR)


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## major (Apr 4, 2008)

azninferno said:


> Would this motor be sufficient? my goal is 65+ mph with a 15mile range. Donor possibly coming this week (87 VFR)


Hi aznin,

My guess is that it is too small a motor for 65 mph. Rated less than 1 HP at 24. You could use 48 volts and over load the thing and get maybe 4 or 5 HP for top speed. But that is likely shy of what you'd need for 65. And, the motor would be in serious trouble of overheat. I'd look for something in the next frame size up, like a 6.6 incher, at least.

Regards,

major


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## azninferno (Nov 12, 2008)

Plan is to run either 60 or 72v. Just wanted to see. Sizing the motor is the biggest thing for me right now. It seems like all forklift motors are sized similarly, and im shooting for a 6.7" one. But what other variables should i look for? ie wattage, duty cycle...


This is another one i found
24 VOLT
1.7HP CONTINUOUS
1600 RPM
67AMPS​​G.E. MODEL # - 5BC48JB883A​


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## major (Apr 4, 2008)

azninferno said:


> But what other variables should i look for? ie wattage, duty cycle...


 

Hey azznin,

First, you must determine how much power is required to motivate the bike at 65 mph. That would be mostly aero drag at that speed. Not sure how you go about it. There are a few web sites which give formulas, mostly for cars, I think. But you could search the EV Album and see what other guys are getting with their set ups. Maybe find one similar to what you have in mind and contact the guy. Or post in the electric bikes forum.

Once you have a good estimate for required power, you can better select the motor. A continuous rated power from the nameplate at nameplate voltage is a good start. You can normally ratio that figure by a factor of 3 to 4 for like a 5 minute rating. Afterall, you're not going to be able to carry enough battery to run it continuously, meaning for like 2 hours or more. For your 15 mile range, all at top speed, would be like 15 minutes until the battery is flat. Realistically, you'd probably only have like a 5 to 7 miles range at top speed and 15 miles at lower speeds (and lower power on the motor).

So if you take that 1.7 HP motor (cont) and estimate maybe 6 HP for 5 minutes, and then ratio that up by the increased voltage (72/24), you might be able to push it to 18 HP. That might be in the ball park for what you need. You'll need more power capability to get you to top speed in a reasonable accel time factor than you'll need to cruise at that speed. And then you'll be sensitive to uphill grades and head wind. But running that 1.7 HP motor at those power levels, even for like 5 minute, may cause heat problems. You might need to duct a lot of air thru the thing. And you need to watch the RPM limit. 6000 is a good limit for that size motor.

However, you might be better off starting with that motor (2nd one) and building the thing. Experiment with different ratios and see what it does. A lot of other things enter into the performance equation. Like the battery. An 18 HP motor with a 12 HP battery is only going to get you 12 HP. Building an EV, be it a car or a bike, is usually a process. Rarely a first time get exactly what you want type of thing.

Just my thoughts. Hope it helps some.

major


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## azninferno (Nov 12, 2008)

Yea ive spent hours on evalbum. great site. For the most part, those guys all use eteks, perms, mars and advanced dc. im looking for something similar to the 6.7" advanced DC, but hopefully i can use a similar forklift motor for cost reasons. i can deal with the machining of the sprocket to whatever shaft it may have (unless its splined, but i guess you could turn the arm down) and making a plate. I dont need the bike to go 65 MPH continuously, i realize that would kill the battery. the 65 is just top speed, just incase i need to get out of a tricky traffic situation. As for the RPM limit, doesnt the controller handle that? Since its a bike, directing air to the motor shouldnt be too hard. I also plan on running some FLAs or AGMs for now, possibly upgrading to lifepos if they get cheaper. thatll also determine my range, but i do plan on doing the math for gearing ratios. 

My real questions are whether or not certain forklift motors are up to the task. Advanced DC torque curves and other characteristics are easier to find, whereas these a very limit quantity of info is available to them (also why i posted here instead of the Electric motorcycle forums)

Thanks for the responses major


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## major (Apr 4, 2008)

azninferno said:


> For the most part, those guys all use eteks, perms, mars and advanced dc. im looking for something similar to the 6.7" advanced DC,


Hey aznin,

Smart move to stay away from those PM motors, in my opinion.



> the 65 is just top speed, just incase i need to get out of a tricky traffic situation.


Hope you realize that you run out of torque near top speed, so high speed acceleration is likely to be sluggish.



> As for the RPM limit, doesnt the controller handle that?


Unlikely. Some high end model might, if you add speed feedback. Most likely you'll have to do it yourself.



> but i do plan on doing the math for gearing ratios.


Using a series wound motor gives problems doing the math ahead of time. Unless you have a real good model of the load. Otherwise, you don't really know what speed the motor is going to run. It's best to gear over desired speed and then be able to use the controller to run less than "curve" RPM for a given mph. But this takes away torque, so you accel slower. That is why I advise to give it your best shot, but be prepared to alter the chain ratio. Don't lock yourself into a single ratio.



> My real questions are whether or not certain forklift motors are up to the task.


Advanced DC are forklift motors, just without the custom mount and shaft. But forklift motors come in a variety of flavors, that is voltage, windings, brushes, etc.

My friend, Jim Husted, at hitoqueelectric, may be able to help you. Sometimes he has some on hand to sell. Or knows what lift truck motors work the best. I suggest you contact him.

Regards,

major


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## TX_Dj (Jul 25, 2008)

RPM is a product of volts.

If it's rated for 2500 RPM @ 24 volts, it will want to spin about twice that at about twice the volts. It won't ever get there, though... it'd detonate before double RPM.

I think the RPM is going to be a little low to get the type of gearing you need to go that fast. Your gearing would have to be pretty high (low numerically) to maintain 2500 RPM at the motor shaft, which means when you're running around at slower speeds, you're burning lots of amps and making a lot of heat.

If you could get a motor that will do something like 4000-5000 RPM at your target top speed, you'll have snappier acceleration due to lower (higher numerically) gear ratio to hit your top speed at max RPM and won't be running as low RPM around town.


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## azninferno (Nov 12, 2008)

thank you for the responses. i have contacted jim, now to wait...


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