The Great "Gearing vs Hub Motor" Debate

[billvon]

After a lot of number crunching and modifications of formulas (most recently the PWM Current Warping effect)

What's the "PWM Current Warping Effect?" You mean the basic function of bucking a voltage?

The question of gearing vs hubmotor comes down to which transmission you rely more heavily on - the mechanical transmission of the gearing vs the electrical transmission afforded by the motor drive. In general mechanical transmissions are more efficient, so if you could go with a mechanical transmission only, you'd win. However, most ebikes have both; I know of very few brushed motors that are just connected straight to the battery. So you always have the controller loss anyway.

At wide-open throttle, most controllers are at their most efficient; this is generally near the base speed of the motor. Thus, a transmission that allows the motor to remain at or near this speed will definitely help with efficiency.

Mechanical transmissions are an excellent way to minimize the size of a motor. With a transmission, you don't have to size the motor for hill climbing torque while setting the voltage high enough to go at your top speed; you can use a smaller motor that generates less torque then use the gearing to increase the torque at low speeds. (Delta/wye switching is another way to accomplish this.) However, the smaller motor will be less efficient at cruising speeds, since physical size relates to things like winding resistance. So it's always a tradeoff.

 

[etard]

Wow, you guys brought this thread back from the bowels of ES !!! You do realize that safe is no longer with us (he's dead to me at least :wink: ) and this thread is from the dark ages of ES. It's funny to see it back though. :lol:

 

[Jeremy Harris]

Absolutely hilarious to read one of Safe's bizarre takes on straightforward stuff; he sure had a knack for coming at things from a unique, and as often as not wholly incorrect, angle.

Jeremy

 

[Miles]

you can use a smaller motor that generates less torque then use the gearing to increase the torque at low speeds. (Delta/wye switching is another way to accomplish this.)

You get more torque per amp by switching from delta to wye, but the amount of heat generated for a given torque is pretty much the same.

 

[dequinox]

Bumping to ask a basic question without reading 30-some pages. I know I'm lazy lol.

I have a nominally rated 900w brushed motor...and it pretty much will not drive my bike faster than 22mph on the flats. Currently I use a 24v system, and I need to know: Does an increase in input voltage mean an increase in motor torque? I am currently studying a lot of school related stuff and don't have a lot of time to go back into my physics book and research this one. I'm looking less for an increase in top speed, and more for an increase in available torque. I have a range of torque available due to my cyclone-like setup...but the uphill crawl needs some help.

My controller usually never spikes beyond 600w even though it's rated to 24v 40a. I am guessing either the batteries don't want to provide the remaining current because the resistance is too high, or the controller is over-rated.

Thoughts and advice? I am considering purchasing one more SLA and a 36v controller...but I don't want it to have been for nothing.

 

[Drunkskunk]

Bumping to ask a basic question without reading 30-some pages. I know I'm lazy lol.
Currently I use a 24v system, and I need to know: Does an increase in input voltage mean an increase in motor torque?
Thoughts and advice? I am considering purchasing one more SLA and a 36v controller...but I don't want it to have been for nothing.

more torque will be a biproduct. more voltage, more speed, more wattage for the same amperage, more torque.

but if you're only able to pull 600 watts from a 24v, 40Ah system, you have other problems limiting you. more voltage might just blow something up.

 

[dequinox]

It's not quite 40ah, the controller is rated for 40amp output. It just never really spikes past 25amps or so. If it did I would of course be using up my 12ah batteries in no time though Lol. Thanks for the info. It may be that my motor simply won't put out any more power, or it may be the controller for all I know. They are cheap controllers though, so I may go ahead and just buy the 36v and another battery...put them in series and see how I do.

 

[dumbass]

It's not quite 40ah, the controller is rated for 40amp output. It just never really spikes past 25amps or so. If it did I would of course be using up my 12ah batteries in no time though Lol. Thanks for the info. It may be that my motor simply won't put out any more power, or it may be the controller for all I know. They are cheap controllers though, so I may go ahead and just buy the 36v and another battery...put them in series and see how I do.

I can tell you that my little 360w Cyclone motor (brushless) will pull 720+ watts under a heavey load. It will do that until my pack is pooping put. Then it will only give what my pack will give. Bottom line your proble is not a need for more voltage but is in ether your pack or still in the controller. Your assuming that your controller can handle the added voltage to make the jump to 36v. Maybe yes, maybe no.... No matter what if you jumped to 36v you have to buy another 12v battery so why not buy the battery but connect it with only one of the old batteries and see if that improves the situation. If it does improve things you know where your problem is and you can then put your money into another 12v battery rather in a new controller/throttle for running 36v. And your pack will not increase in weight.