Hub vs BLDC (weight question)

[CMo44]

Hi, my build is something in the way of a small EV (4 wheels, custom frame, light body). Some parts and inspiration from go-karts, atv's, and golf carts. Thus: MUCH lighter than an actual "car". My specific question is there any approximate agreed upon maximum weight/application for using hub motors? I've read some of the reasons they're not used in heavy passenger vehicles (durability, weight, cost). BUT, if I were to use 4 "electric car" hub motors (think QS or whatever) what would be a general loaded weight limit (or speed limit) before it makes sense to go with a single BLDC motor?

Esp since I'm trying to maximize a lightweight build with speed (max 45mph ability, usually 35mph max, but with a fast launch too). It seems that one BLDC will be about the weight of one of the 4 hub motor wheels. Would a loaded vehicle weight of 400-500lbs (just a guess) rule out hub motors straightaway? Or does it seem this would be light enough to negate those concerns? Thanks!

 

[bengxe]

I would think about the kind of suspension performance you want from it and whether you can make the extra unsprung weight of the motors work with that. If you want to try to stay under 500lbs with 4 hub motors you'd need to use small e-bike sized motors. 4wd and lightweight are fairly contradictory goals.

 

[E-HP]

It seems that one BLDC will be about the weight of one of the 4 hub motor wheels. Would a loaded vehicle weight of 400-500lbs (just a guess) rule out hub motors straightaway? Or does it seem this would be light enough to negate those concerns? Thanks!

Can you explain what you mean by “BLDC motor”, since hub motors are BLDC motors?

 

[neptronix]

Nah, they make some damn strong hub motors.. but there is a negative impact on ride quality,

 

[CMo44]

Can you explain what you mean by “BLDC motor”, since hub motors are BLDC motors?

Yeah, sorry. I didn't know what the name for a non-hub motor was (LMAO). I happened to be browsing golden motors at the time and their section of those is just called "BLDC motor". A stand-alone non-hub motor. I guess that would just be "motor".

 

[CMo44]

Nah, they make some damn strong hub motors.. but there is a negative impact on ride quality,

Yeah I thought that could be the case.

I saw this guy's build while looking up e-carts last week: https://www.motor1.com/features/718121/quad-motor-go-kart-fixes/
The only similarities between that and what I'm planning are the 4WD and small/light frame. But he used 4 hub motors so I thought it could be an option.
It is very funny how his thin laser-cut steel control arms just bent to hell in the previous installment.

Anyway, does anyone have recommendations on sellers/manufacturers motors of this type? I saw some other threads on here mentioning overheating with the golden motors ones. Thanks!

 

[E-HP]

Hub motors are outrunners and motors with a shaft are usually inrunner. Out meaning the rotor is located outside of the stator, versus the rotor located inside the stator. Given two motors of similar dimensions, the outrunner will have a mechanical advantage due to the greater stator diameter. The inrunner has the advantage when it comes to increasing torque by dialing in the gearing for a particular application. Similarly, a geared hub motor uses internal gearing to increase torque, while the direct drive does so simply by virtue of having a larger diameter stator.

If it's going to be 4WD using an inrunner, what do you estimate the weight of the transmission and differential will be? Using 4 geared hub motors wouldn't require a differential.

 

[CMo44]

Hub motors are outrunners and motors with a shaft are usually inrunner. Out meaning the rotor is located outside of the stator, versus the rotor located inside the stator. Given two motors of similar dimensions, the outrunner will have a mechanical advantage due to the greater stator diameter. The inrunner has the advantage when it comes to increasing torque by dialing in the gearing for a particular application. Similarly, a geared hub motor uses internal gearing to increase torque, while the direct drive does so simply by virtue of having a larger diameter stator.

If it's going to be 4WD using an inrunner, what do you estimate the weight of the transmission and differential will be? Using 4 geared hub motors wouldn't require a differential.

Not sure what weight of the transmission means. Physical weight? Or are you just asking the differential ratio?

 

[E-HP]

It seems that one BLDC will be about the weight of one of the 4 hub motor wheels.

what I'm planning are the 4WD and small/light frame.

I thought you were doing a weight comparison between 4 hub motors, that require no drive train, to an inrunner that will need a drive train of some sort; that adds weight to the system and 4WD seems challenging. I guess the assumption is that those additional components will weigh less than 3 hub motors?

 

[CMo44]

I thought you were doing a weight comparison between 4 hub motors, that require no drive train, to an inrunner that will need a drive train of some sort; that adds weight to the system and 4WD seems challenging. I guess the assumption is that those additional components will weigh less than 3 hub motors?

I'm assuming I can run two inrunners? Each one driving a set of wheels. But I haven't explored that enough as I've not worked with them (only hub motors). Or is it not feasible to get/run two DD motors that each drive one set of wheels? I assumed with the light weight of my build DD would be an option. I like it bc of the simplicity.

In that case the two motors would weigh the same that two hub motors would have. So added weight would now be in having axles or whatever connects the motor shaft to the wheels. (IDK if there are dual shaft motors that exist for such an application.)

 

[Papa]

Why 4 wheel drive?.... Intended purpose? Low speed city go-fer, off-road, racer, pulling a plow?
What's your metal fabrication experience? And... electrical experience?
Is there a financial limitation? How much?

 

[CMo44]

Ah now that I've looked up that topic (DD to the wheels in an EV setup) I see that is not possible or ideal. So yes, I would need to reduce/convert it to higher torque. Otherwise I'd need a crazy overpowered motor I suppose.
Ok I'll need to explore that aspect now with the diff/reduction. I know there's some e-differential axle kits already built for atv's and the like. I'll have to see if those are a good solution.

 

[CMo44]

Why 4 wheel drive?.... Intended purpose? Low speed city go-fer, off-road, racer, pulling a plow?
What's your metal fabrication experience? And... electrical experience?
Is there a financial limitation? How much?

Oh 4 wheel drive for speed/power...but it may not be necessary if I'm not using hub motors. If I can get a good enough power to weight ratio with RWD I'd be fine with that. I just wanted AWD to see if I can make something small and light go stupid fast. (Even if I'd be scared to use it all.)
Intended purpose is theoretically a platform that can be both LSV/NEV and racer by changing power specs and body etc. But I want to build a fast racer first for fun.
I can weld and build a basic ladder frame (steel). I can fab the body too. So I just need to spec the power and drivetrain. As I said above I've only dealt with e hub motors not a stand alone "inrunning" motor and how to get that power to the wheels.
Electrical experience is fairly minimal but I'm not planning on doing anything more complex than buying a motor, controller, batteries (and throttle, etc) and hopefully connecting them with standard wiring/connectors. I'm sure it'll be more complex than clipping in e-bike connectors from a kit, but not crazy.
Budget is a couple of grand+. I know the drivetrain components can run a grand each depending on what I get. But I'm also hoping by keeping weight down (steel frame non negotiable at this point) that I can get speed with less power and save some that way. So if one motor is enough power and torque I'm happy to ditch the second one and save $.
Any feedback and suggestions are appreciated! Thanks to you all!

 

[Papa]

You don't need 4WD for speed - just big HP, low weight, and suspension. 4WD will easily double the build cost, and add unnecessary complexity and weight.... for zero gain in speed.

Two quad examples come to mind (not racers):

2WD - www.utahtrikes.com/PROD-11620731.html
4WD - Outrider USA Coyote

 

[Chalo]

Goosing one of these things at 2-3X its rated voltage would take care of at least half your problem:

https://www.amazon.com/ICONSPORTSS-Differential-High-Powered-Brushless-Electric/dp/B0D5HJB6NM

The motor mount might accept a higher rated motor like Cyclone 6kW, and whatever the prime mover, Statorade and/or forced air cooling would help keep it from self-roasting.

P.S. -
I used to run my e-bike at loaded weights of over 500 lbs with only one big front hub motor. 500 pounds gross weight is kid stuff.

 

[CMo44]

You don't need 4WD for speed - just big HP, low weight, and suspension. 4WD will easily double the build cost, and add unnecessary complexity and weight.... for zero gain in speed.

Two quad examples come to mind (not racers):

2WD - www.utahtrikes.com/PROD-11620731.html
4WD - Outrider USA Coyote

Wow the Outrider is very expensive! The Utah Trikes Not-A-Wheelchair is much more reasonable. And I've never seen anyone use a hub motor like that - not in the hub! They mounted it in the middle of the frame behind the seat and chain drive the axle! Mind blown. That's a great way to use a cheap motor (or two!) and not have it affect ride quality! I'm going to investigate doing that for a bit...

 

[CMo44]

Topping this thread for a question:

If I were to use a hub motor to drive an axle via chain like in the above "Not-A-Wheelchair" build, how could I calculate the gear ratios and speed/torque?
For example, let's say I were comparing two hubs that Grin sells:
- The Wheelbarrow (high 30:1 Gear Reduction Ratio, (3.1 RPM/V))
- The eZee fast wind project motor (11.1 RPM/V)

In the video for the Wheelbarrow motor, Justin says it's got 120nm torque, which on the 16" tire equals 130lbs pulling power. He also says it runs 9kmh / 5mph and can't be safely run faster due to how it's built. That's at 36v which I will likely be running it at since I already have a spare battery of that voltage.
The eZee obviously runs faster speed, but much lower torque (400rpm vs 111rpm at 36v). Not sure of the torque #, but the Grin motor simulator says 30nm on 16" wheel (should that be tire?) at 450lbs and 8mph. I am trying to keep the vehicle between 5-10mph in general.

SO, the question is: how does this affect the gearing? If I were to put the 16T cog on the drive motor, I can't figure out how many teeth to put on the axle cog to optimize the speed&torque I'm looking for.
- If I go with the wheelbarrow motor and 16T at the motor, how many teeth at the axle cog? If this motor is all torque and max 5mph, what makes sense at the axle to maximize speed (safely)? (And since it's not direct driving, does the 5mph quoted make any difference since I can gear the axle to be spinning faster than that with a freewheel?)
- If I go with the eZee and 16T, same question. Since it has a lot less torque, but more speed, I would like to reduce the gearing to increase torque and reduce speed (if 450lbs loaded doesn't reduce speed enough already)?

Which combination of the above motor choices and chainring/cog teeth gets me to a good amount of torque to pull 450lbs loaded and still be able to go up to 10mph max on a flat 0% grade? Keep in mind there is no human input power via pedals or anything.

Thanks for any and all replies - this is a multi-part question that has me stuck.

 

[Hummina Shadeeba]

If the motor is spun fast and a gear reduction is added so the speed is turned to torque that works well but if u have a slowly spun motor and then gear it so the wheel is fast it’s going to be low torque and low overall power possible with poor efficiency

 

[CMo44]

Thank you! That's the answer I've been looking for.

I guess I'll go for the eZee rather than the wheelbarrow bafang. And I'll gear it to the axle for more torque.