Hub Motor choice for lightweight E-vehicle

[Ecorunner]

Lets just start with a little introduction so you all know about the project am doing and the advice am looking for.
For a school project I am changing the drivesystem of a lightweight e-vehicle for an endurance/economy race. So the goal is to be as energy efficient as possible. The system is powered by a hydrogen fuel cell system that gives about 24V - 26V. The current motors are 2x 36V 350W 8FUN bldc HUB motors in the rear wheels.

The vehicle is allready build a few years ago, changing the powersource is out of the question.
The problem with this setup is that the current HUB motors are 36V motors, to drive them propperly there is a 24 DC to 36DC conversion wich is really crap and unefficient.
So it needs to be more effecient.... Thus matching the motors too the output voltage of the fuel cell.

I've been looking into finding a 24V Motor + Controller system but this quest is proving to be a bit challenging.
BLDC motors @ 24V are hard to find or they dont have matching power or speed, or maybe i am looking at the wrong place, vendor etc? Help here?

My other idea is to use a DC brushed motor, I found the Crystallite 409 hub motors @ 24V. They seem promissing, but how promissing are they? Would 2 of these motors be powerfull enough to let the car start from a standstill without the risk of damage to the motors...
Using a DC brushed engine is my favourite, due to simplicity with controlling it. I could easily make a H bridge with IGBT's as controller system.

Currently there is also no regenerative braking system and this is no priority at the moment so a simple controller is good enough to my knowledge. Getting the car to run as effecient as possible is priority, cause it won't be braking to much during the race.

Vehicle specs:
+- 250KG (with driver)
2x Hubmotor rear wheel driven
16" wheels
Desired speed aprox 15-25 Km/h

I hope you guys can help me give some insight or even suggestions about a motor choice. Because I got zero experience with HUB motors at the moment.

 

[cal3thousand]

You could run your same motors at 24V instead of 36V. Your controller would just have the be configured for that.

 

[Ecorunner]

Forgot to mention that.

The current motors @ 24V dont have enough speed/power to drive the car up to desired speed.

 

[Jeremy Harris]

If you can get hold of a Code 8 Bafang motor then that would give you around 19kmh at 24 V in a 16 inch diameter wheel, a little faster if you could squeeze a 20 inch wheel in.

The problem is finding a reliable vendor who can sell you a Code 8 motor. You absolutely cannot rely on BMS Battery, for example, as they will just lie to you about specs, as I found out recently when buying a motor from them. It may be possible to buy one from greenbikekit, but you'd need to double check that the motor they have is really the right one (it should carry the code BPM 36V500W 16(8) ).

A direct drive alternative might be the Nine Continent 2805 direct drive hub motor. I reckon that should get to around 20 kmh in a 16 inch wheel on 24 V. Being direct drive it might be a better bet for an economy-type vehicle, provided you don't have to accelerate and decelerate a lot, as a direct drive hub may give slightly better efficiency at a fairly constant speed, due to the slightly lower frictional losses.

 

[John in CR]

I thought it was supposed to be a lightweight e-vehicle. 250kg ! Cutting 50-100kg should be a top priority. If the terrain is flat and cruising consistent, the sure weight doesn't matter, but otherwise it definitely does. I sell some high efficiency hubmotors that hit the high end of your speed range in a 16" wheel at 24V. They're much higher efficiency than typical ebike hubmotors and capable of higher power than you need. I need to understand the nature of the riding and what kind of current you have available if the competition simulates real world riding with plenty of stops and starts and/or hills in order to determine which one meets your needs best. 2 motors would be overkill unless you're driving that big load up hills.

John

 

[Ecorunner]

Thank you for the replies,

@Jeremy, You're basicly saying i should try to get the beefier version of the current Bafang 8fun 250W we have now, due to the differences it would probably reach the desired speeds?
Just a little question though, about the codes, I've seen different codes on the Bafang motors, does a lower code, mean high speed but lesser torque Or what are the differences?

If so, it would be usefull, cause I could just contact the previous supplier of our motors and check if they can hook me up with something.

About running the system on 24V, are there any good high powered controllers that could deliver the power? First thought was to loan a Gen4 controller from a company , but that might be a overkill and the tuneability of the controller could backfire on me.

@John
First off, 250Kg is the weight of the vehicle + driver + obligated "baggage". It's just circuit laps, terrain is flat and cruising speed is constant, there are just some start stops every few laps
To awnser the question about the availible power, the fuel cell can give about 50Amps @ 24V
What kind of motors do you have for offer then?

 

[Jeremy Harris]

@Jeremy, You're basicly saying i should try to get the beefier version of the current Bafang 8fun 250W we have now, due to the differences it would probably reach the desired speeds?
Just a little question though, about the codes, I've seen different codes on the Bafang motors, does a lower code, mean high speed but lesser torque Or what are the differences?

If so, it would be usefull, cause I could just contact the previous supplier of our motors and check if they can hook me up with something.

The last digit (in brackets) on the motor code refers to the number of turns the motor is wound with on a Bafang. The same applies to other motors, too, for example a Nine Continent 2805 has five turns, and is therefore faster for a given voltage than a Nine Continent 2808 with eight turns. A lower turn count means a higher Kv (the rpm per volt constant). It also means that you need to put more current through the motor windings in order to achieve a given torque (because torque is equivalent to motor winding turns x motor winding current, the amp/turns figure). The lowest winding count Bafang motor is the code 8, so this is the fastest wind they do. The challenge is getting one or two of the Chinese suppliers to understand what it is you want, as they aren't all aware of the differences between the various motors.

Any wind of motor of a given type will have exactly the same maximum torque as any other. The difference will be the current needed to achieve that torque, the lower winding count motor will need more current to get a given torque than a higher winding count motor. The limitation is that power dissipation in the motor is largely driven by resistive loss, and this is a function of the square of the current x the winding resistance, so although winding resistance drops as the turn count drops, which reduces resistive loss to some degree, because of the square factor the total losses actually increase as current is increased, meaning that the motor may run hotter.

About running the system on 24V, are there any good high powered controllers that could deliver the power? First thought was to loan a Gen4 controller from a company , but that might be a overkill and the tuneability of the controller could backfire on me.

It's pretty easy to either buy a cheap controller and modify it (changing the FETs for ones with lower losses) or spend more up front and buy a controller that's already modded. Ed Lyen here sells Xiechang controllers with known good FETs and will custom build a controller for you. Alternatively, you can buy exactly the same core controller for a lot less money direct from Keywin Ge in China and then fit decent FETs your self. If it were me, then this is what I'd do. A 6 FET Xiechang, fitted with IRLB3034 FETs will be capable of running at 40A or more, at up to around 30V or so, giving you potentially around 1kW of power. These hub motors will take that sort of power as peaks with no problem.

 

[Ecorunner]

This info is great, I can work with this.

So my checklist for now.
Get a Hubmotor with low windings, for maximum speed at low voltage.

Secondly, get a nice controller or mod one.
About the controller, I've seen the golden motor controllers, altough I havent seen alot of talk about those here on the forums so I'm a bit doubtfull. Are they any good? Or just buy one and expiriment.
The max current is configurable. So i thought I might be able to tune the whole system, using the exact amount of amps thus torque, needed to drive the vehicle and get maximum effeciency.

 

[Jeremy Harris]

If you want a fully programmable controller, where you can set the phase current, battery current limit, low voltage cut off point, cruise control settings, switched speed settings etc, then I'd recommend getting a cheap Xiechang. These can be programmed using a serial connection from a PC (there is software to do this on this forum, with lots of chat about what the settings do) and in my experience these controllers are both tough and versatile.

You can buy them cheaply directly from Keywin Ge (e-crazyman on ebay), who will sell you just boards with no FETs fitted if you ask (around $20 or so each including shipping for the last lot I bought from him). You can buy fully built 6 FET controllers from him (like this one: http://www.ebay.co.uk/itm/24V-250W-brushless-controller-E-bike-scooter-/260882371745?pt=LH_DefaultDomain_0&hash=item3cbdcd14a1) which you could then take apart and change the FETs to get better efficiency and current handling.

The FETs are the weak point with most of these cheap controllers, as decent quality, low on resistance, FETs are both hard to obtain in China, it seems, and quite expensive. For example, I bought some IRLB3034 FETs a while ago, from Farnell here in the UK, and they were around £3 ($4.50) each, so 6 of them for a controller would cost more than the controller itself by a fair margin.

 

[John in CR]

So my checklist for now.
Get a Hubmotor with low windings, for maximum speed at low voltage.

Secondly, get a nice controller or mod one.
About the controller, I've seen the golden motor controllers, altough I havent seen alot of talk about those here on the forums so I'm a bit doubtfull. Are they any good? Or just buy one and expiriment.
The max current is configurable. So i thought I might be able to tune the whole system, using the exact amount of amps thus torque, needed to drive the vehicle and get maximum effeciency.

Since your voltage is effectively fixed, and it sounds like your wheel size is also fixed, so your hubmotor selection will be critical in that you want the motor's peak efficiency rpm for that voltage to rpm required for your target speed. That's for the case of steady state cruise, but you mentioned circuit lap, and required stops. I need more info about the competition, ie the goal, the course, and primary rules. eg A course set up in a parking lot (like many electrathons) would have very different requirements than a larger track where constant speed cruising is possible.

I have a motor that may be a great match for what you need, and has much greater efficiency that typical hubmotors. I even have one stateside with wiring harness that was damaged in transit and is easily repaired that I could contribute to the effort. I need more details to give appropriate advice and assistance.

John