Opinions on DD scooter hub motor

I'm posting this in the motor technology forum because it isn't really a bike or scooter question. Does anyone have experience with the 9 inch direct drive hub motors that can be found on Aliexpress?http://www.aliexpress.com/store/pro...ric-skateboard-motor/1279208_32438320428.html for example.I am building a small go kart like object with my high school robotics team for the Power Racing competition. Other than the shipping from China this looks like a great motor. However my experience is with brushed motors geared down. Brushless motor plus direct drive has me worried about torque and ability to accelerate.

Some notes - I'm guessing around 120 - 140kg or kart + rider for the competition. Lots of acceleration needed due to twisting track, hills,and avoiding other cars.

Some additional information -

The competition is limited to 1440W via a fuse.

We would be using two of the hub motors either as rear wheel drive or perhaps as front wheel drive. Another option is two brushless 600W BMC motors with built in controllers (http://www.thesuperkids.com/600wasutocum.html), two brushed motors (MY1020 or Currie) with chain drive to the rear wheels, or just one big brushed motor.

With any of the two motor variants we might put computer control to slow down the inner wheel on turns. Or not if it takes too long.

So with a current limit your best option for winning is the most efficient motor/controller combo. You might want to search the leaf motor. Its extremely efficient and in your power range.

Right now I am focusing on scooter motors. Its a crowded, twisty track with a fair amount of unintentional contact. I'm interested in a larger rear wheeled kart but spoked wheels have not fared well in the past. On top of that there is a style portion and the students want to do a Back to the Future Delorean. The rules end up making a one third scale (more or less) fit well. At that scale a 14" wheel is way too big.

Use the hubmotor not in a hub, but as a "middrive". There are a number of threads on how to do that, if you're interested.

I've been mulling over options for a while now (and distracted by other things) but I'm not sure I'm seeing what you are seeing in the LeafBike motors.

They have a 800W 48V BLDC motor that looks ok. Mid 80s in efficiency which does seem nice but its expensive. I can get two slightly less efficient motors and more power for the lower cost. Plus have two hunks of metal to spread the heat out. LeafBikes Trike Motor 800 W48V says max power of 972W at just over 25A. Since I can't afford a second one to run closer to the max efficiency region (18A) I seem to be stuck. Meanwhile, MY1020 1000W 48V motor curves say max efficiency of 83% at 15A with basically 600W power output and 1.70 Nm at 3369 rpm. I love the torque of the LeafBike motor but two 1000w motor will run cooler, have more usable power, and be cheaper even after I add controllers (partially due to being brushed). A LeafBike hub motor has a similar problem to the trike motor; it loses efficiency and overheats if using anywhere near the 1400W I'm allowed but its too expensive to run two of them to fully use the power efficiently.

A mid sized (600W perhaps) hub motor run with a chain drive is interesting as they seem to have even better torque but its getting hard to track down good data on all the different 500 - 750W hub motors.

There are people running the leaf well over 1500 watts. For highest effeiciency use less amps more volts. I saw a cool new 10 inch 1000 watt scooter motor by qs motors on my facebook feed. It made me think of this thread. I'll look for a link.

http://www.qs-motor.com/product/10inch-1000w-e-scooter-in-wheel-hub-motor/

We've wandered well off of my initial thought so I'd better redirect things a little. The rules limit us by voltage, current from the battery, and budget. Budget limitation mean I have up to $350 for the motor (or motors) and controller; $300 will make the rest of the build work better. Voltage is hard capped at 48V and a fuse is used to limit power to 1440W. Finally, the course is narrow, twisty, crowded with cars, and has a moderate slope (at most 1/2 of the race is on flat ground but the rest is evenly up and down slope).

While it might be possible to drive a Leaf motor at 1500W or more its not going to happen in our competition. Instead I'm looking at 36V and 48V motors run more or less at specced conditions.

maydaverave said:

http://www.qs-motor.com/product/10inch-1000w-e-scooter-in-wheel-hub-motor/

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These look really interesting. Loads of torque claimed on the website but I have some questions about things since I'd be at the very low end of their range. Great find; I"m talking with them.

While this might seem off topic, it applies to the poweryou'll actually get out of whateve rmotor and controller you choose, and affects your choice of each:

Is that cap of 48v exacct at that voltage, or do they mean a max of what an actual 48v pack would be at when charged?

If the former, then 36v is really your limit, if using SLA types. If using Lithium you could go to 11s and still fully charge everything to 4.2v/cell, for 46.2v hot off the charger. However, you might need to use a "36v" controller to be sure it doesn't have an LVC that shuts off too early, before your pack's own BMS (if any), so you can actuallly use the full capacity of the battery pack. If you use a "48v" contnroller it may have too high an LVC (usually being meant for 12-14s packs). You'd need to check with the vendor what the actual controller LVC is unless it is marked on the controller.

If the latter, then a "48v" controller would be fine, because the fully charged voltage would be anywhere from 50-60V depending on what kind of cells and number in series..


BTW, I am not aware ofa fuse that will limit wattage, only current. So the fuse on every vehicle would have to be a bit different current limit from each othe rvehicle, if they are all at slightly different voltages. Also since as voltage drops it then takes more current to get the same wattage, you will only have that wattage for a very short time as you start off the line the first time or so; after that you will always have less--how much less will depend on the battery chemistry and cells that you use, because some will sag more under load and some will simply have a sharper slope on their discharge curve.

If you use LiFePO4 cells you would have the most wattage over the most time, but you will get less capacity for the same weight than with other varieties of Li cells, generally speaking (depending on cell format/etc).

That's not off topic or odd at all.

Due to budget restrictions ($500 for the entire vehicle with a few wiggle room rules related to salvaged parts, some safety equipment, and battery packs counting as half cost) it is likely that we're using SLA. Some teams will run Li cells but I'm using this as a project to introduce a bunch of new freshmen to engineering and we have enough issues with having them design the frame. Next year we can revamp with Lithium.

The 48v limit is nominal. Until this racing season SLA was far and away the default pack so all voltages are set in steps of 12 due to the common SLA batteries.The real limit is current through a slow acting automobile fuse but the required fuse size is set by using 1440 divided by the voltage. Battery pack voltage rounds up for fuse purposes such that a 22.2 lithium pack counts as 24V to determine fuse size. Short races are 15-20 minutes. Long races are 75 min. Pit stops to change batteries as needed but you'd better be able to do 20 min on one pack.Overall, you can pull lots of power especially at the beginning with fresh batteries and the fact that the fuse will not blow instantly on acceleration.

Of course the flip side is that you are going to be working the motor hard for most of the race because the track conditions aren't really going to allow the cars to go flat out. For example; last year we entered a car with 6" tires and a motor geared to 450rpm due to a mistake (salvaged motor that we thought ran faster). We were slow but not insanely out of things since people couldn't use their higher tops speeds

I think the cheapest method would be to get a stand up scooter and take the motor and controller off it. I bought a used 24 volt scooter for sixty bucks and put a thirty six volt battery on it. It would do twenty mph and had good acceleration.

Something like this.

https://www.amazon.com/gp/aw/d/B001T8E6KM/ref=mp_s_a_1_11?ie=UTF8&qid=1472246610&sr=8-11&pi=AC_SX236_SY340_FMwebp_QL65&keywords=electric+scooter

The motors being discussed aren't nearly enough motor for that kind of racing, and they will fail miserably from heat failure. Handling repetitive low speed acceleration of 100kg vehicles plus driver is extremely demanding even if it is limited to fairly low battery power. You're looking for a minimum of a 3kw motor, especially if running it in-wheel. You want to run the smallest wheel possible too, because for their designed use all DD hubmotors are geared too steeply running in your application.

I know! Last year two teams fried their motors completely and one team was losing power as they came close to burning up. We might have burned ours out except that we snapped our steering in a wreck first. $500 for everything doesn't get you a 3kW motor even if you use Harbor Freight $6 wheels! That's one of the reasons I initially thought of two biggish motors so that they could spend at least part of the race not having to deal with more than their rated power assuming that the seller properly listed power as their continuous safe power output without overheating.

I'd love the scooter style hub motors for their looks (there is also a style component to this - we're mounting a Back to the Future Delorean on whatever drive train we end up with) and initially approached Endless Sphere because you guy have used them. The specs, especially torque, on them are hard to find. A high torque geared hub motor used as a mid drive might be more reasonable but, as is to be expected for bike use, they focus on light weight and the wide flat shape is not as useful in a go kart shaped frame. Thus I'm now looking at an e-trike motor but they seem to be rare unless you directly import from China. Ultimately I might have to go with a big brushed motor as I can get them easily on ebay.

There is a chart /spreadsheet in the wiki and/or a thread in this subsection with specs on a number of motors, (sorry I dont' have a link).

You can also use the http://ebikes.ca/simulator to play with various motors and configurations to see how some of them perform with various battery voltages/current capabilities. All the data the simulator is based on was taken from real world tests.

amberwolf said:

There is a chart /spreadsheet in the wiki and/or a thread in this subsection with specs on a number of motors, (sorry I dont' have a link).

You can also use the http://ebikes.ca/simulator to play with various motors and configurations to see how some of them perform with various battery voltages/current capabilities. All the data the simulator is based on was taken from real world tests.

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I love the simulator but it frustrates me. Someone (or someones?) spent a ton of time making a great but its heavily bike centric and I need go kart/mobility scooter/stand up scooter type info. That's maybe even more than a first world problem I know!

Also frustrated because UUmotors and the QS motor listed upthread are not answering their email.

If you go with a brushed motor, you need one with high efficiency, not typical ebay fare. Sufficient power in a brushless isn't difficult to find. Mars for example has a number of suitable motors, and they don't break the bank.

Another issue with hubmotors not previously discussed is that the vast majority aren't designed to take side loads, and don't have the correct bearings to do so. In a hubmotor you're looking for something with single sided support for things like golf carts or ATV's (if the rim isn't too wide and can't take a small diameter tire), because they'll have the proper conical bearings to take side loads. If the design includes leaning in the curves, the that limitation goes away and you can be faster and more efficient through the turns.

No matter what motor choice some type of mods for cooling is critical, whether it's a centrifugal fan blade sucking air through an open frame motor or venting a sealed motor. If the goal is only for the motor to survive, a main point is missed. While still delivering the power and performance required, you want electric motors to run as cool as possible. Copper losses in the windings is the primary loss, and in our operating range the resistance of copper increases about 0.4% per degree C. That means a warm motor can have 20-30% less copper losses than the same motor running at higher commonly seen operating temps that don't kill the motor, but do waste energy, and at your low power limit efficiency gains mean a lot.

John in CR said:

If you go with a brushed motor, you need one with high efficiency, not typical ebay fare. Sufficient power in a brushless isn't difficult to find. Mars for example has a number of suitable motors, and they don't break the bank.

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Breaking the bank is relative. The $500 budget (defined by competition rules not by my wallet) has to cover everything so I really have at most $300 for the motor plus controller. Even to get that much involves compromises like needing cheap battery packs and cheap wheels.

Another issue with hubmotors not previously discussed is that the vast majority aren't designed to take side loads, and don't have the correct bearings to do so. In a hubmotor you're looking for something with single sided support for things like golf carts or ATV's (if the rim isn't too wide and can't take a small diameter tire), because they'll have the proper conical bearings to take side loads. If the design includes leaning in the curves, the that limitation goes away and you can be faster and more efficient through the turns.

Click to expand...

Good call. Originally I'd been looking at the stand up scooter style hub motors figuring that I could put in some bearings on the axles since I wasn't limited by the space between the forks on a bike. I've also looked at the single axle hub motors. The one from QS(mentioned upthread) looks nice. I was frustrated over the weekend but when they answered this morning it turns out that they have a very nice one axle 10" wheel, 2kW 48V, 600 rpm rated motor for $209. Very tempting although I'm a little worried about steering with one powered rear wheel and one unpowered.

{quote}No matter what motor choice some type of mods for cooling is critical, whether it's a centrifugal fan blade sucking air through an open frame motor or venting a sealed motor. If the goal is only for the motor to survive, a main point is missed. While still delivering the power and performance required, you want electric motors to run as cool as possible. Copper losses in the windings is the primary loss, and in our operating range the resistance of copper increases about 0.4% per degree C. That means a warm motor can have 20-30% less copper losses than the same motor running at higher commonly seen operating temps that don't kill the motor, but do waste energy, and at your low power limit efficiency gains mean a lot.[/quote]

I left all of your comments in as they are important. Keeping the motor cool is critical for best operation. For the previous brushed motor cart (still running this year with a newer motor) we've mostly gone with venting a sealed motor. Right now I'm worried much more about getting a decent motor; the students and I can work on cooling after we know the motor.

With those kinds of $ limitations, you've gotta forget new and find something to salvage or re-purpose...maybe a car alternator conversion to a motor. I'd hit every recycling center for toolpack batteries before even considering using lead. Lead would be limited to a zombie apocalypse scenario with scrounging lead batts as the only source for batts, but I have my end of the world stash of nicad D cells to cover that.

why not run a hub-motor inboard and chain drive it down to a rear end like this


https://endless-sphere.com/forums/viewtopic.php?p=586459#p586459

A Diff so you wast no power on turns and you need a at lest 3 bearings 1 on ether end and at lest 1 next to the center where the drive cog is

http://www.northerntool.com/shop/tools/product_35768_35768
they can also be found in some older ride on mowers

add on 1 of these

http://www.northerntool.com/shop/tools/product_35624_35624

and 2 of these

http://www.northerntool.com/shop/tools/product_52526_52526

and some wheels
http://www.northerntool.com/shop/to...o-kart-minibike-parts-accessories+wheels-rims

this way you end up with a rear end that can take a beating and the motor is untouched
you can also gear it to match your needs
now that the lateral load is taken OFF the motor you can drill and cut alot more holes in it for cooling

That's basically the set up we're using although I have some comments/questions which I'll post later today after classes.

I initially created this thread just to talk about the DD motors because I had no experience with them. So I didn’t spell out the full rules. I’m not trying to spring extra constraints on people but we’ve become much broader than my initial questions. Some rules that enter into the current discussion;

Cars can not be wider than 36” or longer than 60”
The seat can not be lower than the drive axle
There is a slightly nebulous rule against racing go kart bodies to avoid having team "find" a fully complete kart.

Finally, we have my team’s constraints. I’m working with a bunch of high school freshmen. They want to make a 1/3rd scale DeLorean (Back to the Future). We’re not going to be perfect but that means we’re not going to be wider than 24”. I could overrule them but I think its better to make sure they understand the balance issues and make the call. Similarly we’re going to go with 8” or 9” wheels. Maybe 10” if we have to because we’re distorting the vertical profile some to fit their knees in. Probably not perfect but not unsafe or outrageous.

So the short answer is that a chain drive is almost certain as you guys and a ton of Googling have convinced me that the e-scooter hub motors will not do what I want unless I go with the $200 option single axle types and then I can't afford 2 of them. A go kart rear axle is too wide to work which is part of why I was initially looking at two motors (either two scooter hub motor or any two motors). One other possibility is to just drive the left rear and freewheel the right. My fear with that set up is braking.

1:- that is not a gokart diff its a lawnmower diff (originally they where in rideons then people saw there good for gokarts)
2:- you can cut it down to make it how ever wide you want it
3:- braking see the diff center see the bolts sticking out on ether side of the center on 1 side you bolt the drive cog on the other side you bolt the disk brake disk like this

Adverse Effects said:

1:- that is not a gokart diff its a lawnmower diff (originally they where in rideons then people saw there good for gokarts)
2:- you can cut it down to make it how ever wide you want it
3:- braking see the diff center see the bolts sticking out on ether side of the center on 1 side you bolt the drive cog on the other side you bolt the disk brake disk like this

Click to expand...

My mistake on the wording; yes they are really lawn mower parts but in this context I'm going to call it a go kart diff. It is very easy to attach a brake if you have that form of diff. The only reason I mentioned braking issues was in connection with a one wheel drive.

Cutting works fine. I shouldn't reply during the school day (distractions). On the other hand it is odd to have someone list out the parts as if I had no idea what was available but then assume that I know exactly what to modify.

I've thought about just not posting this last part because it seems ungrateful but I'm going to include it. The suggested parts list (axle, 2 hubs, 2 rims, 2 tires, and drive sprocket) comes to around $220 from Northern Tool. Frame and chain adds a little more. That's without the front end (wheels, steering component). Batteries are going to run at least $40 for a 24v SLA pack and up to $80 for 48v (batteries are cheaper due to budget rules). Doing all that a team would have a budget of just over $100 (depending on how expensive you wanted to go on the steering but 2 wheels, knuckles, stub axles, and so on are not cheap) for the motor. Thus you get Unite brushed MY1020 motors and some scrap alternator type motors.

The other way you can go, to my mind, is a better motor and seeing what you can do cheaply to improve things over a live axle + one motor set up. This requires not purchasing a $100+ differential. Some teams make their own (I have plans for one but those parts are in use elsewhere and I don't fully trust the freshmen to be able to fabricate it yet). Others just run a live axle and trust that a better motor + scrubbing losses beats a worse motor and diff. Other teams do one wheel drive. Finally, and perhaps most common, is a two motor solution with, in some cases, computer controlled throttle settings on the two controllers to sort of act like a differential (that was my initial thought but you guys have swayed me to wanting a more efficient motor! instead of two cheap MY1020's).