Hub motor axle strength? Toughest one?

I've searched for a bit and didn't find anything about this.

I'm considering building a 3 wheeled pedal/electric rv and I want to put a hub motor in both front wheels. The top speed will only need to be 20 mph for these but they'll need to have really tough axles and have the ability to pull 800 lbs up a 50% grade. The wheels will be 18" 36 hole motorcycle rims with MEFO MFE99 130/90-18 tires. Is there anything out there that will do this or am I into custom territory here?

I'll post the build in a new thread if I decide this is something I can do so it would be good from an efficiency standpoint if we can limit discussion in this thread to hub motors. :wink:

It sounds like you'll want to use a pair of the big hubbies meant for small cars with the one sided axle.

I typed in hub motor axle to google images and found one with a solid axle....a hubzilla! I might have to go to a smaller rim/tire combo to get it to climb like I want though.

Off to do more research!

I was just thinking hubzilla. Don't they have bigger (thicker) axles than the typical 14mm with 10mm sides?

I think they do. I didn't see a spec, just looked at a pic of the motor in someone's hand. The cool part is the wires don't go through the axle! It's not hollow which is awesome.

There is a catch though. At $600 a piece + $300 each for controllers to run them + $3600ish for a 100ah 48v pack, I'm going to need donations to fund this build. Probably going to have to get creative and come up with something else. This vehicle will be used for accessing remote locations so it's going to have some suspension. Looking at quad diffs and cv's now so maybe I can get away with one motor to drive the front end and one for the rear.

The rear wheel will have the most weight on it when climbing on the grades. The Bafang front wheel geared hubs have solid axles with the wires coming out the side. Since the front wheels can only contribute a small percentage of power on grades, I wonder if they might be powerful enough. They would certainly be light weight and that would be good for suspension compliance, plus they are affordable. M12 X 1.25 axles seem a good dimension and you might be able to upgrade to a stronger material if desired?

Cool. Maybe I can swing two of those for the front and a cromotor for the rear. I want motors up front for regen and for pulling the wheels up ledges. I also like the idea of having backup in case a motor or controller fails in the middle of the desert.

Did some research on the bafangs. It looks like they have trouble holding up under regular ebike use so they definitely aren't up to hauling 800 lbs up a mountain. I need to find a quad junkyard so I can get a decent deal on a diff, some spindles, and cv's. Still on the search for the right motors but it looks like two cromotors at this point.

If you are looking at using Cromotors I can help with some of the specs needed for the controllers based on the parameters you specified and basically figure out if it's even doable. I do discount quantity, 10% off 2, but I'm almost out of stock and won't have more until around Nov is my guess, but then I'll have plenty, at least 50.

There is one weak point of the Cromotor axle and that's where the wires go against it. It narrows down from 16mm to around 13mm. I have one customer who broke one during severe abuse in +30" tires with improper torque arm mounting allowing movement allowed and only supported on one side, but that's the only failure I know of. I beat the snot out of mine with hard launches and have tried to brake stuff mechanically and electrically without success. I still believe these axles are the strongest out there and they are of good quality metal.

Another option to consider is possibly going off of Alibaba and buying motors rated for high power that can be laced into a wheel. Just watch the KV on them I am guessing for this application you don't want a high KV motor and would prefer something around what the Cromotor is 9.3KV so you don't get into needing crazy amps.

Even with 2 motors 800lbs up a 50% grade is probably asking too much in direct drive with the 27" tires you specified. You setup might require a gear reduction mid drive setup in the rear to pull that kind of load. I have one customer using a single Cromotor as a mid drive to move a +2000lb vehicle at 10mph using something like 72V and 80A and it works great.

At that kind of cost it might worth while looking into alternate configurations such as a high power mid drive for the rear, going with a brushed motor could reduce your costs as well.

mdd0127 said:

I'm considering building a 3 wheeled pedal/electric rv and I want to put a hub motor in both front wheels. The top speed will only need to be 20 mph for these but they'll need to have really tough axles and have the ability to pull 800 lbs up a 50% grade.

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The performance benchmarks you specify mean pedal power will be irrelevant unless you want to go 2mph. And by the way, to ascend that 50% grade at 2mph, you need motors that can deliver 1500W output at 29rpm (assuming 23" diameter 2.50-18 tires). At 1mph, you only need half that much power, but the motors have to do it at less than 15rpm-- thus the same phase current will be required.

That's 362 pounds-feet of torque, by my calculation. 181 lbs-ft, or 245 Nm, per motor. The Crystalyte 5403 delivers that much torque if you feed it 280 phase amps. Overheat in one minute.

My thinking is you'll need car hub motors to do this, with a pretty special controller and batteries. You picked a job that hub motors are uniquely ill-suited for, and for which pedal power is about as useful as a chicken pulling a tow rope.

The pedals are mainly for show incase I get hassled by the man but I was going to gear them for walking speed. Basically, if all else fails, I can still make some kind of forward momentum. If I do run into a 50% grade, it probably won't be for more than 100ft and I understand the concept of momentum and keeping the motors spooled up. My last build with the 3220/hv160 combo, geared for 40mph in a 26" wheel would climb anything I threw at it if I kept the speed above 15mph. I may be a hubbie noob but I've got a decent grasp of how things work electrically so I can operate the vehicle with that stuff in mind.

It does look like I'm going to need a transmission for the front wheels at least so I'm looking into quad stuff for that and some axles and spindles. I'll probably have to use a cheap hubbie in the front running through the quad diff at a 5:1ish reduction. I like the idea of running an etec or agni to the rear too. I'm afraid that financing this is going to be the toughest part of the project but I have some ideas for that too. Probably going to try indiegogo with build instructions as the prize. I'll definitely post the build thread here but people that contribute will get a slick set of detailed plans and tech support.

I really appreciate everyone's input here! This project is the last step to free me from needing currency almost completely, which will let me focus my time on the nonprofit permaculture campground/hackerspaces for artists and inventors that need a stress free place to create.

Don't forget the side loads, which require conical bearings unless you're building a leaner. I've turned away customers wanting our motors to build 3 and 4 wheelers for exactly that reason. Only hubbies for cars are made the way you need, but they're wound for higher speeds, so they'll burn up while rock crawling. I did see one for golf carts, but it was underpowered and inadequate for your needs. I think it was designed for using 4 on a light weight golf cart, which would be low stress use.

I love hubmotors, but I think you need to eat the drivetrain losses and use stuff from a 4wd quad and a central motor, unless you can find a special purpose hubbie built for quads or a swamp buggy or similar.

I agree completely.

What about some of the motors Golden motor offers... maybe like the one Luke liked to torture on the Death bike. Geared and run at reasonable levels it might be affordable for the speeds you are looking at. Agni95's make me drool. My lack of any fabrication skill prevents me from playing with cool stuff like that.

You mean the flaming cockhole motor? Lol! I'll have to look into the golden motors. The agni was actually the first motor that I spec'd for my ultimate but sanity overcame me and I went with the 3220 instead.

What about Amberwolf's wheelchair hubbie? Those should be wound slow enough to be ok for rock crawling, and wheelchairs are heavy to get enough weight load to remain upright, so the one sided axles may be up to the task. Run higher voltage to get your speed. Something like that might work.

they'll need to have really tough axles and have the ability to pull 800 lbs up a 50% grade

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50% is an incredibly steep grade. heat will be a problem, even at only 20-MPH. I recommend a non-hub using John's mini-monster at a minimum.

http://endless-sphere.com/forums/viewtopic.php?f=28&t=48439&p=713337#p713337

The wheelchair hubbie is a great idea! I think I'm still going to want to run whatever motor I use through a differential in the front though. I don't want too much unsprung weight and just the battery pack on this thing is probably going to run $3500 so if I can buy a couple hundred bucks worth of used quad parts for the front drive system, I'll have a system that's geared properly for it's task and likely to be pretty reliable. I have about $5k worth of possessions left to sell and I've been working a bit lately so the budget is going to be really tight on this build. If I can get away with two motors/controllers instead of three, it will probably knock $1k off the total build cost. I definitely want separate drive systems for the front and rear though. Just because each system could be properly setup for it's application and between the two motors and the pedals, I'll have triple redundancy, which is a very important thing when you're on the road alone, possibly far from civilization, with limited funding.

I've been looking at the mini monster as a possibility too. If I give it enough voltage to spin at what would be 40mph in a 26" wheel, and put it in front of a reduction gearset of some sort, I'm pretty sure that it will make the power I need and it should also provide excellent regenerative braking at the higher speeds that the rear drive will be tuned to. Just have to be careful not to spin the front motor too fast so that will have to be accounted for with gearing.

As far as the grades go, most highway and forest road grades won't exceed 6% which is where this thing will predominantly be used. There are a few trails that I've come across though that have super steep sections but the steep incline usually doesn't go for more than a couple hundred feet. They're usually found when you dip down into and back out of a wash. If my 75lb 3220 single speed equipped bike could take these hills with no problem at a total weight of 300lbs and never pulled more than 160A for any extended period of time so I think that something with more mass, therefore momentum, and stability, will easily cruise up them if I size/gear everything correctly.

Why not one of Johns BiG frock motors mounted as a mid drive? or two..?

KiM

Maybe a big monster mid driving the rear and a mini monster in the front. I'll have a better idea what this thing will weigh and what I'll have for reduction gearing soon and can go from there.

mdd0127 said:

Maybe a big monster mid driving the rear and a mini monster in the front. I'll have a better idea what this thing will weigh and what I'll have for reduction gearing soon and can go from there.

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Since one Hubmonster pushes 400lbs up to 100mph and up any hill, then geared down to 20 or 30mph it will climb anything with just one sending power to all 3 wheels. That is ventilated though, so for desert use you'll need to give it a shield and some way to filter the intake. I've got ideas for how to do that. If you expect really slow rock crawling type stuff on occasion, then regardless of the motor you use, you'll need to go with active fans to force ventilation. That would include if you were using a water cooled motor, since it would need a fan on the radiator.

After three encounters with the cops tonight, all for having no license plate light (vehicle wasn't even made with one), in the same town, I've done some more thinking about this plan. This country is, without a doubt, a police state, so there's no reason to play games. I like my freedom and don't want to have to defend it with violence so it's going to be in my best interest to comply with the law while on the road...at least visibly. I'm still building the three wheeled hemp/bamboo camper but there's no way I'm going to attempt driving it on the highway in this country. That means that I don't have to bother with putting pedals on it, or make it capable of going more than 20mph. These revelations will greatly reduce both the cost of the project and the possibility that the pigs will hassle me over this thing.

When I'm on public roads, I will tow the rv pod with my bike, using a towbar with a torque sensor and regen braking sensor built in. When the bar senses pull, it will activate the throttle until the trailer is going bike speed. When I slow the bike down, the trailer will apply regenerative braking. Hopefully, this will make it feel like I'm just out on a bike ride and cops can't say a damn thing about a guy pulling a trailer with a bike, especially when there are no wires going from the bike to the trailer (might have to nerd out and design an rf, remote throttle in case I need a tiny boost )

I only average about 8-10 mph on the road on long rides so if the trailer can just haul it's own weight at 10mph, everything will be great. When I get to an offroad or remote area with no traffic, I can hop in the trailer and tow the bike instead. I'm not in a hurry ever so 20mph will be fine. I found a great deal on a wrecked 4x4 atv that I'm going to rob the drive train out of. For $400, I can have a cvt transmission, two speed transfer case, drive shafts, long travel cv axles, front a arms, spindles, brakes, front wheels, and tires. Pretty sure that I can find a rear end from a shaft drive motorcycle for the back wheel for cheap too, then I'll just have to size the tires so all the gearing jives. I'm thinking that the mini-monster might work perfectly for this app if I monitor the temp with the ca and take a break if things get too hot.

Hopefully, next week, I'll be going down to phoenix to pick up the atv parts. I'm going to make a new thread titled Hemp/Bamboo Electric 3wheeled camp trailer and post the build thread there. Just have to figure out which sub-forum to post it in.

Toughest hub motor axle? Solved. As far as I can tell, for anything e-bike, the Cromotor/Hubzilla wins.

What about designing the "trailer" so that the bicycle can dock to it and become a 3/ 4 wheeled vehicle (front 2 wheels are inline)? Could still have a fully functional ebike that is part of the drive system, then run a mid drive to the trailers wheels that is controlled from the bike. Cops aren't smart so if it looks like a bike pulling a large trailer then that's what it is to them. Batteries on both bike and trailer. This could make riding less complex than dealing with trying to tow a trailer. Of course setting it up to be towed would be nice too if you needed extra articulation for vertical climbs/hill cresting/gully's.

Just a wild idea that popped into my head. Wish I have a welder/fabricator I could pay to build some of the designs I have floating around in my head.

That would be neat to try but I really like the idea of having the bike look like just a bike, with no wires or batteries at all, not just for legality, but because riding the bike as is is a blast and probably saved my life. If I build the trailer/towed ev right, the only input from the bike will be steering and since the tow bar will attach to the rear axle, I'll actually have a leverage advantage on that. If it's obviously a bike with no power source, there's very little chance that they'll even ask about the trailer having power or anything along those lines. I think the powered trailer thing is a legal grey area anyway but no reason to push it. I'd rather have them think that the trailer is much lighter than it looks or better yet that I have super human strength. In the second situation, they'll be even less likely to give me a hard time. "This guy's an animal! Come on, lets go harass some defenseless old ladies instead!" :lol:

BTW, welder/fabricator here...barely surviving and looking for decent paying work.... :wink:

Just for reference, here's a crappy pic of one of the trails that leads to one of my favorite spots. It's crappy because it doesn't show how steep it is. I had to hook the frame triangle on that big rock to keep it from sliding back down while I took the pic. It's a 20-40% grade for three straight miles then flattens out to an easy 6-10% grade once you get up the first nasty section. A total of 8 miles to the top. It's appropriately named Grief Hill. Little rocky though. It's beyond gnarly to pedal/hike&carry up but an absolute blast to come back down. It takes me two hours to get to the top and ten minutes to get back down! Anyone wanting to climb hills and go back down them fast should look into the Giant Faith models. Other than the fork, I freekin love that thing! Giant aptly named their maestro suspension for sure (even if it is a DW link)..