MAC 10T @ 36V vs 12T @ 48V??

ions82

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Aug 15, 2011
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Albuquerque, NM (USA)
I am helping a friend figure out the best drive for an off-road handcycle. It's a beast of a rig that, when outfitted with a motor and battery, will weigh in at 70+ pounds. Off-road handcycling is a slow-going affair. It's not uncommon to be going 2-3 mph on rough, uphill terrain. We have been leaning toward using a geared hub motor for efficiency and freewheeling ability.

The plan was to buy a 12T hub from em3ev and run it at 48V (in a 26" wheel.) However, the folks at em3ev are recommending a 10T run at 36V as it has more copper in the motor. I was under the impression that using additional copper as a heat sink isn't always the best idea and that running fewer amps is the preferred way to avoid heat buildup. For a heavy bike going uphill at 3-4 mph (or less) I assumed lower amps would be paramount. Does anyone have some advice to offer?
 
More copper means means you can go higher amps in the motor.

36V as apposed to 48V is your speed requirements and of course a cheaper battery using less battery in 36 then 48.
 
markz said:
More copper means means you can go higher amps in the motor.

36V as apposed to 48V is your speed requirements and of course a cheaper battery using less battery in 36 then 48.

Thank you for the reply. Does more copper just mean it can soak up more heat before it's saturated (and bad things start to happen), or is it perfectly fine to run more amps in such a setup? Will higher amps also put more strain on the *cheaper* battery and controller, as well? I've always thought that, even if it's CAPABLE of doing it, "lugging" an electric motor is something to try and avoid.
 
A handcycle usually has a crank up high and a chain to the front wheel. If possible I would use a BBSHD with the smallest chainring and a large cassette on the wheel.
If it has to be a hub motor try to use a smaller wheel to put it in. A 24" or even better a 20" would be great for better torque.
 
SlowCo said:
A handcycle usually has a crank up high and a chain to the front wheel. If possible I would use a BBSHD with the smallest chainring and a large cassette on the wheel.
If it has to be a hub motor try to use a smaller wheel to put it in. A 24" or even better a 20" would be great for better torque.

Those are all great ideas, but the design of this one doesn't allow us to use a mid-drive. Smaller wheels could be run, but it would significantly compromise the ride quality, geometry, and tire/rim selection. We are pretty much stuck with a hub motor in a 26" wheel. Here is the handbike.

http://www.reactiveadaptations.com/nuke-recumbent-offroad-handcycle/
 
You could most likely install a mid drive on that if you move the idlers and install a 3 gear crank set.

http://www.cyclone-tw.com/Parts.html
and go with
http://www.cyclone-tw.com/Coaxial.html

A more refined build is the BBSHD models for mid drive. Lots of people can comment on that, I am fond of the Cyclones as it was my first mid drive experience. I bought the 4kw coaxial model, but I was not a fan of how it stood out and the noise of the gears. Not sure how the noise compares with a geared hub motor, but assume its about the same noise.
 
markz said:
You could most likely install a mid drive on that if you move the idlers and install a 3 gear crank set.

http://www.cyclone-tw.com/Parts.html
and go with
http://www.cyclone-tw.com/Coaxial.html

A more refined build is the BBSHD models for mid drive. Lots of people can comment on that, I am fond of the Cyclones as it was my first mid drive experience. I bought the 4kw coaxial model, but I was not a fan of how it stood out and the noise of the gears. Not sure how the noise compares with a geared hub motor, but assume its about the same noise.

You're exactly right. In my opinion, mid-drive with an IGH would be great for this handbike. However, it would likely require some design changes to the frame. Eventually, that would be the ideal as more and more of these handbikes are being sold with electric drives (but it's still a VERY small niche market in general.) Users are finding that an electric drive allows them to explore off-road without injuring upper extremeties. This is important as most riders are also wheelchair users. Additionally, an electric drive allows handcyclists to keep up with their able-bodied counterparts.

As of now, we are kind of relegated to using a hub motor. Other styles of handbikes use a mid-drive (and have fantastic results.)
 
The link you gave to the handcycle shows a vehicle with 24" wheels and not 26" as you stated in your first post. A 12T MAC in a 20" wheel would fit perfectly. Just swap the shock for a slightly longer one if you want to return to the same ride hight. But I don't think the 2" lowering at the rear axle will pose any problems.
If you contact MAC motors directly they can wind you an 16T or even 20T as they did already for others needing high torque at slow speeds.
 
SlowCo said:
The link you gave to the handcycle shows a vehicle with 24" wheels and not 26" as you stated in your first post. A 12T MAC in a 20" wheel would fit perfectly. Just swap the shock for a slightly longer one if you want to return to the same ride hight. But I don't think the 2" lowering at the rear axle will pose any problems.
If you contact MAC motors directly they can wind you an 16T or even 20T as they did already for others needing high torque at slow speeds.

That is some great info. The bike was originally running 24" tires, but it most customers go with 26" some even requesting fat tires.) Thank you for the tip about custom MAC motors. I had no idea that was even possible. Very good to know.
 
markz said:
SlowCo said:
24" wheels and not 26"

Does a smaller diameter wheel give more torque in a geared hub, the same as direct drive?

Same torque, more thrust at the contract patch.
 
In general, it's more efficient to run higher volts/lower speed motor to achieve a desired top speed, than to run lower volts/faster speed motor.
Go to the sim. @ Ebike CA and try the different parameters you are interested in.
 
motomech said:
In general, it's more efficient to run higher volts/lower speed motor to achieve a desired top speed, than to run lower volts/faster speed motor.
Go to the sim. @ Ebike CA and try the different parameters you are interested in.

That's kind of how I've always understood it. A few of those riding this style of off-road handcycle have had trouble burning up DD motors and controllers. We are hoping that high-turn/low-RPM geared motors might be the solution for a lot of folks. Virtually all of the riders of these don't have the ability to walk. So, reliability is rather important. Also, the handbikes alone cost around $8K. Add the cost of an e-drive system in there, and people expect reliability for the price being paid. A 48v system that maxes out at 15 MPH is perfectly fine. No need for speed.
 
FWIW.
We have a pair of FS26 trikes.

One has a 48v 30amp peak MAC 10T total weight of 250 lbs. Climbs 15% no problem, 10% with ease tops out above 28 mph. I pedal about 50% of power and it burns about 6wh/mile.

The second has a 36v 15 amp peak MAC 12T weight at 210 lbs. Climbs 12% like mine does 15% (15 amps......). 20 mph peak.

Both have pretty equal efficiency.

Triketech.com has an article on mine.
 
Triketech said:
FWIW.
We have a pair of FS26 trikes.

One has a 48v 30amp peak MAC 10T total weight of 250 lbs. Climbs 15% no problem, 10% with ease tops out above 28 mph. I pedal about 50% of power and it burns about 6wh/mile.

The second has a 36v 15 amp peak MAC 12T weight at 210 lbs. Climbs 12% like mine does 15% (15 amps......). 20 mph peak.

Both have pretty equal efficiency.

Triketech.com has an article on mine.

Thank you for the info! Those write-ups on TrikeTech are a gold mine. Sounds like a MAC/Phaserunner FOC/CA3 is the trick setup.
 
Paul knows his shit a lot better than me, (em3ev). However, did you tell him 3 mph? That needs a mid drive, and a very very low gear.

IMO, when you want to go that slow with a hubmotor, under a heavy uphill load, you will need the slowest rpm motor you can get, combined with the smallest wheel you can get it in. I think that motor can lace to 16".

Other considerations apply though, if its off road, where a 16" wheel could be too small. But bottom line, load up a 10 or 12t motor enough, in 26 or 24" wheel, and ride up the hills at 3 mph, and I guarantee it will melt that motor if you do it long enough. Long enough might be as short as 15 min.

The sim should show that, btw.

A better solution might be to use a larger dd motor, able to run 2000w or more, in a small wheel. then you never get limited to 3mph. Instead you blast up steep hills at 15 mph, with a cool motor. Now the wind barely matters, since you don't stall the motor to death.

A well powered mac in 10t should scamper up moderate off road trail though, easily. I ride a similar motor off road all the time. But when the rock stairs make you slow to 3 mph, that is when the motor fries. There are trails I will avoid, because I can't ride over the rocks fast enough. Just too hard on my body to roll that trail faster.
 
dogman dan said:
Paul knows his shit a lot better than me, (em3ev). However, did you tell him 3 mph? That needs a mid drive, and a very very low gear.

IMO, when you want to go that slow with a hubmotor, under a heavy uphill load, you will need the slowest rpm motor you can get, combined with the smallest wheel you can get it in. I think that motor can lace to 16".

Other considerations apply though, if its off road, where a 16" wheel could be too small. But bottom line, load up a 10 or 12t motor enough, in 26 or 24" wheel, and ride up the hills at 3 mph, and I guarantee it will melt that motor if you do it long enough. Long enough might be as short as 15 min.

The sim should show that, btw.

A better solution might be to use a larger dd motor, able to run 2000w or more, in a small wheel. then you never get limited to 3mph. Instead you blast up steep hills at 15 mph, with a cool motor. Now the wind barely matters, since you don't stall the motor to death.

A well powered mac in 10t should scamper up moderate off road trail though, easily. I ride a similar motor off road all the time. But when the rock stairs make you slow to 3 mph, that is when the motor fries. There are trails I will avoid, because I can't ride over the rocks fast enough. Just too hard on my body to roll that trail faster.

That is some very good practical insight. What you described at the end is exactly the challenge that the off-road handcycles often face. Sometimes, the terrain is just too gnarly and technical to blast it. Too much speed would send you off the trail, into trees, rolling down the side of a mountain, etc.

Being able to get a little assist while crawling along is a lifesaver. A max of 500w would plenty, and any drivetrain could handle that from a mid-drive. Perhaps we've been trying to avoid the inevitable and just need to consider some design changes. Nonetheless, it might be worth trying one of the custom MACs that were mentioned (16 or 20T).
 
If you slow down to under 10mph on climbs then a geared or direct drive hub motor will heat up too much.
You should look into what E-S member LightningRods is building as a business. He makes left hand side mid drives that are independent from the bicycle drive train components. A set op like that would allow for very low gearing, Look at this thread:
https://endless-sphere.com/forums/viewtopic.php?f=28&t=82938&start=300

For steep climbing you could even lace in a trails bike rear rim and use a trail bike tire for serious grip.
 
People have been repeating the idea that the motor will always overheat if you go slow. When I had a 350w hub motor bike I would just put it in the granny gear and pedal like I would without a motor and add a 200w or 250w of assist (as seen on a Cycle Analyst) with partial throttle and the crawl up the climbs. Didn't overheat. Perhaps monitoring motor temp and using low assist level would work fine?

edit: on the real steep parts I used 250-350w for a short while
 
If you're set on a hub motor maybe a low speed 201rpm Q128H is a better choice than a MAC: https://bmsbattery.com/ebike-kit/775-q128h-36v800w-rear-driving-ebike-hub-motor-ebike-kit.html
A C128H from BMS Battery has a higher internal gear ratio (1:16 if I'm correct) than a MAC (1:5) so might have less overheating problems at lower speed? Get a lower watt controller with it to further reduce the risk of overheating. Or a Bluetooth programmable one so it is possible to dial down the current before going uphill. https://bmsbattery.com/controller/8...r-brushless-motor-with-bluetooth-ios-app.html or https://bmsbattery.com/controller/849-s09p-bl-36v48v-450w-controller-for-with-bluetooth-ios-app.html
I would still have it laced in a 20 inch (fatbike) rim though for better gear ratio to the ground.

And if you're warming up to a low power mid drive motor look up the Cyclone motor with internal gear reduction and internal controller. That motor might fit under or above the swing arm just in front of the rear wheel driving/helping the rear chain:
http://www.cyclone-tw.com/motor.html (first one on the page, the 24V / 500W version)
 
There have been a few offroad and rockcrawler wheelchair or handcycle projects here on ES. Multiple motors often played a role as a means to use conventional hubmotors in very slow speed situations simply because it splits the load and hence the heat issue. You friend's undertaking is not that new and the success of the single motor approach with a Mac will probably rely on how much rock crawling is going to be expected.

Although the Mac is a torquey solution is suffers from cooling difficulties like all gear motors. This isn't a show-stopper, but it means that long stints of low speed, high current lugging are going to toast it up and heat won't dissipate very quickly at all. Looking at the current design, we have:


handcycle.jpghandcycle2.jpg


Two other approaches spring to mind:

  • Use two Grin All-Axle motors up front. These are DD and are amenable to Statorade and HubSink cooling. Two motors will split the heat and arguably give better traction. Since they are DD they would provide reverse mode (which is supported by Phaserunners). These motors will run fine with a single-sided axle - Justin recently provided some assist to get a trike so configured with some custom front axles/steering knuckles. Still using only a single battery/throttle/PAS, there are really no electrical or control complications. Being 2WD there is the benefit of redundant controller and motors so stranding out in the boonies is less of an issue although muscling one side drive might be challenging in some situations. A quick simulator run shows dual Grin 8Ts in 24" wheels w/Statorade @48V running up a 20% grade at 18mph without overheating. I would expect this to work pretty well for steep trails, but super-slow rock-crawling would still need some care and a CA3 to watch overheating - though these motor cool off pretty fast. 20" wheels would clearly be a help , but probably not so good for drivability.
  • A custom gear motor StokeMonkey affair utilizing a custom rear swing arm and the Stokemonkey2 right-side chain routing. Here the motor would live on a bracket above and slightly forward of the rear wheel. The present jackshaft would need a freewheel added. Here the motor would drive through the gears with the usual advantages/disadvantages. You can browse available StokeMonkey parts at the Grin site.

    A related approach would finagle a BBS or other middrive into place on a modded swingarm to position the drive as with the Stokemonkey motor behind the seat/above the wheel. In the BBS case cranks would be removed and the internal PAS sensor unused with the controller PAS input plugged into a remote 24 pole sensor on the hand cranks.

    Either of these swingarm mount approaches would give a lot of low end thrust with no real overheating issues. The primary design upgrade would be a new swingarm which is a nice modular electrification component.
Anyhow - just some thoughts....
 
Wowza. Thank you to all for sharing such a wealth of knowledge. It seems.there are far more options than I had originally thought, but most are a bit more complicated than simply bolting on a hub motor. We are working redesigns for the next generation, so we will have to take a close look at all of these options.

Going forward, I see more and more customers getting e-drives from start. Hopefully, a new design will still allow for a modular aspect to an e-drive system. Ideally, the bike could upgraded to a newer/modern drive system as needed. As I mentioned before, reliability will always be a top priority. Most customers have limited mobility and won't be able to handle anything more technical than airing the tires and MAYBE lubing the chain(s). Fortunately, modern drives seem to be quite robust.
 
RE Jon Ncal, I don't doubt what you say. It just depends on the load, which could be big weight, or just big grade.

So if you need to go slow because its rough, but not so steep, and the rider is not so heavy, works like a treat. The load is just not that high.

But if the rider is 200+ pounds, and the trail is a steep ass rock staircase, trouble brewing.

Duration also matters a ton. As does weather, especially bad is low humidity. long enough grade, loaded enough, and motors do heat, never reach an equilibrium temp below 300F, and melt.. Believe me, I melted several a year, trying to push smaller motors too slow on too steep. I live near big mountains.


Bottom line is this,, if you are putting 1000w into a motor that is working at 50% efficiency because of load lowering the rpm, then you have a 500w heater. This will get red hot fast!

You describe more like a 100w heater. This takes much longer to overheat, since the heat can slowly escape, particularly in humid and cooler conditions.

But using the motor as you describe, it would not help much with my local "extreme techincal" trails.. Works fine on the easy stuff, but it sounded to me like these guys wanted to go ride with the big boys.

Mid drive IMO, or if any hubbie, a big fat heavy DD able to put out 3000w all day and stay cool. You'd be heating it up on the bad stuff too, but have much more thermal mass, better ability to cool later, and most likely, blast over the hard stuff fast enough most of the time anyway.
 
The off-road handcycles commonly encounter terrain which requires one to move along very slowly. However, it's not necessarily a steep grade or something that would require a lot of power. Just plodding along using careful navigation so one doesn't flip over. However, I'm sure there will always be the riders who try to ride up sandy hills and just abuse the heck out of the system. But, for reasonable riders who are just navigating tricky terrain, even 250W is enough power to move over/around it.

That said, would a torque-y geared hub (MAC 12 to 20T) be under strain if it were only going 1-4 mph but limited to, say, 300W? I don't have enough experience with these systems to know how they would handle such a scenario. I just don't want people to get stranded or melt down a $2,000+ drive system. We are hoping that, in the future, we can go strictly mid-drive, but the current design and customer base will need a reliable hub-motor system.
 
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