Well, the title sums it up. I'm building a new cargo climber, so I need very high torque (at least 160n.m!) but only moderate top speed (45kmph). Just finished a bbs02 build which is awesome, but not nearly strong enough for steep climbs (8.2% average, 20% max, 10.5Km distance) with a trailer full of cargo (total weight: 200Kg). Mostly streets; some gravels. So for the second bike, I'm either considering a 2wd build, where one motor would be able to capture regen energy, or a powerful L-R / Cyclone / GnG kit with some custom modification, so that I can also have regen. First options seems easier to do mechanical wise (almost zero custom parts apart from strong torque arms) but kind of a puzzle when it comes to electronics, the second option would probably be the opposite and weight a bit less. Total cost would probably be the same. I'm a bit scared by weird handling in the 2WD option, but still open to that solution, and not biased, as I've seen the advantages of both mid drives and hubs. So what are your thoughts ?
2WD vs high power mid drive kit ?
- Thread starter qwerkus
- Start date
motomech
10 MW
There's not much point in putting anything more than a geared mini (System Watts-900 to 1300) on the ft. of a 2WD cargo carrying/pulling ebike to climb hills. As he rear wheel drives the load, it unloads the frt. wheel and the frt. tire tend to spin. Probably the trailer tongue weight would compound this. On the other hand, a sm. hub motor wouldn't have much of a detrimental effect on steering/handling.
If it is a long cargo bike with cargo in front of the rider, like Bullitt, or other longjohn types, then at least when it's loaded up near the front wheel, there should be plenty of traction with that wheel...but the rear lifting the front does still apply, if not as badly.
If it is a long cargo bike like my CrazyBIke2, with cargo carried in the rear on either side of the wheel, and rider just in front of that, but heavy DD hubmotor in front and battery in front /below the rider, it oculd be more susceptible to front traction loss than the above, but less so than a regular bike. My 2WD on that bike worked pretty well, but there *were* times I could lose traction on the front while under power there, with around 2kW on the front (26" wheel) and about the same in the back (20" wheel).
As a note about cargo carrying and front traction...my SB Cruiser trike has plenty of traction in the rear for braking or acceleration, but in front when braking hard, there's not enough weight transfer to the front so it skids pretty easily. I'm working on battery boxes to go either side of the headtube area to move the nearly-40-pound traction pack up there over the front wheel, which should help that out (and give me back significant cargo space in the seatbox)...though it lengthens the main power wires by a few feet. :/
If it is a long cargo bike like my CrazyBIke2, with cargo carried in the rear on either side of the wheel, and rider just in front of that, but heavy DD hubmotor in front and battery in front /below the rider, it oculd be more susceptible to front traction loss than the above, but less so than a regular bike. My 2WD on that bike worked pretty well, but there *were* times I could lose traction on the front while under power there, with around 2kW on the front (26" wheel) and about the same in the back (20" wheel).
As a note about cargo carrying and front traction...my SB Cruiser trike has plenty of traction in the rear for braking or acceleration, but in front when braking hard, there's not enough weight transfer to the front so it skids pretty easily. I'm working on battery boxes to go either side of the headtube area to move the nearly-40-pound traction pack up there over the front wheel, which should help that out (and give me back significant cargo space in the seatbox)...though it lengthens the main power wires by a few feet. :/
amberwolf said:
I gave up on the long john - heavy, too expensive (4 time the price of a regular bike!), not flexible enough. Also I can't imagine the fork / steering of a long john surviving downhills fully loaded. I think this is a city or flatland cargo option - nothing for mountains. The price is also a problem for dedicated long tails, at least until the new mongoose is available in europe :/. I found an older ebike with a small seatpost battery, which means around 15cm more wheelbase. This will have to do. Anything heavy goes into the trailer, including the kids
. This puts them at a very low gravity center behind the driver, which from my experience is the safest place by far.motomech said:
Yeah, I read about front wheel slip, but have no idea how problematic it is. For sure pulling the trailer won t help in that way, since it has a tendency to lift the front wheel even more. My guess is as long the riders weight + battery + front motor > rear motor + trailer, it should be ok. Also in the 2WD FAQ someone wrote front is better suited for a DD hub to recover regen, though a heavy fork will for sure not improve handling.
The powerful mid option seems better when it comes to weight distribution, since the motor sits approximately in the middle of the setup... when carrying the trailer. 30% of the times I leave it downhill.
But let's get real and talk models. I was thinking double mac 2WD, with the rear beeing the new Grin MAC which can do regen. The smallish bafang g310 could also be an option. The high power mid option on the other hand is quite flexible when it comes to the motor (probably something like an L R small Block), as long as it fits between the seatpost and the rear wheel. Though if I want regen, there is no way around a dual chain setup, and some complicated disk / chainring adapter on the left, plus the problem of the first stage reduction for added torque, and finally noise.
Since the weight is in the trailer, maybe you could consider powering the trailer wheels. They'd have better traction than the bike's front.
Design it's power assist specifically so it is most effective on hills, since that's where you need it most, and it would be most efficient there (instead of least efficient, which is what happens with systems designed to power the bike under normal flat conditions).
Design it's power assist specifically so it is most effective on hills, since that's where you need it most, and it would be most efficient there (instead of least efficient, which is what happens with systems designed to power the bike under normal flat conditions).
dogman dan
1 PW
Moving, that front wheel might not slip as much as you think. It will on a standing start at 20% of course, but moving 15 mph it won't be slipping that much.
But the main thing, is it is still a hub motor, and unless in 20" wheel, it needs to run 15 mph or so up those hills, or it will smoke on long hills.
Since you mentioned regen, a 1000w dd front hub would work. As long as you get towards 2000w of total power, you will get up 10% grades at 15 mph I think. 20%, hope that hill is pretty short.
If you could do a 20" wheel pusher trailer, that would be a great solution. Perfect if you have a bob trailer.
But the main thing, is it is still a hub motor, and unless in 20" wheel, it needs to run 15 mph or so up those hills, or it will smoke on long hills.
Since you mentioned regen, a 1000w dd front hub would work. As long as you get towards 2000w of total power, you will get up 10% grades at 15 mph I think. 20%, hope that hill is pretty short.
If you could do a 20" wheel pusher trailer, that would be a great solution. Perfect if you have a bob trailer.
amberwolf said:
That one actually sounds like a plan, though this will require A LOT of work. Not sure a bob is an option, as you can't carry a lot with those, and there is no bob trailer for kids I know of! Also, I'm not sure the push bob will work in curves with that coupling axle.
So 2x wheel trailer would mean either a central motor somewhere beneath the storage room and a differential, or two hubs. I know mac makes hub with custom axles and plate covers for trikes, but 2x mac in the rear would probably be total overkill, on top of adding 9kg unused weight. Two g310' would be my premium choice, but I don't know if the half axles can support cargo weight. And than I'd need some sort of control, so I guess a long cable running all the way from the back of the trailer to the handlebar and a throttle (though I do hate those - PAS is my favorite way of controlling a bike motor).
Any link to someone who actually did it ?
I would use double-ended axles, with frame around the wheel. Aside from the doubled ability to resist axle torque from hub motor power, it also provides almost doubled support for the cargo load, since the inboard axle, dropout, and frame isn't supporting the whole thing and bending on every bump.
LIke either of my trailers here:
Teh small one, which can't take nearly the load the big one can, more because of the way I used the BMX forks than it's size; they're flexy enough with only forward-end outboard support that they still allow wheel to cant inward at the top under heavy loads (have several fixes I could do to prevent that, but never did them cuz I built the big one and have rarely used the little one since then).
https://endless-sphere.com/forums/viewtopic.php?f=2&t=63781
The big one (which now has duallies so I could carry a piano a while back) has wheels that go in from the top so a wheel or tire can be changed without unloading it. But the best part about it is it keeps the deck / load down low, but has large diameter wheels that give it a MUCH better ride than the little wheels on the small trailer. These pics are from when I was tacking it together to ensure it was built right before fully welding it all:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=76539#p1158726
Depending on your needs, you could use DD hubmotors so you can have trailer braking (regen), or two geared hubs. hubmotors make the drivetrain very simple to implement; no need for live-axles or complicated chainlines or whatever, which can happen with "middrives" of various kinds.
On my big trailer, with duallies, I have a "plan" to use DD hubmotor wheels for the inboard pair (since they'll have more of the load on them they'll have better traction), and can use them for braking, too. Then two regular bike wheels on the outboard pair, for the strength they have over most hubmotor builds.
I had also "planned" to use a pair of powerchair brushed motor wheels (small airless tires, around 14" diameter) on the trailer, instead of the bike wheels, but the disadvantages of the small tires are high. Another plan would put sprockets on the output of the powerchair motors, and use rear wheels on the trailer instead of front wheels, and drive the wheels via chain. But no braking that way, unless I locked the freewheels on the wheels, or used disc-brake-mount sprockets on the wheels (could use front or rear for those, but prefer front).
For throttle control, there is actually an automated way to handle it, I think discussed in one of my trailer threads above. Basically you make the trailer hitch telescoping with springs (gas or coil or whatever), and a "plunger" potentiometer (or similar) that is moved by the trailer moving forward and backward along the telescoping hitch (or a strain gauge on a fixed hitch). This can be setup so that whenever the trailer is being pulled on, the throttle output increases until it reaches a neutral position; if it begins pushing on the bike harder than a set amount, then it decreases throttle, and it just keeps balancing around this point so it's "neutralizing" the mass and rolling resistance and air resistance of the trailer and load. If throttle decreases to zero and it's still pushing on the bike, it engages the regen braking, until again it reaches that balance point. I'm sure it can be done without a Cycle Analyst, but since that's designed to take a voltage input of varying types and convert it into a throttle output, it'd probably be easier ot use one.
Then the bike's own motor handles it's own load.
You could of course use a throttle on the bars, or a CA to convert your PAS control to a throttle signal, and run that back to the trailer.
I've yet to power one of my trailers, but I keep planning different ways to actually do it.
LIke either of my trailers here:
Teh small one, which can't take nearly the load the big one can, more because of the way I used the BMX forks than it's size; they're flexy enough with only forward-end outboard support that they still allow wheel to cant inward at the top under heavy loads (have several fixes I could do to prevent that, but never did them cuz I built the big one and have rarely used the little one since then).
https://endless-sphere.com/forums/viewtopic.php?f=2&t=63781
The big one (which now has duallies so I could carry a piano a while back) has wheels that go in from the top so a wheel or tire can be changed without unloading it. But the best part about it is it keeps the deck / load down low, but has large diameter wheels that give it a MUCH better ride than the little wheels on the small trailer. These pics are from when I was tacking it together to ensure it was built right before fully welding it all:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=76539#p1158726
Depending on your needs, you could use DD hubmotors so you can have trailer braking (regen), or two geared hubs. hubmotors make the drivetrain very simple to implement; no need for live-axles or complicated chainlines or whatever, which can happen with "middrives" of various kinds.
On my big trailer, with duallies, I have a "plan" to use DD hubmotor wheels for the inboard pair (since they'll have more of the load on them they'll have better traction), and can use them for braking, too. Then two regular bike wheels on the outboard pair, for the strength they have over most hubmotor builds.
I had also "planned" to use a pair of powerchair brushed motor wheels (small airless tires, around 14" diameter) on the trailer, instead of the bike wheels, but the disadvantages of the small tires are high. Another plan would put sprockets on the output of the powerchair motors, and use rear wheels on the trailer instead of front wheels, and drive the wheels via chain. But no braking that way, unless I locked the freewheels on the wheels, or used disc-brake-mount sprockets on the wheels (could use front or rear for those, but prefer front).
For throttle control, there is actually an automated way to handle it, I think discussed in one of my trailer threads above. Basically you make the trailer hitch telescoping with springs (gas or coil or whatever), and a "plunger" potentiometer (or similar) that is moved by the trailer moving forward and backward along the telescoping hitch (or a strain gauge on a fixed hitch). This can be setup so that whenever the trailer is being pulled on, the throttle output increases until it reaches a neutral position; if it begins pushing on the bike harder than a set amount, then it decreases throttle, and it just keeps balancing around this point so it's "neutralizing" the mass and rolling resistance and air resistance of the trailer and load. If throttle decreases to zero and it's still pushing on the bike, it engages the regen braking, until again it reaches that balance point. I'm sure it can be done without a Cycle Analyst, but since that's designed to take a voltage input of varying types and convert it into a throttle output, it'd probably be easier ot use one.
Then the bike's own motor handles it's own load.
You could of course use a throttle on the bars, or a CA to convert your PAS control to a throttle signal, and run that back to the trailer.
I've yet to power one of my trailers, but I keep planning different ways to actually do it.
LeftieBiker
100 kW
- Joined
- Nov 5, 2012
- Messages
- 1,117
I'm not sure that anyone has mentioned the big drawback with a mid-drive setup: if you do any shifting under power, the strain on the transmission is going to be great - especially if done while going uphill. Are you planning on using a derailleur or an IGH for the pedal drive?
dogman dan
1 PW
Yeah, you have to think ahead, if you are going to pull a huge load up a hill with a mid drive. Might have to climb a whole hill in your lowest gear just because of one steeper section near the top.
But a front hub pulling all the way, that could help a lot to keep you in a 15 mph gear. 8) Seriously, I still think adding a front hub is a great idea, if it will be used seldom, a larger geared motor. Sure it may get hot fast on the hills, but two motors should prevent a 5 mph crawl up it. Get to 12 mph, and most geared motors can take a few miles of hill without damage. It might not be perfect efficiency till 15 mph, but it still gets it done.
But a front hub pulling all the way, that could help a lot to keep you in a 15 mph gear. 8) Seriously, I still think adding a front hub is a great idea, if it will be used seldom, a larger geared motor. Sure it may get hot fast on the hills, but two motors should prevent a 5 mph crawl up it. Get to 12 mph, and most geared motors can take a few miles of hill without damage. It might not be perfect efficiency till 15 mph, but it still gets it done.
amberwolf said:
Thanks a lot for the details. The "telescoping" potentiometer seems an interesting way to control the trailer. The main issue I have with the trailer option are the kids. I'd need to built a custom trailer where I can mount a seatbank for the children, and remove it when hauling cargo. Also, it would require some sort of suspension, as the road uphill is quite bumpy. Right now I'm working with 2 trailers - much easier to swap. But Powering both of them is no option. It would certainly be a super thing, but I don't have the time or the tools to build a custom trailer.
LeftieBiker said:
Nah, the mid drive option would have been Direct Driven - second Chain on the left. The hassle of setting this up is the main reason why I'm not convinced by this option.
dogman dan said:
Yeah, seems doable. Grin GMAC rear for power and regen (DD are not an option for climbs, and on flats, even a small geared hub works out), and smallish g310 front. I'm going to check if someone can help me build the custom trailer. Otherwise it's going to be dual hubs.
The big trailer I use could easily be done that way; since it's a low deck already then the seatbank won't be up all that high, plus if you can make yours wide like mine you can put htem side by side instead of tandem. If you like you can make a "stakebed" style deckframe, so a cargo "wall" to secure everything to, or retain it in the cargo area if it's tall enough so it doesn't bounce out.qwerkus said:
The seatbank can have curved prongs at the back that seat into the frame, with bolt-hole tabs to secure it down in the front (or vice-versa). Have you ever seen retail fixtures, like the pegs products hang from? Well the prongs at teh back would be like the pegs' mount that goes into the pegboard holes. It would twice as easy to install and remove as having bolts front and back, and just as secure if the curved prongs are thick enough.
You can also add hooks below the surface of the deck, like many pickup trucks have, to hook tiedown straps to, for cargo. Or on the frame itself at the edges.
If you built the trailer like my big one, with deck suspended below teh wheels, you could use verticals at either end of the triangular section of frame the dropout is on, and "hang" that frame from the verticals with springs, or bike shocks, etc. Or use a pivot at one end of that section, and the spring on the vertical at teh other. Even a leaf spring, mounted upside down, might work (probably not like it was intended to, though)
That's how I planned to do it; I don't know if i ever will get around to it though, since the larger diameter wheels have been good enough for the roads around here (29" or 700c would be better, but I didn't have four of those, or tires & tubes for the ones I do have, and mine is just made of stuff I already had lying around).
Another (if clunky) way to do it is to use a pair of rear suspension bike frames to hold the wheels, and build the deck between them attached to the frame, so the triangles still oeprate the suspension as designed.
kevinscargobike
10 W
- Joined
- Nov 1, 2017
- Messages
- 66
I've been back and forth on this too. I bought a used Cetma cargo bike because I was confident that the steel frame would flex enough to fit a 138mm MAC 10t in the back, to use along with a MAC 8t on the front - but since LR is local to me, I've also thought about one day getting a Rohloff hooked up to one of his mid drives.
What actually ended up happening was that I started with the 8t in front, and I liked the belt drive and nuvinci that the bike came with enough that I decided that I didn't want to give it up for a second motor. From experience with a Bosch, Tzdz2 and Stokemonkey, I found that I just didn't enjoy sharing the transmission with a motor - I want to shift for me, not for a motor.
My climb is short but steep, and there's really only 100 feet or so that is a 15% grade. I've found that when carrying 150+ lbs I can get enough momentum to carry past that stretch if my 14s5p Panasonic GA battery is relatively fully charged, but if I'm down to 54v or whatever then I might have to have an adult passenger get out, or if it were stuff I'd have to walk the bike. I feel like moving to a larger battery or maybe a higher power battery might solve that.
Sooner or later, I think I might try putting a GMAC on the rear and have a cassette and chain again to see if it's worth the trade off.
The part that I didn't account for was how much the FOC in the Phaserunner can do for getting speed out of a higher torque motor. I chose the 8t on the front because I wanted to get to the 25mph-ish range at least, and now that I've allowed for FOC I've found that this motor will go 34mph at ~2.2k watts, which is WAY faster than I need.
I think it would be really interesting to do something crazy like a 16t MAC at 72v with an FOC controller.
Ohh, my other experience is that the 8t MAC in a 20" wheel seems to be quite a bit louder than the 10t that I have in a 26" wheel - I probably need to add some more grease inside, but I think the higher RPM is a factor. So that would be a benefit of a dual motor setup where you can use a quieter motor when the throttle is below 2.5v or whatever and both motors when it's above 2.5v.
Also, carrying weight down hill has felt fine on both my Cetma and my wife's Packster 80.
What actually ended up happening was that I started with the 8t in front, and I liked the belt drive and nuvinci that the bike came with enough that I decided that I didn't want to give it up for a second motor. From experience with a Bosch, Tzdz2 and Stokemonkey, I found that I just didn't enjoy sharing the transmission with a motor - I want to shift for me, not for a motor.
My climb is short but steep, and there's really only 100 feet or so that is a 15% grade. I've found that when carrying 150+ lbs I can get enough momentum to carry past that stretch if my 14s5p Panasonic GA battery is relatively fully charged, but if I'm down to 54v or whatever then I might have to have an adult passenger get out, or if it were stuff I'd have to walk the bike. I feel like moving to a larger battery or maybe a higher power battery might solve that.
Sooner or later, I think I might try putting a GMAC on the rear and have a cassette and chain again to see if it's worth the trade off.
The part that I didn't account for was how much the FOC in the Phaserunner can do for getting speed out of a higher torque motor. I chose the 8t on the front because I wanted to get to the 25mph-ish range at least, and now that I've allowed for FOC I've found that this motor will go 34mph at ~2.2k watts, which is WAY faster than I need.
I think it would be really interesting to do something crazy like a 16t MAC at 72v with an FOC controller.
Ohh, my other experience is that the 8t MAC in a 20" wheel seems to be quite a bit louder than the 10t that I have in a 26" wheel - I probably need to add some more grease inside, but I think the higher RPM is a factor. So that would be a benefit of a dual motor setup where you can use a quieter motor when the throttle is below 2.5v or whatever and both motors when it's above 2.5v.
Also, carrying weight down hill has felt fine on both my Cetma and my wife's Packster 80.
