I am interested in building a 2wd bike with trailer that will be used in the woods on steep hills. I prefer large hub motors and I will also be converting a cpu cooling system to keep the hub motors from overheating. Up to 30 percent plus hills with heavy trailer is going to require a lot of power and a strong bike. Thinking about using 3000 Watt gearless qsv3 motors in the front and back on a 72 volt system with two 150 amp controllers, hooked to s cycle analyst. Bike will be 20" x 4" fat tires. Any suggestions?
2wd hub motor build
- Thread starter 1263
- Start date
SlowCo
1 MW
1263 said:
Use a mid drive instead of two hubs... :wink:
999zip999
100 TW
Two 3,000 wat would be very heavy plus a big battery to run it. I'm looking at middrives now and hard to except the noise on the 3000 watt models. They are wheelie machines till you tone the throttle.
I have a 3,000 d.d. @ 5,500 Watts and can heat it on long steep hills or rough hilly trails. Compromise.
I have a 3,000 d.d. @ 5,500 Watts and can heat it on long steep hills or rough hilly trails. Compromise.
Similar to what you're wanting, don't know what your total weight would be so just went with 500lbs.
https://www.ebikes.ca/tools/simulator.html?bopen=true&motor=MX4504&batt=B7223_AC&cont=cust_150_500_0.03_V&hp=0&mass=227&cont_b=cust_150_500_0.03_V&motor_b=MX4504&batt_b=B7223_AC&mass_b=170&hp_b=0&add=true&blue=Lbs&grade=30&axis=mph&wheel=20i&wheel_b=20i
Full throttle would get you about 22mph up that hill...but it'll take about 3.5kw on each motor (7kw total!) and overheat the 3kw motors in 5 minutes, over 250C (two and a half times what it takes to boil water, the windings will probably be on fire along with the now-shorted-out controllers
), and is going to take about 400wh/mile to go up the hill.
In the simulation above, actual battery power used will be more like 10kw, so there's 3kw of wasted heat inside the battery, controllers and wiring, etc., so you're going to have to cool all of those down too, not just the motors.
Dunno how well it will perform at slow speeds in woodsy terrain, but the slower you go with a high load and high current demands vs what the hubmotors are trying to spin at for the input, the more waste heat is generated (vs the power making you move).
Depending on actual conditions, actual weight, actual speeds, etc., etc., then if you need a lot of range, you'll also need a big heavy battery pack, could be 50-100lbs more added on top of what you've already got planned, depending on how long a range and how much power you must actually have to do whatever it is you want.
You can play with that simulator to figure out more or less what you will really see performance-wise, using your actual numbers.
https://www.ebikes.ca/tools/simulator.html?bopen=true&motor=MX4504&batt=B7223_AC&cont=cust_150_500_0.03_V&hp=0&mass=227&cont_b=cust_150_500_0.03_V&motor_b=MX4504&batt_b=B7223_AC&mass_b=170&hp_b=0&add=true&blue=Lbs&grade=30&axis=mph&wheel=20i&wheel_b=20i
Full throttle would get you about 22mph up that hill...but it'll take about 3.5kw on each motor (7kw total!) and overheat the 3kw motors in 5 minutes, over 250C (two and a half times what it takes to boil water, the windings will probably be on fire along with the now-shorted-out controllers
), and is going to take about 400wh/mile to go up the hill. In the simulation above, actual battery power used will be more like 10kw, so there's 3kw of wasted heat inside the battery, controllers and wiring, etc., so you're going to have to cool all of those down too, not just the motors.
Dunno how well it will perform at slow speeds in woodsy terrain, but the slower you go with a high load and high current demands vs what the hubmotors are trying to spin at for the input, the more waste heat is generated (vs the power making you move).
Depending on actual conditions, actual weight, actual speeds, etc., etc., then if you need a lot of range, you'll also need a big heavy battery pack, could be 50-100lbs more added on top of what you've already got planned, depending on how long a range and how much power you must actually have to do whatever it is you want.
You can play with that simulator to figure out more or less what you will really see performance-wise, using your actual numbers.
What is the bike/trailer being used for? If you are trying to move a trailer around, an electric version of this may be an option.
[youtube]https://www.youtube.com/watch?v=W7U-X0LlgSE[/youtube]
I have two Invacare wheelchair hub motors that would be ideal for this with the appropriate tires.
[youtube]https://www.youtube.com/watch?v=W7U-X0LlgSE[/youtube]
I have two Invacare wheelchair hub motors that would be ideal for this with the appropriate tires.
I ran a lot of simulations using different combinations of motors. Will someone check my work. When you use dual motors are you supposed to put the total weight on each motor or split it between the motors. I put 330 lbs on the front motor and 180 lbs on the front one. Don't know if this is the way you are supposed to do it. I could not get any combinations of hub motors to work so I went with a bbshd middrive and a crystlyte hub motor in the front. This combination was able to handle a 36 degree slope without overheating. But again I am not sure about the weight and about running a front hub motor in combination with a middrive motor!
When you setup a 2wd system on the simulator, via "Two-System Mode" it has "Compare" and "Add"; you choose Add.
This then "disables" a number of "shared" controls on System B, so you can only enter the weight/etc on System A (the left side), as these are things that affect the entire setup.
Regarding "a crystalyte hub", there are multiple ones on the simulator, so you would need to specify which one for us to know, if it matters. If you wish to "save" a simulation, you can simply copy the whole URL in the URL bar of your browser, and paste that as a link (in your post if you want others to be able to see it, for instance to help you tweak it to help you find the right system).
Keep in mind that the simulator is not perfect...and not all motors are thermally modelled, so some of them will tell you "not modelled" which means the simulator has no idea if the motor will overheat or not. But the results *generally* come close to what I see in the real world for the motors I have here that I've compared to it.
Also remember that the simulator assumes the motors / etc start from "room temperature". If your start conditions are a lot hotter, you should add taht to the final temperature, plus some, to have a better idea of final conditions. If you have several hills in a row, then unless your motor(s) have time to cool off to "room temperature" between them, the simulation of each hill won't be accurate--if a motor was already 150F at the end of the first hill, then the next one may well overheat it even though the simulation doesn't think so, because it doesnt' know it would already be hot to start with.
You can generally use a front hub and a middrive on the same bike; it's different from using two hubmotors primarily in that the middrive can be used in greater speed or torque ranges via shifting gears on the bike drivetrain (dpeending on the middrive design--most middrives don't allow shifting of the *front* chainrings, only the rear ones, at least as far as what affects the motor drive section).
If you need both speed and torque, you could use a fast-hubmotor setup on the front, and then gear the rear wheel sprockets and the ooutput sprocket of the middrive very low (very very low for 30% hills!), and then use the middrive for hillclimbing, where you mgith only get 5MPH but it'll do it all day long just fine, and the hubmotor for road use where the middrive coudln't go any faster than that 5MPH but you need to do 10 or 20MPH, for example.
BTW, the slopes in the simulator are in percentages, not degrees...if you really have a 36 degree slope (which equates to something like a 75% slope), you're likely to have some trouble even keeping both wheels in contact with the ground, much less going up it.
Red numbers are percent slopes, black are degrees.
This then "disables" a number of "shared" controls on System B, so you can only enter the weight/etc on System A (the left side), as these are things that affect the entire setup.
Regarding "a crystalyte hub", there are multiple ones on the simulator, so you would need to specify which one for us to know, if it matters. If you wish to "save" a simulation, you can simply copy the whole URL in the URL bar of your browser, and paste that as a link (in your post if you want others to be able to see it, for instance to help you tweak it to help you find the right system).
Keep in mind that the simulator is not perfect...and not all motors are thermally modelled, so some of them will tell you "not modelled" which means the simulator has no idea if the motor will overheat or not.
But the results *generally* come close to what I see in the real world for the motors I have here that I've compared to it. Also remember that the simulator assumes the motors / etc start from "room temperature". If your start conditions are a lot hotter, you should add taht to the final temperature, plus some, to have a better idea of final conditions. If you have several hills in a row, then unless your motor(s) have time to cool off to "room temperature" between them, the simulation of each hill won't be accurate--if a motor was already 150F at the end of the first hill, then the next one may well overheat it even though the simulation doesn't think so, because it doesnt' know it would already be hot to start with.
You can generally use a front hub and a middrive on the same bike; it's different from using two hubmotors primarily in that the middrive can be used in greater speed or torque ranges via shifting gears on the bike drivetrain (dpeending on the middrive design--most middrives don't allow shifting of the *front* chainrings, only the rear ones, at least as far as what affects the motor drive section).
If you need both speed and torque, you could use a fast-hubmotor setup on the front, and then gear the rear wheel sprockets and the ooutput sprocket of the middrive very low (very very low for 30% hills!), and then use the middrive for hillclimbing, where you mgith only get 5MPH but it'll do it all day long just fine, and the hubmotor for road use where the middrive coudln't go any faster than that 5MPH but you need to do 10 or 20MPH, for example.
BTW, the slopes in the simulator are in percentages, not degrees...if you really have a 36 degree slope (which equates to something like a 75% slope), you're likely to have some trouble even keeping both wheels in contact with the ground, much less going up it.
Red numbers are percent slopes, black are degrees.
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John in CR
100 TW
SlowCo said:
+1...Offroad and slow steep climbs is no place for a hubbie, though a mid-drive rear for most of the power plus a hubmotor on the front for 2wd makes sense and with the right motor and wheel size, the front wouldn't need active cooling, since a front can't be run at high power anyway.
John in CR
100 TW
1263 said:
Without a loaded heavy duty front rack to put weight on the front wheel I think it will be very difficult to get 180lbs on the front wheel going up a steep grade. 36° is crazy steep. Even a 36% grade is extremely steep unless it's short enough that a running start gets you most of the way. Then there's coming back down on the way home, and no way I'd try that with a trailer, though I'm inexperienced in that kind of riding.
dogman dan
1 PW
The flaw in your original plan is this. No matter how powerful your motors are, they will run horribly in efficient, and possibly overheat if you run slower than about 15 mph, heavily loaded, up those hills.
Sure, the build will do em at 22 mph, so no problem. WRONG. Unless you are on nice graded roads, you cannot ride as fast as that, particularly with a heavy trailer behind you. Rocks, roots, even trees down across the trail. All will slow you to the inefficient rpm of your wheels. You will blow your battery capacity on heating the motors every time you have to creep with that much load on the bike. And even 15 mph gets a bit challenging, on graded gravel when your rig is that heavily loaded. Because of the limitations of bike tires, when they sink into a soft spot in the gravel, and you need so much traction to keep up your speed. Its a job for a big fat motorcycle knobby, not a bike tire once you pack so much load.
What you need, is a mid drive. And possibly for more speed on easier parts, a front geared hub motor. You need to be able to creep, when the trail or road gets gnarly. Creeping 5 mph on the tough bits, your bike tires can be enough.
Your original plan will work great though, on paved, or exceptionally good gravel road.
As for actual 36 degrees. That's a simulator result Ever even walked up one? This is rated black diamond on a ski slope. My honda dirt motorcycle, even if it could climb it power wise in first gear, would never handle that steep for more than a 50 feet or so. Basically, you wheelie off. Sure, you can ride up steeper jump ramps on dirt bikes by hitting the slope at 70 mph, but I mean start from 0 mph at the bottom of 36 degrees. You make it a ways, then wheelie off it.
Steepest thing I ever rode straight up, on dirt bike or electric bike, was 20 degrees. Not pulling no trailer!!!! Neither vehicle was stopped. just wheelie off at the same spot every time. About 16 degrees is pretty possible, but I just wheelie off at where it gets steeper, time after time.
Sure, the build will do em at 22 mph, so no problem. WRONG. Unless you are on nice graded roads, you cannot ride as fast as that, particularly with a heavy trailer behind you. Rocks, roots, even trees down across the trail. All will slow you to the inefficient rpm of your wheels. You will blow your battery capacity on heating the motors every time you have to creep with that much load on the bike. And even 15 mph gets a bit challenging, on graded gravel when your rig is that heavily loaded. Because of the limitations of bike tires, when they sink into a soft spot in the gravel, and you need so much traction to keep up your speed. Its a job for a big fat motorcycle knobby, not a bike tire once you pack so much load.
What you need, is a mid drive. And possibly for more speed on easier parts, a front geared hub motor. You need to be able to creep, when the trail or road gets gnarly. Creeping 5 mph on the tough bits, your bike tires can be enough.
Your original plan will work great though, on paved, or exceptionally good gravel road.
As for actual 36 degrees. That's a simulator result Ever even walked up one? This is rated black diamond on a ski slope. My honda dirt motorcycle, even if it could climb it power wise in first gear, would never handle that steep for more than a 50 feet or so. Basically, you wheelie off. Sure, you can ride up steeper jump ramps on dirt bikes by hitting the slope at 70 mph, but I mean start from 0 mph at the bottom of 36 degrees. You make it a ways, then wheelie off it.
Steepest thing I ever rode straight up, on dirt bike or electric bike, was 20 degrees. Not pulling no trailer!!!! Neither vehicle was stopped. just wheelie off at the same spot every time. About 16 degrees is pretty possible, but I just wheelie off at where it gets steeper, time after time.
