The E-cumbent - A project by Matt Shumaker
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paultrafalgar
10 kW
Miles said:
The URL you pointed out says:
Friction in rotary bearings: A rule of thumb
Friction in rotary bearings generates heat which can eventually destroy the bearing. With friction in mind, a common rule of thumb used for the allowable speed of ball and straight roller bearings is:
( B + D ) · n/2 < 500,000
Where B = bore diameter in millimeters
D = outside diameter in millimeters
n = speed in rpm
From a picture of the motor we will guess that B = 7.5 , D = 10 , so 17.5 x 5000 = 87500
which is less than 500,000
So that motor will last forever if you use it to pull the Queen Mary across the Sahara!
Thanks for the reference! I never realise engineering was so easy! :wink:
P.S. A bit like handing a man a table of logarithms when he asks you whether you think hovercraft are efficient.
:? :lol:
safe
1 GW
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Obviously it's easy to make things complicated when you dig into the details, but from the larger perspective it's easy to figure that since the resistance of the wires is the source of heat and heat is the in-efficiency of the motor, then the less resistance the better. There have been people who have built near absolute zero motors just to try to capitalize on the zero resistance possibilities of absolute zero.Miles said:
As a rule the better motors have lower resistance and the cheapo motors have worse. Plug those numbers into the motor formula's and you get better efficiency with the lower resistance.
Sometimes some of the motors require such high speeds (the PMG 080 for example) that they become impractical if you don't have a significant geardown even though they have 0.025 ohm resistance figures.
I think the ideal would be a pancake designed motor like the PMG 080 but designed for lower rpms. If they could do that and then allow it to operate at about 48 volts then you would have the ultimate ebike motor.
One day... one day...
Drunkskunk
100 GW
safe said:Obviously ----werds here----
One day... one day...
48V / .3R = 160A = 7,680 Watts at stall
48v / .03R = 1600A = 76,800 Watts at stall
Lower resistance means more heat, not less.
And there are some very good reasons for higher coil resistance that have nothing to do with quality. The first is the number of windings. The higher the winding count, the higher the resistance, and the lower the RPM. In many cases, a lower RPM is more efficent.
recumpence
1 GW
I am not an electrical engineer. I am much more mechanically inclined. But, there has to be alot more to it that just internal resistance. For whatever reason, these RC motors are super small, yet extremely powerful and reliable.
What I cannot believe is how little heat I have. The controller runs cool, the motor runs cool, the pack runs cool. Everything just runs smooth and cool!
Anyway, I have one minor hickup. One of the primary jackshaft bearings has a knock in it. No big deal. I will pick up another. Other than that, I want to make a slipper clutch for it and increase the gearing for about 40mph top speed. That should make the bike pretty much perfect for my needs.
Matt
What I cannot believe is how little heat I have. The controller runs cool, the motor runs cool, the pack runs cool. Everything just runs smooth and cool!
Anyway, I have one minor hickup. One of the primary jackshaft bearings has a knock in it. No big deal. I will pick up another. Other than that, I want to make a slipper clutch for it and increase the gearing for about 40mph top speed. That should make the bike pretty much perfect for my needs.
Matt
lazarus2405
10 kW
Thanks for bring the thread back to the real topic.
Safe, Miles, others, the discussion you're having is useful, but this is not the place for it. Please take it elsewhere, like a new thread. Thanks.
Remember, it isn't that small of a motor; It's the size of a soda can. In RC it is designed as a motor for larger planes, in the 15-30lb range, running continuously at 2kw and up to 4kw to climb. The motor he is using and others like it are not designed for a few minutes use at low load (if those were your needs you'd use something much smaller, lighter, and cheaper, like a $20 ~200w outrunner.) It's a relatively expensive motor, and as such meant to last a while.
Your mind's eye fools you. A motor's power output is not directly related to its size, but rather the product of its speed and torque. Because (gearless) hub motors spin so very slowly, in the 100rpm-1000rpm range, they need to be heavier and larger to produce enough torque to do the job. Because we're looking at low-rpm motors and 14mm axles so often, his high-RPM motor looks weak, puny, and fragile by comparison.
That's why: the high RPM.
That's because of exact manufacturing and strict quality control. :wink:
Also, the motor's bearings and shaft will be subjected to much less than those of a hub motor. When he hits a pothole, the weight of the bike and rider won't be sent as shock through those bearings and shaft spinning at 10krpm. This more than anything makes that motor last.
Under what use patterns? How fast, for how long, over what terrain and with what weather conditions?
I get the feeling that you're trying to measure things with a DVM poking somewhere while trying to ride. I think you need a CycleAnalyst. They make a shunt-based model that can plug in between your battery and ESC.
I bet you're surprised at how cool it is zipping you along at 25-30mph. Remember, though, that cruising at those speeds you'll only be using 200w-400w at the wheel. For a motor, controller, and battery designed to provide 2kw-4kw, I sure hope it would run cool!
I really want to know the limits of the machine. Can you please do a top speed test, and measure current draw at that speed? Or rather, more than one with different gear ratios. And some hill climbing and headwind tests?
Safe, Miles, others, the discussion you're having is useful, but this is not the place for it. Please take it elsewhere, like a new thread. Thanks.
Remember, it isn't that small of a motor; It's the size of a soda can. In RC it is designed as a motor for larger planes, in the 15-30lb range, running continuously at 2kw and up to 4kw to climb. The motor he is using and others like it are not designed for a few minutes use at low load (if those were your needs you'd use something much smaller, lighter, and cheaper, like a $20 ~200w outrunner.) It's a relatively expensive motor, and as such meant to last a while.
Your mind's eye fools you. A motor's power output is not directly related to its size, but rather the product of its speed and torque. Because (gearless) hub motors spin so very slowly, in the 100rpm-1000rpm range, they need to be heavier and larger to produce enough torque to do the job. Because we're looking at low-rpm motors and 14mm axles so often, his high-RPM motor looks weak, puny, and fragile by comparison.
That's why: the high RPM.
That's because of exact manufacturing and strict quality control. :wink:
Also, the motor's bearings and shaft will be subjected to much less than those of a hub motor. When he hits a pothole, the weight of the bike and rider won't be sent as shock through those bearings and shaft spinning at 10krpm. This more than anything makes that motor last.
Under what use patterns? How fast, for how long, over what terrain and with what weather conditions?
I get the feeling that you're trying to measure things with a DVM poking somewhere while trying to ride. I think you need a CycleAnalyst. They make a shunt-based model that can plug in between your battery and ESC.
I bet you're surprised at how cool it is zipping you along at 25-30mph. Remember, though, that cruising at those speeds you'll only be using 200w-400w at the wheel. For a motor, controller, and battery designed to provide 2kw-4kw, I sure hope it would run cool!
I really want to know the limits of the machine. Can you please do a top speed test, and measure current draw at that speed? Or rather, more than one with different gear ratios. And some hill climbing and headwind tests?
recumpence
1 GW
I am ordering more pulleys and belts tonight for various ratios. I\
Here is what I know so far;
#1 It runs cool. I have run it full throttle (28 to 30 mph depending on the grade) for over a mile mostly up hill (I do not run it down hill or even on the flats much because I already am capable or pedalling over 20 mph on the flats anyway). At the end of those runs I cannot feel any discernable heat on any part of the motor what-so-ever. I will be installing a couple heat sensors on it eventually.
#2 The bike draws an average opf 450 to 500 watts total to mantain 30 mph. This is done on the same road averaging two runs, on ein each direction. All data was logged on an Eagle Tree Micrologger.
#3 The bike seems to really like high loads. I mean, going up hills does not change the amp draw much versus running on the flats. I think that is due to the capability of this motor versus the final drive ratio I am running. I want it geared for about 40 mph. That should be the best ratio for my type of running.
If I had to hazard a guess, I would say this thing is capable of well in excess of 60 mph easily. I mean, at 30 mph, I am only using 1/8 its output capability. Normally doubling speed requires 4 times the power. So, 60 mph should be possible with 2000 watts. Heck, even if it takes 3000 watts, I have much more than that on tap. But, honestly, I think this thing would be scary at anything over 40 mph. So, I will gear it for 40 next and see how I like it and what the numbers are.
This system is not the ultimate, IMO. It does prove a few points, though. I built it because I wanted to see if it could be done, how well this equipment woud work, and because this is all componentry I am used to.
At any rate, I am not, by any means, trying to make myself out to be the end-all, be-all of E-bike builders. Admittedly, I am not really all that knowledgeable with electronics. Actually, I am a high school drop out. I do in home appliance repair for a living. All the machining knowledge I have is self taught using basic small machines manufacturing small, high end, RC helicopters in my spare time. I really have little knowledge of E-bikes or electronics in general. I have done a HUGE amount of fabrication, and mechanical R&D on a large number of projects, though.
My thought on this is, if I can learn how to machine and match components, then build something like this, anyone can.
The only catch is, it took me years to accumulate the equipment and knwledge to do this.
Anyway, I am glad there are electronic engineers out there to answer some of my bone-head questions. :wink:
I sure hope this thing proves out in the long run.
Matt
Here is what I know so far;
#1 It runs cool. I have run it full throttle (28 to 30 mph depending on the grade) for over a mile mostly up hill (I do not run it down hill or even on the flats much because I already am capable or pedalling over 20 mph on the flats anyway). At the end of those runs I cannot feel any discernable heat on any part of the motor what-so-ever. I will be installing a couple heat sensors on it eventually.
#2 The bike draws an average opf 450 to 500 watts total to mantain 30 mph. This is done on the same road averaging two runs, on ein each direction. All data was logged on an Eagle Tree Micrologger.
#3 The bike seems to really like high loads. I mean, going up hills does not change the amp draw much versus running on the flats. I think that is due to the capability of this motor versus the final drive ratio I am running. I want it geared for about 40 mph. That should be the best ratio for my type of running.
If I had to hazard a guess, I would say this thing is capable of well in excess of 60 mph easily. I mean, at 30 mph, I am only using 1/8 its output capability. Normally doubling speed requires 4 times the power. So, 60 mph should be possible with 2000 watts. Heck, even if it takes 3000 watts, I have much more than that on tap. But, honestly, I think this thing would be scary at anything over 40 mph. So, I will gear it for 40 next and see how I like it and what the numbers are.
This system is not the ultimate, IMO. It does prove a few points, though. I built it because I wanted to see if it could be done, how well this equipment woud work, and because this is all componentry I am used to.
At any rate, I am not, by any means, trying to make myself out to be the end-all, be-all of E-bike builders. Admittedly, I am not really all that knowledgeable with electronics. Actually, I am a high school drop out. I do in home appliance repair for a living. All the machining knowledge I have is self taught using basic small machines manufacturing small, high end, RC helicopters in my spare time. I really have little knowledge of E-bikes or electronics in general. I have done a HUGE amount of fabrication, and mechanical R&D on a large number of projects, though.
My thought on this is, if I can learn how to machine and match components, then build something like this, anyone can.
The only catch is, it took me years to accumulate the equipment and knwledge to do this.
Anyway, I am glad there are electronic engineers out there to answer some of my bone-head questions. :wink:
I sure hope this thing proves out in the long run.
Matt
lawsonuw
1 kW
recumpence said:
Huh, not a good sign. What's the no-load current draw on your motor? Is it a large fraction of the current required to cruise? (say 20% or more) I think you might have too big a motor
(like you didn't already know that 
)I look forward to more updates!
Marty
recumpence
1 GW
The idle current is 14 watts.
The current drawn by the motor alone is 111 watts. The motor driving the wheel (with the wheel off the ground) draws 185 watts at full power.
I thought that was high. However, my 48 volt 10 AH pack calculates to about 20 to 25 miles of riding, which is about right for a typical E-bike. But, I have alot more power on hand if I need it versus a typical e-bike.
It just seems strange to me. But, hey, it runs smooth, cool, and gives good range. I am thrilled with it, I can tell you that!
Matt
The current drawn by the motor alone is 111 watts. The motor driving the wheel (with the wheel off the ground) draws 185 watts at full power.
I thought that was high. However, my 48 volt 10 AH pack calculates to about 20 to 25 miles of riding, which is about right for a typical E-bike. But, I have alot more power on hand if I need it versus a typical e-bike.
It just seems strange to me. But, hey, it runs smooth, cool, and gives good range. I am thrilled with it, I can tell you that!
Matt
Dee Jay
100 kW
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I was really excited to see an RC motor being used but intimidated by the need to fab a gearbox. I have no experience with gearing. Anyone thought of using an SRAM internal gear hub? I figure the disc brake mounting holes can be used for a large sprocket and single gear freewheel at the motor . . .If so, would a 3 gear internal hub do? 9 speed hub?
J
J
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lazarus2405
10 kW
Well, power requirements increase with the cube of the speed with respect to wind resistance, not the square. This becomes more true the worse the aerodynamic characteristics of the vehicle (the 4x approximation might apply better to aircraft, being more aerodynamic, but with upright bikes it's very close to 8x above 20mph). In that respect, the recumbent has a huge advantage over all of us using mountain bikes. http://www.kreuzotter.de/english/espeed.htm says that with 4000w of power you could get somewhere between 50 and 80mph, depending on the characteristics of your bike. By adjusting some details to to get your "450-500w at 30mph", it looks like 2000w should get you to 55mph, and 4kw should get you to 65mph.
That's where us on big, unaerodynamic mountain bikes have the advantage. The ride is a lot nicer above 30mph, with all that nice plush suspension. And being further above that very fast-moving ground is much less unnerving.
recumpence said:
Hi Matt and lazarus
Air drag goes up by the square of the speed but the power requirement to overcome it goes up by the cube (as you say, lazarus). So, if you're drawing 450 Watts to overcome air drag at 30 mph, you'll need 3600 Watts at 60 mph. Obviously, the absolute requirement varies with CD and frontal area but the cube law doesn't care whether you're an upright bicycle or an aircraft, AFAIK.
lazarus2405
10 kW
Of course the cube law applies equally well. However, it does affect the accuracy of quick approximations. "Double the power, 4x the speed", a second-order approximation for a third-order phenomenon will be "close enough" at relatively low speeds. With a lower CD and/or frontal area, the approximation is applicable for longer, since the relative divergence of the two graphs is less over a given interval. That is, at a given speed the cube looks more like a square when the CD and/or frontal area are lower. In fact, with good enough aerodynamics, a linear approximation can be applicable. (Try a kreuzotter graph of a white hawk between 10 and 20mph, copared to a mountain bike).
Link
1 MW
Dee Jay said:
If I had to venture a guess, I'd say they'd have problems. In normal use they should never go above a few hundred RPM. Don't know what would happen if you tried to use one to reduce R/C motor speeds.
Malcolm
10 kW
Hey Matt
Congratulations! I've been dying to hear how this turned out and I'm really pleased that it performs to your expectations, especially that the motor runs cool and quiet. Never mind all these grouches mumbling into their beards about efficiency, this is the first well-designed and implemented ebike drive I know of that uses RC components, so I'd be very proud of it. Of course it can be refined, but for a proof of concept it's first-class!
Dee Jay:
A three-speed internal hub would be great to adjust gearing so as to keep the motor running in its sweet spot (assuming it could cope with the torque), but it wouldn't provide the 25:1 gear reduction that Matt's multi-stage reduction provides. That's where the difficulty lies for anyone who wants to copy this approach.
Congratulations! I've been dying to hear how this turned out and I'm really pleased that it performs to your expectations, especially that the motor runs cool and quiet. Never mind all these grouches mumbling into their beards about efficiency, this is the first well-designed and implemented ebike drive I know of that uses RC components, so I'd be very proud of it. Of course it can be refined, but for a proof of concept it's first-class!
Dee Jay:
A three-speed internal hub would be great to adjust gearing so as to keep the motor running in its sweet spot (assuming it could cope with the torque), but it wouldn't provide the 25:1 gear reduction that Matt's multi-stage reduction provides. That's where the difficulty lies for anyone who wants to copy this approach.
hi Matt,
is there any chance you can get some video up next time you go for a ride?
Your ideas are great, lots for us to ponder and question you about as we (i) haven't seen any of this kit before and would love to see it in action???
cheers
D
is there any chance you can get some video up next time you go for a ride?
Your ideas are great, lots for us to ponder and question you about as we (i) haven't seen any of this kit before and would love to see it in action???
cheers
D
Hi Matt
Super job, it really looks like its going to work well, very well! I would also love so see some video of it in action, your build is just what this hobby needs really, more people pushing past the kits and making real and practical alternative drives, I am sure the efficiency of the system will be fine as well, if your motor and transmission is running quiet and at low temps your efficiency must be high, most of the overvolted hub motors (mine included) are not great under high loads and are pretty inefficient, however for most of us with short commutes and the occasional ride out at the weekends it is not a problem.
I saw Randys posts re the project over at PA, I also find that he can come across quite badly with folks but a lot of what he says is tongue in cheek to be honest, his system is a great concept and he he knows it! the trouble is he bites back and then flame wars start and its not nice to hang out, I listen to what he says and ignore the flame wars.
We used belts on the Lemco bike, they are so quiet in operation I like the belt drive approach, I would love to belt drive the rear wheel like a harley! that would be nice, I have seen shaft driven rear drive on bikes as well? however this may not be very efficient?
Thanks again for sharing all of your hard work over here on the forum, please get some video of the machine sorted if you can even a wheel off the floor spinning clip and some footage of the gearbox would be awesome!!
Thanks
Knoxie
Super job, it really looks like its going to work well, very well! I would also love so see some video of it in action, your build is just what this hobby needs really, more people pushing past the kits and making real and practical alternative drives, I am sure the efficiency of the system will be fine as well, if your motor and transmission is running quiet and at low temps your efficiency must be high, most of the overvolted hub motors (mine included) are not great under high loads and are pretty inefficient, however for most of us with short commutes and the occasional ride out at the weekends it is not a problem.
I saw Randys posts re the project over at PA, I also find that he can come across quite badly with folks but a lot of what he says is tongue in cheek to be honest, his system is a great concept and he he knows it! the trouble is he bites back and then flame wars start and its not nice to hang out, I listen to what he says and ignore the flame wars.
We used belts on the Lemco bike, they are so quiet in operation I like the belt drive approach, I would love to belt drive the rear wheel like a harley! that would be nice, I have seen shaft driven rear drive on bikes as well? however this may not be very efficient?
Thanks again for sharing all of your hard work over here on the forum, please get some video of the machine sorted if you can even a wheel off the floor spinning clip and some footage of the gearbox would be awesome!!
Thanks
Knoxie
safe
1 GW
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- 5,681
I know people like quiet, but on mine the #25 chain makes a lot of noise and I use that to know the rpms of the motor. From the sound I know my shift points better. If it's completely quiet then how would you know when to shift?knoxie said:
(obviously this only applies to geared bikes, but anyone using a belt is going to have some sort of gearing)
HAL9000v2.0
10 kW
install the shift light.
recumpence
1 GW
Warren from Recumbents.com is coming by tonight to test ride the bike and take some video. So, we will have video up and running soon.
Don't expect much. The only sound is a touch of motor whine and I cannot accellerate very hard due to main belt skip. But, you will see it in action so you know it is not all a conspiracy. :wink:
Anyway, I am moving right along with development. The belt skip issue is the only technical bug in teh system other than artificially low gearing. Both will be cured soon.
Read the updated web site page for more specific info.
Matt
Don't expect much. The only sound is a touch of motor whine and I cannot accellerate very hard due to main belt skip. But, you will see it in action so you know it is not all a conspiracy. :wink:
Anyway, I am moving right along with development. The belt skip issue is the only technical bug in teh system other than artificially low gearing. Both will be cured soon.
Read the updated web site page for more specific info.
Matt
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