Using RC motors on E-bikes [Archive]
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gwhy!
100 kW
safe said:You (and I) both got excited about the motor price and then realized quickly afterwards:
"Oh no... now how do you use it?"
...everything that recumpence has been doing for the last six months or more applies to solving the gearing issue. There are all kinds of additional work needed to make it functional on an ebike.
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The MY1016Z3 with the 10:1 geardown is a simple bolt on to my bike and the sprocket they give with the motor fits perfectly into my gearing plans. So for the bike I'm doing now (Project #003 as seen in my present avatar) I'm not going to change anything.
But I'm starting to follow the RC threads closer and closer because the performance is just sooooooooo good with these that they are the eventual destination for all of us.
As Im gonna make a smaller drivetrain (eventally :wink: ) if all the power/torque stuff works out for my prototype I think I have a nice and compact, easy to make 2 stage design but at the moment its just in my head
. I did start looking at bearings and pulleys last night 
( and the wife seen me looking which raised a few question like YOUR NOT SPENDING ANYMORE MONEY ARE YOU :lol: ) but its my money and I spend it how I choose :? .. edit: sorry 3 stage ... each stage with a 2.75 reduction final output driving a 10 tooth bike chain sprocket to drive the back wheel sprocket.
GGoodrum
1 MW
I'm with Matt, regarding the cheap ESC route. Even high quality RC controllers, like the CC HV series and the $400 Kontronic PowerJazz have problems in an ebike environment, which can have lots of starts and stops. The initial loads are a lot more as well. It doesn't take anywhere near as much initial torque/power to turn a large prop or helicopter rotor. The sensorless part of the controller logic can also get confused. This is not to say that some of these newer cheap Chinese ESCs won't work, but none of us have tried one yet. You'd definitely be plowing new ground.
As for the motor, I really have a hard time believing the $66 motor, basically a knockoff of the AXI, which itself runs hot, will do the job without problems, even limited to 1000W. Although the AXIs work fine in airplanes, I never found one that worked worth a damn in an RC helicopter, even at modest power levels. I think if I were going to try one of these, it would be the larger version: https://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5139
-- Gary
As for the motor, I really have a hard time believing the $66 motor, basically a knockoff of the AXI, which itself runs hot, will do the job without problems, even limited to 1000W. Although the AXIs work fine in airplanes, I never found one that worked worth a damn in an RC helicopter, even at modest power levels. I think if I were going to try one of these, it would be the larger version: https://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5139
-- Gary
safe
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Doing the math:GGoodrum said:
$66 and $150... so 150/66 = 2.27 times the price.
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I think the RC motor has three areas in which it really shines.
You can get huge amounts of power. You can get efficient power. You can reduce weight....the first part is of no interest to me because I'm building legal powered ebikes. The only thing that will be illegal is the final speed based on gearing, everything else should be fine.
It's the efficiency and weight that really matters to me. (and the efficiency rates slightly higher than weight in importance to me)
Somehow I just doubt that a motor that can handle 2500 watts would have troubles at 1000 watts... the heat would be reduced to levels that are less than half. Heat goes up exponentially with battery side limited motors at low rpm. (I^2 * R)
Finally... let's not forget our homework on Armature Current Limiting. If you really want to protect a motor from overheating you limit the current on the motor side... it's the motor side current that is solely responsible for the heat, so set a limit on that and you solve the problem. Since Fechters latest RC motor circuit has the potential to do that it would be another way to go if heating was encountered. But I just doubt a motor running at half power is going to overheat.
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What do I gain?
If I'm doing a 1000 watt restricted motor then all I gain is the efficiency gap between a lessor motor and the RC motor. So from my "have to stay legal" perspective I only gain a small amount.
So if a Unite get's 80% efficiency, then my power output is 800 watts.
If the RC motor is 90% efficient, then my power output is 900 watts.
...now 100 watts is not a huge difference, in absolute terms, but in a racing situation it's a winning edge. 100 watts for Europeans is near what the ebike is allowed in the first place. :lol: (sorry... I shouldn't make fun of the Europeans and their laws)
gwhy!
100 kW
Has anyone had any experience with the tornado thumper range of motors ? they seem to be a very reasonable price they are selling them for here in the UK £65.00ish for a 2500w 200kv outrunner.
safe
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Efficiency is mostly a matter of lower resistance. Lower resistance motors tend to be more efficient than higher resistance motors. Unfortunately the specification for resistance is conspicuously absent on the HXT 63-74, but the one with the same price right next to it has 28 mohm which is very good.Miles said:
https://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=4188&Product_Name=HXT_63-64-B_230Kv_Outrunner_(Eq._5330/18_or_5330/24)
$63
Even within the Unite motors there are better ones and worse ones, but I'd guess the RC motors are still an order of magnitude better than a typical Unite motor.
erth64net
100 W
safe said:
Depends on how you define "easier", if saving $30 by going with a no-name motor, just for its lower claimed Kv values (notice how the site says +/-10%...the Scorpions are more closely-engineered at a +/-1% variance - IIRC)...and that a number of people have already pointed out plausible heat-related issues...
Here's how I rationalized the purchase of my motor (aside from the fact its from a proven manufacturer using better materials):
* 200Kv @24V = 4,800RPM for a wheel spinning @612RPM = 7.8:1 reduction ratio
* 332Kv @24V = 7,968RPM for a wheel spinning @612RPM = 13:1 reduction ratio
The 1st stage of Matt's eBox provides ~5.45:1 ... so:
* 200Kv needs a final reduction of 1.43:1 - that equals a 25/35 #25 final drive sprocket pair
* 332Kv needs a final reduction of 2.36:1 - that equals a 25/59 #25 final drive sprocket pair
For me...coming up with a 59 or 60-tooth wheel-mounted sprocket was a heck of a lot easier than trying to get a 35-tooth to fit (because such sprockets are readily-available for the Currie line of e-scooters/e-bikes).
safe
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Is there a website devoted to classifying and rating all these RC motors?
I'm worried about the "Cadillac Syndrome" where people convince themselves of their spending more thinking that it must mean you are getting more. Sometimes you just spend more and get the same. :?
Bargains are when something that is good sells at a discount. I like to buy things that are at their lowest price and avoid the hype about the top of the line stuff. People might say that "cheap means junk" but I have not found that to be true. Many times things are at a lower price because the seller is overstocked.
I also like to buy something and run it UNDER it's limit. Most of the folks running these RC motors go right up to their limits and then wonder why they get overheated. Anything pushed to their limits will tend to break... the secret is in buying something at an affordable price that you then use in a careful manner... that way you get your money's worth.
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My little pearl of wisdom would be:
"If you spend time trying to make your ebike more efficient shouldn't you also make your money more efficient?" :wink:
Isn't frugal supposed to be the "new cool'?
I'm worried about the "Cadillac Syndrome" where people convince themselves of their spending more thinking that it must mean you are getting more. Sometimes you just spend more and get the same. :?
Bargains are when something that is good sells at a discount. I like to buy things that are at their lowest price and avoid the hype about the top of the line stuff. People might say that "cheap means junk" but I have not found that to be true. Many times things are at a lower price because the seller is overstocked.
I also like to buy something and run it UNDER it's limit. Most of the folks running these RC motors go right up to their limits and then wonder why they get overheated. Anything pushed to their limits will tend to break... the secret is in buying something at an affordable price that you then use in a careful manner... that way you get your money's worth.
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My little pearl of wisdom would be:
"If you spend time trying to make your ebike more efficient shouldn't you also make your money more efficient?" :wink:
Isn't frugal supposed to be the "new cool'?
erth64net
100 W
safe said:
Not quite all the info you might be seeking, but a good chunk of it: http://progressiverc.com/Brushless_Motor.html
Good intentions, possibly bad results; these motors are designed to be run at certain loads & speeds, if run too far under their designed-for capacity, then you're actually hindering performance and cutting efficiency...at what cost...a couple of $20's? Hmm, I'd rather buy the better motor, do less maintenance, carry around fewer batteries, and simply deal with fewer complications...by going with a more established and proven brand. Personally, I'm building something that'll Just Work, without a bunch of tuning & tweaking over the long-term.safe said:
safe said:
Yes, and mine is often; "A fool and his money are soon-parted" ...obviously, my motor selection doesn't work for everyone's target use, but personally, I'd strongly caution against trying to shave a few $$ of the purchase price of such a core/critical part. On the other hand, if the math works out, and you've found something better than the others, for a lower price...well then, more power to you.
recumpence
1 GW
I have much more experience in RC than E-bikes. However, in RC my experience has been "If you buy quality, you will never be disappointed."
Now, quality does not have to mean high price. Nor does high price garrantee high quality. But, they do tend to follow each other. That does not mean you have to spend a grand on a Plettenberg like I did. But, a little more cash can go a long way when dealing with these projects. That is assuming you did your research and found the best price and/or customer service for what you are looking to build. I also look at how much time a project will take me versus how much money I can earn in that length of time. If I can hand machine something in 3 hours, or buy one for $20. I would rather buy one than lose many times that $20 in my own labor time. Also, if I can pay 50% more for an item that I know for sure will work versus saving that money on something I am gambling on, I would rather go with what I know will work. You can also save a lot by merely looking in the right place. I am buying nearly everything for my latest build off e-Bay. When all is said and done, I will have bought every part brand new in the box for amost half price!
At any rate, in RC, I have never been disappointed with quality components. I have tried many cheap components as well, some worked great for my applications and some were a total waste of money.
If someone wants to try out a cheap motor or ESC, I say go for it! You may save us all a lot of money and we can all move toward that component as a viable alternative. I am in no way against trying something new..........
Matt
Now, quality does not have to mean high price. Nor does high price garrantee high quality. But, they do tend to follow each other. That does not mean you have to spend a grand on a Plettenberg like I did. But, a little more cash can go a long way when dealing with these projects. That is assuming you did your research and found the best price and/or customer service for what you are looking to build. I also look at how much time a project will take me versus how much money I can earn in that length of time. If I can hand machine something in 3 hours, or buy one for $20. I would rather buy one than lose many times that $20 in my own labor time. Also, if I can pay 50% more for an item that I know for sure will work versus saving that money on something I am gambling on, I would rather go with what I know will work. You can also save a lot by merely looking in the right place. I am buying nearly everything for my latest build off e-Bay. When all is said and done, I will have bought every part brand new in the box for amost half price!
At any rate, in RC, I have never been disappointed with quality components. I have tried many cheap components as well, some worked great for my applications and some were a total waste of money.
If someone wants to try out a cheap motor or ESC, I say go for it! You may save us all a lot of money and we can all move toward that component as a viable alternative. I am in no way against trying something new..........
Matt
Bobocop
100 W
Read this thread a few days ago, and thought, nice, maybe i'll save some money and get one of these setups next summer for another project.
Then i read the recent posts and noticed safe putting up some decent priced motors, and thought wow, maybe i can get one sooner
so i went and read some of the peoples comments on their website (people that have these motors), and most of them are positive but there are some (with both those motors posted above) that have bearings over heating and magnets coming loose on these cheaper motors,
one comment says the motor gets so hot that you can't touch it (and these things have huge propellers cooling it)
another comment on there says not to run these at full throttle for more then 3 minutes.
well thats enough for me to save a few more bucks and get a better quality motor. if it's getting hot for them, it's going to get hot for me, so whats the point of paying $60 + for a motor thats going to over heat and have bearings blow up and magnets coming loose.
guess it will be awhile for my next build
Then i read the recent posts and noticed safe putting up some decent priced motors, and thought wow, maybe i can get one sooner
so i went and read some of the peoples comments on their website (people that have these motors), and most of them are positive but there are some (with both those motors posted above) that have bearings over heating and magnets coming loose on these cheaper motors,
one comment says the motor gets so hot that you can't touch it (and these things have huge propellers cooling it)
another comment on there says not to run these at full throttle for more then 3 minutes.
well thats enough for me to save a few more bucks and get a better quality motor. if it's getting hot for them, it's going to get hot for me, so whats the point of paying $60 + for a motor thats going to over heat and have bearings blow up and magnets coming loose.
guess it will be awhile for my next build
Let's compare the continuous outputs of 2 motors of the same size and design - one with an efficiency of 80% and the other with an efficiency of 90%
80% efficient: 1000W input - 200W loss - 800W output
90% efficient: 2000W input - 200W loss - 1800W output
Big difference.........
80% efficient: 1000W input - 200W loss - 800W output
90% efficient: 2000W input - 200W loss - 1800W output
Big difference.........
safe
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The thing about electric motors is that when they are run "lean" (as in at the higher rpm nearer to the max efficiency) they tend to use less heat and run more efficiently.Bobocop said:
Heat is really caused by bad gearing.
When the motor attempts to increase it's rpm from a low rpm to a high rpm it has to do work and the RATE at which this work is done is the RATE at which the motor heats. This is why a lower current limit with a controller tends to produce a cooler running motor and doing this also increases the overall efficiency. The secret to keeping the motors from overheating is to use it in a way that does not cause the heating in the first place.
Multispeed gearing is the shortest route to high efficiency and lowered heating.
...but if you really want to become a master of heat reduction you need to go to the Armature Current Limiting controller limiting method. I can do that on a brushed motor and would like to do that on an RC motor... but that's never been done yet and it sounds more difficult.
I've actually ridden an Armature Current Limited bike (I tested it on my Project #001) and I did the same track of 10 miles and my final time was the same with Armature Current Limiting as with Battery Current Limiting but my motor did end up cooler. (slightly) You could really feel how totally different the two powerbands were to ride.
The problem with the ESC's as they exist now is they have NO CURRENT LIMITING and that's a serious problem. Fechter has made a circuit to remedy this and I'd want to do that as a minimum.
(some of the ESC's limit current to protect the ESC, but none of them go out and limit based on the motor)
Safe.. you really need to stop trying to give advice... please...
safe
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This is an often misunderstood point though...Ypedal said:
https://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=4188&Product_Name=HXT_63-64-B_230Kv_Outrunner_(Eq._5330/18_or_5330/24)
If you look at what this motor looks like from a heat perspective it looks like this:
...the RC motor is a great motor, but I think for the ebike world it lacks the controller limiting features we are all used to. The core problem with the RC motor appears to be the controller. (ESC)
Fechter has been working on this problem and has designed a circuit to deal with the problem. (so I'm in line with all the opinions on this... more work needs to be done in this area)
GGoodrum
1 MW
Safe, you really should listen to ypedal, and stop with the charts, etc. You simply don't have the experience with using these, so quit making it look like you do.
Although cheap bearings don't help the problem, that is not what is causing these cheap motors to get so hot. The problem is mostly material related. They tend to use cheap steel in the stators plates, and end up with inconsistantcies in the "mix". This will cause eddy currents to form, which generate heat. Heat losses go up as a square function of the current, so it doesn't take much. Also contributing to the eddy current problem is that the cheap motors tend to use fewer, thicker, plates in the stators. Better quality motors use thinner plates made from high-quality steel, which really cuts down the eddy current problem.
Anyway, my point is that you can't just look at a motor's kV and Rm numbers, and use these to compare. Even the idle current values can be misleading. These are typically done at 10-12V, with zero load on the motor. You can have two motors with similar Io ratings, but once up to speed, and under load, there can be huge differences.
I stand by what I said. I think maybe the big HXT might work fine in an ebike setup, but if it does it will be because it won't be used near it's "potential" limit.
-- Gary
Although cheap bearings don't help the problem, that is not what is causing these cheap motors to get so hot. The problem is mostly material related. They tend to use cheap steel in the stators plates, and end up with inconsistantcies in the "mix". This will cause eddy currents to form, which generate heat. Heat losses go up as a square function of the current, so it doesn't take much. Also contributing to the eddy current problem is that the cheap motors tend to use fewer, thicker, plates in the stators. Better quality motors use thinner plates made from high-quality steel, which really cuts down the eddy current problem.
Anyway, my point is that you can't just look at a motor's kV and Rm numbers, and use these to compare. Even the idle current values can be misleading. These are typically done at 10-12V, with zero load on the motor. You can have two motors with similar Io ratings, but once up to speed, and under load, there can be huge differences.
I stand by what I said. I think maybe the big HXT might work fine in an ebike setup, but if it does it will be because it won't be used near it's "potential" limit.
-- Gary
gwhy!
100 kW
I know Im the new boy here, but to be fair I can see where safe is coming from on this one. Until Safe actually gets access to a RC motor ( im in the same boat ) its all theory and trying to make sence of it all. Its only when you start playing with these types of motors or anything new, thats when you will start getting the experience ( and experience comes at a price ). Can the motor/controller combination also cause heat problems as you are revering to eddy currents then ?
safe
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Heat (Power) = R x I^2
It should not matter if it's a brushed motor (which I've tested all these ideas on and it all is correct) or a brushless. It's current that heats up motors. That motor chart posted above (a couple back) is an accurate picture of the heating that takes place for that specific motor, the HXT 63-64. If someone where to build an RC plane and use the wrong prop (forcing the rpm too low) you can see how rapidly the heating would take place. Ebikes present even more challenges because they need to go from zero mph upwards while pulling a load. The RC motor is designed to freewheel up until the props start to cause significant wind resistance, so the ESC's are probably not all that great for starting up. This is probably the best argument for the more expensive ESC because they use more sophisticated control logic. (at least we assume they do)
GGoodrum you are correct when you say I'm never going use the full "potential" of an RC motor if I restrict it so severely, but that was my goal in the beginning. It's NOT always about power... sometimes you want just the efficiency and light weight and yet you want the motor power to be within some limit like the legal limit of 750 watts. Restricting current enhances efficiency and does not worsen it.
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The brushed motor is easy and cheap and you can build an Armature Current Limiting circuit with very few parts. (comparator, current sensor, voltage regulator, resistors and a capactor) But I do expect to step up to the higher complexity of the brushless eventually... hopefully by the time I do it all the "pioneers" we have here will have worked most of the bugs out. It's good to see reasonable prices.
I will definitely use current limiting on my RC motor when I build it.
But for gwhy! your Trials riding bike would not want current limiting because you want to have the low end torque.
Everyone has their own design goals.
recumpence
1 GW
I can tell you from experience that RC motors are fantastically high output for their weight and size. I can also tell you from experience that quality makes a HUGE difference.
I am not knocking Safe, here. He is trying to understand how these motors work. The issue I have is the fact that cost is not everything. When you get down to a very low price point, you WILL sacrifice a large amount of quality.
It is as simple as that.
Matt
I am not knocking Safe, here. He is trying to understand how these motors work. The issue I have is the fact that cost is not everything. When you get down to a very low price point, you WILL sacrifice a large amount of quality.
It is as simple as that.
Matt
JEB
100 W
Guy's- I thought this is a forum, even if you don't agree with Safe's posts, (don't get upset, you don't have to read them) to me he throws out information that makes me think! I injoy his graphs, and input.
Here is a question for Safe-(and everyone) If you make a hi freq. pulse width generator, well filtered output, that would effectly lower the input voltage to the rc motor/controller would that reduce the current into the motor to a acceptable level? (say, 72volt batt.- pwm down to 24volts)
Here is a question for Safe-(and everyone) If you make a hi freq. pulse width generator, well filtered output, that would effectly lower the input voltage to the rc motor/controller would that reduce the current into the motor to a acceptable level? (say, 72volt batt.- pwm down to 24volts)
safe
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From the way I understand it (and it took me a long time to accept that PWM really works this way) the motors tend to have a certain degree of inductance. When there is a lot of "space" between the pulses that more or less allows whatever current to flow in a less restrictive manner. The way I try to view it is to think of a traffic mess in a busy freeway... if you have an empty freeway you can travel at 80 mph if you want. But if there is a lot of traffic then the cars start to order themselves in such a way that the speeds are lower, but the volume is the same. Basically PWM means that total power is a constant and voltage and current are proportionally opposite to each other. (when using battery current limiting)JEB said:
Power = Current * Voltage
Power = (2 * Current) * (Voltage / 2)
etc...
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There also is this phenomenon of "discontinous current":
http://en.wikipedia.org/wiki/Buck_converter
...and this tends to occur at low duty cycles. However, I seem to recall that it tended to happen more with LOWER frequencies than higher, but I might be wrong about that.
That's the best I can figure... my guess is that there is really no way to get Armature Current Limiting (which is what you are trying to do) by just fiddling with the control frequency.
So my "guess" is the answer is "probably not". (how's that for certain?) :lol:
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With brushed motors it's easy to implement Armature Current Limiting because all you have to do is place a current sensor on the motor wires. But with a brushless motor it gets more complicated because the currents change direction. It's not a sign wave, but instead it's a square wave that switches from positive to negative. So brushless is just plain harder to deal with. :?
Bobocop
100 W
Well, I don't know anything about these motors (i'm just going by what i'm reading about them)
and I would like to see these cheaper motors work on EV's,
so if safe is willing to try it, all power to him.
these motors can run on 24 volts, so if he is right and does get these (cheaper) motors working, that is a huge difference in price to what is being used now.
If safe tries it and fails, well then, we'll know that it's not worth it.
36 and 48 volt packs are selling for over $600, for me that is just redicuosly to much.
I could go for a $100 24 pack thou,
the hub motor kits (without batteries) are going for $500 and more for some of them.
I can go for a $60 motor (if they work)
Even if you buy 2 motors and use them something like this.
it would divide current, and double the torque would it not ?
buying 2 of these motors is still less then half the price of a hub motor
As i said, I don't know about these motors, I just like the idea of them being used on EV"s because of cut prices and weight.
and I would like to see these cheaper motors work on EV's,
so if safe is willing to try it, all power to him.
these motors can run on 24 volts, so if he is right and does get these (cheaper) motors working, that is a huge difference in price to what is being used now.
If safe tries it and fails, well then, we'll know that it's not worth it.
36 and 48 volt packs are selling for over $600, for me that is just redicuosly to much.
I could go for a $100 24 pack thou,
the hub motor kits (without batteries) are going for $500 and more for some of them.
I can go for a $60 motor (if they work)
Even if you buy 2 motors and use them something like this.
it would divide current, and double the torque would it not ?
buying 2 of these motors is still less then half the price of a hub motor
As i said, I don't know about these motors, I just like the idea of them being used on EV"s because of cut prices and weight.
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