Using RC motors on E-bikes [Archive]

[John in CR]

Safe,
You're leaving out the critical aspect of the NuVinci's losses, so your graph should look more like this, and is why I think only specific conditions would warrant more and why I'll blast right by you on the straights, which you will never overcome with most of the riding taking place in the right half of the graph. With the 2 speed I'd probably get you in the first 100 yards or so never to see you again, at least till I lap you.

 

[dirty_d]

ok, so whats the best/easiest/cheapest way to set up a 6000rpm motor with multiple gears while still having pedals, preferably without having to hack up a shitty freewheeling crank?

 

[John in CR]

ok, so whats the best/easiest/cheapest way to set up a 6000rpm motor with multiple gears while still having pedals, preferably without having to hack up a shitty freewheeling crank?

I'm leaning toward a retro-direct on the left side, because I think a 2 speed is the way to go, though dual motors is awfully tempting instead of gears.

 

[recumpence]

ok, so whats the best/easiest/cheapest way to set up a 6000rpm motor with multiple gears while still having pedals, preferably without having to hack up a shitty freewheeling crank?

I'm leaning toward a retro-direct on the left side, because I think a 2 speed is the way to go, though dual motors is awfully tempting instead of gears.

Hmm, seems like I have seen something like that before. :wink:

Matt

 

[John in CR]

ok, so whats the best/easiest/cheapest way to set up a 6000rpm motor with multiple gears while still having pedals, preferably without having to hack up a shitty freewheeling crank?

I'm leaning toward a retro-direct on the left side, because I think a 2 speed is the way to go, though dual motors is awfully tempting instead of gears.

Hmm, seems like I have seen something like that before. :wink:

Matt

:lol: Dirty_d said cheap and easy, not original. :wink:

John

 

[dirty_d]

when you say dual motors do you mean a motor each with its own sized sprocket, or like a high kv brushless running next to an etek through the same gears?

 

[John in CR]

when you say dual motors do you mean a motor each with its own sized sprocket, or like a high kv brushless running next to an etek through the same gears?

No, I'd want to keep it simple and easy by using identical motors combined on a common shaft with a clutch bearing on each. Then I could run either and alternate them for a 50% duty cycle instead of continuous, and both for high power needs (hills and acceleration). I'm torn between buying one of the big 130Kv HXT's or going this route and running a pair of the smaller $60 motors, since someone got over 50mph with just one of the smaller ones. Less money, less weight, and dual failures required to be left with pedal power alone is very appealing. Of course, trying anything with these powerful RC motors is really intriguing.

With that big HXT you probably have enough power to keep it simple and go single gear unless you have some really high hills to climb. That gets you on the road quickest, and you can easily go retro-direct with minimal waste later if you really need gearing. Based on Matt's results, multiple gears is probably an unnecessary complication and introduces more possible points of failure.

I'm still unclear what gets you up into the best efficiency range with these motors. If it's just a matter of running high amps, then maybe just some kind of battery switching to halve the voltage at lower speeds is the way to go. I don't think maximizing power is required, just minimizing waste heat since I believe heat is the real enemy in an RC motor app. Who really wants to run 8hp in 1st gear anyway?

John

 

[Knuckles]

John,

I have to ask. Are you riding yet? Gosh I hope all is well in CR land.

Cheers and Salutations
K

 

[dirty_d]

John, you can get real high efficiency with these motors because they are so powerful that you can run them near no-load the whole time and still get a lot of power out. having a current limit automatically keeps the motor near its no load while accelerating, thats why that graph on the first page of this thread is like that. by limiting the current the controller lowers the voltage, keeping the motor near its no-load for that voltage. the higher the voltage gets, the closer the motor gets to its no-load rpm for the voltage its at since the current is static but the voltage is dynamic during acceleration with the active current limit. thats why the efficiency rises exponentially instead of linearly like when you have a fixed voltage at the motor. as a result you get a constant torque with quickly rising efficiency.

i agree, you dont really need more than one gear with these powerful motors, though it would be nice, you have 4000W on tap, just gear it at some sane speed for a bike like 35mph, and you will have tons of torque for hills.

 

[eP]

i agree, you dont really need more than one gear with these powerful motors, though it would be nice, you have 4000W on tap, just gear it at some sane speed for a bike like 35mph, and you will have tons of torque for hills.

Two gears/ two motors are more universal than single gear.
More than two gears are needed for racing purposes only.

Lets look again for at PMG_132 characteristics:
http://www.enigmaindustries.com/PMG_132/PMG_132_graphs.htm

@ 72V we can get out ~6hp @~90% efficiency, @3200 rpm
but @36V we can get out similar power (6hp) @ ~70% efficiency only,
however if we don't care about ultra quick acceleration (for racing) and we are quite comfortable @ ~3hp power out level for slow or moderate acceleration, so we can get it @ ~85% efficiency level.

We also should keep in mind the PMG_132 is not a last word in the motors universe.
Some RC motors are even much more efficient than 87% @36V.
They are able to reach 92-94% efficiency for the same voltage (36V) and they are the same level powerful as PMG_132 at 36V or even more.

So if you did right choice ( for right motor ) so you could feel quite comfortable at single gear if you don't care too much ultra high efficiency or you don't care about racing acceleration ability.

 

[johnrobholmes]

Running a PM motor most efficiently occurs at light loading, so to get best efficiency you could use multiple gears to keep amp draw low during acceleration (or maybe just use a light throttle hand). I do like the dual motor idea too, double the power and decrease the amp draw per motor.

Where can one find clutch bearings suited for out application? I have been looking for some sprague clutches with 6mm ID or 10mm ID, can't find any yet.

 

[safe]

340 Watt Average At Tour De France

Watching the tour this morning they flashed on the screen that the riders were averaging 340 watts while climbing the hills. It seems to me that 750 watts output (which means more like 1000 watts input) is enough to do some impressive things.

We ought to remind ourselves periodically that there are laws about power and for America it's 750 watts. They make no rules about having or not having gears only they mandate that the motor has a cap of 750 watts and when you sell the bike it's supposed to be geared to only go 20 mph.

So the main reason I see the gears as an important part of ebiking is that the "base machine" is always going to be built to the 750 watt power spec. It has to be. Some areas will likely permit the full use of gears while others will not, but the spirit of the law is that the power is "tame" because it's supposed to imitate human power. Missouri allows 30 mph for all their ebikes and mopeds for example and many other state also allow 30 mph. That's high enough to make having a three speed worthwhile for 750 watts.

If the best cyclists in the world can't pump out more than 340 watts and the law already allows 750 watts to assume that infinite power is allowed for ebikes (making the one speed practical) is not a good idea.

I'm still convinced the Optibike is on the right track... keep the power right around 750 watts and integrate the power with the pedals and the gears. That's all the power we need. Beyond that and we're really talking about motorcycles and not bicycles. The RC motor (high rpm motor) is simply an addition to the Optibike... an increase in focus on the main theme... towards this perfected system.

For a 3000 watt ebike the pedal power for a typical rider (250 watts) translates to about 8% of the overall power. It's a motorcycle with pedals added as a joke. :lol:

 

[scottclarke]

Running a PM motor most efficiently occurs at light loading, so to get best efficiency you could use multiple gears to keep amp draw low during acceleration (or maybe just use a light throttle hand). I do like the dual motor idea too, double the power and decrease the amp draw per motor.

Where can one find clutch bearings suited for out application? I have been looking for some sprague clutches with 6mm ID or 10mm ID, can't find any yet.

John, drawn cup roller clutches with a 6mm I are a bad idea - the max torque these handle is less than 3Nm........ some as low as 1Nm.

I use 10mm - which I got from my local bearing supplier - though you can get them from a place that sells model helicopters since they are used on mainshafts of those with autorotation ability. I am talking big heli's here - not little tiny ones!

As regards dual motor - you can only take it so far. Each motor has a parasitic load (no load current) and if you are running 2 motors you are essentially wasting twice as much power right away - this can pale into insignificance but until you draw so much current it doesn't - you are onto a losing streak

 

[eP]

I'm still convinced the Optibike is on the right track... keep the power right around 750 watts and integrate the power with the pedals and the gears. That's all the power we need. Beyond that and we're really talking about motorcycles and not bicycles. The RC motor (high rpm motor) is simply an addition to the Optibike... an increase in focus on the main theme... towards this perfected system.

For a 3000 watt ebike the pedal power for a typical rider (250 watts) translates to about 8% of the overall power. It's a motorcycle with pedals added as a joke. :lol:

So tell us how much PMG 132 - your best choice - is effiecient at 750 W power out level ?
If you don't care the wats above 750W level than why you want all that gears to cover such small area (less than 10% and mostly above 750W level) of whole powerband ??

 

[johnrobholmes]

My likening to the dual motor idea is more of the cost issue and novelty. I would prefer to keep a unit as one motor and controller for simplicity, but having oddball ideas is good.

 

[scottclarke]

340 Watt Average At Tour De FranceI'm still convinced the Optibike is on the right track... keep the power right around 750 watts and integrate the power with the pedals and the gears. That's all the power we need. Beyond that and we're really talking about motorcycles and not bicycles. The RC motor (high rpm motor) is simply an addition to the Optibike... an increase in focus on the main theme... towards this perfected system.

For a 3000 watt ebike the pedal power for a typical rider (250 watts) translates to about 8% of the overall power. It's a motorcycle with pedals added as a joke. :lol:

Have to agree with you here - been saying the same for as long as I can remember. My latest bike really just confirms it for me - in person. But then, that was my intention - to create something that passes as a pedal bike but is actually more of a light motorcycle. If it lasts 3 years of 26 miles per day, 4 days a week, 47 weeks a year without falling apart I think the concept is sound - ie. some pedal bikes can actually do 40mph average and keep you safe. I am not sure who said pedal bikes SHOULD travel at 15mph - it definately was not me!

My experience every day confirms people in general don't want pedal bikes to do the same speeds as them in their mobile coffins - and my experience today with the police shows a bike at 25mph is a target for them.

Scott

 

[Miles]

and my experience today with the police shows a bike at 25mph is a target for them.

Hi Scott,

Do tell us more...

[edit: Ah ok, just seen your post on this in the other thread...]

 

[cerewa]

As regards dual motor - you can only take it so far. Each motor has a parasitic load (no load current) and if you are running 2 motors you are essentially wasting twice as much power right away - this can pale into insignificance but until you draw so much current it doesn't - you are onto a losing streak

But if only one motor is turning at a time (both being coupled via freewheel) this does not apply. Of course, there is still the freewheel drag, which probably amounts to 1 watt or so.

On the other hand, if you just size your motor with magnets & coils that can handle high torque or high speed (say, a 250 gram RC motor with high torque at 9v80a and high speed at 18v40a ... something like 480kv and 1:14 reduction by chain drive) then you don't need two motors, just a switch that'll change your input voltage.

Also, if we're talking street-legal ebike speeds (usually 30mph/48kph or lower), most folks will find that 750 watts will accelerate them to the speed they want to be at very quickly. Most folks will also find that, most of the time, they're running far below 750 watts if they want to stay at street legal speeds.

 

[recumpence]

Hmm, performance will always be pushed to the edge.

One nice thing about E-propulsion is no emissions. What I mean by that (I am not really an environmentalist per-se) is that you can go for perfomance without any issues related to emissions such as emission testing, etc.

I can see a new generation of gear head emerging in the next decade, one that does not mill and port heads, but, rather, reworks controllers, rewinds motors, mods control/management systems, etc.

Hmm, wait, we are seeing that now!

Matt

 

[Miles]

Hmm, performance will always be pushed to the edge.

Certainly, if it's you doing the pushing

 

[recumpence]

Hmm, I'm really not a pushy person.

I prefer to pull (drag?) others along behind me. :wink:

Or is that the fact that they are just behind me anyway?!

Oh, also, humility is one of my strengths (along with good looks, sense of humor, etc).

Matt

 

[cinejeff]

This thread and the pioneers working on RC motors on ebikes has really got me excited.

One thing still troubles me however. Im still not convinced that these rc controllers are the way to go, they just don't seemed to be properly designed for our application. The Castle boat HV esc seems like a promising candidate but man it is expensive. What I would like to personally see is a ruggedized version of a high voltage ESC that works with regular ebike throttles, has current limiting built in, more caps and can handle spike, etc... or a least a way to hack something from available components. Most dont want to be frying ESCs on a regular basis, and hopefully Matt can get a sponsorship deal or at least a beta tester thing going as this is going to be a HUGE market in the near future.

The big rc brushless motors are more then capable (and relatively inexpensive)...
I maintain my original theory that the ESCs are the weak link.
Admitting we have a problem is the first step in finding a solution.


These ESC arent going in a rc plane, I would think we could add a few ounces for increased reliability/longevity.

Cheers,
Jeff

 

[scottclarke]

Jeff, agreed.

The controllers are not built to drive a stalled motor who's resistance is less than .5ohm............. So you are going to see a limit but at least that limit will save the motor from melting down. As you say, whats needed is a ruggedized controller that can actually ramp down when it gets near its limit - the Power Jazz due to be with me in 2 days seems to promise that function albiet probably temperature activated.

I am not at all sure about the throttle thing - I set out to avoid one of those at all costs - way to many issues with water. I do hear magura make one that works but does it work underwater? Thats a serious question.

Having said that - right now I am having doubts about 3KW rc motor on a bike. Others run 6kw hubs without issues but I rather suspect that 6kw is a peak rating - the max it will ever pull (what is the resistance of the windings on a big CL?). My motor will pull over 200A (VIR) from a 24V source if its asked to deliver the goods, that means 5KW and on 36V you are looking at the best part of 8KW. So right now I am sitting on a bike thats out to kill me and I'm not at all sure I set out to create this.

 

[cinejeff]

Hi Scott, I love your bike picts. Small motor-Huge power!

You would not one of these bad boys to go into a full power situation when you arent expecting it. There seems to be a lot of really smart electronics guys that hang out in the forums, surely the collective wisdom of these fine folks could work something out.

Im a video/multimedia producer,RCer and backyard tinkerer let me know if anyone needs any video help on any of there projects and I would gladly help out. Unfortunately, electronics is not my thing.

I guess if money was no object, we could have this sorted out quickly. I look forward to Matt's experience with the hydra HV240 ESC from Castle Creations, I think it holds promise. My comment on throttle is guess isnt really about the throttle in retrospect. Its about how to program a power curve into the ESC so you dont break chains, strip belts and blow ESCs when adding power/amps and smoothing out the spikes/surges. I am starting to understand the adding caps can help with some of this, as well as larger dia power cabling, etc...

I am debating ordering some brushed unite motors and controllers from TNCscooters or if I join in on the search for an esc solution. I really like the big HXT 130kv, it scares me a little as well but its all good.

Cheers,
Jeff

 

[eP]

I guess if money was no object, we could have this sorted out quickly.

I have one idea: Group ESC project. Group owners will gain access to all PCB files and private code. All other members could develop open source code and they could buy the ESC at production cost (bargain price). Members without own input (to project) could buy ESC at slightly higher prices.
I think these are fair rules. Guys most interested in such project could become group owners for some money input.
Instead buying expensive ESC they could create own alternative + made some pressure on commercial ESC producers. This way ESC prices could come down.
I think some cheap freelancers could do great work for few hundred $.
Group lider could create account at some freelancer's site (Rent a coder or anyone else) and would be responsible for paying for the work done.
I think $100 or $200 are not a huge money for someone ready to spend $1000 for motor + ESC or motor only.

What you think guys ?
It's a briliant idea or crap ?

Best regards