RC motors, efficiencies, gearboxes and more?

I've just discovered the RC motors, and more specific the build by recumpence. It seems those RC motors are really high spinning beasts with amazing powers. Delivering efficiencies from 70% around 1/10 of max RPM and tops out at around 93% at full RPM.

I saw another thread about a dog shifter here, will those work well with Matt's crazy RC motors? Seems it can take 2 motors......pneumatic gear changes. Just thinking of the svosj sound makes me grin.
Don't know if anyone tried to use a gearbox for high powered e-bikes? Will they work well and have acceptable longevity?

Or would it be possible to use a jackshaft with an enclosed schlumpf speed drive inside? Seems those are build tough as nails. And handles several hundreds lbs of torque. Have anyone here used a schlumpf speed drive for a jackshaft?

I am trying to best understand how to get most usable power from RC motors, for both low end torque for mind blowing acceleration yet be able to speed of more then 40 mph.

In my very first thread here I got several comments about mid motors, but I was still so new here that all I knew about mid motors was the big names like bosch etc - and their low power motors. One even mentioned mid motor and dog shift (John in CR maybe?). But I thought that was useless cause I had not seen mid motors with more then 750w motors. It sounded just boring.

Then I now realize those RC motors are build like tanks. Withstands 200 degrees Celsius of temp, where Cro and Crys start to melt around 90-120 degree Celsius. Not to mention those big DD hubs puts a significant unsprung mass in your rear tire. If the RC route is not desirable one could use a regular DD hub as done by Simon. His build was a true beauty. And of sourcing motor from 4motus one could even get high powered water cooled motor.



So what you guys think. Twin RC motors or singel water cooled Crystalyte 4 series? What is more fun and more durable?

If you have to put weight into a powertrain, make the weight you add be in the form of copper/magnets/iron and you will end up with the highest power capability. Adding weight that just spins or whirls chains around isn't weight that is actively converting your pack's energy into the propulsion force you desire, it is just wasting it.

macribs said:

I've just discovered the RC motors,



I am trying to best understand how to get most usable power from RC motors, for both low end torque for mind blowing acceleration yet be able to speed of more then 40 mph.

Click to expand...

Just a jack shaft will do what you want, a fraction of the weight of a bigger motor, and fraction of the cost ( as long as you don't get sucked into the very expensive rc motors and controllers) .

Edit: and you do not need two RC motors to achieve this :wink:

Two is more then one - more is better, yes?
The power from those two RC motors just got my head spinning. And imagine all that power comes in a small feather weight package. Using two of those just seems obvious. It could make for insane powered bike while still keep things light and drivable. Power = Fun. After all, could you ever have too much power? As long as the price tag is within sanity.

I don't even know if a gearbox would work with that kind of power. But I did see a couple of mid motor builds here with some sort of gearbox. So that is why I asked if it is a necessity. But as long as jack shaft reduction will work there is no need to add extra weight, costs or complexity to a build.

Will those RC motors work with any controller of the well known brands often used for DD hubs? Or do they require special purpose build small form factor controller tailor made for RC motors? If they need special controllers I guess that will add to the price tag rather quickly.

I have not really looked into this RC motor enough yet to have gotten the whole lay down yet. As of controllers I have no idea what kind of controllers works with those tiny RC motors. If this route is too complicated or too expensive I could still do a mid motor build more like Simon's. Would still have the benefits of mid motors, like more centralized weight and less unsprung mass.

liveforphysics said:

If you have to put weight into a powertrain, make the weight you add be in the form of copper/magnets/iron and you will end up with the highest power capability. Adding weight that just spins or whirls chains around isn't weight that is actively converting your pack's energy into the propulsion force you desire, it is just wasting it.

Click to expand...

Luke, your logic is infallible...but the reality is: there are no motors that bolt onto a "off the shelf" pedal bike, with a reasonable battery, say 1300watts of energy on board (still more weight than I would want to pedal home).

If we are going to select some hp generating micro motors, the reductions are there to make them work....& a multi speed (dog box or bb drive) will expand the operational envelop.

Until some one shows me an example of = weight vs performance, on = voltage's...I will keep plugging away on my motor designs....the ultimat goal making it as simple as posible.....but no simpler

The main and biggest draw back with using rc motors is the fact that they are toy rc motors , what I mean by this is that ( from my experience ) you need to have a 100% reliable way of starting them and I have not come across any rc esc that can do this yet , my solution to get around this problem is to retro fit sensors and using a off the shelf e-bike controller but with modified firmware settings and depending what powers you are looking for you may even have to re-wind the rc motor to achieve those powers. So as far as I know its not a complete off the shelf solution to use these toy motors. Two motors are better than one but comes with a cost of additional complexity, but if you can manage the additional complexity then yes its more than worth it ( from a power/size/cost point of view ) .

gwhy! said:

The main and biggest draw back with using rc motors is the fact that they are toy rc motors , what I mean by this is that ( from my experience ) you need to have a 100% reliable way of starting them and I have not come across any rc esc that can do this yet , my solution to get around this problem is to retro fit sensors and using a off the shelf e-bike controller but with modified firmware settings and depending what powers you are looking for you may even have to re-wind the rc motor to achieve those powers. So as far as I know its not a complete off the shelf solution to use these toy motors. Two motors are better than one but comes with a cost of additional complexity, but if you can manage the additional complexity then yes its more than worth it ( from a power/size/cost point of view ) .

Click to expand...

Yeah imagine my surprise when I saw what those RC motors can do - 86 mph run on a trike with Matt's twin motor setup. Max output of like 20 horespower. And all this from motors made for use in radio controlled toys
The small size is also a factor to be honest. That makes it easier to have a sleek looking bike - or one can use that space for extra batteries. I will try to read up and see what the other RC powered e-bikes in here are using for controllers and see if there is any firmware available. Another bonus from using RC motors might be that one stand a better chance of walking away without a ticket if pulled over by a cop. Open a cover and show the tiny tiny RC motor while making sure you hit the "hidden button" that limit the bike to 25 km/h. Guess they will fall for that easier then if they spot a 25 lbs monster motor in the rear wheel.

Thud said:

liveforphysics said:

If you have to put weight into a powertrain, make the weight you add be in the form of copper/magnets/iron and you will end up with the highest power capability. Adding weight that just spins or whirls chains around isn't weight that is actively converting your pack's energy into the propulsion force you desire, it is just wasting it.

Click to expand...

Luke, your logic is infallible...but the reality is: there are no motors that bolt onto a "off the shelf" pedal bike, with a reasonable battery, say 1300watts of energy on board (still more weight than I would want to pedal home).

If we are going to select some hp generating micro motors, the reductions are there to make them work....& a multi speed (dog box or bb drive) will expand the operational envelop.

Until some one shows me an example of = weight vs performance, on = voltage's...I will keep plugging away on my motor designs....the ultimat goal making it as simple as posible.....but no simpler

Click to expand...

Not sure how to read this Thud. Are you saying that a gearbox or a dog shift is a good thing for RC motors? Like give them a wider power band/usable range? For longevity and to not overheat them puppies I guess keeping them in the lower end of efficiency would be a good thing.
And with the option to change gear it seems motors would work much easier - even if there is losses from gear box and the added weight. Well at least the extra weight will be where it hurts the least - in the triangle and centralized.

You are reading correctly mcribs.
I advocate a 2 speed dog shifter with a wide ratio to capitalize on the power delivery of electric motors.
I will caution you though....the uber performance videos posted around here give a somewhat skewed view of the true nature of micro drives....& take any quoted watt #s with a grain of salt....every one brags on how much power they consume.....with no base in reality of the torque they are generating or for how long.

Gwhy, myself,&a few others have a long history with the Chinese outrunner's on bicycles. Recumpence is the athority on setting up astro flight drives on bicycles.

There are numerous ways to make power. You can run a huge motor at low RPM with very little (or no) reduction, or you can run a smaller motor at high RPM with a reduction and achieve the same thing. However, most often (not always, but most often) a huge hub motor will be less efficient. That being said, you do lose some efficiency with reduction units. So, quite often, you end up at the same place.

Here is my take on this;

With a huge hub motor, you eliminate the reduction complexity while retaining good power. One benefit of a large hub motor is thermal mass. Yes they generate heat, but they have so much mass, that heat takes a long time to overheat the motor. The highly efficient RC motors generate less heat (because they are normally higher in efficiency), but their thermal mass is less. So, they will put out huge power, but for less time. Now, when you are running two of the RC motors, you cure numerous things......

First, you have soooo much surplus power, heat becomes a non-issue because the motors are only running at high power for very short bursts.
Second, you double the number of controllers in the system. While this increases complexity, it also cuts the load in half per controller for a given power output.

That last item that cannot be avoided is handling. The LAST place you want to add weight is at the outer extremity of a vehicle. And the worst possible application of that weight is rotating weight. That is not to mention unsprung weigh (if this is a suspended vehicle). From a handling perspective, you always want to centralize mass and keep the wheels as light as possible. This makes a mid drive like and RC build, or something similar, very attractive.

Being that I sell drive systems, I admit bias. That must be made clear. However, there is a reason I design and build the systems I do. There are benefits to them. That being said, you can compare this to car engines in some ways. Let me explain;

If you want huge acceleration and do not care about handling, you can throw a huge V8 with a blower into an old sedan and have a "Fast" car. However, you can, also, install a turbo charged smaller displacement engine into a Lotus or other small and light car and achieve the same thing, but with far greater handling. Of course, you may pay more to squeeze lots of power out of the tiny engine. Also, the Lotus will generally cost you more than the old sedan. So, there are tradeoffs. Same thing here. A twin motor RC system that is ready to go from me will cost you more than a powerful hub motor. Yet, you can achieve better performance per pound and those pounds will be correctly placed in the chassis for MUCH better handling. However, you will pay more for it.

Lastly, as far as multi ratio gearboxes are concerned, Thud has the best philosophy on this. If you want multiple ratios, you really only need two ratios when running an electric system because of the HUGE torque involved. That being said, if you have enough torque, you eliminate the need for a gearbox. That has been my experience with twin motor systems (or at least the twin Astro systems I have built and run). They have soooo much power, a gearbox becomes unneeded. Even Tesla found that out with their Roadster. They originally came with a two speed box. But, after a few months of production, they began having problems with the boxes from all the torque and they found that the car was quicker when it was left in second gear anyway. So, they went to a single ratio.

With enough power, you do not need more than one ratio. But, with less power, multiple ratios become beneficial.

Matt

What kind of peak output and continues power do you harvest from those outrunners?
I never really looked into anything other then DD hub motors, as I was so naive to think those lame Bosch mid drive motors was what could be expected from mid motors. So I quickly brushed (!) off anything but DD hubs as motors for old people or girlie boys. I now realize there are a heap of options for motors. Most of which will even fit as a mid motor with some losses from jack shaft or gear boxes. Now matter a mid drive will put the weight in the right place. So seems the hub motor is not the best solution due to massive unsprung weight.

When I first got hooked on e-bikes I figured I would throw something together within a few weeks. But the more I hang around this forum, read up new threads, old threads and venture off into unknown sections and threads here at ES I learn something new each time. Seems the hardest part of the build will be to gather enough information about possibilities and boundaries - plain boring fact collecting. Not the actual build when that time comes.

I mean why not make it right the first time?

macribs said:

So I quickly brushed (!) off anything but DD hubs as motors for old people or girlie boys.

Click to expand...

Yawn.....

I mean why not make it right the first time?

Click to expand...

If someone loves the sound of a small V-12 Ferrari, that doesn't make them wrong, and it doesn't make them right. I would say that LFP and recumpense are at the two extremes of the ES design philosophy. Matts Astro builds have been run up to 10,000-RPMs, with a high amount of reduction going to a 20-inch wheel, with his builds often being geared to attain 50-MPH, while using only 44V.

Luke is the big block guy, he is running big volts into a large motor (from a Zero motorcycle) on a steel 20-inch wheeled frame that is as light as possible, but still "just" long enough to make the tendency to wheelie more controllable (if desired). He can do 100-MPH, and accelerate to that speed in a very short amount of time with no transmission.

Both designs provide brutal acceleration, but Thud is trying to get acceptable acceleration from a 4,500-RPM 80mm diameter RC motor. His motor (and volts) don't have the big size of LFPs build, and he doesn't have the 10,000-RPMs of the Astro builds, so...he is broadening his systems effective performance by adding a 2-speed transmission. When he couldn't find a transmission that fit his needs, he made one from scratch...

Here is Thuds DIY 2-speed: http://endless-sphere.com/forums/viewtopic.php?f=28&t=8644&start=150#p195730

Which one is best? I love all three of these systems I just described, and I would take any one of them in a second. The real question is...what is your budget? and what are you going to use your project bike for? I can drive nails with a big wrench, but a hammer works better for that particular job.

Thanks for your inputs Spinningmagnets. As always your comments makes sense and you always have great reads too. If you happen to have bookmarked other great RC builds/gearboxes or mid drives threads feel free to drop more links here.

I found a chart and graphs over those RC motors the other day. Cos I forgot to bookmark and now I can't find back to it.
The thing that got me the most from that chart was the relative decent amount of power those RC motors delivered even in the lower RPM.
Sure the efficiency was little below 3/4 but still I was baffled. I will search and find it and post it here as well. It is interesting to say the least.

I sure get the Big Block approach too. I mean there are some great motors out there, well known hub motors, more exotic ones and even some crazy high powered motorcycle motors as well. Even outrunners and what not. But placing a cromotor in a wheel might not give the best handling. If paved roads in other countries are anything similar to what we got out in the boon dock even every day use of a heavy wheel hub on paved roads might cause premature failure due to large pot holes, and a general lack of maintenance of public roads. If roads are slick and one does not care for dirt roads, green laning or air time I guess where you anchor your power source is not as important.

For people that do fancy adventure trails,down hill, air time and stuff every now and then I think a big cro/crown might live better within the triangle then laced into a rim. But as you say people are different and have different needs. What fit one might not fit the other. The dedication to explore possibilities and take things to the max is what really make me enjoy this forum. So many great builds, so many well drawn up solutions and to think people do this on there spare time. I wonder what they achieve at work. And for the most part people are civil and well mannered, and that makes this great forum even more enjoyable.

Below is the missing graph, RC motors power band chart.

Here there is a limit of 100A current to prevent meltdown.



As you see the power band is rather wide - more so then what I expected from those tiny RC motors.

On a side note, why does those motors run sensorless?

You can run them sensored, and a number of the MIT people who build small EVs with them will use them with a Kelly KBS controller and then mount Hall sensors to them with the boards and adapters from Equals Zero Designs. Most of us tend to run the Turnigy/Kelly combo on at least one or two vehicles, and Charles's daily driver (as well as Ben Katz's tricycle both run 80mm "melon" motors mated to a 50A/120A Kelly controller. There are a few drawbacks to running sensored motors, primarily due to the risk of damage to the sensors if they're mounted poorly or the board is unprotected from the elements; still, a Kelly controller (with appropriate max eRPM for the motor and voltage you're using) works really well with most small RC motors and should provide pretty good performance for most medium- to high-power applications.

They also work very well with infineon controllers but you need to reprogram the controller suit your needs ( much cheaper than kellys ) , The external boards from zero designs is one solution to retro fit hall sensors , I have used the same spacing as theses boards but was never very happy when used on the 80mm motors, the spacing works much better on lower power setups but have my doubts at higher powers . Some have fitted there sensors internally @ 120degrees and some have also fitted externally @ 30degrees .

So if sensors are added, will it be possible to run sine wave controller and get a more quiet smoother motor?
I guess the same applies to RC motors as to ie 3 phase DD hubs with sine wave?

macribs said:

So if sensors are added, will it be possible to run sine wave controller and get a more quiet smoother motor?
I guess the same applies to RC motors as to ie 3 phase DD hubs with sine wave?

Click to expand...

Yes.

Regarding price it seems that the Colossus outrunners are probably to most powerful yet affordable mid motor.
The colosuss wf 120 is 895$.14 kw of continuous power and > 30 kw peak power. All that from a motor that is so light, only 4.5 kilo.
I've read somewhere that they looked into a 6 phase version of that motor. I guess that would make the wtf 120 even easier to handle as it would be less stress on each controller and one could opt for lower specced controllers. And that would give some redundancy, which in turn should give you a better durability and longevity.


But I can not see anything about the 6 phase on the Croatian website. Very little information. Did they make a 6 phase version of that motor? Anyone made a build with 6 phase colossus?

Is motor/contoller noise really an issue with the high rpm of rc motors? I thought the fet ringing growling noise in hubs was from the low rpm and hollow side covers resonating at a frequency that is easy to hear.

Colossus stuff looks really cool but from reading the colossus thread it looks like there are not controller options to really take advantage of it yet. The people playing with it are what i would consider more advanced users, some of which are building thier own controllers to run it.

I guess those Colossus motors are not even available for sale anymore. Seems that they discontinued those motors.
Shame really.

Well I have to look for other alternatives then. There is always Golden Motors BLDC. Heavy but they got power.
Don't know if people have used those outrunners for their builds here?

http://www.revolt.org.il

Rv120

With the light weight and high powered RC motors, has anyone done a e-bike 0-60 test?
I imagine a twin RC motor setup with right reduction would be about the fastest e-bike from standstill.
Someone been at the strip doing a 1/4 mile or any other form of reliable testing of 0-60 acceleration?

This became an issue during lunch at work today, and I could not give any specific 0-60 time or 1/4 mile time.
So if someone has done testing and care to fill me in I will be most happy.

The yellow trike in my Youtube video ran 0 to 70mph in 4 seconds. There are faster e-bikes out there. But, these are the numbers I was able to achieve. This was done on fresh pavement with a warmed up tire.

Bear in mind, in my case, I was on a trike that would not wheelie. I relied to some wheel spin to mitigate the huge torque. Wheel spin became an issue trying to get the power to the ground.

Matt

macribs said:

Or would it be possible to use a jackshaft with an enclosed schlumpf speed drive inside? Seems those are build tough as nails. And handles several hundreds lbs of torque. Have anyone here used a schlumpf speed drive for a jackshaft?

Click to expand...

I'm looking for a schlumpf central drive to be used as jackshaft from years.....It was projected for velomobiles, trikes and similars.....but haven't found one. even brand new directly from schlumpf......

My 2cents on the topic:
Obviously Depends from what kind of load and duties you would like to do with your bike, and the whole weight of the vehicle, But I can say, coming from an MX and motorcycle in general life-time experience, that a single Astro setup (3220 at less than 700$) properly tuned, in a <30Kg bike, could be more than enough for most duties and riders...

As Matt has yet noted should be hard to really use more than 1 digit Kwatts (even more than 5-6kw on my bike) if not looking at the higher possible top speed or doing power wheelies at sustained speed (over 40-50Kph) or climbing something really crazy steep and dirt....Max peak I've logged has been about 7Kw but usually more likely 4-5Kw for wheelies (up to 35kph) and hard climbing accelerations.
I've the impression that my high gear (19:1&24"x2,5" tire) and consequent low max-speed (only 55kph at 50v) makes this system bombproof. I have more than 5000Km made with that Drive, and "only" serviced chains and 2 times the spokes damaged from an internal derail.
Having a 2nd gear (paying no more than 1-2 kg for this) to reach something close to the max speed this motor is capable to sustain with me and my bike in flats is what would make this system ideal for me.

A better dead start is the other need but with the idle feature I'm using on the tracks, thru a throttle residual made by the CA, The system is smooth even in the very lowers.
Also, as yet stated, Adding Halls or Opticals to these motors (both in-/out-runners) would avoid all that....