Aiming for 40+mph with RC

Hello,

After reading about MrBoots success with the turnigy 6374 150kv motor, and after looking up some specs on it, I am planning on running it at 12s Lipo with a Turnigy 100a 12s ESC and a direct-drive 11:90 reduction to a 26" rim, which is roughly 27-28" after the tire thickness is included. Assuming 70% of unloaded RPM at load, this would put me in the range of 45+mph, but I'm uncertain as to whether or not this motor could actually accomplish this. I was just wondering if anyone on here had any input as to whether or not these components are compatible at this level of abuse and if I would need more than 2.2-2.7kw to hit 40+

Other motor considerations include the Turnigy Rotomax 1.6, and although I'm open to suggestions, I'm still in college so I'm trying to keep this a relatively low-budget build, otherwise I'd just grab a Turnigy 80-80 and a castle 160A HV ESC.

Thanks for your time!

The gearing is too high for that motor. You want about two stages of reduction, around 20:1 total. Even then, if you plan on going up any large hills, I don't think you want to gear for 40 mph. For the most power, I would recommend picking a faster wind motor and gearing down appropriately. You could also add hall sensors or optical sensors and use a ebike controller such as those sold by em3ev.com or Lyen on this forum.

For 40-MPH on a 26-inch wheel, I would plan on using one of the 80mm diameter motors. They have over twice the copper mass of the 63mm motors, and the smaller ones would likely overheat.

I can tell you that 40mph with one RC motor is definately doable, but requires doing everything right. I would take the advice of those who have already chimed in, But, I would add two bits of advice;

#1 Start with the bike geared slower than you think you need and work up from there. This will give you a good starting point to understand how the motor and controller will react to the load.

#3 Use 20C lipo cells. You could get away with less than 1kwh of pack and still have the power to run 40mph. Just remember, you do not want to overdischarge the pack. Run it for a few miles and recharge. Then monitor how much energy you used in that given amount of mileage and you can calculate how much range you will have with the size pack you are running. You want to stay above 20% state of charge in your pack at all times.

Matt

Thank you very much for the quick responses! The area I would be using it in doesn't have many hills, so low climbing power wouldn't be a problem. My lipo cells are 6s 5AH 20C, and I currently have 4 of them, but I would most likely purchase 4 more for a 2s4p layout. If heat generation will be a problem, I'll definitely look into a larger diameter motor as well as higher reduction. Has anyone tried using a heat sync attached to the motor mount of a non-exposed motor? I was planning on placing the motor in a more or less water-tight environment, since it'll have to be left outside while I'm in class, although I could try to add air flow channels or something. Any idea what efficiency these motors generally see in this environment?

I'm afraid that you cannot run the 63-74 geared for 40mph. I had one geared for that and it blew up on the second start. I'd guess that the maximum gearing for that motor on 12s should be about 25mph if you want reliability. That is assuming that you only have one gear.

You definitely want plenty of airflow, and the motor doesn't need to stay dry. I've ridden my bike through torrential rain with the motor completely exposed and it's still ticking along.

fizzit said:

I'm afraid that you cannot run the 63-74 geared for 40mph. I had one geared for that and it blew up on the second start. I'd guess that the maximum gearing for that motor on 12s should be about 25mph if you want reliability. That is assuming that you only have one gear.

You definitely want plenty of airflow, and the motor doesn't need to stay dry. I've ridden my bike through torrential rain with the motor completely exposed and it's still ticking along.

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These small motors are fine for that speed and cope with the heat very well for normal riding, but I agree that to be reliable they need to have a very robust esc, I have always run them using a e-bike controller and have fitted halls sensors to the motors.

Go with the advice from recumpence and start off with gearing for around 20-25mph and work up, dont just just stright in at aiming for 40-45mph cos it will end costing a lot more money in blow up parts.

The folding bike in my signature could comfortably hit 37mph, when geared down 16:1 (via two stages). That's 12s LiPo, Castle HV-160, and AstroFlight 3210 (6 turn winding). I didn't have the skills/tools/discipline then to check the HV-160 log to see if I was pushing my luck with respect to controller temp and/or voltage ripple, but I did occasionally trip the CAv3's max amperage cutoff (99 amps) geared that way.

I'm confident this suite if equipment would have been quite reliable. But it's a small bike with skinny tires. It was simply too scary to ride geared that way, so I re-geared it for 20:1 reduction and now the max speed is a still thrilling 30mph (and has been very reliable with respect to belt, chain, controller, motor, etc.)

Thanks for the replies!

So the new updated plan is a 2-stage reduction of a Turnigy 80-80 160kv of around 1:16 overall to begin with, the larger motor size should help control the temperature and I'm also looking into designing higher airflow to the motor to help with that as well. I have also seen people wire capacitors in front of their ESC's, and the purpose of them is to reduce voltage ripple, which I'm guessing is the fluctuation caused by voltage drop - would voltage drop still be an issue with 20AH of 25C lipos (12s4p 5AH)? I'm trying to make sure I'm not biting off more than I can chew by trying to use an RC ESC, the amp capabilities of moderately-priced e-bike controllers (<300 dollars) are too low for this motor, I think, and would require installing hall sensors.

Also, is it "necessary" to freewheel an RC motor? Does anyone know how hard these are to fight when they aren't being powered? Right now I have a 1000W direct drive hub motor, and biking without the motor running is like having a parachute attached to the back of the bike. Obviously freewheeling would be the best option, but I don't know how frequently I'll be riding this without the motor running, so I'm considering solving it as an after-thought if I decide it's necessary. Any input?

Yeah an RC motor really slows down your pedaling with no motor freewheel. You'll need one if you want to pedal without assistance.
Also, if you are planning on running 1:16 on 26" wheels, be careful with the throttle. I just blew up a castle controller because I started hard in third gear (trying to do a wheelie and forgot I wasn't in first gear) which for my bike, is a total reduction of 21:1. I have started in 2nd or 3rd gear a few times though and not damaged things, but if you go hard off the line your RC controller (or probably any other controller) won't last long. The only RC controller that I know of that would be appropriate for this application is the castle HV160. Hopefully the guy with the 420 amp controller comes out with something good that RC users can switch to.

As for the capacitors, you really need them for an ebike. They don't exactly stop the voltage drop from the batteries - no matter how big your pack, you'll still want external capacitors. When the controller FETs switch, it creates really short voltage spikes, which will blow up the controller if left unchecked. The wires between the controller and the batteries have too much inductance to let the batteries absorb these spikes, and the batteries have too high internal resistance, so you need caps that have very low ESR and are located very close to the controller. The controller has some caps but probably not enough.

For mine, I used 5 of these:
http://www.mouser.com/ProductDetail/Panasonic/EEU-FM1H681L/?qs=3buz8ytw9h213HsDKDKoOw%3d%3d
They are the same ones that are used in the Castle controllers but they are bigger.

I think this is completely possible. I routinely cruise at 32-33mph using a 6374 149kv with only a 7.5 reduction on 6s and a 100A YEP controller. Obviously, this is not a setup for torque, but for those saying I will have trouble with hills, I live in San Francisco and bike to work every day, and have had no trouble climbing the 3-5% grades I encounter at 20-30mph. Please keep in mind I weigh about 155#, and ride a ~20lb road bike with the e-bike setup probably adding about 6# including the 2x 5ah batteries(I haven't actually weighed it). According to my Turnigy watt meter, I rarely see over 65A or 1500w, although I have seen peaks of over 2000 watts on acceleration.

With little reduction and RC components, you have to be very careful with accelerating from a start, which is where you will see highest current draw. I rely heavily on my legs for initial acceleration, with electricity helping greatly above 20mph. Think of it more as a bicycle with an assist, rather than an electric motorcycle.

As for power, 2kw sounds about right for 40mph and a mountain bike according to the online calculator. I've found it to be pretty close at 32-33mph and 1kw for me.

http://www.kreuzotter.de/english/espeed.htm

About the freewheel question. When I first had my bike, the freewheel wasn't working properly. I didn't notice a huge dropoff in unassisted speed. I was still able to cruise at 20-21mph, vs 21 or 22 before the electric conversion. What I noticed most was the extra inertia of having to spin the motor up from a stop. It really hurt my acceleration from stoplights.

Thanks for the input! I'll have to look more into the capacitors between the controller and the batteries and how to handle the high amp charge/discharge when connecting the batteries, I've seen people recommend resistors and whatnot. I'm not sure how often I'll be riding the bike without the motor running, so I'll probably play the freewheel by ear if I think I need it. I'll most likely be going with a Castle HV160, I've heard they're very high quality.

Not to contradict Jasonv8z - there are so many ways you can implement an RC setup - but the two RC bikes I run can start from zero speed on a 20% grade and accelerate very aggressively up that hill to 25mph+. This is using the Castle HV-160 (I have no experience with anything else).

The spark we see when plugging in the battery is more a function of voltage than current if I understand things correctly. The HV-160 max voltage is 50v. It gives a healthy spark and a loud pop! but if you use high quality gold plated connectors like EC5's they'll be fine for hundreds of connection cycles without damage at 50v or below.

Posted this table in the Hub conversion thread http://endless-sphere.com/forums/viewtopic.php?f=28&t=45245&start=315#p684237, i know it's a double post but I guess it will help:

Gearing a middrive for good speed and hill climb isn't simple as we all know. The spread is dependent on the motor torque, and thus we have determined a max speed of 35mph we can calculate gear spread for a given motor power (if geared/reduced right). I made some calcs about a bike with a weight of 150kg including rider. What came out is this rough contract:

1kw: 400% spread needed
2kw: 200%
4kw: 100%=single speed.

It's all about torque at the rear wheel. One can not push infinite power into it without flipping over (As can be demonstrated spectacularly on one of LiveForPhysics bikes for example)

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Since this chart was made for 35mph max and 30%gain, you will need more than 5kw if you wanna get up a 30% hill except your body is as lightweight as mine

There are some nice single speed builds out there using the Astro and the Turnigy 80/100. You will find them is you search for them. Matty's build is a very nice one for example.

I hope I can come up with a rotomax 80cc (would be a turnigy 110/70 in old terms) soon. I only aim for 35mph since I have no inclination of frying my motor/controller on a steep hill.

Engineering is all about compromises and picking the best route to fit your needs. I wanted something as light (I was aiming for a 25lb bicycle) and powerful as possible, and that meant a single stage reduction. A 149kv motor on 100A at 8.5:1 reduction will produce around 40lbs of thrust at the tire. Using this calculator:

http://www.mne.psu.edu/lamancusa/proddiss/bicycle/bikecalc1.htm

I determined that a 10% grade @ 30mph would require 26lbs of thrust at the tire, or about 65A (not accounting for losses) on 6s. These numbers are well within what a 6s 100A controller can do. I have yet to encounter a bike route in my area with a hill over 10%, so I felt this was sufficient.

40lbs of thrust yields about 0.22g acceleration given my weight, which should me to 30mph in under 7 seconds. It's not going to win many drag races (although I destroy busses and give Hybrids a run for their money), but it was enough for my needs. Evaluate your needs, and design accordingly.

Thanks for all of your input, I've been thinking about whether I should run my 160kv motor at 44v or 22v, since I want to only have a single stage reduction, and if you halve the voltage and keep the max amp draw the same, you halve the available power. But, from that awesome calculator (thanks Jazonv8z), it seems like to achieve 45mph, I only need around 2kw at the wheel, and with 200A max draw at 22v, the "max power" of the Turnigy CA80-80 is around 4400 watts, although I'm sure most of the amp draw is during acceleration and not during peak rpm and that the calculator makes assumptions about my choice of clothing to reduce air drag. From a practical standpoint, will I have the same top speed if I run the motor at half the voltage and half the reduction? And for the power that both setups would be capable of managing (say, under 3kw,) I'm assuming running at higher voltage will result in a lower amp draw, and therefor will be more efficient. But going back to the practical differences between the two setups, will the loaded RPM be the same % of max RPM at each voltage? I suppose that's effectively what I'm asking by with the previous question.

I look at your propositions and they don't make sense to me. The RC motor is designed for a certain envelope of power, duration, and air cooling, but you don't aim to conform with those limitations. You look only at the power it can produce and assume you can do it for longer duration and with much less cooling than it was intended to have. It's not a good assumption.

So you are only going to stuff 2000W through the motor? At 85% efficiency (an optimistic number), you have to evacuate 300W of heat from the motor, or burn it up. How do you intend to accomplish that? If you can do that, how do you intend to keep the system running when it bogs down and produces not 300W, but 1000W of heat?

High powered traction motors are big and heavy for a reason. If you think you can do something performance-wise that industrial engineers can't, maybe it's because you'll have to come up with controlled conditions that industrial engineers don't have the luxury of assuming. Your ride might thus be a nuisance of constant vigilance and holding back from what the machine would be capable of if it were more fault tolerant.

If you already own a 160KV motor and want to use only single stage, you should go for 22V. BUT you have to be aware that using 100amps+ is really difficult. It's simpler to redetermine your motor to WYE config, then it has 160/1.73=93KV and use 44V. Redetermine a motor isn't hard to do, I did this myself when I was a noob. You'll find a how-to on the sphere, if not PM me. You can calc with a loaded motor speed of around 3000rpm. A 1:8.5 reduction seems to be fine. Be aware that you wont use the full potential of this motor, you wont see 4kW at your wheel. Don't bother about motor cooling, it's likely you will find a solution for that if you really wanna go this route. It's much more likely you kill your controller, feel warned

Also I have to warn you to use small sprockets at high speeds. The smallest motor sprocket that is likely to work at this speed is a 12T, larger is better (google polygone effect on chains)

Over all you have chosen a great setup for a noob. You just have to find a controller and throttle for your setup now. That wont easy :? RC ESCs are not simply buy-and-use. They are made for planes, not for e-bikes. The sensorless e-bike controllers loose sync on high rpm, and there are only 12Fet ones available yet, which is too weak for your setup. Also they often loose sync on motors that have more than 100KV (the controller just stops working then, it wont spin up the motor to fulls speed).

hope i could help you a bit with my knowledge, good luck with your build, keep us posted

I made an excel sheet, so you can play around a bit with numbers. PM if you can't open the sheet.

You can't always assume you can half the gearing and double the current and expect everything to be the same. This may hold true at lower currents, but eventually the iron starts saturating and adding more current becomes a dimishing return. I'm sure there are other losses as well, but the net result as I understand it, is lower efficiency.

Without having actual data on the motor (e.g. a dyno graph), you should make a conservative estimate to fill in the blanks. If you expect the torque of 100A output with 100% efficiency, maybe you plan for 150A in reality.

Most people feel the RC stuff is "optimistically" rated. Meaning, if you have a 150A controller, it might be ok for a few seconds of acceleration, but asking that controller to do 150A continuous is asking for trouble. I think without actual data, cutting an RC rating in half is a good place to start. My 100A YEP controller seems to be perfectly happy at 50A, and doesn't even get warm. Ditto with the 6374.

I also believe it's a good practice to use the controllers at lower than rated voltages. A 12s controller might get destroyed on a 12s ebike due to ripple, but may be ok at 10s.

Like everyone else, I recommend you go with as much reduction as possible. Reduction keeps the current down, which keeps things from blowing up. Why not do a 9s build with gearing for 45mph? That should still be possible for a single stage.

ndawsonelli said:

Thanks for all of your input, I've been thinking about whether I should run my 160kv motor at 44v or 22v, since I want to only have a single stage reduction, and if you halve the voltage and keep the max amp draw the same, you halve the available power. But, from that awesome calculator (thanks Jazonv8z), it seems like to achieve 45mph, I only need around 2kw at the wheel, and with 200A max draw at 22v, the "max power" of the Turnigy CA80-80 is around 4400 watts, although I'm sure most of the amp draw is during acceleration and not during peak rpm and that the calculator makes assumptions about my choice of clothing to reduce air drag. From a practical standpoint, will I have the same top speed if I run the motor at half the voltage and half the reduction? And for the power that both setups would be capable of managing (say, under 3kw,) I'm assuming running at higher voltage will result in a lower amp draw, and therefor will be more efficient. But going back to the practical differences between the two setups, will the loaded RPM be the same % of max RPM at each voltage? I suppose that's effectively what I'm asking by with the previous question.

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One of my bikes has 12s, 80-100, 2 stage reduction, 18 fet controller, and can go over 50 mph. These motor make their power by spinning fast. That is why you need a lot of gear reduction and most people get it in two stages. Using a single or two stange reduction, you still need the same amount of reduction. It can be done with one large costly sprocket if you want to spend the bucks.

Bubba

"max power" of the Turnigy CA80-80 is around 4400 watts

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http://www.hobbyking.com/hobbyking/..._CA80_80_Brushless_Outrunner_50_80cc_Eq_.html

The 4400 watts is probably optimistic. And even then, it would assume the highest volts combined with the lowest amps to achieve that (low volts/high amps will run hot), plus quick acceleration to top speed in a light RC aircraft (E-bike will be slower to accelerate than an RC plane, would cause high heat), and as Chalo pointed out, lots of airflow (too low of airflow would result in...too much heat). Make sure to run whatever motor you get at its efficient RPM range.

I recommend that you copy an existing RC build that works. Some of these motors have a real problem with inductance. Best of luck with whatever you choose.

dontsendbubbamail said:

ndawsonelli said:

Using a single or two stange reduction, you still need the same amount of reduction. It can be done with one large costly sprocket if you want to spend the bucks.

Bubba

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from what ndawsonelli wrote i assume that he knows that. He might be a noob, but an educated one. Large sprockets are not that expensive. You may get #25 sprockets suited for you purpose (125T is part # A 6C 7-25125 ) https://sdp-si.com/eStore/ be aware that you will need a hub for large sprockets, since in raw condition they weight about a ton. A large sprocket made from plastic would be awesome, they could even be printed.

Haha yes, I am indeed a noob, but I've been trying to do my homework. I'll most likely be looking into re-terminating the RC motor to wye to get a much more manageable 92kv, and then possibly using an 8.5:1 reduction, which, with the stock highest timing belt pulley I've seen being around 120 teeth, and more options around 100-110, would allow me to get a larger drive pulleys, which is never a bad thing. As Thud said in another thread (http://endless-sphere.com/forums/viewtopic.php?f=28&t=25623) sometimes reterminating turnigy motors can be a nightmare, so if that's the case, I'll have to figure something else out or re-wire it. This isn't my first electric bike, I have a Giant "hybrid" bike that has a massive 1kw hub motor on it that hits ~32mph if I pedal with it, but making an enclosure for that bike would be tiresome, since my main concern with this bike is going to be making everything on it theft-proof, as college campuses aren't very forgiving to velcroed down controllers or batteries not to mention it weighs about 60 pounds and hauling it up my apartment stairs has been annoying.

The plan right now is to make a custom carbon fiber frame designed with the battery storage and motor mounting systems in mind, and it's heavily based on the new Audi electric bike, although the drivetrain will be a much cheaper alternative . I've also been doing my homework in that field and it should be fairly safe as long as I make the walls thick enough, and I'm going with the female-mold-interion-bladder forging technique, which gives both a better strength:weight and a more professional-looking surface finish, as long as you get the fabric:epoxy ratio correct. I'll probably make another thread for that once I finish that documenting it, if there's any interest.

The major debate I've been having right now is chain vs belt. It sounds like the pros of chains include being easier on the motor bearings, being more positive, and possibly being stronger per dollar, since #25 and #219 chains and sprockets are fairly available and are really strong. But, then the size of the drive sprocket is really important due to the polygon effect, and chains are noisier. Also, the motor drive sprockets for those chains seem to start at 18-20T, which means I'd need a reallllly big rear sprocket (150T+). It seems like I'll be fairly able to get the necessary reduction using belts, and their tendency to skip might help me put less stress on my ESC, but all that tension on the belt means I'd need to support the far end of the shaft, which isn't impossible but is definitely something I'd have to plan for.