Beach Cruiser E-Bike Build *Help Needed*

Hello all, this is my first post on here as I'm currently planning my first E-bike build. I've decided to go with a mid-drive system, I've already pretty much figured out how I want to mount everything I'm just having trouble figuring out the correct placement configuration for the motor, battery, and controller. I just want to make sure that everything I order is compatible. I plan on using a Turnigy RotoMax 1.60 Brushless Outrunner Motor (http://www.hobbyking.com/hobbyking/stor ... Motor.html) with 1 or 2 Turnigy 5800mAh 8S 25C Lipo Pack (http://www.hobbyking.com/hobbyking/stor ... _Pack.html). The problem is that the motor is rated for 37V but the battery is only rated at 29.2, will this be a problem? the only problem I'm having is determining how much power I am going to use with the motor. I'm not sure if 1 5,800mAh battery will be enough, so maybe I'll just buy 2 and wire them in parallel to get a 11,600mAh battery, but again I'm not sure if I'll have enough Volts to run everyting. My next problem is the controller, I've researched a good bit and found that a sine wave controller(should)give me the smoothest and quietest ride from the motor. I have found plenty of controllers rated for 36V but only up to 1000W (the motor is rated for 2960W). I want to be able to use the full power of the motor as my goal is to be able to ride around 20 miles with a top speed around 30 mph. I cant find an appropriate controller to control that large amount of power. Could someone please give me a recommendation on what I should be using? I was told a Mamba XL2 ESC (http://www.castlecreations.com/products/mamba_xl2.html) would be good enough but I'm not really sure. As this is my first build any advice is appreciated. Thank you all

Ok,

Not sure about motor positions etc but here is some battery info

Unsure what you mean by battery rating being 29.2v I assume you mean that is maximum charge
To reach 30 mph you will usually need a 48v battery.

You say the motor is rated at 2960w and 36v? Usually a motor does not have a voltage rating it's more a power rating because more power equals more heat depending on the motors efficiency. More voltage means the motor spins faster which equals more speed.

You can achieve 30 mph with much less than 2960w. Somewhere in the region of 1000w will do

As for mAh you will need a lot more than 11600 if you intend to use the throttle all the time. Normally 0.75ah per mile is a good figure for WOT. If you pedal a lot then you need much less to reach your desired 20miles

For simple plug and play have you had a look at the bbs02 from a reputable seller like em3ev.com?

Good luck on your build. You're going to need it. You don't have a clue.
http://endless-sphere.com/forums/viewtopic.php?f=3&t=70169&p=1058597#p1058597

Nothing wrong with your approach, if you plan on riding next summer. It is a big bite to chew, doing a home engineered mid drive on the first build. But I predict you will have a blast doing it!

The simplest approach, will be mounting the motor right behind the seat on a rear rack of some kind, then belt or chain driving it to a puller or sprocket on the left side. Not really a mid drive per se, not driving the bikes original chain. You see this approach with guys who convert a weed whacker motor to run bike a lot. It works.

If you want to ride this year, then get a bafang mid drive, and slap it on a beach cruiser that has a 7 speed rear gear, and the three piece crank and bottom bracket. That is to say, the standard bike bottom bracket, vs the cheap one found on $100 bikes.

Easiest of all, slap a hubmotor on any beach cruiser, front motor if you have coaster brakes.

Welcome to the forum

This sounds like a very ambitious project. I originally got started in Ebikes after seeing just how powerful RC motors were.

First, about the batteries. The Amp hour rating is not the same Amp rating. An amp hour is how many amps the battery can supply for an hour. "5800 mili Amp Hour"(5.8 ah) is the battery's capacity. If you think of the battery like a round can, 5.8 amp hours is like saying the can is 5.8 Amp hours wide. The voltage would be how tall the can is, and the watts would be how much power is in the can.
The battery's Amp rating (no hour) is how many amps it can put out at one time. Its often rated by "C" which stands for Capacity. a 25C battery can handle putting out 25 times the amp hour rating. So a 25C 5800mAH Lipo could put out 145 amps. You can think of this as how big of a drain hole you can put in the can. The bigger the Amp and C rating, the bigger the hole to let the power out.

Next, the motor. While those are nice, It's rated for 231KV. That means 231 RPM per volt, or 8547 RPM at 37 volts. That is going to need a massive gear reduction to get down to the 300-400 RPM you need at the rear wheel. You will likely need a multi stage gear reduction system, so you're going to need a fair amount of engineering skill to build it.

As for the controller, you should forget about anything designed for RC. RC controller's components are built small, and they just don't have the size to dissipate the heat encountered when the motor needs to labor to get something the weight of a human moving. You need a controller built for high load operation, like those made for Ebikes.

There's another advantage to an Ebike controller over an RC controller. Your motor is limited to 2960 watts, an RC controller won't limit the output, so you could very easily overload and melt the motor. An Ebike controller has a hard limit to the amount of power it will feed the motor. once you reach that limit, no more power will be used. On many systems, that's programmable.

As I mentioned in the beginning, I got lured to Ebikes thinking I'd use RC motors to build the ultimate bike. I very quickly found out there were good reasons not to, and many easier, cheaper, and better alternatives. While there have been many people who have built RC powered Ebikes, I've never regretted leaving the idea behind.

Thank you so much for the replies, you guys have definitely helped clear up some concepts I was vague on. I'm fully aware that this is a big project to drive into, but as I'm a college student I have a lot of time to sink into research and the actual build itself. I'd prefer to put custom parts into it as opposed to a kit just so I know exactly what going into the bike. The bike is a pretty nice aluminum beach cruiser(https://www.giant-bicycles.com/en-us/bikes/model/suede.silver.blue/9020/48873/) so I don't want to drill into it either. My theory is that I could put a freewheel next to the already existing chain wheel to drive the whole system but one of my worries is that the motor will turn the pedals too. I took what you guys said into consideration about using rc parts for an E-bike not having the power needed to reach my goals. So I looked around for a bit and found these 2 motors; A Leaf 48V800W E-Tricycle motor(http://www.leafbike.com/products/e-tricycle-motor/800w-electric-bldc-motor/48v-800w-tricycle-motor-863.html) or a Golden motor BLT 800 (http://www.goldenmotor.com/frame-bldcmotor.htm). They are very similarly priced and the specs are the same but I wonder if anyone has any experience the reliability and performance differences. As for the battery, I played around with the simulator a bit and found what you said completely accurate, I wont be able to achieve the desired speed and range with what I wanted to use. So I searched the forums a bit deeper,readjusted my budget and came up with this battery. Its 48V 18AH LiOn with charger for $370 (http://www.conhismotor.com/ProductShow.asp?id=461). Again I want to say thank you to all of you guys for really simplifying everything and for the advice.

I think you might have missread what we are saying about the RC motor. It's not a power issue. The RC motor has plenty of power. The issue is in how it delivers that power and how you feed it power.

For 20mph, you need around 400 watts of power.
For 30mph you need around 1000 watts.

The RC motor peaks over 2900 watts, so more than enough. It could probably hit 40, if the bike holds together.

The 800w motors would be easier to convert, not because of the power, but because the rpm will be lower and make getting the gearing reduction easier. But that 800 watts is nominal power, where the RC was rated at peak. the 800w motors can probably peak well over 3000 watts.

If you power the bike through the left side gears, then the chain will spin the pedals. The answer is you use a freewheel crank. that lets the chain spin and the pedals freewheel unless you are pedaling. They are pretty common. I got mine through Sickbikeparts.com.

You'll have to get over that idea you don't want to modify the frame too.

Hang with us, you'll be switching to steel, so you can cut and weld on the frame.



That started out as a 100 buck coaster brake Schwinn. Now it's longer, and has dual disc brakes, and 7 speed gears. Best street ebike yet for me, after years of experiments.

Some like to build, some like to ride.
Obviously you are the first kind, because you will spend more time building and fixing than riding. :wink

I'm quite ready for the build at hand, I know that it will take a while but I'm fully prepared to invest the time. The bike has a nicely welded together and study frame so I'm not too worried about the bike falling apart at my desired 30+. I have access to a TIG welder so I can in fact weld to the frame, I would just prefer not to. I've decided to dig my DIY hole deeper and build my own battery. I have found several options to do this; I could buy 18650 cell holders and wire those together with, yet to be found good source of Li Ion 18650 cells. I did a bit of math and found that 36 cells at 4.2V 6000mAH would make at 50.4V 18AH (12s3p) battery. Looking around I found a bunch of high power cells from ultrafire in china, but upon further research I discovered that they weren't a good source. I realize my numbers may be a bit optimistic, individual cell power wise, but if I could find cells near that I would be happy. Does anybody have any experience in making their own batteries? How hard is it really to do?

You mean these 6000mah cells?
http://lygte-info.dk/review/batteries2012/UltraFire%20SJ18650%206000mAh%20%28Black%29%202015%20UK.html
In case you don't understand any of this, at a 3A load it has less than 1000mah of energy. IOW's nowhere close to 6000mah.
My advice to you would be to drop the whole project until you've learned a lot more.

Or alternatively you could continue to ask questions and receive answers from the great wealth of member knowledge here on this forum, until you get it right.

Also, welcome to ES.

You really are digging quite the DIY hole. Soon you'll be able to climb down to those Chinese suppliers, and avoid shipping charges.

Many of those high power claims from 18650 cells are simply pure fiction. You aren't going to get 6000mAh from an 18650.
At the upper end you might get 2900mAh, but in a format that can't deliver high amps. The higher the rated amp output, the lower the capacity of the cell.

There is a ton of great info on building batteries in our Battery section. There are also instructions on building a battery tab welder. That will need to be your first project, as a successful round cell battery needs to have the tabs welded. Any other construction method is so much inferior as to not be worth the effort.

I have a question about the bike the OP linked: https://www.giant-bicycles.com/en-us/bikes/model/suede.silver.blue/9020/48873/ Any issues you see mounting a BBS02 above the BB instead of traditional below the bottom tube location?

Can't see behind the chain guard but there is probably a metal tag there to hold it on which would be in the way. If you were to remove that I don't see why not.

I always try to get them up as high as possible.

Beach cruiser= almost armchair comfort, however I'm about due for a recliner or a motorized hammock. :lol:

Thank you guys so much again for all the great advice. I'm looking forward to the build, but I think I need to research the battery build before I do anything else. I was already whether or not that was a question for a different thread.. I'll do some more research in the battery section. As for mounting a BBS02 above the bb, this is what I plan on doing except with the Golden motor BLT-800. I want to fit everything, i.e. motor, batteries, and controller, in the frame itself so that it looks cleaner and is more contained. I'm trying to avoid using a kit because they tend to be relatively expensive as opposed to buying the separate parts and assembling everything myself. I have no problem putting the time and effort into building the bike, so I figure I might as well save some money and feel more confident about the bike, along with added advantage of actually be able to fix something if it breaks. I'm off to learn more about building batteries in that section, I'll keep this thread updated with everything I'm doing as well as asking more questions. Thank you guys again for the great informative introduction to the forum.