Working on an ebike with my son (with help from others)

[timmydbrady]

I'd like to share the plan my 14 year old son and I have for an ebike to see if there is some helpful advice from the group (pitfalls or improvements).

We are trying to convert an old moped into an electric bike. We were looking at purchasing an ebike and my son gravitated toward the Vintage Electric (https://vintageelectricbikes.com/pages/tracker) and Monday Motorbike (https://mondaymotorbikes.com/). Both are heavy bikes (like mopeds) where it is more about throttle than peddling. My son is on a robotics team and I want to promote his interest in building things, so we decided to build versus buy.

We found a local mechanic that fixes old mopeds and makes custom moped who has agreed to create the frame and work with us to add an electric bike kit. Here is the mock-up of what my son hopes to build.


It will be based off an old PUCH moped step-thru. The mechanic will add a top bar, remove the gas motor, and modify the top tank to be a cover for the battery. We hope to add a clasp or hinge to open or remove the tank to get access to the battery, but keep the old moped look.

We are on flat roads and would like to follow ebike rules of keeping it under 20 mph with the throttle. With a bike that will weigh about 80 lbs, we were advised to go with a rear hub motor with 500 watts or more of power and 42V. We like what we read about the Luna kits and believe this 750w hub motor should work for us:
https://lunacycle.com/geared-hub-ebi...front-or-rear/

The mechanic suggested he could help us thread it into a moped rim. We would also add a disc brake in the front wheel.

Are there obvious flaws in the plan? Have we chosen the right motor? Any tips? Thanks for your help.

[moarpower]

I know the limitations of the law state 1Hp or 750w watts in most states along with a top speed of 20 mph. Every licensed factory 2 stroke moped I've owned put out 5hp or more and easily ran 35-40mph. No one is going to pull him over and put his bike on a dyno.

I'd suggest a more powerful motor (1500w) to get a similar level of acceleration to its gas counterpart. A good number of kits have a programmable top speed or a jumper wire you add in to limit speed at 20mph. All my builds have had that capability.

if if he ever needs to get out of the way of a car or out of a dangerous situation, 500 or 750 watts is not a lot of power and will feel very slow on an 80 lb bike in real life.

Not to mention that it's hill climbing ability will be quite poor at those power levels. His speed would reduce greatly on a steep grade causing both the motor and controller to bog down into a less efficient range. The byproduct of this is heat and excess heat is the killer of hub motors and especially controllers.

If you really want 500-750 watts build it on a lighter bicycle frame. There is no sense in dealing with all the additional weight if you don't have the power to move it around efficiently.

Just my .02.

edit: One more thing about weight. A 52V 20Ah battery, a large DD motor, and a good bicycle frame will land you at 70-80 lbs. if you factor in a moped frame I think you are looking at closer to 120 lbs for a finished build IMO/IME.

[timmydbrady]

Thank you, moarpower. Having more power to manuever makes sense to me - especially if I can limit the top speed. Do you think this is a more appropriate motor?
https://lunacycle.com/golden-pie-v5-...motor-hub-kit/

And aside from more power for the heavier frame, is there anything else I should consider before starting with this plan?

[moarpower]

I think it is a step in the right direction. You would still find that his moped would likely lose in a race against a stock production moped with a 49CC gas engine. But being the fastest moped on the block isn't the point, is it? ;)

Make sure that the motor/wheel's dropout width matches that of the moped. I believe the standard dropout width of a Magic Pie is 135mm. Also make sure that the axle is the same size.

Consider how you will employ a torque arm (or better yet, two!) to counter the rotational forces exerted by the axle. In a hub motor the motor in the wheel is exerting an equal and opposite rotational force on the axle. This is not true for an ICE engine moped, motorcycle, or bicycle. A poorly secured hub motor axle will "spin out" (rotate "backwards") and rip the wires right out. This case can potentially damage the battery, motor, and controller.

Consider whether you are using bicycle or moped tires/wheels. Motorcycle tires can be employed on bicycle wheels. Motorcycle tires are much more durable and will present a lower long-term expense than replacing bicycle tires every couple hundred miles. There is a good deal of information online about doing this.

Are you changing out the wheels? Will you use drum brakes or disk brakes? Will that change the alignment and require additional work?

If you have a roller frame on hand, taking measurements will be easy. If you don't have a frame yet, research more. There is a lot of poorly organized but quality data on e-bike conversion kits and DIY builds spread across several forums. Ask questions here and elsewhere.

Rushing into a build like this and buying parts without a solid plan or measurements will cost you more headaches and money in the long run than a properly formulated and vetted plan.

Enough about DD hub motors. Let's consider a different direction...

Let's consider for a moment employing a cheap but very powerful motor like the Cyclone 3000w kit from Luna and mounting it where the moped's engine would normally be.

This does not require changing wheels, tires, or other running gear. You probably will need to change the sprocket out on the motor but you will also be able to take advantage of the heavy duty chain on the moped drive line.

Your stock mechanical speedometer can remain in tact.

You can gear the moped to where the cyclone tops out at 20 mph and get LOTS of torque. There are bluetooth controllers for this motor that let you read vital statistics and adjust power levels on the fly via a cell phone. The Emotor app includes a dashboard with battery voltage, current draw, and speedometer.

Your new battery can power a step-down 12V converter for the existing electronics (lights, turn signals, etc).

I could go on but just give it some thought.

In my state, mopeds do not have titles. You just register them. There is a list of approved mopeds though. If you have a stock frame/roller bike on your approved list it should be able to be titled/registered at your local motor vehicle office without any questions asked. If I did an e-conversion on one I'd register it and ride it. Keep the speed sane and follow the rules of the road. How fast it gets to 20 mph or what the drivetrain is not a big concern.

[timmydbrady]

moarpower, I think you have chosen an appropriate user name. Thank you for all the time and interest in offering a more powerful and exciting ride. I wasn't clear in my post that I am building a bike that is more of a Cruiser than a Thrill-ride. If it is not too much of a buzz-kill, can you give me your thoughts on these more detailed specs if I go with the 750W geared hub motor?

https://lunacycle.com/geared-hub-ebi...front-or-rear/
Rear wheel use
Bare Hub Motor (Not Laced into any Wheel)
White Killer Whale 48v GA 17.5ah $579.95
48V Advanced Luna 300W Ebike Charger $79.95 (110v input only)
Dicta 18T 3/32" single speed (requires optional hub spacer) $12.50
Half twist throttle

Are there any concerns with the combination of choices - do they all work together properly?
I understand that this will be less powerful on the 80lb frame. But in cruising mode on flat surfaces, is there a concern with over-heating the motor?
This would get laced into a moped wheel. From your previous post, it seems like that should be fine and possibly offer more durability. Did I read that correctly?

[moarpower]

There is nothing wrong with that setup. You may need to find a motorcycle shop to lace it up for you if you do not have the ability to do so at home. That would be the best way to go if you are committed to a moped build. It will offer greater durability than a bicycle wheel and fit the build a lot better, whatever style you go with.

Everything you selected will work together just fine. It is not enough power to overheat the hub motor cruising at 20 mph. Ideally, you should see close to a 20 mile or more range at 20 mph.

Now, I admit that I may come across as a little bit power obsessed between the user name, Jeremy Clarkson/Top Gear avatar, and talk of higher power drive trains but my comments in this case truly comes from a place of concern for your son. If you use a moped frame he will always be sharing the roads with two ton missiles piloted by drivers who are often more concerned with what's going on on facebook or instragram than they are making sure they do not plow down someone's child. I've watched people thrown ten feet in the air by drivers too busy texting to look where they were going. Not something I want to see ever again.

If you are dead set on using 750 watts power, I personally do not see any good reason to use a moped frame. A moped will have reduced stopping power, reduced maneuverability, and be restricted to use on public roads when compared to a quality bicycle frame. An electric bicycle is permitted on some public paths, in parks, and many other areas that a moped is not allowed. It is much easier to fix by the side of the road and to find parts at most big box stores in a pinch. A bicycle is also lighter, offers higher efficiency (range) and may keep costs down. The moped frame will require insurance and licensing that a bicycle does not.

If you are going to use a moped chassis and take on its compromises I feel it would be wiser to aspire to the performance standards of a regular moped for safety's sake if nothing else. A regular 2 stroke moped can keep up in a 35 mph zone. He will be a sitting duck on a detuned moped at 20 mph, especially in higher speed zones. The same legal performance limitations apply to electric bicycles without the disadvantages of using a moped frame. I understand your desire to follow the law to the letter and not to teach your son not to subvert it with this build. My most recent build does just that. But it's on a fat tire bicycle frame with large disc brakes I use to tow my son's child trailer around with.

I also had often considered electrifying a moped frame but came to the conclusion that it is simpler, cheaper, and more efficient to put electric motors on bicycles. But that's me and not you! ;) Sorry to be so long winded...

[timmydbrady]

moarpower, you have been a terrific help. It is reassuring to know there is such a good community of builders willing to help a newbie like me. I think this set-up will be similar in power and weight to the two commercial products I mentioned (Vintage Electric and Monday Motorbikes). You make a good case for concern, so I'll give them a test ride to see what the experience is like on the road. Thank you very much.

[moarpower]

Glad to be of help!

The Vintage Electric bikes all use 3000 watt setups that can be detuned with a switch. The Monday M1 uses a 5500 watt setup that can also be detuned with a switch. Many higher power kits offer three speed switches (legal, fast, faster) as an add-on.

The M1 features a massive battery that probably costs $1000 in parts alone. If you wish to emulate the overall performance of these bikes you are looking at more expensive and more powerful kits and larger batteries. Installing the legal / sport (off road) switch is the easiest part of that kind of build!

If you just want to emulate them in the road-legal setting, then you already have the right parts picked out.

[timmydbrady]

moarpower, I wanted to post an update on the progress and ask a question on rear disc brakes. We are going with your recommendation on the 1500 watt motor. In the pictures you can see the 1978 Pinto moped frame and 1977 Honda Hobbit forks and wheels we will be using. The top tank will be used to house the battery and the Black Killer Whale 48v NCRB 17ah battery should fit inside the Puch one we plan to use.

I have also included some images of the Magic Pie V5 inside the rear fork and want to know if you or anyone else in this forum has a recommendation on rear disc brakes.

[commuter ebikes]

moarpower, I wanted to post an update on the progress and ask a question on rear disc brakes. We are going with your recommendation on the 1500 watt motor. In the pictures you can see the 1978 Pinto moped frame and 1977 Honda Hobbit forks and wheels we will be using. The top tank will be used to house the battery and the Black Killer Whale 48v NCRB 17ah battery should fit inside the Puch one we plan to use.

I have also included some images of the Magic Pie V5 inside the rear fork and want to know if you or anyone else in this forum has a recommendation on rear disc brakes.

It looks like you might want to try some 203mm rotors in order to clear that housing. When I set up my rear disk brakes on my hub motor, I need to have a large selection of brake rotor spacers, brake rotor mounting bolts in various lengths and brake rotor bolt washers on hand.

I use this rotor https://www.empoweredcycles.com/collections/performance-e-brake/products/replacement-rotors-tektro-dorado-hd-e710-e-brake and these brakes https://www.empoweredcycles.com/coll...ake-203mm-rear. Does your hub motor have a standard 6-bolt ISO brake rotor mounting pattern?

More info: https://www.sheldonbrown.com/disc-brakes.html

I am very glad that I chose hydraulic brakes because they are so easy to set up. Just make sure not to press the brake lever if there is no rotor in the calipers as this can cause the pistons to require rebuilding. You can get a spacer to put in the calipers while the rotor is removed in order to prevent this problem. People in the shop have a natural inclination to pull on levers, not realizing that doing so could cause more work for the mechanic.

[moarpower]

Cool! Good to see progress being made.

Disc brakes are not a strong area of mine. I know how to adjust them and repair them but anything beyond that is simply based on somewhat limited riding experience. I can't comment on brand A vs B or things of that nature.

I can tell you that hydraulic disc brakes are by far the best choice for stopping that moped as quickly and effectively as possible. My newest build has hydraulic brakes with large rotors and nothing else compares. Bigger rotors are definitely better. Budget probably plays into what you can and can't do.

I'll defer the brake discussion to commuter ebikes and other forum members.

[commuter ebikes]

After trying countless other brakes, I use the Tektro Dorado HD-E710 with 203mm rotors on all four of my bikes. If the OP buys them and isn't 100% satisfied, then I will buy them from him. I lost count a long time ago of the number of accidents and injuries minimized or prevented.

[moarpower]

That's a heck of an endorsement!

Your fully loaded bike weighs in over 100 lbs doesn't it? I saw it somewhere on the forum but can't recall the number.

Point being that your bikes are in a similar weight class and a much higher power class so if those brakes work for you they should work for the OP.

[commuter ebikes]

The bike weighs 95 pounds, I weigh 225 pounds and I carry up to 20 pounds cargo at an average speed of 30 mph. These brakes have always come through.

[mrm]

I too have tried all kinds of disc brakes(Hayes,Tectro Avid, ETC...) In my experience the best I've found are TRP's ( Spyre, Skype). Easiest to set up and maintain but, the stock pads leave a little to be desired. Won't do hydraulic, to unreliable. A 203 in the front, 180 in the back, gives me the ability to lock either wheel on pavement. Good enough.

[timmydbrady]

Thank you both for the help. commuter ebikes, here is a link for the recommended brakes:

https://www.empoweredcycles.com/prod...ake-203mm-rear

Since this is a rear wheel, I'm assuming I want a IS mount and assume a STANDARD cable length should be fine. Does that sound right to you?

[commuter ebikes]

Thank you both for the help. commuter ebikes, here is a link for the recommended brakes:

https://www.empoweredcycles.com/prod...ake-203mm-rear

Since this is a rear wheel, I'm assuming I want a IS mount and assume a STANDARD cable length should be fine. Does that sound right to you?

Here are some comparison photos of IS mount vs. post mount. IS mount is more common. You should read up on it before your purchase.

[commuter ebikes]

In the photo below, I didn't see your brake mounts.