"Hot rod" ebike on the cheap

73biker

1 µW
Joined
Jan 26, 2018
Messages
3
Hello all. This is my first post, having chosen this forum as having the most smart cheapskates! I'm not an electrical guru, but like to think I'm smart enough to learn and not afraid of research. DIY type too...even if I had the moolah for a kit. Thank you all in advance for any help with my project!

The bike:
A steel cruiser...old, strong, and heavy. IDK what brand, but it was distributed out of Seattle, WA. I'll likely keep coaster brakes rear, mod front disc, and maybe implement a motor brake too.
I want this bike to be a hot rod for "drag racing" my buds. Likely a single speed 66cc china girl, for one.

The motor:
Undecided, but leaning toward an alternator motor. 100A high output to match the other components. I'll add hall sensors or something for high torque, but NOT spend over $100 on a PM rotor! I've toyed with the idea of an auto. starter too. It would have the best torque of the two, but I'm not a welder so I'd have to outsource attaching a pulley or sprocket to the shaft.

The tranny:
Single speed direct drive on the left. Jackshaft, if neccesary.

The fuel:
(2) 12V SLA/UPS wired in series for 24V. These are meant for fast discharge rates, at 130A for 5 seconds. They'd need not last for more than a couple drag races. They're cheap, not nearly as heavy as a single car battery, and lipos can't match the amp draw from my understanding.

Speed control:
Brushless ESC/6s/100A to power the altermotor. 24V ebike throttle. I'd probably first try to power the field with the 5A BEC output. That could provide good torque, albeit lower rpms, but I'm not looking for high top speed here...40-45 mph at the most. All in the gearing, I hope! When that fails, maybe I'll use an Arduino to contoll the current, or switch to sensored and use halls.

There's the game plan...whatcha think? Inefficient...yes, but if the cells last 2-3 races, don't care.
Heat problems...I hope not for 15-30 seconds at a time. Other motors/setup suggestions encouraged!
 
I don't think such a thing as a ""Hot rod" ebike on the cheap" exists.

I would suggest you read some of the threads by liveforphysics or drbass.
Even if, by some miracle you can out run the 66cc Girl, what would prevent them from installing something like the BBR Stage 4 motor?
 
motomech said:
I don't think such a thing as a ""Hot rod" ebike on the cheap" exists.

I would suggest you read some of the threads by liveforphysics or drbass.
Even if, by some miracle you can out run the 66cc Girl, what would prevent them from installing something like the BBR Stage 4 motor?

Yeah, okay...the pipe dream is starting to fade fast. The only thing that would prevent my friend from installing the BBR is money, like myself with some high-powered ebike kit. I was just betting that dollar for dollar, electric could be faster than gas powered...but now think I'd lose that bet. At $90 for a complete 66cc kit, it may be a POS but can't be beat by an ebike for equal funds. Also free performance mods, like porting and polishing, don't really exist with electric. Thread's dead, thanks anyway!
 
Cheap hot rod bike does exist.

Cheap 500w rated hub motor, the kind in the 48v 1000w kit. Then RC lipo for batteries. 72v 40 amps controller, and viola, a 40 mph bike. can cost about a thou, depending on what you spend on chargers.

Your plan sounds cheap, and fun to build. But the lead will make it a pig to ride. Dangerous as hell to ride 40 mph on an overloaded cheap bike.

At the very least, dump the lead battery idea. Lighten up and it could be fun, till it fries. ( not that hard to fry the cheap hub motor hot rod too btw)
 
I don't think a couple of UPS batteries would add much weight...maybe 10lbs max. Sure, they wouldn't last long but that wouldn't be needed for just a couple of races. The problem with using SLA's would be all of the high-voltage ebike motors out there. 48V+ would be too much weight with them. Why the high voltage...just to keep the amps and wire gauges down? An alternator could be run on just 24V fine, but I can't find out how much power they'd have as a motor. I'm assuming a higher output alt. would also be a more powerful motor, but not knowing the amps drawn, etc. kinda makes it difficult to design the whole build. Doubting now that it would outperform a 2 cycle dollar for dollar!
 
Skip the ups battery idea you wont beat a hamster with them , use car batteries you will get real serious amps , 4 x 13.2v = 52.8 volts and about 300 amps for a possible 15,840 watts.
You can find big ass hub motors on the web ..
That will educate your buddy good
 
You wanna win a race, you need a light battery that does not sag. Hobby king for those, and get the higher discharge rate stuff, not the cheap 20c. And yeah, couple outings, and they will be practice battery, if you want the win.

You also need to up the voltage, which makes the motor spin faster. I nearly won the race using 72v, on a motor intended for 48v. I mistook a black flag for me, when the guy I was following got it. I was way in the lead when I left the track. :twisted:

Next race, I brought 110v, and the motor fried before the end. So you will need to find the sweet spot for what you bring. I should have brought a bigger motor.
 
High Volts and a motor that handles it . I like the idea of a speed record streamliner more then a 1/8th or 1/4 mile racer. A racer would be easy a streamliner not so much.
 
I was browsing on the forum and came across a great motor for a racer or mini type streamliner and its only :arrow: $900

ME1507.png


link to thread :arrow: https://endless-sphere.com/forums/viewtopic.php?f=31&t=92862

Designed for battery pack voltages of 100 VDC or less
Continuous current: 160 Amps RMS, Peak Current: 600 Amps RMS
Maximum rotor speed: 8000 rpm
Continuous power: 17kW, Peak power: 44kW = 22 hp
Continuous Torque: 32Nm, Maximum Torque: 120 Nm
Torque Constant: 120 Nm/Amp
Maximum Temperature: 140C
12 turns per phase, 5 pole motor
Air-cooled IP65 case
Temperature sensor: KTY84-130
Encoder: sin/cos
Thread depth: 19 mm (24 mm max)
Shaft 1-1/8″
44lbs
 
dogman dan said:
Cheap hot rod bike does exist.

Cheap 500w rated hub motor, the kind in the 48v 1000w kit. Then RC lipo for batteries. 72v 40 amps controller, and viola, a 40 mph bike. can cost about a thou, depending on what you spend on chargers.

Your plan sounds cheap, and fun to build. But the lead will make it a pig to ride. Dangerous as hell to ride 40 mph on an overloaded cheap bike.

At the very least, dump the lead battery idea. Lighten up and it could be fun, till it fries. ( not that hard to fry the cheap hub motor hot rod too btw)

Charger you can just get cheap server psu 750w for £8 and 1200w 15a 12-80v boost converter for £10 and cheap volt and amp meter and thats £20 for a 750w charger
 
Yes, or you could spend a fortune on expensive RC chargers. That's what I meant, depends on what you spend on a charger.
 
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