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Motorising 27" flip-flop fixie bicycles

I currently have two 27" flip-flop fixies I plan to motorise, one with a 16 tooth fixed left-hand backwheel gear and one with a 17 tooth (these fixed left-hand rear 1/2" bicycle chain drive gears are what I plan to motor drive on each bicycle). I would very much appreciate a compatibility list for item#MOT-SD175FW. Also, can anyone tell me what size bicycle sprocket attachment for this motor, if any, will give me the max top speed driving 16 and 17 tooth bicycle gears each fixed to a 27" wheel? Thanks!

MOT-SD175FW is an electric scooter motor and its shaft spins to fast to use with a full-size bicycle unless a massive wheel sprocket was used with it. I ran a calculation and found that a 125 tooth wheel sprocket would be needed.




In order to use a standard size bicycle freewheel sprocket on the rear wheel, a gear motor such as out item # MOT-24450G would be needed. 

But that is only 450w, and probably won't get me going much faster than I already travel on a racing bike, which is 18-20. So I would start up manually, accelerate to about 20, then stop pedaling and engage the motor just to accelerate another 5 mph on flat ground... may as well not invest in a motor at that point. Does your company carry anything 750 watt or more for bicycles?
Would item#MOT-24650PL possibly be suitable for my application?

MOT-24650P would work on an electric bicycle and has the right gear reduction so that a large wheel sprocket would not be needed. The only downfalls of using an MOT-24650PL on a bicycle is its large size and that sprockets which fit this motor are only available for #41/#420 chains. It also has a clockwise shaft rotation so it should be used in clockwise rotation for forward use, which means that it would need to either power the right side wheel sprocket for inboard mounting, or be mounted offboard of the bike to power the left side wheel sprocket, and it is a big motor so I think that offboard mounting would not be feasible. 

Is #41 and #420 not standard bicycle drive, aka 1/2" chain, which is what I need for my application? I may be mistaken. Also it says on the webpage that the shaft rotation of #MOT-24650PL is reversible by switching the power leads. Shouldn't I just be able to set up the motor with the power leads reversed for a counter-clockwise shaft rotation? Looks to me these problems should be easily solved.

#41 and #420 chain have 1/2" pitch, however, are 1/4" wide between inner plates instead of 1/8" wide and 3/32" wide like bicycle chain are. I have heard of people running chains that are wider than the sprocket though so it may work. Due to the motor's advanced brush timing, running in reverse is recommended for intermittent reversing applications, however not for continuous forward applications. Some people run brushed motors in reverse continuously though so it is possible.

I see. It seems rather difficult to find standard bicycle chain drive motors of the wattage and RPMs I require. Would you have any recommendations? Or perhaps I should look further into using item#MOT-24650PL, that is, if it will run a standard bicycle chain OK and if reversed shaft rotation shouldn't cause dammage.
Still saving up money for this project, so in the meantime I will scour the market in search of a motor that may be more suitable for this type of bicycle. Thank you very much for your input on RPMs and gearing ratios; now I have a better idea of what I will need. Also, would you be able to send me a compatibility list for item#MOT-24650PL? I would like to get a better idea of what parts I can use and a ballpark figure of what this little project will cost me. Thanks again.

For the MOT-24650PL motor, our 24 Volt 1000 Watt SPD-241000 controller is compatible and we recommend a minimum battery pack size of two 12V 15Ah batteries. The MOT-24650PL motor is 10" long from end to end so it is a fairly large motor to mount on a bicycle. 


Another idea you may want to think about is using two MOT-24450G motors with one chain running between the two motors and wheel sprocket - I have see this done before. These motors are narrow and can be mounted close to the axle to keep the center of gravity low. We carry freewheel sprockets for these motors which in a dual motor setup would allow one motor to be on for low power applications such as slower speed on flat ground, and two motors to be on for high power applications such as climbing hills or going fast. We carry mounting plates for them which is our item # HDW-250. Here are some photos of how the MOT-24450G motor is commonly mounted to a bicycle frame.



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