Electric Dirt Bike

[Charliebuilds]

My last post was 2 years when I was 13 and me and GinDC (my dad) built an electric go-kart with this motor. Went 36 mph and was CRAZY fun!

Hey everyone, I am building an electric dirt bike, and I am using a cheap tao tao db17 125cc frame for the base. I am going to be running the lighting rod's XL BB motor made by mike, capable of 13 kW peak and 62 kV. I am running a 72v 40 ah battery that I'm going to build capable of 300 amps, discharge easy. Furthermore, I am wondering if anyone would help me with gearing and finding a better ratio because I was doing some research, and I was looking up my gearing and I found out that it would go 85mph but have very little torque. I want to be able to climb hills with ease and do around 50-55 mph and off-roading without straining the motor too much. Currently, it is geared at 13t front and 48t rear, and my tire diameter is around 20.5 inches. Can someone help me figure out some better gearing?

Any suggestions would be great regarding frame and motor and gearing would be SUPER HELPFUL. Also, do people think that this motor is well suited for this project or do I need the XXL BB motor which is 18kw peek?


PS: Photos of the bike and the motor mount so far.... not pretty yet. Also, that's my dad @

 

[Charliebuilds]

My last post was 2 years when I was 13 and me and GinDC (my dad) built an electric go-kart with this motor. Went 36 mph and was CRAZY fun!

Hey everyone, I am building an electric dirt bike, and I am using a cheap tao tao db17 125cc frame for the base. I am going to be running the lighting rod's XL BB motor made by mike, capable of 13 kW peak and 62 kV. I am running a 72v 40 ah battery that I'm going to build capable of 300 amps, discharge easy. Furthermore, I am wondering if anyone would help me with gearing and finding a better ratio because I was doing some research, and I was looking up my gearing and I found out that it would go 85mph but have very little torque. I want to be able to climb hills with ease and do around 50-55 mph and off-roading without straining the motor too much. Currently, it is geared at 13t front and 48t rear, and my tire diameter is around 20.5 inches. Can someone help me figure out some better gearing?

Any suggestions would be great regarding frame and motor and gearing would be SUPER HELPFUL. Also, do people think that this motor is well suited for this project or do I need the XXL BB motor which is 18kw peek?


PS: Photos of the bike and the motor mount so far.... not pretty yet. Also, that's my dad @

 

[s-petersen]

You should probably start a new thread on this.. but, if your front sprocket were 9 teeth or the back would be 74 teeth it would solve your issue, if it currently does 85mph. I have no idea about the motor though. If the front sprocket is unavailable the ratio you are looking for is 5.33 : 1 If I knew the max RPM of the motor, I could be more accurate.

 

[amberwolf]

@Charliebuilds
Moved your duplicate post out of someone else's thread into your own that you had already started.

Please use your thread for your project, not other poeple's threads.

I also moved your whole thread out of ebike general discussion to escooters/motorcycles, since it's a dirt bike (motorcycle), not an ebike (electric bicycle).

 

[ZeroEm]

Maybe missing something but does not look 15yrs old.

 

[scianiac]

When factoring the speed you just need 3 things in this case, the motor KV (62), the voltage, and some idea of the motor's operating speed based on it's design and controller. For more basic brushless motors with no field weakening it would be voltage times KV is the motor's freespeed so that's with no load and a rough estimate many use is around 80% of that is very roughly where your top speed will be.

The 3rd factor is where things get interesting, that motor is an IPM motor with quite a lot of salience meaning with a controller that can take advantage of that the 80% value is out the window. 200% is perfectly possible but not a good idea but say 100% is reasonable maybe 120%. You ideally don't want to run the motor above 100% for a long period of time, it's less efficient and builds up heat. It's the pros and cons of IPM motors, cons they can be finicky with controller tuning, but they have just tons of power through a very wide RPM range with a controller that supports MTPA.

I don't know that I explained that very well, I didn't want to get too into the weeds, or do all the math for you! haha Make a spreadsheet with the voltage, kv, sprocket sizes and wheel size all input to calculate speed and go from there changing the variables. Or just ask an LLM to make the spread sheet for you.

 

[Charliebuilds]

Lol that was my dad in the photo he is helping out

Maybe missing something but does not look 15yrs old.

 

[Charliebuilds]

@Charliebuilds
Moved your duplicate post out of someone else's thread into your own that you had already started.

Please use your thread for your project, not other poeple's threads.

I also moved your whole thread out of ebike general discussion to escooters/motorcycles, since it's a dirt bike (motorcycle), not an ebike (electric bicycle).

sorry im still learning to use this platform mb

 

[Charliebuilds]

You should probably start a new thread on this.. but, if your front sprocket were 9 teeth or the back would be 74 teeth it would solve your issue, if it currently does 85mph. I have no idea about the motor though. If the front sprocket is unavailable the ratio you are looking for is 5.33 : 1 If I knew the max RPM of the motor, I could be more accurate.

Max rpm is 5200 at 84v... motor is a torque beast, but I want to optimize it for some hill climbs and trail riding, but mostly road use.