Already posted in Electric Bikes. My sons 50sx

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2/22/2018 12:53 PM

Not sure if many people visit the electric bike section. My brother suggested I post this for people to see here.



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2/22/2018 2:12 PM

That thing looks rad! More info!

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2/22/2018 6:05 PM

Lipo batteries?

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2/23/2018 8:26 AM

Thats so freakin cool! Nice work!

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If you're not mixing gas, you're not haulin ass.

2/23/2018 11:26 AM

Braaaphole wrote:

Lipo batteries?

Yeah, lipo's are the awesome juice!

Right now we have three 6 cell 6000mah RC batteries in series for 72 volts. I'm a little concerned about run time but haven't been able to test because of rain.

I expected to be down on power compared to the 50cc gas engine so weight savings was a big goal. Using downhill mountain bike pieces I was able to get down to 78.6 which is right at 10 pounds lighter than stock.

Plus the MTB parts a super sweet. The shock is a Fox float x2 air shock with high and low compression and rebound.

The forks are custom lowered Manitou dorado pro's. They have air, compression and rebound and something called TPC. To run the forks we had to use their one off titanium axle, and that's basically awesome.

The brakes are Hope Tech 3 V4's which are cool because you can adjust the lever through and the "bite point" and they come with stainless lines. Had to run a Nihilo oversized rotor to get them to work.

The motor is a stock Oset 1400w it's plenty of power, but i'm not sure it will handle the actual high rpm speed without overheating. We used a Kelly controller that is cool because you can plug it to a laptop and make several power curve adjustments easily.

I'm really looking forward to seeing him ride, but it just wont stop raining...

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2/23/2018 11:40 AM

151 wrote:

Yeah, lipo's are the awesome juice!

Right now we have three 6 cell 6000mah RC batteries in series for 72 volts. I'm a little concerned about run time but haven't been able to test because of rain.

I expected to be down on power compared to the 50cc gas engine so weight savings was a big goal. Using downhill mountain bike pieces I was able to get down to 78.6 which is right at 10 pounds lighter than stock.

Plus the MTB parts a super sweet. The shock is a Fox float x2 air shock with high and low compression and rebound.

The forks are custom lowered Manitou dorado pro's. They have air, compression and rebound and something called TPC. To run the forks we had to use their one off titanium axle, and that's basically awesome.

The brakes are Hope Tech 3 V4's which are cool because you can adjust the lever through and the "bite point" and they come with stainless lines. Had to run a Nihilo oversized rotor to get them to work.

The motor is a stock Oset 1400w it's plenty of power, but i'm not sure it will handle the actual high rpm speed without overheating. We used a Kelly controller that is cool because you can plug it to a laptop and make several power curve adjustments easily.

I'm really looking forward to seeing him ride, but it just wont stop raining...

I'm very curious to see how the run time works out. The good thing is if you need more, you can add another set of batteries and parallel them in to double the capacity. Very easy and minimal weight addition.


Does the Kelly controller have a low voltage protection or cut off? I don't know how familiar you are with Lipo batteries. I believe the voltage cut off needs to be around 3.3V per cell, I'd have to look back and double check that number. I haven't messed with them in a little while. Anything lower and you can do some serious damage. I have seen Lipos go up in flames from being over discharged. Well, it wasn't the discharge that caused the flames, but trying to charge them after running the voltage too low. I had one personally blow and catch fire on my while charging. A cell decided to take a dump and went poof.

How are you charging them? I'm assuming an RC charger.

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2/23/2018 11:59 AM

Curious as to why you didn't take the radiators off. That would seem to be a weight saving spot.

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2/23/2018 12:55 PM

Braaaphole wrote:

I'm very curious to see how the run time works out. The good thing is if you need more, you can add another set of batteries and parallel them in to double the capacity. Very easy and minimal weight addition.


Does the Kelly controller have a low voltage protection or cut off? I don't know how familiar you are with Lipo batteries. I believe the voltage cut off needs to be around 3.3V per cell, I'd have to look back and double check that number. I haven't messed with them in a little while. Anything lower and you can do some serious damage. I have seen Lipos go up in flames from being over discharged. Well, it wasn't the discharge that caused the flames, but trying to charge them after running the voltage too low. I had one personally blow and catch fire on my while charging. A cell decided to take a dump and went poof.

How are you charging them? I'm assuming an RC charger.

Yes, you're spot on. I have some experience with Lipo's from my sons Oset that we MX'ed out. The Oset 20R weighs 79 pounds and average run time with an adult rider and 20000mah lead acid batteries is around an hour and up to 4 hours! We are saving over 100 pounds in total weight but running 1/4 the capacity. Still lead acid batteries fade quickly and the lipos don't have near the voltage drop...

I am expecting half the run time of the 20r as my son is not a full throttle ripper (yet).

The kelly does have a low voltage cut out but it is total of all three packs. I have individual battery monitors that alarm if a single cell drops below a set voltage. I usually charge to 4.1 and discharge to 3.2 volts. Some people say the less than full charge allows for many many more charging cycles because the cells are less stressed.

I've got a decent charger from HK that will do 4 6 cell packs. I am actually considering going to 4 three cell packs with higher capacity because the top speed is a little high at 45 mph. So basically trading top speed for run time. Will need to see him ride first.

SHREDDER - I am slightly concerned this motor will not hold up to the heat generated by the added speed. It was designed for about 26mph. If it doesn't, the next step up is a liquid cooled brushless motor. I can plumb in a 12v inline pump and use the stock radiators for cooling. If this motor holds up, I'll probably remove the radiators.

Here is a short video of his Oset we tricked out a few years ago.

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2/23/2018 2:13 PM

Thats crazy seems like a lot of work... Never thought of it but alta should definitely make a mini sized mx bikes

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2/23/2018 3:15 PM

Got to hand it to you dude, this is an awesome build!

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1/23/2020 6:23 AM

Braaaphole wrote:

Lipo batteries?

151 wrote:

Yeah, lipo's are the awesome juice!

Right now we have three 6 cell 6000mah RC batteries in series for 72 volts. I'm a little concerned about run time but haven't been able to test because of rain.

I expected to be down on power compared to the 50cc gas engine so weight savings was a big goal. Using downhill mountain bike pieces I was able to get down to 78.6 which is right at 10 pounds lighter than stock.

Plus the MTB parts a super sweet. The shock is a Fox float x2 air shock with high and low compression and rebound.

The forks are custom lowered Manitou dorado pro's. They have air, compression and rebound and something called TPC. To run the forks we had to use their one off titanium axle, and that's basically awesome.

The brakes are Hope Tech 3 V4's which are cool because you can adjust the lever through and the "bite point" and they come with stainless lines. Had to run a Nihilo oversized rotor to get them to work.

The motor is a stock Oset 1400w it's plenty of power, but i'm not sure it will handle the actual high rpm speed without overheating. We used a Kelly controller that is cool because you can plug it to a laptop and make several power curve adjustments easily.

I'm really looking forward to seeing him ride, but it just wont stop raining...

Sweet build man! I'm interested in your lug/axle setup, how did you get the moto style lugs to go on the MTB lowers?

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