# electric mountain board build thread - MBS Comp 90 dual motor rear



## Camineet (Nov 24, 2013)

Hi all, 

I'm probably 5% into my build and am starting the thread now. So far I've I've gotten a motor mount, sprocket, and chain kit from dirkdiggler a forum member of Endless Sphere forums. Thanks again DD. 

dirkdiggler doesn't have the same wheels I'm using, so he couldn't drill the sprocket holes for me. I'm heading to a friend's house Sunday who has a lot of tools and a drill press. 

I've conceived that a great deal of precision has to be applied in drilling these holes. Even a half millimeter off center, and I can imagine the wheel will wobble, or there will be some kind of undue strain on the chain or motor as the rotations rapidly occur with slightly uneven pull. Is that right? I figure some extremely precise measurement techniques have to be applied to get the holes to be the absolute perfect distance from center. My friend restores cars and has a major home business along with a 5 car garage, so hopefully he has the stuff to make this happen. If not, he says he knows someone who can do anything. So, I should be able to get the holes taken care of within a few weeks or so. 

ESC 

I've been liking the idea of going with 2 of these Hobby King 150A ESCs 

http://www.hobbyking.com/hobbyking/..._150A_High_performance_Brushless_Car_ESC.html 

Motors 

I've come to understand that lower voltage on motors translates into higher torque, an important factor in getting moving. I weigh 140lbs or 65kg. I plan to do some significant grass riding. There are many nice grassy areas near my house known as common grounds in my subdivision. They look like prime emb riding spots and they're about 10 seconds from my front door. These areas aren't the most perfectly manicured grass. They get mowed pretty often, but they aren't super low cut like golf course fairways. Of course, I hope to ride on the many very nice mountain bike trails here in Michigan, but I really need to make sure I can get my bones moving on grass. 

So, I've been looking at two of these 213kv Turnigy motors. 

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=18180 

Do you guys think two of these motors with the (I assume) fairly standard gearing setup that dirkdiggler has provided me, that I will have enough torque to get started on grass? Top speed is probably nice, but it isn't my main concern. 

Battery(s) 

I'm liking those Zippy LiPoly batteries like this one from the Endless Sphere sticky: 

http://hobbyking.com/hobbyking/store/__8582__ZIPPY_Flightmax_5000mAh_6S1P_20C.html 

Do you guys think this is enough battery capacity? I saw that daverobson on Endless Sphere is going with two of these: 

http://www.hobbyking.com/hobbyking/store/__16225__ZIPPY_Flightmax_8000mAh_3S1P_30C.html 

From reading his thread, it looks like he's having to go through some trouble charge the two batteries at once. I'm not strong on electronics, so that would be an issue for me. What do you guys think? Is there a charger you guys can suggest that would work well to charge these two batteries without having to do any rewiring and such? 

I really like the idea of going with two of these flatter batteries rather than the one large battery because I was thinking they could be mounted under the board, which would be pretty cool. What do you guys think of that idea? I was thinking two ESCs on the top of the board in the middle, and two of these 8000 30C 3S Zippy batteries mounted to the underside in the center where the board has the most ground clearance. 

Do you guys think a novice like me can figure out how to get two of these batteries hooked up without too much trouble and perhaps some guidance here? 

Transmitter 

Also from the sticky thread, I'm thinking of going with this transmitter from Hobby King: 

http://hobbyking.com/hobbyking/stor...nd_Receiver_w_Rechargable_Li_ion_Battery.html 

Other items(?) 

Are there any other major items I haven't thought of? Like, isn't there a small battery pack that's needed to power each ESC? I seem to remember that being the case back when I had a radio control car. I can't think of any other items that I've seen in other build threads. Let me know if I'm missing something. 

That's all for now. Let me know what problems or improvements to these plans I should make. Thanks a lot.


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## major (Apr 4, 2008)

Camineet said:


> Motors
> 
> I've come to understand that lower voltage on motors translates into higher torque, an important factor in getting moving. I weigh 140lbs or 65kg. I plan to do some significant grass riding. There are many nice grassy areas near my house known as common grounds in my subdivision. They look like prime emb riding spots and they're about 10 seconds from my front door. These areas aren't the most perfectly manicured grass. They get mowed pretty often, but they aren't super low cut like golf course fairways. Of course, I hope to ride on the many very nice mountain bike trails here in Michigan, but I really need to make sure I can get my bones moving on grass.
> 
> ...


Hi Cami,



> I've come to understand that lower voltage on motors translates into higher torque,


That's not the way I understand it  But whatever.

From what I can see from your motor info, you have a 65Amp max which will give you about 2.9Nm per motor. You'll have to go though your reduction ratio to get wheel torque and then the rolling radius determines the tractive effort (propulsion force). I don't ride these things, so I have no idea what is required.

One battery you listed is 8Ah. 2 motors at full torque pull 130A. That will drain that battery in like 3.5 minutes (17C).* I have no idea how fast (or if) you'll accelerate and what the loading would look like. With that battery and motors, you may get to a couple of kiloWatts power. That seems like a lot for a single person transport, like compared to a bicycle. But you're going to have much increased rolling resistance as well as more aerodynamic load.

Good luck and don't break your neck.

major

*{edit} The 130A would be motor current (phase current for both motors together). So at low speeds, the battery current could be significantly less. I have not used these types of motors and controllers (esc) so I am not sure how the specs actually relate. But you need to watch motor heating as I believe the ratings are based on application with prop air blast moving over the open frame motor. At lower speeds and without the fan, the coils may overheat in a hurry.


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## Camineet (Nov 24, 2013)

I see good to know thanks pal.

Yes, it seems i've missplanned the batteries. For 1 of these kinds of motors, there's a guy doing a build with those two batteries. So for 2 of these motors, obviously I would need to do 2 batteries for each motor, or just go with one of these bigger batteries for each motor:

http://hobbyking.com/hobbyking/store/__8582__ZIPPY_Flightmax_5000mAh_6S1P_20C.html


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## Camineet (Nov 24, 2013)

I was hoping to go with the flatter batteries, I guess 4 of them, because they could be mounted under the board instead of on top for a cleaner setup. 

But I don't know how to connect 2 batteries to one ESC. What do you think?


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## major (Apr 4, 2008)

Camineet said:


> But I don't know how to connect 2 batteries to one ESC. What do you think?


I think you'd better study up on this. These are what is called RC LiPo batteries. They are extremely powerful. A wrong connection can result in severe burn or blinded eye. Connecting 2 batteries to one ESC is pretty basic. You need to know what you're doing. You can easily burn down a garage or house and maybe kill someone in the process. The RC LiPo isn't used much on this electric car forum. Investigate it thoroughly on the ES.


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## markula (Oct 27, 2013)

Hi 

I have a elekctric longboard.
I use a 5055 brushless motor and 200A esc. 
one 5000mah 22.2V battery. 

With this setup i get around 5-6km of range. 

But since you are using outrunner that is made for a propeller that blows air through the motor you have to install a fan. 

I used a 80mm computer fan and just use the blades and mounted it on the back of the motor. 

I order this battery later. 
http://www.ebay.com/itm/22-2V-10C-1...Control_Parts_Accessories&hash=item27d3a20ce8


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## mizlplix (May 1, 2011)

This is what you want...really....
http://www.youtube.com/watch?v=jlab8wI8hwY&feature=youtu.be

OR:
http://www.youtube.com/watch?v=R6IPwp6AY3g

Yah, you do.

Miz


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