Electric Crossboard

George_T · Post by **George_T** » Sun Jan 10, 2016 4:54 pm

"It's a Bird...It's a Plane...It's.." an electric crossboard.
I know I could have come up with a better name, but it's not set in stone yet. Anyway, my goal is to create a mountain board-like vehicle with electric propulsion for recreational purposes. I have a vision of day-long trips on trails among the woods, cross-country style tours, lunch on a tree stump, you name it. I'm aware that there are countless DIY electric mountain board threads on the net, but without wanting to reinvent the wheel, there are a couple of things I plan to do differently. I also did my homework, so I have a basic concept about what I want:

- Wheels: maybe this is the biggest bite for a rookie like me, but I want hub motors, because, well, I like the concept. A plan to put 12" bicycle tires around the hub motors: these tires are cheap, readily available and come in great variety. They also allow more space for the motors and due to the larger diameter, have less rolling resistance compared to MTB wheels, thus increasing range.
- Tracks: instead of using stock tracks, my concept is to design a double wishbone suspension with bicycle shock absorbers. This will hopefully make the ride much more smooth, while enabling high speed cruising on tarmac. I do not know, however, whether it will have a huge impact on riding experience.
- Board: I do not plan to overdo this part, maybe a simple, cut-to-shape plywood board will do for mk1.
- Power supply: luckily, I have a battery guru nearby who suggested simple lead-acid batteries. These are huge and heavy, but I can get them for a fraction of the cost of LiPo-s. I plan to make an mk2 (at least) of this, which can get LiPo-s. I plan at least 24V and 10Ah, possibly much more.
- ESC: this one is causing me a lot of headache. I still have not decided what to choose.

My basic question is, what do you think about the bigger wheels and double wishbone suspension? Will itt be better, or can it cause any trouble?
I have read a lot of interesting threads in this forum, so I'm eager to read your comments. And if you have any questions, feel free to ask. Thanks for reading!

BgSurfer · Post by **BgSurfer** » Tue Jan 12, 2016 10:56 am

Not a lot of traffic at SD these days.
A few immediate issues I see:
Turning mechanism using your double wishbone susp.?
12" wheels potentially create high center of gravity.
Longer axles needed to avoid deck/wheel rub.
Turn radius lower than standard 8" wheel and channel truck.
I see no difference in resistance other than a larger diam. wheel can go over rougher/uneven surfaces better than smaller diam. wheels.
Hub motor is the advantage.

Have fun and build one...

George_T · Post by **George_T** » Thu Jan 14, 2016 3:31 pm

Hi BgSurfer,

Thanks for adding your thoughts. The steering mechanism would look more like of a car on all four wheels and operated by tilting the board. So, hopefully no clearance problems.
I'm no expert on this matter, but as far as I know, bigger diameter wheels have less rolling resistance. This may not be an advantage when all you do is go downhill, but I hope it will add a few percents to the overall range of the board. I think I can show a 3D model in a week or two, so it will be more clear what I'm talking about.
Hope you all will like it.

Flexboardz · Post by **Flexboardz** » Fri Jan 22, 2016 2:03 am

You should look at Bajaboard as it has what you want (double wishbone suspension). Very complicated and expensive though...

George_T · Post by **George_T** » Wed Jan 27, 2016 5:18 pm

Well yes, Bajaboard is beautiful engineering, but there are a couple of things that I want to do differently.
Anyway, the batteries arrived just the other day. I should call this point the project kick off I guess...

Flexboardz · Post by **Flexboardz** » Sun Jan 31, 2016 3:33 pm

impatient to see the project happening

tornadoB · Post by **tornadoB** » Sun Jan 31, 2016 7:40 pm

I am dying for some proper hub motors to power my mountain board with Carve board wheels and have looked at going with scooter/bike hub motors. BG is correct about ride height and knows his stuff about all things carve for that matter..... The ride height can be solved in a variety of ways, steps to longer nose and tails. I have dropped my board with extensions to increase on road carving.

Just my two cents on suspension. Complicated and costly as mentioned with a much smaller market once the price and weight go up. Rolling resistance is an issue that can be solved with another $60 worth of lipos. A fatter tire like fat tire bikes would improve traction on loose stuff and smooth our the ride tremendously compared to a mtb tire, and can be pumped hard for road use.
An easy tire change to road set up is also probably less expensive than suspension. For folks who are not going hard off road AKA "most people" could use regular bmx style 12" wheels.
I am sure you are on endless-sphere.com.. there is an e-skate/scooter frenzy going on there.
Good luck.
B

George_T · Post by **George_T** » Wed Feb 03, 2016 12:01 pm

tornadoB, you brought up an interesting question: I always saw the Bajaboard project as the ultimate in suspension. But my question is: do mountainboarders actually need that kind of suspension? You are constantly standing on your foot after all.
Utilizing four Rock Shox absorbers for increasing the feel only a tiny bit feels like serious overengineering.
Anyhow, stock mountainboard suspensions won't do, since they are not designed to take ANY torque. And a hub motor is supposed to generate a lot of torque. More so if I stick with the 12" wheels, in which case, just as BGSurfer mentioned, there either wouldn't be enough clearance when turning, or some kind of awful proportions would be the result.
As you can guess, I have literally no experience in this, but that's why I'm here. Your opinions are much appreciated, so thank you all guys

Flexboardz · Post by **Flexboardz** » Thu Feb 04, 2016 1:56 am

As far as I know, all double wishbone suspension designs end up being expensive, complicated and unefficient... as it generates wobble (bajaboard uses an electronic control).... overengineering defined.

Wheels size: 12" seems a bit oversized to me... 10" wheels is already greatly improving the ride comfort (but it increases the weight) compared to 8"... better to have wider tires to use low pressure (and solve the suspension problem above)

Regarding electrical component, here is a nice exemple of hubmotor mtb :
https://endless-sphere.com/forums/viewtopic.php?f=35&t=73258

George_T · Post by **George_T** » Fri Feb 05, 2016 12:19 am

Wow... I'm also on endless sphere, but I didn't find that topic! Although using drone/plane motors may not be the best idea: they are meant for high rpm, and as mentioned in that topic, one of a suitable size is serious cash. The design however is stunning.
As for wheels, I chose 12" bike wheels because I actually had no better idea. As far as I know, the first prototype of Bajaboard used the same wheels, then they switched to small scooter tires if I got it right. My main problem with stock mtb parts is that they are painfully overpriced. Well, guess that I have to research the tire issue as well. Thanks for the info anyway!

BgSurfer · Post by **BgSurfer** » Fri Feb 05, 2016 7:57 am

Don't know if you saw HumboldtRc's rigs.

Electric Mountainboard 13 hp (50 mph first vid) by HumboldtRc

http://www.surfingdirt.com/forum/showthread.php?t=6849
http://www.surfingdirt.com/forum/showthread.php?t=6169
https://www.youtube.com/watch?v=kpNEJLlvh1A
https://www.youtube.com/watch?v=QKTgbubRxXk
https://youtu.be/pySuVPG9Qwk
https://youtu.be/kpNEJLlvh1A
https://youtu.be/7-Fdry4sDUU
https://youtu.be/pBjbHdwFlHU
http://www.hobbyking.com/hobbyking/forum/forum_posts.asp?TID=12064

More Humboldtrc videos:

http://www.youtube.com/watch?v=HvzQm8fky8Q Following the school bus up hill
http://www.youtube.com/watch?v=KWeE82sVI1U Off-road
http://www.youtube.com/watch?v=X7g6eaY21t8 Arming sounds
http://www.youtube.com/watch?v=P0zEbHWt4iQ More Off-road
http://www.youtube.com/watch?v=F4S1ftMWd5Q Burnouts
http://www.youtube.com/watch?v=KS0S51bi-I0 Wheelies
http://www.youtube.com/watch?v=u7PMyx7BqB4 No load spool up

George_T · Post by **George_T** » Wed Feb 10, 2016 12:21 am

Humboldt's thread on Hobby King Forums was which originally started to make me think. A lot of these videos were unknown to me though (for which the reason is beyond me).
I make cost calculations for every version that comes to my mind, and I'm currently at version 4

This is great because the most common mistake in design is to start modelling without having a clear concept.

As it appears to me, the wisest approach would be to buy a used board and swap the rear hubs with my own makings while equipping the board itself with the electronics. I googled my area, but had little luck finding any used mtbs so far (guess this sport is not so popular here). Maybe I just have to wait until the right time.
Anyway, what kept me so far from using stock suspensions is that I didn't see how they would keep the stator in one place. Then I realized that most of them are capable of holding brakes, which do generate torque on the suspension. If only all my problems were so trivial

I hope I will be able to make such videos by the end of spring, these footages are very motivating.

Any what are your opininons: old mtb technology with hub motors fitted or completely new system (board, suspension, etc.) for the powered all-terrain fun?

Flexboardz · Post by **Flexboardz** » Wed Feb 10, 2016 2:01 pm

my opinion about old mtb techno is well known on this forum...

And, regarding power chain design, the choice between geared motor and hub motor is still open (without any light/torquey hubmotor available for 8" wheel)

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