E-mountain board research notes and build - Advice please

[that0n3guy]

Hey All,

I'm building an electric mountain board and I thought I would post my research before buying anything.

Background
I bought a used mountainboard about 10 years ago ($25 at a garage sale http://www.sierratradingpost.com/mountainboard-sports-ambush-warrior-mountainboard-~p~99877/) which I motorized with a drill battery geared down twice... motor doing about 18k RPM and 12-24V SLA's. It sucks . I just started doing some research and man has battery and motor tech come a long way.

Project Description
I'll rip off my old motor mount and remove hand brakes. I want to use this thing for commuting to work, mostly streets. I work 2-3 miles to work with a couple hills around 15% grade (according to google earth) that are only a block or so long. I don't want to spend a lot (actually, my wife doesn't want met to ) so I'll probably stick with single wheel drive. I probably don't need more than 20mph (~32kmh)... if I did, I would just ride faster and hurt myself (you should have seen my sweet black eye after snowboarding this year).

Research:
Gearing, battery, motor:
Based on vedder's article (http://vedder.se/2014/10/chosing-the-right-bldc-motor-and-battery-setup-for-an-electric-skateboard/)... this is how I selected my motor gearing and battery:

• - Higher voltage = lower amps = good
  - I'll probably use 12s (about as high as I can go based on current ESC's)

Battery options for 12s:

• - 4x 3s-5Ah 20c = 22.10x4 = $88.40: http://www.hobbyking.com/hobbyking/store/__16786__ZIPPY_Flightmax_5000mAh_3S1P_20C_USA_Warehouse_.html
  - 2x 6s-5Ah 20c = 40.43x2 = $80.86: http://www.hobbyking.com/hobbyking/store/__9176__Turnigy_5000mAh_6S_20C_Lipo_Pack.html

Motor:
Based on vedder's article:

• 12s (this is what I will use):
  3.8*12 = 45.6v
  8600 / 45.6 = 189 KV

Two motors that look close:
http://www.hobbyking.com/hobbyking/store/__18129__Turnigy_Aerodrive_SK3_6374_192kv_Brushless_Outrunner_Motor.html
http://www.hobbyking.com/hobbyking/store/__18181__Turnigy_Aerodrive_SK3_6364_190kv_Brushless_Outrunner_Motor.html

I think the 63mm motor is a good idea for a single motor board (higher torque).

Gear Ratio:
http://www.advanced-ev.com/Calculators/TireSize/
RPM: 8600
Tire Diameter: 8.75 (8.5" to 9" depending on air pressure)
MPH: 25
Differential Ratio: ~1:9 (this seems high... I don't see this type of ratio anywhere on this forum)

Chain vs belts
I looked all over SDP-SI and it doesn't look like there is any way to get anything above a 1:6 ratio with belts (since the motors have 8mm shafts). To get higher gear ratio, I have to go chain.

http://www.sdp-si.com/eStore/Catalog/Group/218#
Wheel sprocket:
sdp-si has lots of hubless carbon steel #25 sprockets from 70-100+. Depending on the steel type, they might suck to drill. Looking for alternatives.
80T #25:
http://tncscooters.com/index.php?route=product/product&product_id=131
http://www.electricscooterparts.com/sprockets25chain-wheel.html
http://www.partsforscooters.com/127-1?sc=31&category=132535
http://www.monsterscooterparts.com/25sp80to2moh.html
http://www.staton-inc.com/store/products/80_tooth_25_A_Sprocket_2_13_ID_with_four_Mounting_holes-1752-45.html
http://www.extremescooters.biz/127-1.aspx
(#25 I think): http://www.amazon.com/Sprocket-80-Tooth-Scooter-Chopper/dp/B0085MCPSK
This would probably work well and are all over the web (electric scooter and pocket rockets use them)... 1:8 is close enough to 1:9. A thread: http://endless-sphere.com/forums/viewtopic.php?f=28&t=9551

Attaching wheel sprocket to the wheel ideas:
- create an adapter like: http://endless-sphere.com/forums/viewtopic.php?f=35&t=68710#p1036962

• 
  Materials:
  - G10: http://www.mcmaster.com/#grade-g-10-phenolic/=x2f7pp
  - ALUMINUM (.08-.125" in 6061) http://www.mcmaster.com/#standard-aluminum-sheets/=x2ff65 http://www.onlinemetals.com/merchant.cfm?id=76&step=2&top_cat=60
  - polycarbinate http://www.onlinemetals.com/merchant.cfm?id=270&step=2&top_cat=181&showunits=mm (no idea if this is strong enough.. but its cheap)
  - GPO - Stronger than poly, cheap https://www.onlinemetals.com/merchant.cfm?pid=17915&step=4&showunits=inches&id=1264&top_cat=181
  

- drill holes


Motor sprocket:
11T #25 A 6C 7MHC25011 (8mm bore)
10T #25 A 6Z 7M251008 plastic (8mm bore)
10T #25 A 6C 7MHK2510 Steel (8mm bore)
10T #25 Aluminum (http://www.andymark.com/product-p/am-0505.htm)



ESC:
I'm not even going to waste my time on a car ESC. VESC is the way to go. If I can't get one from someone, I'll have one made (I'm to busy to build it myself... my 3rd kid should be here any day now).

Controller/reciever:
I like the wii remote idea. I've not done too much research on this one yet.
I think I need a reciever of some kind that hooks into the VESC... is that true? Looks like there is a $50 one on torqueboards site.

Charging + other electronics

• - IMAX B6 - http://www.hobbyking.com/hobbyking/store/__5548__IMAX_B6_Charger_Discharger_1_6_Cells_GENUINE_.html
  - Power supply - The original xbox 360 power supply would do 12v @ 16.5amps... easy to find on ebay for $10: http://www.ebay.com/itm/Xbox-360-power-supply-203-w-watt-FAST-SHIPPING-/111659543956 (look at the plug for version: http://support.xbox.com/en-US/xbox-360/system/power-supply)
  - A paraboard (parallel board) to charge my 3s's or 6s's in parallel
  - A cheap amp meter
  - A cheap volt meter
  - a lipo sack like: http://www.hobbyking.com/hobbyking/store/__4364__Lithium_Polymer_Charge_Pack_25x33cm_JUMBO_Sack.html
  - Something to let me know batteries are getting to low....

Questions

• - Which battery setup should I do? 4-3s seems like its most flexible from a layout of battery standpoint.... and cheaper/easier to replay battery packs (that idea was from torqueboards guide).
  - What is the difference between the 6374 and 6364 (beside 2kv)?
  - Is that gear ratio crazy high?
  - What do I need get the wii controller and VESC to communicate?
  - Does my xbox360 power supply idea look good?
  - Any suggestions on extra electronics (see my section above)?
  - How do you do onboard charging? I would like to not take my batteries out of the box. How do I wire it to do this?
  - Anyone have a good source for custom 80-90T sprockets?

Notes from research:
Lower KV motors have higher torque... higher KV, higher speed.

 

[torqueboards]

Nice info!

- Which battery setup should I do? 4-3s seems like its most flexible from a layout of battery standpoint.... and cheaper/easier to replay battery packs (that idea was from torqueboards guide).
Since that guide. I've moved to (2) 6S 5ah 20C Turnigy packs $40/each for 12S 5ah. Most people are moving up in voltage too.

- What is the difference between the 6374 and 6364 (beside 2kv)?
Bigger motor can deal with heat more as for specifics not too sure besides the standard kv rating.

- Is that gear ratio crazy high?
1:9 is a bit high. Usually ratio is about 1:5 and 1:6 sometimes 1:7.

- What do I need get the wii controller and VESC to communicate?
The Wii Nunchuck Nyko Kama is able to work with the Wii Nunchuck. Checkout Ben's site for details.

- Does my xbox360 power supply idea look good?
No.

- Any suggestions on extra electronics (see my section above)?
On/Off switch.

- How do you do onboard charging? I would like to not take my batteries out of the box. How do I wire it to do this?
You can wire Y connector setup with leads out to charge your packs. You can wire a BMS and/or Charging board.

- Anyone have a good source for custom 80-90T sprockets?
You can find 72T here which is affordable. http://www.vexrobotics.com/vexpro/motion/sprockets-and-chain/25-sprockets.html

 

[that0n3guy]

torqueboards! Thanks for your quick reply and thanks for all your info on the site!

Based on what you've said... I think I'll probably do the 6s's.

I'll probably stick w/ a higher gear ratio to start with, most likely a 1:8 (10T and 80T). If that ratio is too high, I can really easily swap the 10T for an 11T or 12T or 13T. Those smaller sprockets don't need drilled out, slide on and off "easily", and are cheap.

You don't like the xbox360 power supply idea ? It seems roughly the same as your recommendation (in your cheapest option section) of: http://www.hobbyking.com/hobbyking/store/__20971__Hobbyking_105W_15V_7A_Switching_DC_Power_Supply.html ... only the xbox360 power supply should be higher quality and double the wattage. Why don't you like it?

Another quick question, do you use any parallel charging boards/cables that you recommend?

 

[torqueboards]

I don't think its interchangeable like that but I'm not an EE. Also swapping those motor pulleys with only 1T difference won't make a big difference. I would at least go with them in 2T at a time but even that is very small of a ratio change.

I use parallel charging boards and charge with an iCharger 208B at 15 amps. I don't do any on-board charging with Lipos - I think it's much more complicated than it needs to be. I just charge my packs like RC hobbyists.

Not sure if you meant you are going 6S or 12S. But I'd opt for higher but some people have great boards at 6S also.

 

[that0n3guy]

I don't think its interchangeable like that but I'm not an EE.

I think it should work. As long as the IMAX B6 can handle 12V input, I have one of these power supplies I used on my kitchen led strips so I'll test it out maybe.

Not sure if you meant you are going 6S or 12S. But I'd opt for higher but some people have great boards at 6S also.

Sorry, I just meant I would do 2x 6S's... not 4x 3S's. I'm going 12S total for sure.

 

[Harryz33]

I think the xbox supply should work, as long as it can provide enough power for your charge rate. Say you use 15A at 12V and if the charger is 70% efficient (a conservative estimate) = 126W. Divide this by the charging voltage, 6*4.2 and you get 5 amps, so you could charge both batteries in 2 hours.
I use a PC power supply for my B6 charger and it works like a charm, over 20 amps at 12V and really easy to set up too

 

[sl33py]

Not sure about your budget, but also worth looking at some inexpensive server power supplies. Not as small as the XBox PSU, but much "beefier" and rock solid 12v rails (kinda important in servers).

You can get some already modified for 12v for cheap on ebay. Even some in series at 24v. Seems like charger work best at the higher voltages!

GL!

 

[furp]

Nice writeup! About the 6364 vs 6374 difference, the 6374 will probably have more torque since it is a little longer. If the price is not much different and the reviews dont state otherwise, I see no reason not to go with the bigger one. Maybe check beforehand if it would fit with a dual drive should you ever want to move up

Battery: Maybe consider LiIon cells, like the used ones doctorbass sells on this forum. I don't know what exact price you will end up with for 12s5ah but it might well be worth it for longer battery life, no fire hazard and no need to balance those cells, so easy charging with a 50 bucks ebike charger and just one plug. I found that making a (baance) charge plug for lipos does work, but is a lot of hassle and lots of your space will get eaten up by all the wires connecting the batteries and stuff.

 

[that0n3guy]

I use a PC power supply for my B6 charger and it works like a charm, over 20 amps at 12V and really easy to set up too

Good call on the PC power supply... I think I even have some laying around. I did some quick googling and I think I'll eventually go w/ a server power supply. They have better stability and shut off protection and used ones are like 10 bucks (used PC ones would suck... ).

the 6374 will probably have more torque since it is a little longer

Yeah, I'll probably get this one since its only 10 bucks more.

Battery: Maybe consider LiIon cells, like the used ones doctorbass sells on this forum. I don't know what exact price you will end up with for 12s5ah but it might well be worth it for longer battery life, no fire hazard and no need to balance those cells, so easy charging with a 50 bucks ebike charger and just one plug. I found that making a (baance) charge plug for lipos does work, but is a lot of hassle and lots of your space will get eaten up by all the wires connecting the batteries and stuff.

I looked into LiFe, but they are double the price. I'll look at liIon, but my initial research shows pretty pricey too. I don't see doctorbass's thread... but I'll keep looking.

 

[that0n3guy]

I looked into LiFe, but they are double the price. I'll look at liIon, but my initial research shows pretty pricey too. I don't see doctorbass's thread... but I'll keep looking.

I'm definitely re-considering this. I didn't realize the lifespan of lipo's was so short. 100 cycles seems is high. So if I ride to work 5 days a week for 5 months out of the year and charge everytime I ride... My batteries are gone in a year (or really... 5 months). If I mess around and take my time getting to work... I'll have to charge at work so that will be 2 charges in a day. Which would be less than a year.

Onloop is saying 300 cycles for his ultracell (http://www.enertionboards.com/electric-skateboard-parts/ultracell-electric-skateboard-battery/) at the worst. Based on my distance to work I'll only partially discharge the ultracell and so they should last longer (http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries). If I only get 300 cycles out of an ultracell, costs are similar for lipo vs ultracell over 3 years. If I get more than 300 like say 800 (the web makes it sound like this is possible) then ultracell is cheaper. Also, liIon is way easier and less likely to burn down my house... which my wife and kids like .