Oh Noes! Broken Belts!

Broken Belts from McGuire Bearing

New Belts from Polybelt.com (grey ones are steel reinforced)

Well broke 5 of the 6 belts I bought from McGuire bearing. I figure this could be due to a few reasons. One could be is that they just can't handle the load. They work for awhile then break while using the board. Also one of the bigger pulleys was off center a bit and had wobble. Another reason is because with the 1/5" pitch on the smaller pulley there are on 4 teeth in it at any one time. There possibly might need to be more to get a better grip and prevent as much wear. One solution is to buy better constructed belts. The old belts I think were neoprene with fiberglass reinforcement. I bought some of PolyBelt.com. 3 regular rubber belts and 3 steel reinforced polyurethane belts which will hopefully bet stronger and more durable. I also found some kevlar reinforced belts on sdp-si.com which might be worth trying if these don't work. Another solution if that doesn't work is to switch to MXL size (0.08" pitch) pulleys and belts which will have much more teeth per inch. And possibly wider belts.

Semi-Finished

Top View

Bottom View

Side View

The finished product for the time being. I got everything done mechanically I wanted to do. Next step is to add Hall Effect Sensors for the purpose of measuring rotor position to supply power better than the current sensing method which uses electromagnetic feedback to measure sensor position. Adding Hall Effect sensors will have the effect of smoother starts, hopefully more power with less energy and smoother operation. The current motor controllers can work with or without hall effect sensors but the one I want to design eventually I think will need it for the purposes of regenerative braking. Here is the what I want to add. It has a board and sensors specifically built for 50mm 14 pole motors. After that the electronics such as charger, pulse width modulator etc.

Battery Charging

Fabricated Charge Balance Splitter

Added DC Power Connector and Balance Connector (left middle)

Charger hooked up to the DC connector and balance connector

Charger/Power Adapter/Remote

The fabricated charge splitter was made so both battery packs can be charged at the same time. Also added a DC connector so I wouldn't have to take off the bottom plate everytime I want to charge it. The charger I got of Ebay and it is about 50W 2S-6S charger, the power source is a laptop power adapter I got off Amazon that puts out 15V, 16V, 18V, 19V, 20V at 6A and 24V at 5A. I just use 16V setting because the charger accepts an input voltage between 11 and 18V and the 18V setting on the power adapter puts out a little more than 18V. The adapter also has a USB port on the side so I can use it to charge the remote at the same time which is convenient.

Installed Motor Controllers and Wiring

Bottom of Longboard without cover plate

Bottom of Longboard with Plate (drive end)

Bottom of Longboard with Plate off (drive end)

Wiring/Receiver/Etc

Added Bullet Connectors and JST-XH Connectors to Battery Packs

Added Bullet Connectors to the Motor Controllers

5.5mm Gold Plated Bullet Connectors

Installed the Hobby King motor controllers (with double sided mounting tape) and receiver and wired them up to the battery packs. I also added bullet connectors to the battery packs and JST-XH connectors for charge balancing. I also added 4mm bullet connectors to the ends of the wires that connect to the motors. The motors already came with them.

Motor Controllers

I'm using two of the Hobby King 120A motor controllers mostly because I already had one from a different motor, even though the motors I'm using are only rated for 90A. The voltage is supposed to be from 2S (7.4V) to 4S (14.8V) but it will go up to 6S (22.2V). This is the link to the website that tested and looked at the circuitry and concluded that 6S was safe. Here is the link to the actual product website.

The transmitter/receiver I use to for the motor controllers. Basically the only qualification is that it was cheap and worked. Link to the product site.

Belts/Pulley - Parts fabricated and put together

Parts - Pulleys/Washers/Bolts/Belt

Parts Bolted to the Wheels

Parts Bolted to the Wheels (alt view)

Wheels and Motor connected together on the trucks

Wheels and Motor connected together on the trucks (alt view)

For the pulleys I drilled out the holes of the small ones to 5/16" to fit the 8mm shafts of the motors. For the larger ones it was a bit more complicated. I cut off the ends and drilled out the center holes to 1" so it would more than clear the 3/4" truck axle and drilled 6 holes in a diameter that would fit with the holes in the wheels. Also I bought some 1.5" O.D. by 15/16" I.D. washers and drilled holes so that they would fit with the large pulleys. The bolts I used are 2.5" 10-24 size to mount the pulleys and washers to the wheel.

Belts/Pulley - Connecting the Motors to the Wheels

Small XL (1/5 Pitch) Pulley - 10 Tooth

9" XL (1/5 Pitch) Pulley - 45 Tooth

Large XL (1/5 Pitch) Pulley - 30 Tooth

I ordered all the pulleys online, the big one off Ebay and the small one off Servocity.com. I got the 9" belts from a McGuire bearing which were surprisingly cheaper than online. The small pulley has to be bored out to 8mm (about 5/16") from 1/4" to fit the motor shaft. The motor shaft will have to be notched to for the set screw in the small pulley. The large pulley will need to be bored out to about 1" to clear the 3/4" truck axle. Then holes drilled and tapped for mounting to the wheels.

Wheels

I decided to use wheels I found for $30 off ebay. They are Blank Pro Flywheels that come with ABEC 7 bearing and spacers. What's nice about these wheels other than being cheap is that they are larger than the average longboard wheels. They are 83mm in diameter which allows for more clearance between the pulleys I'll mount to them and the ground. Another good thing is that they already have holes through the center around the bearing hole for mounting a pulley, so I don't have to drill my own holes. Plus they come in different sizes such as 90mm and 97mm. I already have a set of the 97mm ones. Theoretically, the pulleys will fit all the sizes and the larger the wheel I use the faster the board will go.

Motors and Motor Mounts

Motor Mounts

Motor Mounts (alt view)

Mounts with the Motors on them

Mounts with Motors on the Trucks

Mounts with Motors on the Trucks (alt view)

Not much to describe except tap holes properly. I used too big a drill bit and ended up stripping the 1/4 threads I tapped so I had to move up to 5/16 bolts/hole. Doing it this way makes sure it clamps properly and stays in place, plus I can adjust how far up or down the motors are.

50mm Brushless Outrunner Motor

The motors being used is a brushless outrunner (the outside of the motor spins as opposed to the inside which usually does) bought off Hobby King. It is 50mm in diameter, the max voltage it is rated for is 6S (22.2V) and the max rated current is 90A. The max power is 2000W at 22.2V. The motor has 3 leads coming off of it because it uses alternating currents to drive the motor because there is no commutator like on a brushed motor. Therefore the motor requires a motor controller to drive it unlike brushed DC motors that can run directly off a battery. What controller is used will be talked about later. Link to product page on Hobby King

Motor Mounts - Design

3D Rendering Wire Frame

3D Rendering

The motor mounts for the brushless motors. The large hole goes around the trucks axle which is about 3/4" round. Not pictured is there will be screws on the motor mount that clamp down on the axle. The motor shaft goes through the top small hole and get screwed in through holes that aren't pictured. The bottom and top pieces are connected with a screw that isn't shown. Hopefully I'll make it adjustable.

Battery Packs

One Side

The Other Side

Finished pack wrapped in electrical tape but no connectors.

Battery pack in the board. Fits well.

One of the two battery packs made up of 30 18650 Samsung Lithium Ion Cells. The same type of batteries that Tesla uses in their cars but I think they use Panasonic batteries. Each row of 5 is wired in parallel with each other with braided wire and those 6 are wired in series to make a nominal voltage of 22.2V (3.7Vx6=22.2V). I used hot glue to glue them together and glue in the wires between the gaps of the batteries. There has to be a wire between each parallel wired row for the purposes of charge balancing. The main end wires are 10 gauge to handle the high amperage. According to the spec sheet each battery should put out 2C with a 2.6 amp hour capacity equals a 5.2 amp max discharge current per cell. That times 30 cells equals (30x5.2A) 156 amps max discharge per pack. Which is more than enough for the two 120A motor controllers and the two 90A BLDC motors. Link to the Samsung 18650 cell spec sheet.

Frame for Longboard with Top and Bottom Plates

Top

Top (alt view)

Bottom

Bottom (alt view)

Top with Top Plate

Top with Top Plate (alt view)

Bottom with Bottom Plate

Bottom with Bottom Plate (alt view)

Frame is made of 1/8" thick 3/4" square aluminum tubing. End plates are 1/4" thick aluminum plate with a 1" wide 1/4" thick piece helping connect the end plates to the tube frame. Overall length is 40" long and 9" wide. The dimensions of the inside are 24.5" by 7.5" which means the dimensions of the aluminum frame are 26" by 9". The holes on the end plates are so the trucks can be mounted on the bottom or the top through the hole. The top is 1/8" aluminum thick plate that is 28" by 9" and the bottom plate is 26" by 9" of the same metal as the top. I'll add grip tape to the top plate later.