Electric Sit Down Skateboard

At 76 I’m getting a little old to keep my balance while standing on a skateboard. And I don’t particularly enjoy planting my face in the pavement. So I figured sitting down might be a viable option to still enjoy a little skateboard speed. So I set out to build my Butt Dragster…a five wheeled electric skateboard that can zip along at over 20 mph. Which feels more like 50 when you are three inches off the ground.

The basic concept is to mate a typical long board with a drive wheel attached at the rear and power the thing with a couple tool batteries and a small DC motor. The big challenge is that the drive wheel needs to remain vertical and flat on the road or sidewalk while the long board tilts and twists for steering.

This would be a fairly costly project (over $200) if you are purchasing everything new. It also requires welding or access to someone who can do the welding for you.

The drive wheel is constructed using the front wheel and fork from a salvaged Rascal mobility scooter. (Photo 1) To attach the rear sprocket to the wheel a steel plate is cut from 3/16 x 3” flat stock to fit snug on the rim. (Photo 2) A center whole is drilled for the axle shaft/nut and 5 equally matching holes are drilled in the plate and the sprocket. (Photos 3 and 4) Quarter inch rivet nuts (Photo 5) are inserted through the holes drilled in the plate (Photo 6) and then welded on the back side. (Photo 7)

Matching holes are drilled in the steel plate and the wheel rim. Note that this is an airless tire and you can drill directly through the rim and into the tire if necessary. (Photo 8) The plate is bolted to the rim using self tapping screws. (Photo 9) The sprocket is mounted to the plate using 1/4” bolts and washers to space the sprocket far enough from the tire to allow free movement of the chain. (Photos 10 and 11)

The motor mount is cut from 1” and 3” flat stock and is bolted to the fork. (Photos 1 and 2) As an alternative the mount could be welded to the fork, which would be less time consuming, but using bolts allows for easy disassembly and for making corrections should they be required. The wheel and sprocket can then be mounted in the fork. (Photo 3) The motor is set in position making sure the sprockets are aligned and bolt holes are marked and drilled. The motor can then be bolted in place. (Photos 4 and 5) I am using a MY1016 motor which is rated at 24 volts and 300 watts.

The brake pad is a rubber sanding block with a hinge screwed onto one end and a threaded rod inserted into a hole drilled through the block. (Photo 1) The brake pad is bolted to the engine mount and has a spring attached to keep it just off the drive wheel. (Photo 2)

The brake cable is from a bicycle and comes with a round head. (Photo 3) Fortunately, this head fits perfectly into the wide end of a 1/4” threaded rivet nut. (Photo 4) The rivet must be cut lengthwise to insert the cable. (Photo 5 ) A link is cut from 1/2” wide flat stock and drilled to fit the threaded rod on the brake pad on one end and the threaded rivet on the other end. The link is then bent at a right angle. (Photo 6) The pieces of the linkage can then be assembled (Photo 7) And the linkage can be mounted on the drive wheel. (Photo 8)

I couldn’t find a 9 tooth sprocket for bicycle chain that would fit the MY1016 motor so I had to make a sprocket from scratch. If you find you need to do this there are some pretty good videos on the web that explain the process better than I can. But here are the basics. Sprocket teeth are spaced evenly around a circle and the size of that circle is determined by the number of teeth you want, the pitch of chain you are using and the size of pin that holds the chain links together. The formula PD=P/(sin[180/N] will get you started.

PD = Pitch Diameter

P = Pitch

N = Number of Teeth

PD or Pitch Diameter is an imaginary circle through which the center of each chain pin travels as it rotates around the sprocket. Once we know the Pitch Diameter we divide that number in half to get the radius of the Pitch Circle. We can then draw that circle on paper or on a steel plate. Using a compass, scribe or other marking tool we can then mark every chain pin center all around the circle using the chains pitch (the distance between any two chain pin centers) as our distance. Once those chain pin centers have all been marked they can be drilled using a drill diameter equal to the chain pin diameter. The peripheral material is removed and the basic sprocket remains.

For example, I wanted a 9 tooth sprocket that would drive a bicycle chain. Thus, my “N” was 9 and my “P” was .5, which is the pitch of almost all bicycle chains. Using the formula for Pitch Diameter my result was 1.4619”. So using half that amount as my radius a circle was drawn on steel plate (in my case I used an old and ruined power saw blade). I then used a compass set at .5 inch to mark the pin centers around the circle. (Photo 1) I then drilled each hole with an 8mm (or 5/16) bit to match the pin size of the chain links. (Photo 2) The outer material is carefully removed using an angle grinder with a cutting blade and then with a file. (Photo 3 and 4)

The MY1016 motor uses a “D” type drive shaft with one side of the shaft cut flat. (Photo 5). To match the flatted shaft and prevent the sprocket from slipping when under power, a small triangle is cut from 1/8” steel plate and attached to the sprocket with a dab of JB Weld. (Photo 6) This holds the small tab in the correct position until it can be mig welded in place. A steel washer is cut to complete the circle around the drive shaft. (Photo 7). The sprocket assembly is removed from the motor and the triangular tab and the washer are welded to the sprocket and ground as smooth as you can get it. (Photo 8) Mine is not real pretty but it works.

The chain tensioner is made using three 1/4”x5/8”x10/19” bearings. (Photo 1) The three bearings are pressed into plastic 5/8” irrigation tubing. (Photos 2 and 3) Excess tubing on the ends is trimmed off square with a box cutter. (Photo 4) The tensioner is bolted to the motor mount framework and a spring is attached to keep things snug. (Photo 5) The plastic tubing will wear over time but is easily and cheaply replaced.

The Getfun 41” longboard was selected because it has a nice flat deck which allows for easier modification. (Photo 1) The original drop through trucks were removed and reattached as top mount trucks (trucks mounted directly to the bottom of the deck). The trucks were also moved inward about three inches. (Photos 2 and 3) This provides more room under the board for mounting the batteries and controller. The tail section of the board is cut off and removed. (Photo 4) Thin wall 1x1 steel tubing is cut, welded and bolted to the wood deck. This steel frame provides a strong base for attaching the drive wheel, seat, hand grips and other items. (Photo 5)

Three inch wide steel door hinges are welded to the rear of the steel deck frame. (Photo 1) A short length of “Superstrut” (available in Lowes or Home Depot electrical department) is cut to fit the drive wheel fork. (Photo 2) The strut is welded to the fork head. (Photo 3). The drive wheel fork can then be welded to the hinged mount. (Photo 4) Note that the mounting plate for the fork is held in place with a series of bolts which allows for easy removal of the drive wheel if necessary.

To keep the drive wheel in firm contact with the pavement an adjustable bicycle suspension spring is used. (Photo 1) A mounting post is cut from 1x1 square tubing and drilled mounting tabs are welded to the top end of the post. The post is welded to the deck frame at a 15 degree angle. (Photo 2) Mounting tabs are welded to the fork housing and the spring is installed. (Photos 3 and 4)

The upholstered seat and back rest were salvaged from a discarded wheelchair. The back rest support is bolted to the suspension spring post. (Photo 1) The upholstered back rest is bolted to the mount. (Photo 2) The seat cushion is screwed to the deck from the underside. (Photo 3)

Bicycle handlebars are bolted to the steel framework to provide stability, to assist with turning the skateboard, and basically just to hang on for dear life. (Photo 1)

An “outrigger” bar with wheels on each end is used to prevent the skateboard from flipping over in tight fast turns. The bar is made from two bicycle seat posts with the post clamps left in place and a seat stem. (Photo 2) The seat stem is inserted into the two seat posts so that the posts can be butt welded together end to end. (Photo 3) Wheel mounting plates are cut and drilled using 1 ½ x 3/16” flat stock. (Photo 4) The wheel mounts are welded to seat stems. (Photo 5) A skateboard wheel is bolted to each wheel mount. (Photo 6) The outrigger assembly is bolted to the steel frame. (Photo 7) The outrigger bar is fully adjustable using the seat post clamps. The wheel height can be adjusted by rotating the seat stem and the wheels can be made wider or narrower by sliding the seat stem in and out of the seat post.

A 1x1 square tube bar is bolted on the nose of the deck. This bar allows the rider to use their feet to apply additional turning force to tilt the deck. (Photo 8)

The main electrical components are attached to the underside of the deck. A Currie controller is on the left. This is a 24 volt controller but so far has performed well with 36 volts of battery power. The two Rigid power tool batteries (Home Depot) are 18 volts wired in series for a total of 36 volts. The orange plastic battery mounts can be found on Amazon and eBay and are known as Power Wheels adapters. They make mounting and wiring the batteries an easy task. (Photo 1)

An emergency shut off switch is used to totally cut off battery power to the electrical system in the event of a “runaway” event created by the motor or controller. (Photo 2) The shut off is mounted within easy reach of the rider. (Photo 3) A cut off switch is highly recommended for any motorized electric vehicle.

A twist throttle is mounted on the right handlebar and connected to the Currie controller. (Photo 4)

It should be noted that I am “over clocking” both the motor and controller, using a 36 volt battery pack, which actually reaches over 40 volts when fully charged. The motor is designed for 24 volts and the Currie controller is also rated at 24 volts. Thus far both have performed without any problem at the 40 volt level. The over clocking increases top end speeds and puts more zip in the ride. Not all controllers can handle the increased voltage so it is preferable to match your controller voltage to your battery pack voltage. The skateboard has a design speed of 20 mph and is capable of that and more.