The Next Generations


Taking all the good features of each plow and combining them will produce a unit with the following features:
- Scooter wheels and steel front.
- Vee shape to reduce chances of catching in cracks.
- Folds up for transport.
- Higher profile to get snow up out of trough.
- Wings to shape sides of trough and fling snow farther out.
- Ability to be pushed by hand in deep snow.
- Not too heavy.
- Room for a bucket if additional weight is needed.
- Simplified construction.

See the comments below about my experience with this plow in January 2005.

The (almost but not really) Ultimate Plow 

(Or, it seemed like a good idea at the time...)

  Front Front     Push Plow Right Rear Back view with wings folded    Push Plow Bottom Wings out


 Hitch Hitch Detail   Bottom Bottom

Interior Interior looking toward front

Drawing
Construction notes:
By having a 60 degree cut angle on the plywood and a square nose corner on the base, most of the other assembly angles come out to be 45, 90, 60 or 30.  The only tricky angle is the bevel on the edge of the 2x4 that reinforces the bottom of the front.  It is 54.7 degrees from horizontal.  One can avoid having to cut this angle by using thinner wood, such as plywood, and building up the bevel in layers.  There is probably no reason why the reinforcing wood has to match the angle of the plywood perfectly.  Caulk or expandable foam might help fill in the voids.  I had actually considered building the whole unit out of styrofoam and then gluing on a thin plywood or aluminum skin.  (Amazingly strong and light model airplane wings can be made out of foam with a balsa skin.)

I made the sides out of one piece of plywood but decided to hinge them since the tip to tip spread was a bit wide for most doorways and I didn't want to catch a tip while the plow was up on the rear rack.  The hinge line is parallel to the nose line so the plow cuts vertical sides when the wings are folded.  This makes the new plow compatible with deep sided troughs made by the old model seen on the previous page.

The platform is large enough to match the rearmost extent of the wing tips.  A longer wheelbase might help reduce fishtailing.  This also makes the wing braces simple and provides room for a bucket.  The bucket could hold a few pounds of snow to provide additional downward force so the nose doesn't ride up.  When done plowing the snow can be dumped out of the bucket so riding with the plow stowed is not too much work.

The platform will also be outfitted with a brace to hold the tip of a shovel or the end of the tee handle from the walking push plow so this unit can be used as a walking push plow when the snow is too deep to pull it behind the bike.

The axles rest against the bottom of the platform and are captured in notches in the surrounding blocks of wood.

Parts are:
Plywood -  A 24" x 48" piece of 1/4" exterior grade should be enough. Thicker would be stronger but heavier.  The two sides can be cut from one 12" x 44-3/4" piece.  The bottom uses two pieces cut from one 8-1/2" x 36-1/2" piece.  The leftover plywood is used for diagonal bracing and the top "splash" panels.

Scooter wheels - the exact size is not critical as long as they are all the same size and have nice bearings.  You will need three.  I used the standard 100 mm diameter.
 
Steel rod - Axel for the scooter wheels.  Mine uses 5/16".  Check your wheels.  Can be smooth or threaded. One 3 foot piece should be more than enough.

Steel Flat with holes - 1 piece of 36" x 1-3/8" x (I think) 0.070" galvanized with 3/8" holes every 3/4".

Steel Flat - 1 piece of 36" x 2" x 1/8".  Should be in the same bin as the strapping.  This is for the front cutting edge of the blade.  You could use another piece of strapping or even aluminum depending on how you want to trade off weight and durability.

Assorted wood - A 2x4 for the nose. 2x2 is good for connecting blocks and the hitch. 1x2 or similar for the hinge mounting.  1x1 or base shoe for the edges.

Deck screws - I like the square drive heads.  I have boxes of 3/4", 1-5/8", 2" and 3".  Make sure they are good exterior grade.

Plastic or other slippery material for the surface.  You'll need about 4 square feet.  Should be fairly sturdy but flexible enough to make curves of a few inch radius.  Or if you don't mind the angles then the wood can just be painted or stained.

Bolts - 3/8" (galvanized or stainless if you don't like rust) 2" or 2-1/2" long.  I think four should be enough.
Nuts - Pozi-Lok (tm) or other nylon insert jamming nuts for the bolts.  Get one for each bolt.

Hinges - If you want the wings to fold out of the way you will need four hinges.  2" or so is a good size.

Clevis pin - 3/8" to use in place of a bolt if you want the hitch to pivot for transport.

There are probably a few other small items but this will get you just about fully outfitted.

The Hitch on the Bike

I decided to try making a hitch that would center the forces and give some symmetry to the installation.
It needs to pivot horizontally, vertically and rotate (not that this bike ever tips over).

The conduit clamps are joined by a 1/4"-20 bolt with a nylon insert lock nut.  The bolt is tight enough to minimize rattling but loose enough to allow rotation.

Hitch Hitch with plow up         Hitch Hitch with plow down

The aluminum angles are held against the seat stays by hose clamps. The aluminum tubing is reinforced by a wooden dowel inside.  The tubes can be loosened so the bottom tips swing up to provide more ground clearance.

A clevis pin in the small conduit clamp allows for quick release of the plow hitch.

The wooden box on the left side of the bike rack is the shovel holder.

A Really Simple Plow 

For those of you needing something quick and simple.  This won't drag you down yet will still get some of the snow out of your track.
Scraps of 2x8 will make a plow 10" wide.

     Simple Plow A Simple Plow    Simple Plow Top View of a Simple Plow

This plow works well to clear enough snow out of the way so the next bike pulling the main plow can get good traction.


More Comments

January 2005 started off with about 8" of wet snow arriving over the course of 24 hours.  It started snowing during the day and was about as deep as I could handle (maybe 2" of very wet snow) and still maintain riding speed on my way home from work.  Another 6" fell overnight.  Attempting to plow in the morning revealed a flaw in the design of the new plow: It works too well!  The wet base was now icy and packed and the nose of the new design cuts right down to the pavement.  Even walking I could not make much progress against the ice and heavy snow.  I was the first one out in the snow that morning but by noon dozens of walkers had been out and the trail was getting packed down.  Even the push plow made little progress in the hard packed snow.

The next morning I reverted to the good ol' blue plow (shown on the previous page).  The scooter wheel ahead of the blade gives it the advantage of riding up on the hard packed snow and skimming only the lighter loose snow off the top.  The aggressive cutting feature of the new design may still prove useful when dealing with ice or soft spring slush.

The Drift Cutter

Later in January we received about 8" of fairly light snow over a Friday night into Saturday morning.  I got out early Saturday and the push plow cut through very nicely.  That afternoon and into the night the winds picked up and the snow drifted deeply in some of the open areas.  Drifted snow can be very difficult to cut through.  By Sunday afternoon there was a hard packed base, a few inches of power and then a crusty top.  The push plow could not make much progress since the snow was as deep as the body of the plow and thus the wings were not rolling the snow out but just jamming like a cork in a bottle.

I decided I needed a plow that would have the following features:
- Two wheels to allow me to tilt the blade to cut or skim depending on the base.
- Shallow angle for maximum lifting force.
- 16" total lift height.
- 17" front blade tapering out to about a 32" total width.
- Short enough (4 feet) to fit in the trunk of the car.

I really liked the blue plastic roll-up toboggan that I used on the original bike plow.  I had been looking for more of those or something similar to cover the plow and provide a slippery surface.  I was considering using the inexpensive self-stick vinyl flooring tiles when I stumbled upon the ideal material.  It is a 0.060" thick white plastic wall covering intended for bathrooms and kitchens.  It comes in a 4' x 8' sheet for about $14 at the local building supply centers.

Here is what I ended up building:
Drift Cutter Rear Rear view.  Note the handle from the Push Plow
 Drift Cutter Side Side view
 Drift Cutter Bottom Bottom view

The main frame is 2x4s with plywood in the front to hold the steel cutting blade and on the bottom to provide a sledding action when the unit is tilted up.

Some pine 1x10 across the rear support the pocket for the Tee handle.  1x2s are used for the truncated tetrahedral frame.  The plastic sheeting is screwed on almost like upholstery.

Scooter wheels are used again.  They are placed about 12" back from the front so the blade touches the pavement at about a 20 degree angle.

Initial tests show it works well.  The variable blade angle is handy for getting over the ice that would be too hard to cut otherwise.

Some Modifications

An unusually snowy 2008 has prompted me to do some modifications.  Last year I added a vertical cutting blade to separate clumps of wet snow and some plastic angle to help encourage the snow to move off the sides.
Drift Cutter Bottom Left front view

Clumps of snow tended to fall under the plow so I added a "skirt".  This seems to greatly reduce the roll back and helps form the trough shape.

The skirt pivots near the front of the plow.  It slides along the ground while still allowing the plow to tilt up and down to follow the terrain.
Drift Cutter Bottom The skirt with the plow fully down.

Drift Cutter Bottom Plow raised a bit.          Drift Cutter Bottom Plow tilted way up.



Plow Physics

With the heavy snows of 2005, I decided actually spend some time thinking more about the optimal shape of the plow.  It seems intuitive that a sharper plow would be easier to pull but I wanted to calculate some values, even if they were just relative.  Here are some results:

Think first of the low speed case or the action when one is using a regular shovel.  Obviously some work is involved and it is mostly just moving the snow against the force of gravity to get it up and out.  Good old m·g·h.

The high speed case is typical of the action of the plow in thin snow. If you believe in conservation of energy then one can determine the work involved. Assume the plow is easy to pull and the plow surface is frictionless (generally not the case). Assume the snow is just resting on the pavement and not stuck (again, this is often a bad assumption).  The plow is a simple triangular shape where the nose has a half angle of theta relative to the direction of travel. 
Theta
Assume the plow does not collect any snow so all the snow encountered must exit the plow.  The exit speed, Vexit, of the snow is just tan(theta) times the speed of the plow. 

The energy of the exiting snow is
0.5*msnow*Vexit2 

So the power required goes like tan(theta)2 and like the cube of the speed (as it should). 

The tan(theta) assumption seems valid for snow that exits the plow in a laminar fashion.  It is apparent that even a flat plate (i.e 90º half angle) will push snow out of the way but the mound of snow ahead of the plate forms some natural angle of shear.

Experience shows the following assumptions are generally true:

In the simple case where the plow picks up a blob of snow and carries it along at V, the energy of the snow is

0.5 * msnow * V2

As the plow moves along it is constantly encountering new snow that gets picked up, carried along and dropped off to the side.

Since
Power = energy / time
the power required to pull the plow goes like

0.5 * msnow / time * V2

Again, the mass of snow encountered per unit time is proportional to the speed of the plow so the power required goes like the cube of the speed (as it should).

One can plug in some numbers for typical snow density, plow angle, bike speed, etc.   Ballpark calculations show the power required to pull the 45º plow 6 MPH in 6" of wet snow is about 127 watts.  This does not include the difficulty of riding a bike in 6" of wet snow.

Additional Complications

A Sharp Plow

Any engineer likes to have constraints on the problem.  I figured the plow should be as long as possible but not so long as to make stowing unwieldy.   A 20 degree half angle makes the sides about 24" long which is convenient for using standard materials.  It is also 24" from the bike hitch bar to the top of the rear rack

I incorporated some of the latest materials and ideas:

1) Although plywood was handy for the structure, it is heavy and difficult to work with.  The new design uses more pine.
2) The sheet plastic used on the drift cutter is great and rigid enough that no superstructure seems to be needed.
3) The longer plow requires a different rack holder.  When stowed for transport the plow bottom now faces the rear tire.


The Sharp Plow, top left view.          Rear view.
(Click on any picture to see a larger version.)

 Bottom view.     Nose detail.

Start by cutting a 45 degree bevel on one edge the whole length of the 1x4.

The key to construction is the 2x4 in the middle.  I first cut the 20 degree sides then beveled those edges 45 degrees along the cut line.  This gave me the base for attaching the 1x4 sides.  I attached one side piece and did a vertical cut for the nose.  I then removed that piece and attached the other piece and cut it.  This procedure was much simpler than trying to figure out the wacky angles and setting the saw for the cuts.

I then added the reinforcing blocks for the rear axle.  These are beveled 2x4s.  It works out nicely that the scooter wheels give the bottom of the plow just about the right ground clearance when the axle sits on top of a 2x4.  The wheel spacing is maintained by washers on each side of the wheel bearings and an 8" piece of 3/4" PVC on the axle.  The axle is captured in holes in the 1x4 and retained by wood screws to plug the outside openings of the through holes.

A 1x2 rear brace seems like a good idea.

The nose of the plow is cut to accept a 2x4.  The front wheel is supported by aluminum plates on each side of the 2x4.  The hitch bar is captured by the 5/16" axle bolt.

The 1x4 sides get a vertical cut to trim them to the 17" final width.  Then the plastic sheet is applied and then the metal edging.  I used 22" long 16 Ga. galvanized deck strapping.

Update:  This plow did not have enough lateral velocity to clear the snow far enough out of the cut.  It has since been modified to have a nose half-angle of 30°.

30 degree plow
The sharp plow modified to have a 30° blade half angle and a 45° exit angle. 

30 degree plow bottom
Bottom view.

Also note that the hitch arm has been moved up above the front wheel.  This is an attempt to put the arm more in line with the attachment point on the bike and reduce the lifting of the nose of the plow.
It looks like a disadvantage is the plow tends to oscillate more.  I think this might be due to the high arm being more rigid than the previous attachments and also not "steering" the front wheel of the plow.  The old blue plow tracks well and steers a bit due to the slop in the axle bolt holes.

Modifications for 2008 include adding a box for a standard 1 gallon plastic milk jug and reinforcing the plow so another biker can rest their front wheel on the plow while they walk behind and use their bike to help push. 
Filling the jug with water adds enough mass to damp some of the oscillations and also forces the front wheel down.  The scooter wheels are narrower than my knobby bike tires so the 8 lbs. gets the plow to cut into the snow at about the right level.  Cut too deep and it is like tossing out an anchor.  Don't cut deep enough and the next bike sinks in.

30 degree plow bottom Left front view               30 degree plow bottom Rear view

The Rack Holder




Rack holder.  

This just uses a piece of pine "base" molding and two 1x2s.  The thin pine is wedged between the bike bag and the rear rack. The gap between the 1x2s captures the PVC axle tube.  The 1x2s just fit between the plow wheels to keep the plow from sliding side to side.

 
Plow stowed for transport.  Note that the hitch allows the plow to rotate so the bottom can face the bike's wheel.  This is perhaps my most notable innovation so far!

A "New" Bike and Bracket

In fall 2006 I needed to get my own bike since my daughter was taking hers to college.  I found a 1988 Trek 820 for $35. 


1"x1" Aluminum angle makes a bracket for the plow hitch.

Studded Tires

The extreme hard packed snow and ice conditions of 2008 have prompted me to get studded tires.  The Nokia W160 (26") have quickly shown to be well worth the investment.  I now must remind myself to not panic on glaze ice.  The only times I have slipped are when I stopped pedaling and tried to walk.
I have never enjoyed falling off my bike.  Falling in snow doesn't hurt too much but pavement rips my jacket, ice is dangerously hard and slush is cold and wet.
(Studded tires cost $30-$100 each depending on the manufacturer and model.  A trip to the hospital involves at least a $75 emergency room co-pay.)

A Better Cutting Plow

For the 2007-2008 season, I decided to revisit the dynamics of the plow in heavy wet snow.  The Drift Cutter works so well in all kinds of snow, I wanted to see if a similar shape would work behind the bike. 

Some observations of the behavior of wet snow led me to reconsider the shape.  As mentioned above, a problem with the Sharp Plow is oscillation, especially when clearing a bit of lumpy snow or slush in an already well established but packed trough.  The plow does not have enough mass to force the blade to cut the snow.  Rather, the snow pushes the plow to the side until it hits the wall, then the opposite blade bites into the snow and swings the plow back the other way.

A much more aggressive angle (large Theta) would cut into the snow and slush and have less lateral force to push the plow off course. Since wet snow does not "fling" off the plow very well in any case, I thought it might not matter too much what the initial contact angle was.



Top view of the plow with a 70 degree attack angle.

The lifting angle is 45°.  This seems to be a bit too steep.  The snow and slush tend to clump and not slide up or out as desired.

A plow with a lifting angle of about 25° has been tested. (Photos coming soon.)
Although the more aggressive angle of attack cuts lumps better and does not oscillate as much, the shape of the plow does not seem to move the snow to the side very well.  Snow builds up, the metal digs in and the drag goes way up.  This shape is great for the cleanup runs but I don't like to use it if there is any more than about an inch of new snow.

The 30° model is still the best plow for most situations.

Back to Page 1.
Created by Dave Peterson
email:   email address
Original: February 26, 2004
Updated: January 10, 2005, Feb. 2, 2005 with drift cutter. Feb.11, 2005 with Physics and the Sharp Plow. January 29, 2007 with modified sharp plow and new bike. January 28, 2008 with a better cutting plow.  Feb. 19, 2008 More plow photos, comments on physics and notes about studded tires.

Key phrases:
Bicycle pulling snow plow, Bike path plowing, Shoveling the bike path, A plow behind a bike, Bike Snow Plow, Clearing snow from bike path.  Snow Plow Physics.  A Sharp Plow.