Wednesday, May 18, 2016

Meet Walter "the Weeder" - Chemical Free Weed control - automated!

Walter has arrived!  Walter the little sprouts weeder robot!

If you remember last year, we toyed with the idea of heat based biological safe weed control . And those tests were quite successful! You can browse through the blog post and see our test plot of using heat to treat the ground before planting.. and the huge difference it made in subsequent weeding.  The use of heat killed sprouted weeds, but also weed seeds, so that the newly planted veggies have little competition during their critical first few weeks.  It is a great no chemical way of weed control!

But ... the down side, our first attempt was VERY labor intensive. So much so  that we actually gave up half way through. We had mounted a propane infrared heater behind a metal 4 wheel wagon and manually pulled it along. Way too heavy, way to slow. Not practical even for the weeding savings.

So.. this year.. we made WALTER! we gave him a name because watching this little guy work is like watching a robot. He slowly plods along burning the weed seeds in the ground as you sit back and watch . Its a BEAUTIFUL thing!

So here is how he works.. We have a few pictures and a couple videos to explain the design. The basic setup is :

  • Pulling engine
    • a 120 volt winch mounted to a pallet
    • a long metal cable (340 feet!) of a very thin diameter
    • some safety switches
  • Burning platform
    • a 120,000 btu propane heater mounted on metal skids
    • a wooden cart on skids to hold the propane tank
    • some safety switches
  • Safety features
    • the pulling engine has a pipe that works to kill the winch when the burning platform gets close enough
    • The burning platform has a pipe that hits the pallet when it gets close and kills the propane burner
That's Walter! Just line him up, turn him on, and for the next 35 to 40 minutes he patiently burns the ground on a 340 foot row.  The ground is hot, very hot, so hot that a foot behind Walter, you can not hold your hand against the ground. I have not measured, but suspect it is about 120 degrees , and probably about 150 to 200 under the burner.  Hot enough to penetrate a quarter to half inch and kill many weed seeds, but not hot enough to kill the subsoil organisms underneath. 

Some pictures of "Walter the Weeder"

The burning platform, first run. As you can see below, we actually had to change the pull method from the sides to the middle back, becasue this one caught too much dirt by digging in too low in the front. The changed version below worked much better

Propane tank on the holding platform with skids. There is room for two tanks, but used only one today.  The cable attaches on the right of the picture to pull it. The rod at the bottom is the burner safety setup. AS the platform approaches the pallet of the pulling engine, the pipe hits the pallet, slides through the pvc housing, and hits the switch, which turns off the propane burner.

Closeup of the burner safety switch. The pipe gets pushed from the left, through the pvc housing, and the end (wrapped in duct tape) hits the switch (covered with a pad of duct tape). The contact is enough to flip the switch, but then the pipe keeps pushing back without breakinging anything. This allows the burner to turn off long before the winch quits pulling, making synchronizing the two easier. 

View of the burning platform from the front.  The plywood plate on the bottom right of the pic is where the winch safety switch hits the platform to kill the winch. 

Walter in operation! This is the full 330 foot row.  Can you see the pallet??

The updated setup. Instead of a wire down both sides, we put a eye hook in the center of the wooden platform, and ran a wire from the two burner skids through the eyehook That keeps everything going straight and adds just enough up pull to keep the burner from digging into the dirt. 

Closeup of the updated pull system. 

This is a closeup of the winch safety switch on the engine platform. The pipe is inside the pvc housing going to the right, and the end of the pipe is a big ball of foam, wrapped in duct tape. As the rod gets pushed inside the housing from the approaching platform, it slides in  and hits the switch mounted in the brown housing. That switch kills the winch. It takes a few seconds to come to a stop, so the end of the pipe is about 3 inches of foam, plus the actual switch is mounted with a half inch of foam between it and the housing. That provides enough play to keep everything stable, but let the winch come to a halt without breaking anything. 

Engine pallet platform from the burner side That cable going off the bottom is 340 feet of 1/16 inch metal cable. Safety strength is about 100 lbs, enough to pull the burning platform but small enough to fit all that cable on the winch pulley.  The rocks are added weight to keep the pallet from moving towards the burning platform. It takes about 50 lbs to keep the pallet stable. 

Another view of hte pulling engine. The original winch controller is still attached and works, to manually pull the cable in when necessary.  the plywood plate on the upper right is the plate that the burner safety switch hits to kill the burner when it approaches the pallet. 

And now the fun part! a video of Walter working away!

This first video is the burning platform moving. It takes about 40 minutes to complete the 340 foot row. The speed changes of course as the winch winds up the cable, which is a problem to be solved next year.  This is the speed at the far end, when it is just starting. 

The next video is the winch engine pulling. The cable actually wrapped up quite nicely! The motor didn't get too hot running that long, since there is only about 50 lbs being pulled. 

The last video I tried to capture the safety switches running at the end of the row to safely shut Walter down. First the burner safety switch activates to turn off the burner, then the winch switch activates to shut it down to a rest.  I started the video a little late, so its hard to see the first switch activating, but its there in the first 2 seconds. 

UPDATE! Here is a better video of the end of a row showing the safety switched working

Overall we are VERY pleased with Walter... He performed beautifully with only the one small change. I would love to get some temp readings if we have time.. but the priority now is getting these seeds in the ground. 

We may be making Walter available for rent, to anyone local that wants to use heat weed control in your own garden. If you are interested, contact us and lets talk. 


  1. For those interested... It takes right at 30 minutes to burn the current 110 yard row, and about 5 minutes to reset for the next row.

    one correction, the burner we are using is only 60,000 BTU, not 120 as listed above. Sorry for the mistake.

  2. Hey, this looks cool! Thanks for inventing it and sharing! You might want to either 1) get a patent to protect it, or 2) state that it is open source so someone can't steal it.