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Arduino R/C Lawnmower (painted)

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Step 6: Mounting the motors

Picture of Mounting the motors
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This was the most difficult part to plan out on the frame. We need the motors to be adjustable so we can adjust the tension of the chain, however they just have 4 holes in the bottom of each motor and nobody makes a mounting plate that I could find.  

The simplest way I could come up with was to mount the motors to an 8" long piece of 2" angle-iron, and then mount that piece of angle iron to the frame through some specially cut holes that allow the motor mount to travel forward and backward (but not side to side) along the frame.

Make the motor mount plate:

Cut an 8-10" section of 2" angle-iron, depending on how much room your motors need to mount. Mine only needed about 4", so I made it 8" to have plenty of room for the mounting bolts. Drill a hole about 1.5" from each end of the top of this bar, this is where the mounting bolts will go through the frame.

Mount the motor to the motor mounting plate:

Now you have to find the center of your motor mount plate (the 8" long piece of 2" angle iron) and measure the mounting holes on your DC motors. Use a sharpie marker to plot the hole pattern from the motor, centered onto the motor mount plate.  My motors have (4) 1/4" diameter tapped holes in a rectangular pattern on the bottom of the gear box.

Drilling and cutting the adjustment holes on the frame:

Next you need to drill and cut the holes in the frame to let the motor mounting plate become adjustable. I cut these holes using a dremel tool and a cutoff wheel. You have to line up the motor mounting plate (with motor mounted preferrably) onto the frame rail and use a sharpie marker to mark where the holes will need to be on the frame rails. Start as far back as you can (without hitting any other bolts underneath the frame), and mark the center of each hole. Then move the motors forward 2" and mark the holes again. You want to cut the holes out of the frame so that the motor mount plate (with bolts going through the frame), can move forward or backward about 2". The holes in the frame are the width of the bolt and about 2" long. I drilled 1 hole at each end and used the dremel to cut out the rest.

The holes drilled in the motor mount plate are just single holes for the bolt to fit through, the holes through the frame were cut with a Dremel tool with a cutoff wheel to make channels for the motor mount bolts to travel forward/backward through. You want the 2" angle-iron motor mount bracket to set as much on top of the main frame rails as possible, the bolts (which you can't see with the motors mounted) that hold the motors to the motor mount plates will keep the motor mount plate  from laying flat against the frame bars. Go ahead and mount the motors loosely to the frame using 2 bolts on each.

Cutting and connecting the chain: 

Now get your 10' of #25 chain and wrap it around the main drive sprocket on the wheel. With the motors pushed all the way toward the back of the frame (closest to the drive wheel sprockets), wrap the chain around the motor drive sprocket and mark where they overlap. You need 2 of the universal chain links from to connect the 2 loose ends. Cut the 2 pieces of chain and connect them to each side with the universal links to connect them.

Tensioning the chain:

Push the motor mounts forward until there is good tension with the chain, and tighten up the bolts that hold the motor mount plates to the main frame.

Now you can generate electricity. Connect a voltage meter to 1 set of motor terminals and push the bot around.
 
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