Front and rear bumpers.
The front and rear bumpers are made from 40mm x 2mm flat aluminium.
The aluminium came in a 1 meter length, so I cut it in half to form 2 x 500mm pieces.
I curved the bumpers to a radius about 18mm greater than the radius of the bottom deck. The best I could get was to carefully bend the aluminium around the deck, then carefully spread it back to increase the radius. This was not an easy job as it is so easy to get tight bends and flat spots!
The 40mm angle brackets I used came with 2 holes on each side, but needed drilling out to accept the 6M bolts and the momentary switches, on one side. I then fitted 2 x 3 sets of brackets to the underside edge of the bottom deck with 4Mx20mm bolts.
The bumpers are attached to the brackets with 6M x 30mm gutter bolts. I used gutter
bolts because they have quite a big head, which allows a bigger hole to
be drilled in the bumper, to allow for the bumper to slide over the tube.
When marking out the position of the holes for the bolts on the bumper, I centered the 2 bracket holes to the center of the bumper, then marked these 2 positions along the length of each bumper with a pencil.
I fitted the momentary switches to their correct position in each bracket. The outer brackets
use the top holes, and the middle brackets the bottom holes.
I drilled a hole for the bolt in the top/center position in each bumper, then attached them to the center brackets, tightened the bolt so it just touches the momentary switch.
Note: I placed a small piece of tube over the bolt, and the holes drilled in the bumper must slide over this tube, as when the bolts are tightened up, they do not move. The tubes should be about 12mm long, The tube I used was from an old writing pen.
Now the positions for the outer bolts can be marked an drilled.
Springs are fitted around each tube, between the bracket and bumper. I had to cut the springs from a larger spring, then trim pieces off to get an acceptable return. These help return the bumper to its correct position after a collision.
Each bolt should be carefully tightened so that the bumper just touches each momentary switch,
so that the slightest touch on the bumper will trigger the switch.
I had to put a packer between the switch and bumper to get the correct distance. The
packers I used are self-adhesive gliders, used on the bottom of furniture legs to help them
move easier on carpet etc.
Note: There is a nut on both sides of the bracket to hold the bolt in a fixed position. The bumper slides over the tube when compressed.
Top view of miRover2's front bumper.
Bottom view of miRover2's front bumper.
Close-up views of miRover2's front bumper. Left is from below, right is from the side.
(Note the packer between switch and bumper.)