bike4life
Well-Known Member
Right now i am working on my predator 212 rear drive...
It consists of a mounting plate i made out flat bar section of thickness .375" and width of 6". This is pretty beefy stuff, and most commercial ones in kits are probably stamped sheet metal. but the plate needs to span around 20" because its a custom set up, therefore there will be quite some deflection without reinforcement.
The moment of inertia of this section is 0.026. Under 20" span it would not meet tolerance.
But by simply welding an 2.5" x 2.5" x 1/4" thick angle iron to the bottom of the flat bar stock, forms an L channel like thing.
The moment of inertia of this section is around 1. Which is nearly 40x stronger..... 1/0.026. This surely passes tolerance...
Because as a rule of thumb strength is proportional to depth cubed in a pure shape, by adding that 2.5" angle iron underneath the mounting plate which is only .375" thick, you get about 6x the depth, but once cubed, you get 216, but because its only 2.5" angle iron and not a continuous rectangle solid of 2.5" thick flat bar, its only 40x stronger.... Which is still a massive improvement for not much extra cost and weight.
The new mounting plate can withstand 2000lbs of center loaded weight and be ok, only deflect 1/100 inch. The old plate barely took 200lbs and that was with an 1/8" delfection. I think the weak point would not be the plate, but obviously the welded connections to the frame here... The thin wall steel tubing of the frame isnt that strong, and my welds arent either lol. So far the rear drive is making good progress. Probably be 2 weeks left.
It consists of a mounting plate i made out flat bar section of thickness .375" and width of 6". This is pretty beefy stuff, and most commercial ones in kits are probably stamped sheet metal. but the plate needs to span around 20" because its a custom set up, therefore there will be quite some deflection without reinforcement.
The moment of inertia of this section is 0.026. Under 20" span it would not meet tolerance.
But by simply welding an 2.5" x 2.5" x 1/4" thick angle iron to the bottom of the flat bar stock, forms an L channel like thing.
The moment of inertia of this section is around 1. Which is nearly 40x stronger..... 1/0.026. This surely passes tolerance...
Because as a rule of thumb strength is proportional to depth cubed in a pure shape, by adding that 2.5" angle iron underneath the mounting plate which is only .375" thick, you get about 6x the depth, but once cubed, you get 216, but because its only 2.5" angle iron and not a continuous rectangle solid of 2.5" thick flat bar, its only 40x stronger.... Which is still a massive improvement for not much extra cost and weight.
The new mounting plate can withstand 2000lbs of center loaded weight and be ok, only deflect 1/100 inch. The old plate barely took 200lbs and that was with an 1/8" delfection. I think the weak point would not be the plate, but obviously the welded connections to the frame here... The thin wall steel tubing of the frame isnt that strong, and my welds arent either lol. So far the rear drive is making good progress. Probably be 2 weeks left.
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