# [Feasibility] Spider (Hexapod) carrying and firing a 4-pound nerf gun

Dear all,

I saw some examples of hexapods ("spiders") built using Arduino:

I also have a Nerf Hyperfire (https://www.amazon.com/Nerf-N-Strike-Elite-HyperFire-Blaster/dp/B018KLHT5O/) whose dimensions are 4.1 x 12.1 x 24.1 inches for 4.1 pounds.

I was wondering if the examples of hexapods mentionned above would be strong enough to carry the Nerf gun ? If not, would you know any example of hexapod that could carry such a gun ? If still no, should I consider it's not possible ?

Thanks a lot for your help !

flmart: I was wondering if the examples of hexapods mentionned above would be strong enough to carry the Nerf gun ?

What do the sellers have to say about that? They do look really really small compared to that massive gun. Get the size (and weight) of the hexapods and compare it to your gun. If the hexapod is less than half the size/weight of the gun, no chance.

Quickly browsing the reviews also gives you good clues, such as one comment with the arcbotic thing: "The servos these ship with are useless, they cannot lift the body."

The Elsky weighs less than a pound so that is unlikely to work.

The Hexdrake project could be scaled up to use larger servos. There is probably SOME model of servo that has the torque you will need.

Calculating that necessary torque may not be easy. The servos that sweep the leg left and right probably don't need much. It''s the ones that move the feet up and down that have to do all of the lifting. Figure three legs will be supporting the weight at any one time. I'd guess the body weight including the Nerf gun at about 6 pounds. For a safety margin I would expect three pounds per leg. Multiply by the length of the leg in inches to get the required torque in pound-inches.

The SG90 servos are rated 17.5 ounce-inches or about 1.1 pound-inches. Divided by the three pound load per leg gives you a maximum leg length of 0.37 inches. That's not going to be practical. I would guess you will need a leg length of at least three inches so you need a servo that can provide more like 9 pound-inches (144 ounce-inches) of torque. That's about 8 times the torque of the SG90.

Good luck!