Do I Need #35 Chain?

[Mastermime]

Hello everyone,

I am building a 200 pound search and rescue robot that will be carrying 200lb loads.  I am using two 400 watt scooter motors with a tank track assembly.  I am using #25 chain.  My calculations of using two 400 watt motors were based on analogies.  If one 300watt (e300 razor electric scooter) can go 15 mph with around a 200lb load, then I figured 800 watts can provide enough power for the 200 pound robot and the load it will carry along with the coefficient of friction of the treads. 

First question is, will the robot be able to pull 200 lbs at 10 mph? Yes, I calculated the gearing so it will go 10 mph with the treads, but will it have the torque for inclines and terrain it may encounter? I'm new to this so I don't have much expertise so that'd be great if someone could who has some more experience could give me their expertise. 

Second question is; will #25 chain be suitable for this robot or will it break in mid operation?  I've read that the tensile strength is 925 lbs but the connecting links are weaker?  Should I go with #35 chain or would it be ok to keep the #25 chain that's on the robot right now?

Thanks

[jwatte]

On flat ground, the cool thing with torque is that you only need to overcome the friction; any amount of torque over that will make you /eventually/ reach your goal velocity (modulo air drag and other high-speed phenomena :-) More torque just means faster acceleration.

Once you start climbing hills, torque to overcome gravity becomes more important. The math is still pretty basic: Mass times turning radius (divided by gearing.)

[Soeren]

Hi,

My calculations of using two 400 watt motors were based on analogies.  If one 300watt (e300 razor electric scooter) can go 15 mph with around a 200lb load, then I figured 800 watts can provide enough power for the 200 pound robot and the load it will carry along with the coefficient of friction of the treads. 

Given all things like speed, gearing, wheel size etc. are kept the same, then, when the weight is increased with a factor n, you need n^2 times the power - that's why it's a very good idea to keep things as light weight as possible. (And if you halve the weight, you only need 1/4 power)