Is there a difference between force and load weight?
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So I was just running some numbers on the the stingray, im basically just trying to make a quick refernce sheet for my self with all the numbers I would ever need for motor control. When I calculated the force(F=Torque/Wheel Radius) or (1.89=4.6lb-in/2.423) I get about 1.9lbs per wheel, but when I run all the sting ray numbers through the robot shop motor sizing tool, It tells me at a 0 degree angel I can carry 13lbs at a max speed of 6.59ft/sec with an acceleration of 6.59ft squared/sec. Now I know force is pushing power so according to my math the sting ray can push 3.8lbs with no angels involved, put wouldn't force also include weight pushing own on the robot?
This isnt all so important, I was actually trying to decide how many slices I wanted in my encoder discs, but somehow got sidetracked making a cheat sheet for important numbers and equations.
This isnt all so important, I was actually trying to decide how many slices I wanted in my encoder discs, but somehow got sidetracked making a cheat sheet for important numbers and equations.
Comments
That is why you put things you want to move on wheels. Ex. if you put a 100 lbs of rocks in a cart, it may only take 10 lbs of force to move it. You would only need a 100 lbs of force if you wanted to lift the cart up.
Al
How does one manually calculate, the amount of load weight, given a 0 degree angle and target acceleration value? I know calculators can do this well enough but id like to know how its done by hand.
John Abshier
Agreed.
This topic has came up with your other bot.
Obviously a robot can carry a lot of weight without any powered motors, if it's going down hill. Theoretically any motor that can overcome the friction of the robot's system could move any amount of weight on a level surface. You could use the torque to calculate possible acceleration and how steep of slope the robot could overcome but it's often just easier (with these relatively small robots) just to try it.
It is a good idea to "run the numbers".
As mentioned the torque of the wheels don't really tell much about a robot's load carrying ability but it does tell you something about the robot's acceleration and hill climbing ability.
I think your previous robot could have theoretically climbed a vertical wall (if it had enough traction). This new robot can climb a 54.4 degree hill if it had the required traction.
Angle = arccosine(7.56 lb force from wheels / 13 lb force on robot from gravity)
Force resisting robot motion from weight of robot = 13 lb * cos(angle of slope robot climbs)
The above assumes no friction (which dosn't happen very often). I also used the words "from weight of robot", this is the gravitational force, there's also a resistance to acceleration caused by the mass even without gravity. (As you may have guessed, this can get complicated, hence the "try it" advice.)
BTW, if you get a chance to take a physics class, I'd suggest you do. Lots of useful stuff to be learned in a physics class.
There ought to be some 'rules of thumb' about this. For instance*, an all terrain outdoor robot should have enough torque to climb a vertical wall, a carpet running bot should be able to pull 40% of it's weight up the wall and a hard level surface bot, 15%.
* all numbers pulled out of thin air