Arm calculation

To rotate a robot by 90 degrees that is 29" long which weighs 160lbs or 72.6kg, with uniform mass distribution, in 3 seconds, it takes a whopping 90 watts, and 262nm (193lb*ft) of torque at minimum and assuming 100% efficiency. Things are never 100% efficient, assuming 70% as an average efficiency for the lifting system, we need 130 watts and 374nm. The torque calculated is at the shaft of the arm. This solution makes sense to me since we were able to lift the 2010 robot to 90 degrees in less than 3 seconds at full power if I recall correctly.

Using a single full sized cim motor driving the shaft, this calls for a minimum reduction of 155:1. That estimation is not a good one since it uses stall torque, and motors dont spin too quickly when stalled out. In fact, they don't spin. Looking at the motor curve, I would recommend a minimum reduction of 312:1. this will allow the robot to be lifted in a minimum time of 1.88 seconds and better prolong the life of the motor.

There are a number of assumptions that were made, including the following:
treating the robot as point mass, at its centre of mass
the calculation was made to 90 degrees because that is where one of the highest energy points is, and it makes calculations easier

I would consider the solution to be in the ball park for power and torque required.

Do you Ken remeber the reduction we used in 2010?
Did we also have the cable loop back around a pulley.
Now I know the winch pulled on the arm.
I also remember it to be reasonably fast but it could have been faster.

I believe it was a 16:1 we used in 2010

I just put a post up and it did not work so I am typing it again.
A planetary gear box from anymak with 3 stages gives 181:1 reduction
GEM 500 Gearbox, 1 stage (am-0449)
The rest could be done with chain at 1:2
Or only 2 stages and more chain reduction

Andymark is already out of stock on some gear units.

This could become a problem.
I think we need to wait to determine more design and also team structure
but if parts are not available as has happened in the past we may need to rethink things.

Rahul's team roll is parts organizer.
I will ask him to come in and look for the winch that we used in 2010 tomorrow so we can see what gear ratio was on the motor.

There is atleast 1 gem500 gearbox kicking around in the school parts bins somewhere, its a heavy chunk of metal.
The gem gearboxes and stages are in stock from what I see, in total according to andymark, the weight of the gearbox alone would be 3.8lbs or 1.81kg, about 3.6 500ml bottles of water.

http://www.andymark.com/product-p/am-0270.htm
http://www.andymark.com/product-p/am-0301.htm

Andymark also has a worm gear box which might me more ideal because of the braking ability. It does only have a 16:1 reduction, so it would need to be coupled to another gearbox to be practical, and it uses nylon gears, although they have large teeth.
http://www.andymark.com/product-p/am-0917.htm

Here are some weight figure that would be added by this method as compared to a power take off
Weight: 1.8 pounds----- single stage planetary
Weight: 0.2 pounds --- speed control
Weight: 2.82 pounds ___cim motor
I could not find weight for 3 more stages of reduction but iwould guess at least 1.5 pounds
Total 6.12
This figure will be doubled so
12.24 pound increase as compared to a power takeoff where only a servo and a ½ inch shaft and maybe a gear or two.
Weight –estimated 1 pound doubled
2 pounds

But even taking power from the drivetrain, we will need atleast 181:1 between the 2 motors and the arm shaft. 5:1 or 6:1 would be the maximum feasable amount to get out of the gearbox and the rest has to be done somewhere

I think the gear boxes we have have the following
24:1 low
9.4:1 high

Depending on how a take off shaft is installed more reduction can happen in the box.
I do not understand your reduction figures (Ken)

I think that not a lot of reduction should be done with chain.
The arm shaft gets moved in from the edge of the frame with a larger sprocket.
Max. 3 inch sprocket, maybe????

There is good points on each method, seperate winch or take off shaft.

I am done tonight

Will, matt, Adnaan and I discusses an idea that may be able to utilize all the drive motors on one arm and pivoting the robot that seems feasible but I haven run any numbers on it yet