Hi All, I have a question about the robot motor calculator on this site, I ran a 50 pound wheelbot, with two motors capable of going up a 6 degree incline, at 7fps, with 9"diameter tires. After doing some of my own old fashioned calculations for wheel speed at 7fps I came up with around 180 rpm, when I click the rad/sec and rev/min drop dopen I get 2010 rpm, that figures out to about 53 mph more or less a lot faster than I figured. Is there something I missed?
The torque came out at around 38 in-lbs, which seemed low to me I ran the same machine is a copy of RMSC (robot motor selection calculator)
and the speed came out close but the torque was over 200 in-lbs. again did I miss something? A “one stop” shop for the correct formulas to calculate these type of things would be real nice.
Regards Ryan
Let me try again
Mass=50 lbs
Drive motors=2
Tire radius=4.5 inches
Velocity=7fps
incline=6°
voltage= 24 volts
Acceleration=.2fps^2
operating time = 1hour
efficiency=65%
Please run again and I will do likewise, then we will compare notes OK?
The part that bothers me the most is the output rpm, and the torque required per motor.
Ok I ran it again and got 306.74 ozf-in converted to 19.17 lbf-in
the rev/in is still nearly 2000. see attached screen shot
http://img.photobucket.com/albums/v48/Earthshaker/Clipboard-1b.jpg
I am glad is was a bug, I have been checking all over the place and even did my own spread sheet, based on formulas from a “major” Hydraulics company I will check my results on here against the spread sheet, and see what happens. If the two results are close I will be a happy camper. If not back to the calculator.
Also just for the sake of discussion there are no data entry points for gearbox reduction on the robot motor calculator, this should be included somewhere IMHO, that way the speed of the motor and before the gear reduction could be compared, same as the torque result.
Thanks for checking into this for us 
Oh the agony of frustration. Ok I ran the problem again on the us site the speed came out OK, the torque was different but I may have changed something. Ok testing time, I invite anyone who reads this to try this spreadsheet I built. Let me know if there are any anomalies compare the results in the spreadsheet with as many other sources you can find.
I really want to get this ironed out and accurate (reasonably).
The spreadsheet is protected only, to eliminate data entry in the wrong places, it is not password protected. On some of the cells there is a small red square in the upper right-hand corner.
I do not know if it will work in anything other than Open Office-Calc. Have fun and report back to me via this thread or via PM.
Find the attached zip file inside is the .ods file.
I am guessing gravity is 32.16ft-sec squared, or simply 32.16 if that is the case
I will try it out, I am also guessing this is the father (master)equation, am I correct?
Hi TSPCO,
Inputting the following values:
Mass: 50 lbs
Drive Motors: 2
Radius of wheel: 4.5 ft
Velocity: 7 ft/s
Incline: 6 degrees
Voltage: 12 V (not changed)
Acceleration: 0.2 m/s2 (no mention otherwise)
Operating Time: 1 min (not changed)
Efficiency: 65% (not changed)
Gives the following values:
Angular Velocity: 160 rev/min = 160rpm
Torque: 256in-lbs (converted)
Check the calculator again - perhaps one of the units was not changed? We certainly appreciate your feedback and encourage everyone to try to find errors or suggest improvements to the tools.
Hope this helps,
Hi TSPCO,
You have indeed found a bug. We compared the dynamic tool on the .us website and compared the results to the .ca website. The .ca website has since been changed. You should get the following results:
Angular Velocity: 178 rpm
Torque: 306.74 oz-in
Hi TSPCO,
The easiest thing to do would be to compare the final equation for torque with that of the tutorial (you can also follow the steps used to derive this equation):
http://www.robotshop.ca/content/images/learningcenter/teff.gif
a: robot’s acceleration
g: gravity
theta: angle
M: total mass of robot
R: radius of drive wheel
N: number of drive wheels
e: efficiency
Note again that the torque found is per drive wheel and factors in inefficiencies.
Hi TSPCO,
Correct. You can also take a look at the tutorial that goes along with the tool. For simplicity, all non-metric values are first converted to metric prior to being used in the formulae, then converted back to imperial for the output. Therefore the value of 32.16ft/s^2 is not used in the calculations. The conversions are hard coded.
Hope this helps,