New motor/speed calculator available for testing.

[nottoooily]

Hello.

I've made a calculator which I think will be directly helpful for a lot of people trying to predict how fast their robot will go with a particular motor. Admin's tentatively put it up here:

http://www.societyofrobots.com/robot_speed_calculator.shtml

It usually takes quite a bit of maths to predict how long a vehicle takes to accelerate up to speed under linear acceleration. The calculator solves this for you to quickly give a feel for the expected performance.

It compliments Admin's existing RMF calculator by using different variables which may sometimes be more easily available.

Please have a got on it and let me know what you think. Especially:
Is it helpful?
Is it easy?
Is it confusing?
Is it wrong?


Cheers.

[waltr]

Just gave it a quick try with the values for my bot.
It indicates that the bot will reach 50% of top speed in -9.01 sec. The negative sign is a problem and I know my bot gets up to speed much sooner than 9 sec (measured less than a sec).
Also the time to 50% and top speed is the same for a level surface as it is for a 50° grade.

Thanks for the new calculator. I'm sure its just a small bug on the time numbers.

[nottoooily]

Cheers.

Negative results can come from invalid inputs. Or maybe an unknown bug. Can you tell me your input values?

[waltr]

Sure, I could have the incorrect assumptions or conversions.

mass = 0.5 lb (8oz)
RR = 0.02 lb (just a guess)
angle = 10°
Wh Dia = 0.137 ft (1.65in)
no load speed = 120 rpm
stall T = 0.052 ft-lb (10oz-in)

[nottoooily]

Cheers. There's a couple of mistakes in my equations. I'll re-work it and be back.

But can I ask if the top speed was OK? 0.80 ft/s uphill and 0.85ft/s on the flat.

[waltr]

Ok, a little tweeking of the calcs.

 The top speed of the motor un-loaded with those wheels would be 0.86ft/s so the top speed numbers look very good.

[JamesG]

I don't know if you've fixed the calculator yet, but I also don't seem to be getting the right values for the acceleration time. In my motor calc thread I had calculated that the robot would have about 3.6m/(s^2) of acceleration which should (according to v=v0 + at) reach the top speed of about 2-3m/s in about 1s or so. Your calculator says it would take 3.47s for 50%.

Also, when I was playing around with values I noticed that the relation between torque (in kg*m) isn't linear with the time required to reach max acceleration, which doesn't make any sense does it? Surely the more torque, the higher the acceleration, regardless?

James