FTFY. The power out of a gearbox is the same as the power into the gearbox, minus any inefficiency in the gearbox. The power is neither geared up nor geared down.
If obtaining or making gear is box out of question, consider 2 stages of chain reduction - 5:1 each?
This is what I would suggest. When I was a rookie in 2004, and COTS gearboxes weren’t easily available, we had to make a drivetrain using two stages of chain reductions.
You are going to have a hard time doing more than a 3:1 per stage with shaft driven sprockets, since the large tooth counts tend to be plate sprockets. Not sure what size sprockets are easily available there.
Yes, though it’s partially based on the assumption that the strap we’re using doesn’t wrap exactly straight (which in our testing it typically does not). Even so, you need about an inch of extra strap wrapped up before it starts to cause problems.
If you don’t mind the slower speed a 15:1 will give a more comfortable margin.
To sort of cut through what has been posted – a single CIM has PLENTY of power to execute a robot climb in a very few seconds. The key factors are – did you gear down enough so that you can wind up on your drum diameter? How much will your effective drum diameter increase as your rope wraps on top of itself? As a reference point, 3946 is planning to wind some 3/8" line on a 1/2" shaft with a 12.75:1 reduction. Our biggest problem appears to be keeping the rope centered on the robot. Larger diameters will require more aggressive gearing, but will be less susceptible to a wrap or two of line.
He’s not using a strap. He’s using a 1.5 cm diameter cord:
Didn’t see that response.
In that case would depend on how that specific cord wraps up.
The example I gave was based on my own testing and estimates, individual results may vary. :rolleyes:
Maximum robot mass = 70 kg. Maximum robot weight = 70 x 9.8 = 690 N.
Effective winch radius = (winch diameter + rope diameter) / 2 = 2.25 cm.
Winch torque needed to lift robot = 2.25 x 690 = 1550 N-cm = 15.5 N-m.
At maximum power, CIM motor torque = 1.2 N-m.
[Note: climbing is fastest at maximum power.]
Climbing time = lift height x robot weight / winch power = 1 meter x 690 N / 330 W = 2.1 sec.
Gear ratio required = 15.5 / 1.2 = 13:1.
Andymark Toughbox with 12.75:1 ratio is in stock as I type this.
All of the above calculations are simplified by neglecting fricition losses. A real robot will require more climbing time.
You’ve described very well. Thank you all. I’ll inform you about the advancements.
If we can find a gearbox, which model do we need for CIM motor? 15:1 Ratio
Thank you.
For a direct 15:1 ratio you could get a VexPro VersaPlanetary with a 3:1 and a 5:1 reduction (which combine to create a 15:1), you would also need a CIM Adapter and 2 ring gears.
Alternatively you could buy this 16:1 BaneBots Gearbox from AndyMark that comes with all the parts you need (though costs more).
You could also use a ToughBox Micro with a 12.75:1 ratio and add a sprocket reduction using a 12 tooth and a 15 tooth sprocket.
I believe both Vex and AndyMark ship internationally.
Can we use Gearmotor am-2971?
http://www.andymark.com/PG71-Gearmotor-With-Encoder-p/am-2971.htm
Or we have a planetary geared motor similar to this:
Not without a sprocket reduction between the output shaft and the shaft of your climber, even then chances are it won’t be able to lift your robot all the way up the rope within the 30 second end game period. It has 1/10th the power of the CIM, so it will be much slower compared with a properly geared CIM.
If you want to continue to use your current setup, it shouldn’t be too difficult to integrate a Versa Planetary into it as it has the same mounting holes as the CIM ( you’d would probably need to use a different sprocket).
You might not have enough time to get it done before Bag day, but I’m sure there would be plenty of teams who would be happy to help you get it working at the NYC regional.
Just realized you guys will be at the nyc regional. I’ll be there all 3 days without too much to do so if you need me to I an bring some versaplanetary parts and I can help you guys get running.
In theory, any motor can lift anything, if geared properly. But the power of the motor will determine how fast it can (theoretically do so).
Do you have someone local (a physics teacher, perhaps) who can help you with the math?
I was responding to someone from Turkey who appeared to have neither an engineering background nor English as a first language. Assuming that, I tried to frame my response in simple terms.
“Gearing up” is a phrase that typically refers to changing to a higher gear, either in a car or a bicycle, resulting in more speed and less hill-climbing ability. And, vice-versa. I did not think that a treatise on work per unit of time, torque or RPM was necessary - or helpful - in this instance.
Similarly, given that the team is in Turkey, it might not be helpful for any of us to advise ordering this or that gearbox from AndyMark. (he asked, “Can we find another solution but using gearbox? On the motor side small gear, on the shaft side big gear possible?”) Just sayin’.
I understand you were trying to help, and I applaud that.
But I guess we’ll just have to agree to disagree whether it is clearer or more confusing… especially for other students reading this thread who are just beginning to understand the concepts of torque and power and gearing.
No treatise is necessary. Maybe just a footnote.