Hello Everyone
The only guy on our team who knows about the gear ratios and gear box has graduated. And I am taking his role this year. What I need is how to calculate gear ratio and torque calculations. Anyone can help me is greatly appreciated
Thank You
Try looking through the white papers. When I was trying to learn about this kind of stuff I found this one really helpful to get started. Once you’ve learned all you can from that try looking at some of the other papers about different gearbox designs like the TechnoKat’s for shifting or the Who’sCTEK’s for combining motors. If you need any help beyond that try asking around. I’m sure most people here would be happy to help answer any questions you have.
A quick search provided this: http://www.chiefdelphi.com/forums/showthread.php?s=&threadid=14261&highlight=help+gear+ratios See, I was once right at your current point and today I am the drivetrain master of my team. This quick explanation I believe will serve you well.
Thanks guys
How do you calculate torque of the robot with T=F*D and how do you calculat force
Well, say you have a motor with 20 ft-lbs of torque and spins at 400 rpm. (just an example by no means a realistic figure) It has a 20 tooth sprocket on it. Your wheel has an 80 tooth sprocket on it that is linked by chain to the one on the motor. You now have a reduction of 4:1. The torque is increased four times and the speed is reduced by a factor of four. The wheel has 80 ft-lbs of torque about its axis and is moving at 100 rpm. Still with me?
For the force, it depends on distance, which in this case is the radius of the wheel. Given perfect traction, a smaller radius wheel will place more force on the ground than a large radius wheel. If there is 80 ft-lbs of torque about the axis of the wheel, and the wheel is 2 feet in radius, 40 lbs of force will be applied by that wheel to the ground.
Now, if you have the same setup on the other side of your robot, you will now have two motors, two reductions, and two wheels. Together, they will provide 80 lbs of force. This means that if the robot had the traction to be driving straight up a wall, it could have a total weight of up to 80 lbs ad still be able to maintain movement in the upward direction.
Sanddrag is right, as the rpm’s reduce, the torque proportionally increases.
But, don’t forget efficiencies and losses.
On a simple application where you have two sprockets - one on the output of the motor (or gearbox) and the other on the wheel, there is a simple loss in the chain system. I estimate this loss at about 2-5%, depending on sprocket alignment and chain slop.
Then you have losses in the wheel rotation. For a simple system of one properly-aligned driven wheel, then the losses are minimal. If this output sprocket is driving more than one wheel, or if the wheels are misaligned, or if the sprocket is driving treads, the the losses add up significantly.
These losses is where alot of teams get in trouble. If the wheel system is free of these losses and mis-alignments, then you can translate your torque calculations and rpm reductions (with minimal losses along each step of the way) as Sand said above.
Good luck.
Andy
I did a presentation at the Novi Kickoff last year called “Motor Selection & Drivetrain Sizing” It has a lot about gear ratios, friction, and motor sizing. it is located here
-Paul
Thank you all. They are really helpful
If anyone has any additional questions on this PM me and I’d be glad to explain it further or e-mail you a (different) powerpoint I have.
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Hi
I know there are a lot of topics about multi-motors gearbox and I read some of them. But, I found that they don’t actually tell you how to calculate or balance the different RPM ratio. Anyone who can help me please e-mail me at [email protected]
thanks