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: Upward Gearing 3:1
: Upward Gearing 3:1 -- S. Kerns	Post Reply	Top of thread	Forum

Posted by: randykimball ® 07/03/2008, 15:37:52 Author Profile eMail author Edit

Welcome aboard. Well, there is one thing you must take into consideration. Anytime you increase RPM you decrease torque. You can think as if you trade torque for RPM or trade RPM for torque when you are doing gear range changes. This is exactly why you have a transmission on your car. Also, you loose some torque due to friction losses, and you loose more if you increase RPM. So... for the sake of simplicity, if you double the RPM you loose more than 1/2 the torque... or if you cut the RPM in half you come close to doubling the torque. Does this help? The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them. Modified by randykimball at Thu, Jul 03, 2008, 15:39:09

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: : Upward Gearing 3:1
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Posted by: zekeman ® 07/03/2008, 23:22:54 Author Profile eMail author Edit

Why not use a DC servo motor which are widely available and can get you that speed (4500 RPM) and more directly without any gearbox?

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: : Upward Gearing 3:1
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Posted by: S. Kerns ® 07/03/2008, 16:09:08 Author Profile eMail author Edit

Hi Randy, Thanks for helping. Every gearbox that I've worked on in the past has been a reduction drive. I haven't had the need (until now) to increase the RPM's from the motor shaft. I need to move a screw (with a .2 lead) at the rate of 15 inches per second. The Compumotor MPP1428Q41 meets my requirements if I can gear it up 1:3 Could I use The Boston Gear PL2142 Reduction Drive (3:1) in reverse to give me the 1:3 gear ratio?

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: : : Upward Gearing 3:1
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Posted by: Jboggs ® 07/03/2008, 22:14:24 Author Profile eMail author Edit

Have you checked the stiffness of that screw at that RPM? Sounds like you might be getting into a very dangerous region of "whipping" the screw. For high speed applications, I prefer belt drive actuators. I would recommend that you run this one by the screw manufacturer.

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Posted by: S. Kerns ® 07/04/2008, 10:39:38 Author Profile eMail author Edit

Originally posted by zekeman: "Why not use a DC servo motor which are widely available and can get you that speed (4500 RPM) and more directly without any gearbox?" The torque falls off badly in that RPM range for the servo motors that I am aware of. Take a look at the torque chart for the Compumotor MPP1428Q. The screw needs to apply a force of 500 lbs per inch over 6 inches. _______________________________________________________________ "Have you checked the stiffness of that screw at that RPM? Sounds like you might be getting into a very dangerous region of "whipping" the screw. For high speed applications, I prefer belt drive actuators. I would recommend that you run this one by the screw manufacturer." The actuation mechanism can't change for this task. I am modifying an existing test rig, and it would be good if the only major changes were a new motor and gearbox.

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Posted by: Jboggs ® 07/06/2008, 19:48:28 Author Profile eMail author Edit

"it would be good if the only major changes were a new motor and gearbox" I hear you, but just because you don't want to change it doesn't mean that you aren't getting into a dangerous area. I'm not saying you are. I don't know screw diameter, stiffness, etc. But I have seen screws tear themselves up at high speed. There are suppliers out there with software and formulas that can tell you if you might have a problem. I would just check it out.

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