Go to Post It is not for any other team to say what is beyond a person's or a team's capabilities. That's why they have mentors :-) - preussrobotics [more]
Home
Go Back   Chief Delphi > Technical > Technical Discussion
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
Reply
Thread Tools Rate Thread Display Modes
  #1   Spotlight this post!  
Unread 03-15-2017, 08:05 PM
nullmainmethod nullmainmethod is online now
Registered User
FRC #6502
Team Role: Programmer
 
Join Date: Feb 2017
Rookie Year: 2017
Location: North Carolina
Posts: 39
nullmainmethod is an unknown quantity at this point
VersaPlanetary load rating questions

Our team is looking into rebuilding our climber, and we have a few spare CIMs and a VersaPlanetary laying around. Just had a few questions before we put orders in so we don't strip mid-match (always fun!)

Looking at the load ratings chart, it looks as if 63:1 is the sweet spot for a single CIM. The problem is, we already have two 10:1 stages. 1. If we ordered a 7:1 stage and went with 70:1, would that do the job?

2. How much headroom is there with these ratings? I noticed they are for the motor's maximum torque, surely a standard ESC can't even output the amps to get a CIM to max torque...

3. In the past we used a 1.5" radius drum/spindle/spool whatever you want to call it... could we still use this on the 1/2" hex shaft or do we risk stripping the planetary?

Thanks for responses in advance. I've seen a lot of threads about stripped planetaries, I don't want to be the next victim
Reply With Quote
  #2   Spotlight this post!  
Unread 03-15-2017, 08:22 PM
ollien ollien is offline
Registered User
FRC #5202
 
Join Date: Feb 2015
Location: United States
Posts: 402
ollien is just really niceollien is just really niceollien is just really niceollien is just really nice
Re: VersaPlanetary load rating questions

Where are you getting that 63:1 is a sweet spot? 63:1 is a ratio that is said to be out of the load ratings. While the load ratings are conservative, I wouldn't go much beyond them for risk of damaging your motor.

Either way, the point of these load ratings it that you should be able to bear up to your stall torque without damaging the VP.
Reply With Quote
  #3   Spotlight this post!  
Unread 03-15-2017, 08:28 PM
nullmainmethod nullmainmethod is online now
Registered User
FRC #6502
Team Role: Programmer
 
Join Date: Feb 2017
Rookie Year: 2017
Location: North Carolina
Posts: 39
nullmainmethod is an unknown quantity at this point
Re: VersaPlanetary load rating questions

Quote:
Originally Posted by ollien View Post
Where are you getting that 63:1 is a sweet spot? 63:1 is a ratio that is said to be out of the load ratings. While the load ratings are conservative, I wouldn't go much beyond them for risk of damaging your motor.

Either way, the point of these load ratings it that you should be able to bear up to your stall torque without damaging the VP.
Sweet spot as in maximum recommended for a CIM with a 1/2" hex output.

Now that you mention it... is there a way I can calculate the maximum "acceptable" gearing ratio for a specified drum/spindle/spool radius? I'd assume that would factor into reaching the motor's stall torque...
Reply With Quote
  #4   Spotlight this post!  
Unread 03-15-2017, 08:33 PM
meaubry meaubry is offline
volunteer helper
FRC #6099 (Knights)
Team Role: Mentor
 
Join Date: Jun 2001
Rookie Year: 1997
Location: Shelby Twp, Mi
Posts: 795
meaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond repute
Re: VersaPlanetary load rating questions

You should look at this and see if it works for you?

http://link.vex.com/vexpro/jvn-design-calculator
Reply With Quote
  #5   Spotlight this post!  
Unread 03-15-2017, 08:33 PM
ollien ollien is offline
Registered User
FRC #5202
 
Join Date: Feb 2015
Location: United States
Posts: 402
ollien is just really niceollien is just really niceollien is just really niceollien is just really nice
Re: VersaPlanetary load rating questions

Quote:
Originally Posted by nullmainmethod View Post
Sweet spot as in maximum recommended for a CIM with a 1/2" hex output.

Now that you mention it... is there a way I can calculate the maximum "acceptable" gearing ratio for a specified drum/spindle/spool radius? I'd assume that would factor into reaching the motor's stall torque...
The maximum acceptable is the one that meets your design goals best. Unless we're not looking at the same chart, the highest allowable ratio for a CIM is 64:1, and that's only if you use three stages (4 x 4:1). With two stages, 50:1 is the maximum.

I would recommend taking a peek at JVN's calculator and seeing if that helps you determine the ratio you want.

If you truly do want to know the physics behind it, the higher the spool diameter, the more torque on your shaft.
Reply With Quote
  #6   Spotlight this post!  
Unread 03-15-2017, 08:35 PM
nullmainmethod nullmainmethod is online now
Registered User
FRC #6502
Team Role: Programmer
 
Join Date: Feb 2017
Rookie Year: 2017
Location: North Carolina
Posts: 39
nullmainmethod is an unknown quantity at this point
Re: VersaPlanetary load rating questions

Quote:
Originally Posted by ollien View Post
The maximum acceptable is the one that meets your design goals best. Unless we're not looking at the same chart, the highest allowable ratio for a CIM is 64:1, and that's only if you use three stages (4 x 4:1). With two stages, 50:1 is the maximum.

I would recommend taking a peek at JVN's calculator and seeing if that helps you determine the ratio you want.

If you truly do want to know the physics behind it, the higher the spool diameter, the more torque on your shaft.
Cool, thanks for the info.
Reply With Quote
  #7   Spotlight this post!  
Unread 03-15-2017, 08:37 PM
GeeTwo's Avatar
GeeTwo GeeTwo is offline
Technical Director
AKA: Gus Michel II
FRC #3946 (Tiger Robotics)
Team Role: Mentor
 
Join Date: Jan 2014
Rookie Year: 2013
Location: Slidell, LA
Posts: 3,991
GeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond repute
Re: VersaPlanetary load rating questions

Note: I am taking your 63% at face value, and did not check your numbers.
  1. If you're worried about having 11% too much torque for your gearbox, just limit your throttle on the climb to 90%, or use current limiting.
  2. There's probably enough headroom for some minor shock loads, which is probably no more than what you'll have when the climber hits the davit. I wouldn't plan to use that headroom for the main load.
  3. The smaller drum that you use, the less reduction and less torque you will need. If you just wrap the rope around a 1/2" shaft, you can probably use half to a third of the reduction you will need at 1-1/2". This will be much easier on your gearbox!
__________________

If you can't find time to do it right, how are you going to find time to do it over?
If you don't pass it on, it never happened.
Robots are great, but inspiration is the reason we're here.
Friends don't let friends use master links.

Last edited by GeeTwo : 03-15-2017 at 08:39 PM.
Reply With Quote
  #8   Spotlight this post!  
Unread 03-15-2017, 08:49 PM
nullmainmethod nullmainmethod is online now
Registered User
FRC #6502
Team Role: Programmer
 
Join Date: Feb 2017
Rookie Year: 2017
Location: North Carolina
Posts: 39
nullmainmethod is an unknown quantity at this point
Re: VersaPlanetary load rating questions

Quote:
Originally Posted by GeeTwo View Post
  1. The smaller drum that you use, the less reduction and less torque you will need. If you just wrap the rope around a 1/2" shaft, you can probably use half to a third of the reduction you will need at 1-1/2". This will be much easier on your gearbox!
I'm just concerned about speed. I feel like if we lower our drum size too much we'll climb way too slowly.
Reply With Quote
  #9   Spotlight this post!  
Unread 03-15-2017, 08:52 PM
meaubry meaubry is offline
volunteer helper
FRC #6099 (Knights)
Team Role: Mentor
 
Join Date: Jun 2001
Rookie Year: 1997
Location: Shelby Twp, Mi
Posts: 795
meaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond repute
Re: VersaPlanetary load rating questions

Also, watch the rope routing path and make sure any drag across that could increase friction is minimized. Make sure there isn't anything that can ensnare the rope/belt/Velcro whilst climbing.

Try to provide a soft landing for the davit button and a cushion to allow the forces to be spread out - plus provide reaction time for the driver to stop the climb (and/or monitor the climb motor current and build in a gear life insurance program with or without an driver override feature).
Reply With Quote
  #10   Spotlight this post!  
Unread 03-15-2017, 08:56 PM
nullmainmethod nullmainmethod is online now
Registered User
FRC #6502
Team Role: Programmer
 
Join Date: Feb 2017
Rookie Year: 2017
Location: North Carolina
Posts: 39
nullmainmethod is an unknown quantity at this point
Re: VersaPlanetary load rating questions

Quote:
Originally Posted by meaubry View Post
Also, watch the rope routing path and make sure any drag across that could increase friction is minimized. Make sure there isn't anything that can ensnare the rope/belt/Velcro whilst climbing.

Try to provide a soft landing for the davit button and a cushion to allow the forces to be spread out - plus provide reaction time for the driver to stop the climb (and/or monitor the climb motor current and build in a gear life insurance program with or without an driver override feature).
Good ideas, I think we'll wind up using a 1/2" ratchet wrench as our gear insurance
Reply With Quote
  #11   Spotlight this post!  
Unread 03-15-2017, 08:58 PM
meaubry meaubry is offline
volunteer helper
FRC #6099 (Knights)
Team Role: Mentor
 
Join Date: Jun 2001
Rookie Year: 1997
Location: Shelby Twp, Mi
Posts: 795
meaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond reputemeaubry has a reputation beyond repute
Re: VersaPlanetary load rating questions

The ratchet wrench is great insurance from falling after the power is shut off, but it won't do a thing for the gear system in the climbing direction.
Reply With Quote
  #12   Spotlight this post!  
Unread 03-15-2017, 08:59 PM
nullmainmethod nullmainmethod is online now
Registered User
FRC #6502
Team Role: Programmer
 
Join Date: Feb 2017
Rookie Year: 2017
Location: North Carolina
Posts: 39
nullmainmethod is an unknown quantity at this point
Re: VersaPlanetary load rating questions

Quote:
Originally Posted by meaubry View Post
The ratchet wrench is great insurance from falling after the power is shut off, but it won't do a thing for the gear system in the climbing direction.
Don't the sustained breakers in the PDP max out at a continuous 40A? That's well under max torque for almost any motor I can think of
Reply With Quote
  #13   Spotlight this post!  
Unread 03-15-2017, 09:03 PM
nullmainmethod nullmainmethod is online now
Registered User
FRC #6502
Team Role: Programmer
 
Join Date: Feb 2017
Rookie Year: 2017
Location: North Carolina
Posts: 39
nullmainmethod is an unknown quantity at this point
Re: VersaPlanetary load rating questions

Quote:
Originally Posted by ollien View Post
The maximum acceptable is the one that meets your design goals best. Unless we're not looking at the same chart, the highest allowable ratio for a CIM is 64:1, and that's only if you use three stages (4 x 4:1). With two stages, 50:1 is the maximum.

I would recommend taking a peek at JVN's calculator and seeing if that helps you determine the ratio you want.

If you truly do want to know the physics behind it, the higher the spool diameter, the more torque on your shaft.
Played around with the JVN sheet a bit, and threw together my own sheet as well. How viable do you think using a 775 pro with a 100:1 dual stage and just the 1/2" hex shaft as the drum would be for climbing?

Using the numbers from http://motors.vex.com/ assuming a constant 35A delivery from a VictorSP to a 775 pro I calculated 9 in/s climb speed and 250 lbs of pull.
Reply With Quote
  #14   Spotlight this post!  
Unread 03-15-2017, 09:21 PM
nullmainmethod nullmainmethod is online now
Registered User
FRC #6502
Team Role: Programmer
 
Join Date: Feb 2017
Rookie Year: 2017
Location: North Carolina
Posts: 39
nullmainmethod is an unknown quantity at this point
Re: VersaPlanetary load rating questions

Quote:
Originally Posted by nullmainmethod View Post
Don't the sustained breakers in the PDP max out at a continuous 40A? That's well under max torque for almost any motor I can think of
Sorry, to clarify. I do not think current = torque, just using charts from motors.vex.com to estimate motor torque output at specific current input values.
Reply With Quote
  #15   Spotlight this post!  
Unread 03-15-2017, 09:36 PM
JohnD JohnD is offline
Registered User
FRC #3322 (Eagle Imperium)
Team Role: Mentor
 
Join Date: Feb 2017
Rookie Year: 2016
Location: Ann Arbor, MI
Posts: 6
JohnD has a spectacular aura aboutJohnD has a spectacular aura aboutJohnD has a spectacular aura about
Re: VersaPlanetary load rating questions

This sounds really, really slow. Last year we stripped a VP on our low goal shooter, so I doubt one can lift a 120+ lb robot in a reasonable time. I'd look at MiniCIMs (at least) and an AndyMark gearbox.
Reply With Quote
Reply


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -5. The time now is 01:24 PM.

The Chief Delphi Forums are sponsored by Innovation First International, Inc.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi