We’re making something decently heavy that will be rotated around a pivot point and I don’t think a neo will be strong enough to move it and even less of a chance that it will be able to hold it in its place. Anyone know of a motor that would be best suited, or if a neo be fine?
With enough gear reduction and enough motors, you could make any motor work. Here’s a really helpful website to help with arm calculations where you can put in weight, types of motors, and more to see how it would react:
Is this an application where you can have multiple motors connected with gear or chain, or are you limited (by space or otherwise) to just a singular motor?
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Any motor can move the arm with sufficient gearing. The question is how fast using how much current? A neo is about 400w of power at 40a, one or two should likely move the arm
You can use calculators like amb calc to calculate the optimal gear ratio to make the motors run at 40a, getting the maximum power output without popping breakers.
Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.
“decently heavy” and “rotated about a pivot point” are good though starters, but with enough gearing, you can kind of make any motor work… as long as you are willing to wait long enough.
How heavy a load?
What is the distance between the pivot and the center of mass of the load?
How many degrees of rotation?
What amount of time are you wanting to get from A to B?
Do you need it to hold at highest load (typically arm is parallel to the ground)? If yes, for how long?
Try to give some estimates for those values, and folks on here can point you towards methods of figuring out a solution.
The NEO is the second strongest motor for FRC behind the Falcon 500, and will work for your application (And will have to, because it looks like no more stock of Falcons for 2023-2024). However, you’re gonna need to gear it down with a gearbox.
As I was typing this, multiple people already responded with calculators you can use to find what gearing you need.
While it’s easy to design custom gearboxes for certain applications, depending on the space, it may just be easier to use a premade COTS planetary gearbox. Both VEX and Rev Robotics make very easy to use and modular gearbox platforms as part of their VexPRO and ION series respectively. They have their own limits however, so use a gearbox calculator to figure out what you need. You won’t get as exact with the planetary gearboxes however, because of their modular nature, but you can stack various reductions to get close.
For holding position for pivots like this, it’s hard to beat a worm gear setup. It’s like a mechanical diode as the spur gear can’t apply the rotational torque to the worm gear to move it from that side but the motor driving the worm gear moves things very well. That means the arm can’t back drive the motor which means the position is retained when power is removed.
Due to the mechanical relationship, you can get a non-trivial amount of gear reduction just from the worm gear setup but you’llLimelight, an integrated vision coprocessor probably need a gearbox anyway.
It doesn’t have to be the final part of your gear train and could be used as the first stage or even an intermediate stage if that suits things better. It also provides a 90 degree turn as part of it’s natural design which might be a packaging win (or a packaging loss depending on what you’re doing).
Just tossing that out. Just off the top of my head, I don’t seem to recall a lot of worm drive setups in FRCFIRST Robotics Competition that I’ve personally seen but I might have just glossed over them here and there. Andymark has a set with a 10:1 reduction and of course McMaster-Carr has a fair selection as well.
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I remember him. He grew up down the street from me.
Skinny guy, you wouldn’t think he’d amount to much physically but he had this chunk of iron that was pretty long and he knew how to use it.
Never really hung out much with him as he was a few grades ahead of me in school…
Yup, this is a good point to consider.
In my experience it is almost always better in FRCFIRST Robotics Competition applications to have the final drive of an armed be chain (or something with high wrap) just for the greater shock load spreading of forces. Bonus points as it usually allows for low mounting of the motor.
Now the above may be less of a concern, just pay close attention to the specifics of the gearbox and practical considerations (such as motor mounts) when developing the layout of the gear train.
Remember, there is a LOT to be gained (mechanical and software) by making the arm “weightless” with some counterbalancing (see gas springs mounted on sprockets/levers). Then all you are fighting is rotational inertia.
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You bet! That’s a great point and probably your best general purpose go to approach.
I agree with the worm drive suggestion, but I want to throw in a little caution. Most worm drives are actually backdriveable they are just very high friction when back driven. The high friction is still going to be helpful for keeping an arm in place. I like to say that worm gears shouldn’t be back driven, not that they can’t be. Secondly building a custom worm gearbox requires pretty precise machining in 2 directions to function well, which can be surprisingly difficult depending on machining capabilities. The same is true of miter gears, so I machine the box then trial and error shims until the gears run smoothly.
Generally, a lubricated 10:1 worm gear WILL backdrive.
20:1 is pretty reliably self locking. Assuming no heavy vibration, of course!
I would personally try to redesign to use a pneumatic piston for this if you need it to hold. Motors don’t like holding things in place and pneumatics are also a lot less likely to pop a breaker.
Pneumatics can only hold in two positions, fully extended or fully retracted.
If that’s all you need, then another option is to use a motor with an overcenter linkage, like the 2022 Everybot arm.
If the arm needs to be held at arbitrary positions, then another option is to use a brake (perhaps a repurposed bicycle disc brake), and actuate it with a piston, motor, or solenoid.
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