thank you! what i didn't understand though, is why you said we don't count the teeth of the planetary carrier. Why not? Certainly there are in fact a fixed number of teeth on one of those planetary carrier gears
It's just an idea! The idea is that: One to three is a completely balanced gear ratio for one link of a coaxial gearbox. This, for example, is optimal for a wind turbine, where the loads change by about two orders of magnitude - this is 100 times! Switches must be made between these links. And so: 1:3:9:27:81:243 Six-speed transmission. The wind speed acting on the entire washed area of the fan - this theoretical perspective windmill, varies from 2 m / s to 32 m / s! And the power removed from this electric generator varies from 2 kW to 200 kW! That's why you need such a reducer. I mean - It's a crazy idea to use a wind generator for hurricane winds. And, at the same time, - for very quiet winds - almost calm! For small autonomous settlements or even for separate remote buildings. The coaxial gearbox has an advantage both in terms of the weight of the metal, and in terms of the efficiency of the interaction of gears, and, probably, in other parameters. Perhaps the same gearbox is suitable for other technical objects, just need to think about which ones. Considering the remarkable parameters of the coaxial transmission scheme of the mechanical moment.
May I ask you a question? You said that: Planet Carrier = Sun + Ring. In this case, we have 3 planet gears. But what if we only have 2 planet gears connect to the carrier? Is this formula still true?
It would be since it isn’t based on the amount of planetary pinion gears are in the carrier, but on the circumference of the carrier which the pinion gears make up. Think of it like drawing a circle and putting two points on either side of the circle. It’s still the same circumference, even if you double, triple, quadruple, etc. the amount of points, it’s just more areas of contact.
Hi, I would like to know that gear you are using for education belong to which vehicle? Really important for me the information Thanks With Regards Sam Australia 🇦🇺
Awesome Video, Perfectly informative. What is this Specific Planetary out of? I need this type of Planitary to make a Planitary Hub for a racing application, thanks!
shouldnt your ring be the sum of 2x the planet carrier + the sun gear??? so when your sun gear is 30 en your ring is 90 your carriers would be 60 together
The actual physical number of teeth on the carrier gears have no bearing on the gear ratio. The speed and torque of the carrier are the result of the number of teeth on the ring and sun gear.
The number of teeth on the ring is the number of times it turns the the planets is the number of times the sun turns So if the ring has 60 teeth and the planets have 10 the sun turns 6 times because the sun can only turn the number of teeth on the ring
Thanks so much for sharing this! This really simplifies it as opposed to other explanations. This makes planetary gears far less daunting. Thanks Justin!!!
WHAT? You're not going to first make my eyeballs bleed with 30 minutes of riveting footage defining angular velocity? Thanks for the quick and easy explanation! I appreciate it!
THANK YOU Justin! Absolutely fantastic educational video! Straight forward, and to the point! Extremely easy to follow..... and thanks to your Working Examples...... extremely easy to calculate & apply!
Cool explanation ! Quick questions : how does the operator select which gear is the driver then? How do I know the efficiency of the transmission? (there must be some energy loss) How do I use this is real life applications? (say I want to move a 100kg load on a small platform with 2 or 4 wheels. How do I work out the torque required?) Thanks!
+Okan Kurt It is because whenever the planetary carrier is acting as the input or output gear in a set (not just an idler), the carrier is effectively being turned by both the sun and the ring gear. For example, if I were to hold the ring gear still, while turning the sun gear, the carrier would be the output. Note that it is not the planetary gears that are the output, it is the carrier. The rotational speed of the carrier is determined by how the planetary gears are "rolled" between the sun gear and the ring gear. Hence, the sum of the teeth on both gears. I hope that wasn't too confusing!
Is easier to see by the next formula: (Nr+Ns)*Wp=Nr*Wr+Ns*Ws Where "Nr" is the number of Teeth of the Ring, "Ns" is the number of Teeth of the Sun, "Wp" is the angular Velocity of the Planet Carrier, "Wr" is the angular Velocity of the Ring and "Ws" is the angular Velocity of the Sun gear. So you can see that the planet carrier velocity don't depend from the number of teeth of the planet gears, instead depend from the sum of the teeth of the sun and the ring.
Hi, this video was very helpful, thanks a ton. I have a few doubts though. 1. If the number of teeth on planetary gear is calculated by the sum of the teeth on ring and the sun, how do we calculate the teeth on each planet gear? 2. does this depend on the number of planets we have? thanks again
1. The planet gear has to be the right size to fill the gap between the sun and ring gears, so in this case it needs to have 30 teeth as the radius of a gear is proportional to the number of teeth (For a given gear module - which is a fancy way of saying tooth size). The diameter of the ring gear is equal to 2 x planet gears + 1 x sun gear, the sun gear has 30 teeth, the ring has 90, so 90 = 30 + 2 (Planet gear teeth), which solves to give 30 for the planet gears. 2. Only one tooth at a time usually carries the entire load between when 2 gears when they mesh, so the more planets, the more teeth are available to carry the load, so the higher the torque that can be carried by the ringset. The number of planet gears has no effect on the ratio. Keep in mind that for most applications nobody cares what speed the planet gear turns at, it's the planet gear carrier that's working as an input or output. The speed the planet carrier turns at depends on the difference in speed between the ring gear and the sun gear.
What about when the planet carrier is always held still, and the ring is the drive and the sun is the driven, I need help on what I’m trying to make with ratios
Then for the planet gears / pinions, we just estimate the number of teeth on the ring and sun gears, and add them up - or if desired, count the number of teeth exactly, and use the result to do the calculations ? Isn't there a precise formula that would be used for this ? There must be, or engineers would just be guessing when they make their designs.
thank you. this helps me so much. how do you calculate the ratio with different amount of planetary gears? does it even matter? some have different size planetary gears in them.
Justin, can you please tell me where you got the planetary gear set in the video? I am looking for an off-the-shelf planetary gear for a project and it appears that what you have would be about perfect. Thanks!
So if I had a sun gear with 12 teeth, a ring gear with 60 teeth, and the planet gears had 24 teeth each, I would add the s12+r60 = 72 and the p24 x 3 = 72 because I have three planet gears that would be a 6:1 gear ratio?
No, that isn't correct. You don't ever count or use the number of teeth on the planet gear when determining the ratio. The planet gears are idler gears and their speed is always going to be a result of the speeds of the sun and ring gears. To figure out your ratio, you need to determine which of the three components are acting as the input and output gears, and then divide the number of teeth on the output gear by the number of teeth on the input gear. If the planetary carrier happens to be either the input or output gear in your scenario, you should not count the teeth, but use the sum of the number of teeth on the sun and ring gears for your number. I hope that helps!
So is the sun gear turning the planetary carrier, or is the carrier turning the sun gear? If the sun gear is the "drive" gear and the carrier is the "driven" gear, your ration would be p72/s12 = 6:1, just like you said, but it is not because of the number of teeth on the planet gears--that is just coincidence that they add up to 72. You could easily have a fourth planetary gear in your carrier, and it would add 12 more teeth to the mix, but it would not change the gear ratio.
There are two ways to get a 1:1 ratio from a planetary gear set: You can lock the entire assembly together and turn them as one unit, or you can spin the third member of the gear set in the opposite direction at exactly the right speed so that both the input and the output gears are turning at the same speed.
Justin Miller So the second one is what I'm talking about (I don't think the first one really counts), if the only way to get a one to one ratio in a planetary set is to run the same number of gear teeth on the sun and ring gear how would a one to one ratio be possible when the ring gear will always be a larger circumference than the sun gear?
Beach&BoardFan...You can do that with sprag bearings or one way bearings on the planetary gears and carrier such that when the sun gear rotates in one direction, carrier locks & planets spin, you would get the gear reduction of say 3:1 or whatever ratio you have sun to ring... and when you rotate the sun gear in the other direction, the planet gears would lock while the carrier would unlock & spin with the sun gear driving the ring gear directly @ 1:1... done
@@beachboardfan9544 Locking the assembly up is a legitimate use for planetary sets, and it used very often. If a 1:1 ratio is needed in addition to other ratios, it's the simplest design. For your second approach, that would require addition gearing to get the carrier to turn at the right speed, and, if you wanted more than one ratio from that gearset, then you're talking an addition brake for that extra gearset. I'm scratching my head to think of an OEM application where an engineer was able to justify the additional engineering/cost/complexity just to avoid using a simple lockup
