I have a couple of questions regarding my flywheel. First, i am using 4 turbo motors with a 15:1 combination. I was just wondering what is my total gear ratio?
Second, I’ve been reading a lot of posts and I see other teams with ratios of 7:3. How is it possible to get the second number higher than 1?
Take a look at this page: http://www.vexrobotics.com/vex/products/accessories/motion/motors.html
It contains information about 393 motors, such as the internal gearing. For turbo motors, the internal gear ratio is 18:24, or 3:4. This gives you a final gear ratio of 45:4 (15 * 3 : 1 * 4), with a free speed (no torque) of 1125 rpm. To get the second number higher than one, the gear ratio just needs to have numbers which are not even divisible by each other. For example, 45 is not divisible by 4, so the gear ratio would be written 45:4, not 11.25:1. Does that make sense?
I think your gear ratio might actually be 9:1 for speed.
Looking at the video, the motors seem to be driving 36 tooth gears. These gears are then driving a 60 tooth gear, which is then driving a 12 tooth gear
Key: - is gear, = means gears are meshed
Motor Motor
-------=--------=-----------------------=-------
36 tooth gears______ 60 tooth gears_______12 tooth gear
This makes the gear ratio (3/5)*(5/1), or 3:1. When compounded with the other 3:1 gear ratio, it makes the final stage 9 times faster than the first stage, rather than 15 times faster.
Also, it looks like your flywheel has the back plate facing forward rather than upward. Having it face upward would make the ball leave the launcher in an upward motion.
here might be part of your problem, you are using a one wheel shooter.
I think your gear ratio is actual about 30:1 (because the external is 15:1, compounded with the internal 2.4:1 gearing on the turbo gears.
back to the one wheel shooter, in a one wheel system, if your wheel is spinning at V, then your ball leaves the shooter at a forward velocity of 1/2V and an angular velocity(spin) of 1/2V, there for if you want your shooter to shoot at V your wheel needs to spin at 2V. Many teams have found that a good ratio for a one wheel shooter in speed motors(1.6:1) and a 35:1 external gearing
my team had a lot of trouble getting the one wheel shooter to work, because of velocity loss inside the “shoot” that goes around the wheel, and we eventually switched to a two wheel shooter
Thanks ipieroni that makes a lot of sense. To everyone else. Thanks for your comments and advice. So if I turbo charge a motor, do I times the ratio by 2.4?
Im sorry but there is something im not quite understanding. How can you use a turbo geared motor and continue to gear it higher and not stall your motors even faster. I had 3 torque motors powering my shooter and after a few shots it would start to stall the motors. This just doesnt make much sense to me.
bolt is right. The 60 tooth gear in between the 36 tooth and 12 tooth acts as an idler and does not affect gear ratio. Basically you are doing 3:1 + 3:1 gear ratio.
To make a 15: 1 gear ratio:
36 tooth-----36 tooth
-------------60 tooth---------12 tooth
------------------------------36 tooth ----------12 tooth
Torque (normal), high speed, and turbo are just internal gearing settings, so they only change the gear ratio output to 1, 1.6, and 2.4 times, respectively, so nothing should change if the total output is the same (at least, I believe so).
I think the problem may be that your gear ratio is too high, or your gearing has too much friction. Friction can be fixed by WD-40 or something similar.
And to find a gear ratio:
Internal Gearing * External Gearing, so, as an example, a turbo geared with a 1:15 for speed is,
1:2.4 * 1:15 = 1:36 (or 2.4:1 * 15:1 = 36:1 if you prefer it that way)
that must just be due to friction, we have four speed motors and are fine
To nalobots: Looking at the video, I would also recommend that you compress the ball more to increase friction between the wheel and the ball. This should help improve your results significantly.
To thedude019: You may also want to check to make sure everything is aligned and supported properly to reduce friction.
I’m glad to see you’ve fixed your previous problem with your flywheel. Your new structure looks very study–nice work. However, Bot15498 and Vex 9185 are right. Your external gear ratio is actually 9:1, which means your total gear ratio is 2.4 * 9 = 21.6. This gear ratio is too low for a single flywheel with a 5 inch wheel. I thought their explanations were a bit hard to follow, so I drew another explanation (attached). If this makes sense to you, I can help you make a gearbox that will make your flywheel spin fast enough.
Thanks. Bot and vex were saying that the 60 tooth gear is an idler gear, which makes senses now. But in your diagram, you still calculated the 60 t gear. So for future reference, do I calculate the 36t - 60t(3/5) or skip it and calculate the two 36t and 12ts?
Second, I would love any help I can get. I just want to make it to the competition so that my students don’t feel bad about not completing their robot.
Right now, we are trying to do:
Motor Motor
36t----------36t
--------------84-----12
---------------------_60-----12.
I just don’t know if I’ll have enough power. Any suggestions?
Last, how do I convert information from the optical encoder to rpms? I am using easy c 5.
Thanks so much jnmacdnld
I agree with bpalms, the ball just seems to be rolling off the metal, not being compressed. A single flywheel shooter should have around 35:1 gearbox I think.
Yes, the 60 tooth gear is in fact an idler gear. For future reference, if you can identify a gear as an idler, you can ignore it. But, if you include it, you will still get the correct number.
The external gear ratio you have drawn looks like it’s 35:1. I’m assuming you want to shoot from the back corner. For a robot with a straight back plate, this gear ratio is too high to shoot from the back corner of the field. However, you have a long curved back plate, so your ball will be in contact with your flywheel for a longer time. When the ball is in contact with the flywheel, it presses against the flywheel which in turn presses the flywheel axle against its bearing and creates friction. Since your ball is in contact with your flywheel for a longer time, this friction will have a longer time to slow down your flywheel. So your flywheel will be spinning slower at the time the ball is launched compared to a straight back plate.
Perhaps 35:1 will actually be ideal since it will make make your flywheel spin faster initially, and counteract this effect. On the other hand, maybe the effect I’m describing is actually a very small effect and it won’t matter much at all. I’m not sure exactly sure, since I haven’t ever tried this design before. You’d have to experiment. However, if you do try 35:1 and it ends up being too fast, you can always reduce the motor power setting. The choice is yours.
If you’re okay with shooting from mid-field, I do know that 8059F used a 28:1 ratio with a curved back plate design like yours and was able to shoot from mid-field quite well. So you could try that ratio.
In terms of optical encoders, are you using integrated encoder modules or optical shaft encoders? And do you have enough programming experience for a math formula to be a sufficient answer or would you like an example program as well?
In terms of optical encoders, are you using integrated encoder modules or optical shaft encoders? And do you have enough programming experience for a math formula to be a sufficient answer or would you like an example program as well?
Can I have both please? This is my second year trying to do vex so I don’t have any experience.
We rebuilt the robot again. The 35:1 external ratio seems to not work. There is a lot of friction on one side of the flywheel and I think it’s tripping because it will slow down all by itself. Any suggestions?
Ah. I now see you said you are using Easy C. Unfortunately I’ve never used Easy C so I can’t help you write an exact program. I’m going to assume by optical encoders you mean optical shaft encoders. This page should give you some background on how these work and how to write programs that use them in Easy C. I’ll give you a general overview of what your program should do to calculate the flywheel’s rpm.
First, you calculate the velocity of the flywheel. To do this, first record the initial position of the encoder. Then wait for a specified amount of seconds. Then record the final position of the encoder. Use the formula in the attached image to get the flywheel velocity from this. You will now have the flywheel velocity in ticks per second which is the unit of measure of position for encoders. So, convert this velocity to revolutions per minute using the attached formula.
One of your gears is wobbling, which probably means the shaft it is connected to is bent. This would create friction on one side of your flywheel, as you said. Also, you should always support gears on both sides. Especially in your case, the way you have the gears exposed now will allow balls to touch them and slow them down.
Other than friction, another cause of your flywheel tripping might be that one of the motors is spinning the wrong way. Check your program and check that all of the motors are connected correctly. Sometimes you will accidentally connect red to black and the motor will reverse direction.
Finally, does your flywheel have zip ties to keep the rubber tire from vibrating when it spins? This is very important, as a vibrating flywheel will be much slower than a non-vibrating one.
Thank you sir. You are a life saver.
jnmacdnld:
Ok, so I got my gear ratio running, but when I use the optical shaft encoder, it puts a lot of friction on the axel and it won’t spin at all. Is this normal or did I just put too much of the axel in the sensor?
thanks again.
I would try loosening the screws on the shaft encoder and move it around until the axle doesn’t have friction on it anymore, then tightening it again. Just keep doing this until you have little to no friction as far as you can tell by hand.
Be sure to do this while the axles are out of the motors, because otherwise you won’t have an accurate judgement of the friction since you’ll be fighting against the motors too.
I’m a little bit confused. So far as I know, gear ratio is Driven gear/Drive gear.
So for flywheel, it should be (12/84)*(12/60) = 1:35 or something like that. It should be much less than 1 for a flywheel. So why you guys are getting a much larger number? confused…
