Just ordered my first vex kit. I have been looking at the many different designs posted on this site in preparation for building my first few vex robots.
I have noticed that several designs use multiple motors to power a single drive shaft. Such as the Tomahawk (which uses 3 motors for each rear wheel). I was wondering how much additional torque is applied to the shaft as a result. Would the torque of each motor simply be added together or is there a more complicated calculation?
Also, I have been searching for an explanation for how a gear ratio would be calculated for a design that uses multiple types of gears. Such as sprockets, spur gears, and bevel gears. I would assume that the standard way of counting teeth would not work since they are different from each other.
Thank you ahead of time for any helpful posts. And I also look forward to posting my progress on my designs.
(2) motors provide (2x) the torque, at the same speed. Additional motors will provide additional torque. There is no more complicated calculation. It’s that simple.
All gear ratios can be calculated by “counting teeth”. Since each ratio is only with a gear of the same type, the teeth-comparisons still work.
If these gears were in sequence, they would yield a reduction of:
(1/3) * (1/4) = (1/12)
Similarly, a bevel gear reduction can also be calculated by counting teeth.
A 12 tooth bevel gear mating with a 26 tooth bevel gear still gives a reduction of (1/3).
As long as you don’t have gears with different teeth sizes mating together, “counting teeth” will work. Luckily, it is pretty much impossible for gears of different teeth sizes to mate.
Does this make sense?
Let me know if you have other questions.
I look forward to seeing your design/build progress.
I still have a question regarding the gear ratio’s.
I posted this question mainly because I could not figure out how the posted gear ratios for the tomahawk were calculated. The specs read as follows.
Primary Drive 1.66 to 1 Direct Drive
Secondary Drive 4.88 to 1 Dual Chain Drive
I understand the first ratio since the motors have 60t gears going to a 36t gear (5 : 3) = (1.66 : 1). It looks like (I could be mistaken) that the chain drive goes from a 48t sprocket to a 24t sprocket (2 : 1). I don’t get how this can come out to (4.88 : 1). I thought that since they have a different style of teeth maybe the ratio has to be calculated using gear diameter…or something like that.
Ok, I pulled the Tomahawk down off the shelf.
It has 2 stages of gearing:
Spur Reduction - 60:36 = (60/36) = 1.66666667
Chain Reduction - 48:24 = (48/24) = 2
I don’t know why we listed a ratio of 4.88:1, that is just silly.
I will get it corrected, ASAP.
According to the inventor’s guide a gear ratio is the tooth count of the driven gear over the tooth count of the driving gear. That would mean that the main drive is (36t : 60t) = (.6 : 1) and the secodary drive is (24t : 48t) =
(.5:1).
I think:
When it is listed as 4 to 1, typically the driving gear is listed first, and the driven gear is listed last.
It seems like I’ve seen it both ways.
I’ve also had people tell me “always give the gear ratio as a whole number, not as the decimal.”
Does anyone know for sure? Anyone have any experience with standards for this notation?
Please, if you don’t have experience with this, do not chime in opinions.
“In the picture to the right, the smaller gear has thirteen teeth, while the second, larger gear has twenty-one teeth. The gear ratio is therefore 13/21 or 1/1.62 (also written as 1:1.62).”
“The first number in the ratio is usually the gear to which power is applied. In an automobile the first number is the gear receiving power from the engine.”
According to this the driven gear would be listed first. However the wording seems as though it could be interpreted both ways. Also it might be worth mentioning that the example can be written several ways.
13/21 = .619 which can be written as .619 : 1
The fraction can be reduced to 1/1.615 this could also be written as 1 : 1.615
The point is that there are two ways to write the ratio.
Also:
the vex robot speed chart shows that the reduction from a 36 driven gear to a 60t driving gear would be .60
which could also be written as 1/1.67 or 1:1.67
the sprockets would be 24:48 with a reduction of .5 also written as 1:2
