My team is considering whether to stick with 4x 200 rpm direct drive or to gear it up to 257 rpm.
Right now each motor is directly connected to an omni using a high strength shaft which keeps slop/play to a minimum. Using gears would introduce much more play into the system and would make the autonomous potentially less accurate. However the increased speed would make scoring quicker and could improve skills potential. The downsides are the slower acceleration, decreased torque leading to reduced pushing power in defensive or counter defensive situations, more strain on the motors especially since our robot is fairly heavy (7.7kg) , possibly causing excess heat or stalling. In addition, the slower acceleration may impact control and/or turning speed. Anyway, what do you guys think?
I would suggest you gear it up.
I wouldn’t recommend in the first place to put high strength axles on your wheels for drive that is just unnecessary. And gearing up drives depending on how you do it can reduce slop. I personally have a geared drive train and tested the slop and I didn’t see any. I think depending on your strategy you should pick which one would be better for the robot. Or just test gearing it up and see how it goes
i found that an omni wheel with a standard shaft has about 8 degrees at least of slop whereas high strength only has about 1-2 deg
how heavy is your robot? there are ways to greatly minimize slop between gear and wheel on the same axle so I wouldnt worry too much about it
its 7.7kg --------------------
this isn’t actually possible. Direct drive will always be the lowest slop possible with vex parts.
but the slop from gears isn’t terrible if you make sure the gear inserts aren’t worn out. Bolting the wheels to a gear on the same axle helps.
so if you have decent build quality, I would recommend gearing up.
It might have just been the insertes that was in the wheel too. What you can also do if you hear it up is attach the wheel to the gear with bolts to make sure there is even less slop. That helps out a lot with slop and might get rid of the slop within the axle itself
Oh sorry. I read in a thread that if you gear it a certain way it can reduce slop. Sorry about that.
if vex gears had perfect tolerances with no slop, then this would be true. But the way it works in reality means gears add more slop then a torque ratio reduces. (I haven’t tested this, but I’m like 90% sure it’s the case.)
I’d say in a game like this one a fast drive will be very advantageous. Give up a little bit of torque for some more speed. Easy call.
fitting in the gears will be another issue, since we will have to have vertical gearing.
I’m assuming that’s the weight without holding any balls? if so I wouldnt recommend 257 rpm. Acceleration will be slow and you will burn out fast. For referenece, our bot is just over 15 lbs and runs 257 rpm. On a fresh boot up (where motors are room temperature, roughly 25 C) we burn out after ~7 minutes, and then subsequent runs after 5-10 min cooling periods (motor cools to about 40 C) burns out after ~3-5 minutes.
By all means you can try it out and see how fast you actually burn out. Personally my benchmark is if it can last 6 minutes of straight hard driving after starting at room temp its will last for a comp. The reason why 6 minutes is to ensure it can last throughout the entirety of a best of 3 at finals and then some.
Also, if youre worried about slop messing up auton then use tracking wheels. It won’t completely fix the problem but it will minimize the effects.
Are you 1408F. If you are you name is wrong. But is you are no 1408F could you send a picture of you robot so we could see why the spacing wouldn’t work.
old account , cant change the name now lol, yep im 1408f
Ok well first of all you can contact Drow to change the name and give me a sec to see why you wouldn’t be able to put gears horizontally
Uh, there should be almost no slop there. Are you not using bearing or cantilevering your drive?
Yah well I can see why you can’t put gears there. Could you possibly just take those supports off and place then somewhere else on the robot. I bet you could you just need to try it out. Or check it in a cad and see what you could do.
I can feel the slop from literally putting an omni on an shaft and clamping it to a bench
Can you share a picture? That doesn’t make sense. Nothing I have is anywhere near as sloppy as you describe.