# Drive Train Ratios

What is the optimal ratio for a drive train that is using 6 269 motors. What ratio is your team using on their drive train?

Generally, NZ robots on the standard 4 269 2 393 motor layout use a 1:1.6 speed drive. You could probably get away with 2:3 for speed. What I wonder is what else on your robot demands the use of all 4 high strength motors. Is your arm made of depleted uranium?

We’re using 4 393s, which is approximately the same power as 6 269s, and we are powering 6 2.75" wheels at a ratio of 2.5:1 (for speed) and have had no brownout issues, unless you drive into something and keep the power on, but that will happen with any ratio if your wheels don’t lose traction).
We found that 2:1 was too slow, but we were losing power (the PTCs or the current limiters in the ports were tripping) with 3:1, so we ended up with 2.5:1.

Well it’s something you’ll see a week from now :), basically the 4 393’s are used on another part of our robot.

This very much depends on the weight of the robot, and what you are trying to accomplish. I’ve never worked with a robot having this type of motor configuration on the drive, but with a rather lightweight (12 lbs or less, maybe?) robot, I would say you could pull off a 1:1.67 geared up driving 4" wheels with six 269 motors.

~Jordan

what happens if you get in a pushing match? with the 2.5:1 drive? does it burn out/ stall?

We have 4 393 motors on the drive with a 1:1.25

2.5:1 on 2.75" wheels would be ~the same force as 5:3 on 4" wheels, so you could say we were more geared for speed than for torque. It entirely depends on who we’re pushing against, but like I said we generally don’t stall in a regular match. I’m going to be putting in some anti-stall code soon so stalling shouldn’t be an issue for us, we just won’t win in pushing matches. But our strategy has us avoiding pushing matches, so we don’t mind

so would a 1:1 ratio with 6 269’s be to slow. Since you have 100RPM2(3.14)(2)=1256/12=104.6/60= 1.74fps While if we have a 1:1.667 with 6 269’s it would be 100RPM2(3.14)(2)=1256*1.667=2093.752/12=174.48/60= 2.91fps. I understand that 1:1.667 is a lot faster, but im not sure if it will have the torque to push other teams with ease. The decision will be made tomorrow…

For us:
(100)rev/min * (2pi1.375)in/rev * (1/60)min/sec * (1/12)ft/in * 2.5 = 3ft/sec

That’s pretty fast. If you want to be able to push other teams, go for 1:1, but it will be noticeably slow. You will be able to push other robots, and if your coach and driver are well coordinated you won’t need to be fast to block other robots (there’s only a 5’ wide channel the robots can go through). Have you considered 4:3 or 3:2? 5:3 is a bit much for a robot designed for pushing.

Before our current design, we could easily switch between 3:1 (3.6ft/sec) and 2:1 (2.4ft/sec), which was rather beneficial because some drivers liked to drive into things and keep going (they got the high-torque option) while other drivers didn’t (the high-speed option for them).

I think with 6 269 motors, you should easily be able to do 2:1 without browning out. I personally would go with 2.3:1 using gears instead of chain because it didn’t brown out on us with a 15 pound robot and 4 393s. (We don’t use it now)

We have 4 393s with internal torque gearing, geared 1:1 to six 4" wheels. Our robot weighs ~25lbs. Despite the fact that our robot’s not as fast as some others, we’ve been able to beat most of the efficiency bots in our region and we have superb pushing ability (although this is in part because the weight of the robot gives it a lot of downforce and traction).

We have minimal stalling problems. This is fixed by programming button 7U on our controller to cut power to the motors for 5 seconds, allowing the PTCs to reset. If it stalls, and we use this button, it doesn’t stall again for a long while.