Big Dilemma..

If you can’t use chain, I really don’t know what to tell you. You could move the wheels to the interior of the robot, and put a motor on each side of the axle. That could work, although I wouldn’t recommend it.

Ok… we just dropped the chain idea and now we are making the robot only rear wheeled drive. We are trying to have six high speed motors driving just the 2 rear wheels

Although more pictures would help, just from that, it looks like there’s a lot of unnecessary plating, which will add up fast.

This worked to keep our drive from dying, but that was only because we were trying to eliminate the non-conservative forces made by chain looped to form around the drive and not hit the bump. There was too much tension and friction from this to drive well, so we powered the back wheels only.

That being said, you might experience some difficulties while getting over the bump, especially backwards.

The gear ratio with high speed 393 motors is 1.6:1. A 3:1 will be almost twice that, so it certainly won’t work if the high speed motors don’t.

Try making your robot lighter or using chain to make a 5:4 ratio to be slightly faster than 1:1 without sacrificing too much torque.

Use a power expander, and put all 4 drive motors on it. I have internally set my motors for speed for 2 years on this setup, and it never dies unless im in an intense pushing battle, and even after that it still drives.
i do have to agree, go with a 6-bar, saves alot of weight.
just my advice, use what you can from it.

This is something we have never tried, will try so… We use a power expander currently, but it has the lift motors attached.

There is only one reason I don’t tend to do that which is that the power expander tends to have one of the least reliable connectors I have ever came across.
The thing to keep in mind is that if your power expander stops working, your drive just died and you can’t do anything.

The coin does have two sides, it just depends what risks you want to take to keep you drive from staling.

Has anyone else experienced these problems with the power expander? We’ve been using them for years with relative success. I think we’ve had one with a single port go bad, and one where the battery connection started to pull apart because we were careless with it. In both cases, however, VEX repaired or replaced the units at no cost to us.

We’ve never had any problems with the motor ports on a power expander, though the battery connection has come a bit loose over time. This is, I fully admit, an older expander that’s been on at least 4 competition bots in the last three years. The other teams at my school have newer expanders and don’t experience any such problems. I think they work well in drive applications, but currently we have ours on our lift (note: this is only because we wanted to use use fewer wire extenders and with the way our robot was set up, this was the most efficient configuration).

Ya, that’s what I meant.
I have two power expanders that have finicky battery connectors.
they’re both old so maybe they make them better now.

Sorry for the late response,
Usually if you’re connector isn’t properly plugged in, it will be evident before the match even occurs. In autonomous you will probably have to drive somewhere right? So if you can’t drive, then you’ll notice it, and before the driver mode starts you can go plug it in right because it still hasn’t left the starting tile.
(This is one of the reasons I put them on an expander)

Of course you might have become disconnected during a match, in this case it would be a technical failure, and has never ever happened in my case.
But I’m not all teams, personally I think the Cortex has a bad connector, not the expander.

I agree… the vex net port for the cortex has a bad connection and also the battery port on the cortex isn’t very good. Both often are disconnection even with a slight jerk due to the robot.