I only have 1 pack of high strength chain/sprocket kit and I’m trying to get the chain to pull my 4" omni-wheels but I don’t have enough chain to wrap around both wheels (held on 2 1x35x1 c-bar).
Anybody have ideas for gearing up the the drive train? I tried using high-strength gears but I’m having a little difficulty fitting everything so that it isn’t hitting the omni wheel.
If I have the two back wheels pulled by the chain and the two front wheels stationary, would that be ok?
That’s what my team’s robot is like, and it’s working just fine… 
//Andrew
While this will certainly work in moving your robot around, there are a couple of potential problems with that. One, when turning, your robot may “stutter” unless you have omni wheels in the front. Two, if your back wheels lose traction, you will be immobilized. Three, it may be easier to tip over if your robot is back-heavy. If these problems do not pertain to you, I don’t see any reason that your configuration would cause any problems.
All four of the wheels are omni-wheels. Do you have any suggestions for keeping the front 2 wheels moving as well?
You could gear it. What resources do you have available?
Firstly , you could use normal gear(not high str) )
Secondly , you could use gears , connecting to another wheel(close to the middle ) . That would make it a 6 wheel drive train.
Thirdly , you could use gears and chain but that would be troublesome and not recommended .
2 packs of high strength gears
1 pack of high strength chain and sprocket
4 4" omni-wheels
A bunch of normal gears in various sizes
Everything is being mounted on two 1x5x35x1 c-channels, flat sides facing each other. Connected by 2 inch stand offs.
Wouldn’t the normal gears start skipping/breaking under high load/weight?
No. It is extraordinarily unlikely that your drive would break VEX gears. The only time VEX gears “break” (which usually means snapping a tooth off a 12-tooth gear) is when geared down a lot to lift a heavy load. I can’t imagine how you could break a gear in a drive train.
What HS Gear sizes do you have.
Also, could you put a picture of your robots drive base on here so we can see
what you are talking about exactly. Or actually a diagram would work, or a CAD model…
I have two of these packs: http://www.vexrobotics.com/products/accessories/motion/276-2250.html
So…
(8)High Strength 12-tooth Gear (0.58 inch diameter)
(8)High Strength 36-tooth Gear (1.58 inch diameter)
(8)High Strength 60-tooth Gear (2.58 inch diameter)
Here’s a rough drawing in paint.
http://i44.tinypic.com/34zka6g.png
Where are your wheels located on this drawing?
This drive train is almost identical to ours… How funny 
Omni wheels are positioned parallel to each other. One in each corner. Sandwiched in between 2 17.5" (5-hole) c-channels.
I have tried using normal gears before . Using the 12 tooth gear , the tooth would definitely break . However , the 36 tooth gear would not .
You can try gearing by the inside .
I ended up moving the omni-wheels a little closer, enough to fit chains on both sides.
good call
now just make sure the change wouldnt end up getting you tipped
It’s only a 2cm difference. Shouldn’t get us tipped.
By the way, what do most people have their 393-motor internal gearing set to? Does high speed have more of an advantage than high torque?
Most teams would probably have them set to torque so that they can be used with 269 motors as they have the same rotational speed (100 rpm), so that they can have multiple motors on each side of their drive train. If you try to use a 269 motor with a 393 in speed then something will probably break.
were using 4 393’s geared internally for speed. we have found that under a load the 269s and 393s have different speeds which leaves them little use in the same system.
I used to have the 393’s on our robot set to speed, but i found that it made it a lot harder when you needed to change a motor in a hurry during a competition. Because the motors are set to strength by default, if they are supposed to be on strength on the robot you can just screw them in and you’re good to go. But if you need them on speed, then you’ll need to take the motor apart, change the gears and put it back together before you put it on the robot. I would recommend internally gearing for torque, and then if you want the motor to go faster, externally chain or gear for a faster ratio.
I updated this post to include a picture of one way you can match 393 160 rpm motors conviently with 100 rpm motors. Both 1508 and 599 teams use this configuration. It keeps the motors at the rear, keeps them low and allows simple gearing. The main draw back is the cantilever which can increase normal forces on the axles by a factor of 2 or so but it is a tradeoff we were willing to make.