So I finally got around to reading all of the inspection checklists and rules, only to find out you can only use a maximum of 4 393 motors, which leaves me 2 short as I originally intended to use 6.
I read up on each of their specs, and since the 269 and 393 only vary in stall torque (non-high speed internal gearing), I was thinking of having my drive train use both types, one of each on each side of the robot, probably with the 393 in the back.
No, this is pretty common. They go at basically the same speed. However, I would suggest linking your front and back wheels with chain or gears. With your method, if you get tipped on your back or front wheels, you lose some pushing power, but if all your motors are connected to all your wheels, you retain all your torque.
I do not think that this is true. If one of your motors trips in the scenario presented, the good motor would now have to drive the tripped motor as well as the robot, and I think that that negative outweighs the positives of having a 4 motor drive chained together.
He said “tipped up” so that front wheels are not touching ground.
Chaining motors together allows two motors on one side to both provide torque to all the wheels still touching the ground.
Not “Tripped circuit breakers”.
Suppose 4w 4motor square-bot robot, with front right motor shut down,
so there is only one good motor on rear right side.
if chained together, then one motor drives both right side wheels, and a dead motor.
if not chained together, then one motor drives one wheel (hopefully touching the ground); if the wheel on the dead motor is touching the ground, then the wheel either drags, or rotates. If the wheel rotates, then the dead motor is dragged along.
If lifting the front wheel off the ground causes the back motor to shut down, then chaining seems like a good idea.
If you have 3 motors on a side, then chain/gearing them all together seems like a good idea, even if one motor shuts down.
We were running off 5 motors for a while, and we didn’t even notice it (until a couple days ago). The same goes for the arm, ran off 3 motors on a previous design and didn’t see a difference. They are all redundant as well, and they have performed well so far.
My teams have each experimented with direct drive vs. chain drive and all three have come to the same conclusion. They all prefer to have two motors on each side (usually a 269 and a 393) with a sprocket on each, chained to both of the wheels. The one downside to this is that if none of the wheels are direct driven and they lose a chain that side of the drive is dead. One team had that happen last year with the regular chain when it was not tensioned correctly. There have been no problems this year using HS chain. The advantages are that all motors touching the ground benefit from the torque of both motors and they can easily change the sprockets if they decide they want more speed or more power.
This year one of my teams is experimenting with a holonomic drive with all four wheels direct driven. The have been able to implement a “driver-oriented” control system so that when the driver pushes the joystick up the robot always moves away from the driver, regardless of its current rotation. This has allowed their robot to be very maneuverable and easier to operate than a traditional holonomic drive. We will be at the WildStang competition this weekend in Chicago, stop by and talk to Shockwave (323A) if you want to see it in action.