I have questions regarding motor place on the drivetrain . My school is having a 4 wheel drive train with 4 393 , 2 on each side in high speed mode. Would running the robot for continuous minute burn the motor out ? I had tried touching the motor however they seem fairly warm.
And what wheels are best for drive train ? My school had encounter instances whereby our 393 spoil . Our back wheel was high traction 4" wheel while the front was omni wheel . Omni wheel are generally larger , will this small difference put weight on my other motor causing them to spoil ? Is it best to keep both wheel omni ? I would like your suggestion
Thank you very much ! Your help is much appreciated
I think that configuration should be fine, considering you install the bearings properly to support the axles.
Just don’t make your robot too heavy (more than 14lb if you’re using that config) and don’t expect any pushing matches with motors in high speed mode.
If your robot is too heavy, the axles have too much friction, or if you engage in a pushing match you will most likely trip the 4 amp breakers in the cortex and this will cause your robot to stall.
Yes , i indeed have installed the bearings properly to support the axles and my robot is not heavy. We do sometimes push however , my robot would not trip the 4amp breakers in the cortex , what it does is causes my motor to spoil . Anyone can explain this ?
Bot-E Builders: what do you mean by (I am pretty sure it was out 6 wheel drive train causing strain.)
tripping your beakers is a very good thing compared to having your motors burn out. Motors burn out when there is power being sent through them, but they are not physically able to turn. This has to do with how current works in a motor. Basically, counter-current is being generated if the motor is not spinning, and the amperage of the power draw gets too high because there is not counter-current to reduce it. The wires are not meant to handle so much current, and the insulation melts, and there is often a short. Google burned out motors for more information.
My intrepretation of what he is asking is if the motor stalls from tripping the internal thermal overload, can it be reused. The short answer is yes once it cools off and resets it can be used. However as you probably noticed, once you start driving again and subject it to the overload condition, you will be back in a “stall” condition.
Once you look up your combination of motor type, internal gearing, external gearing and wheel size, you will be able to see if you are running in the green, yellow or red zones for motor loading. The other factors you will have to consider youself is robot weight including payload (balls & barrels), and any interaction with other robots.
When larhal says that his motors are “spoiled” I don’t know if he means that they stalled from drawing too much current, or burned out. Care to clarify for us? If they stalled, then yes, you can do what Rswsmay suggests. However, if they’re burned out, then you’re out of luck.
Unless you had a very, very light robot, it wasn’t friction in the drivetrain, it was overworked motors. The minimum chassis power for a a competition VRC robot is four small (3-wire or 269) motors geared for slow speed (less than 2fps), or six small/four 393 motors geared for medium-to fast speed (2-3.6fps). Unless you have them geared way down, two motors of any kind won’t effectively propel a VRC robot.
I’ve noticed a big trend to over-gearing ever since the 393 motors were introduced. They might be stronger than the small motors, but they aren’t magic.
Vex motors are generally protected against burnout by thermal protectors and current protectors. These protection devices can ‘trip’ and cause the motors to halt for a while, but there is no permanent damage.
Some teams have reported that frequent thermal/current trips can cause the protection circuits to trip more easily in the future.
“N motors of type X per side” is not enough information.
“N motors of type X per side, geared for speed Q:R” is not enough information.
“N motors of type X, geared for speed Q:R to two Z diameter wheels on each side, wheels are geared together” IS enough information for others to compare their experiences.
Light robots with 4" omni in front and 4" normal tires in back, chained together at 1:1 with 2-3 Three wire motors per side have performed ok in competitions I have seen.
Higher gearing, hi-trac tires, or heavier robots may not work the same.
4x4" omni wheels is one of the most common competitive drive setups, but many teams still report stalling motors, due to lack of Magic.
The protection device on the motors is refereed to as a PTC and is a polymer switch which has a connection surround4ed by polymer and as the polymer heats up it expands and breaks the connection. The current in then dumped through a large resistor hence the stopping of the motor. When the polymer cools down the connection is made again an the robot begins to work until it heats up again. The main problem is the polymer deteriorates over time and the motor performance begins to go down and the PTC will trip under lower temperature. New PTC can be purchased and it is a very easy solder job but whether this is totally legal or not I am not sure but it fixes the issue until they deteriorates again.
As far as drive trains go we have found it best to use omi’s on all four wheels and gearing the fronts to the rears. This helps to give power to the wheels that need it the most. And if we use 4 269 we stick to at 1:1 up to 1:1.4 ratio. Sometimes we will use 2 393 and 2 269 and go 1:1.6 to 1:2 ratio. We have found the lower ends to be very reliable and much better for positioning in autonomous.
Actually during last years round up our first robot used just 2 393 at High Strength with a 1:1 gear ratio on 4" wheels. Our robot weighed about 13lb and we still had power to push other robots, never burned out. After some experimentation we found that 4 393 motors on High Speed and 4" wheels have plenty of power and can move a 15lb robot with power to spare.
Again, if you are experiencing hot motors and stall conditions where your motors stop rotating while operating, then you are overloading the drive motors. You will need to reduce the motor loading by:
internally gearing the motors for torque rather than speed,
use a combination of gears that provide more toque at the wheels
incorporate more motors into your drivetrain
use smaller diameter wheels
reduce your robot weight
These are all viable solutions that you may have to utillize in combination with each other.
High-strength gearing on 393 motors with 4" wheels results in a theoretical top speed of 1.7fps. That’s pretty slow, and you had about 80% of the power of four small motors available. You chose gearing that was appropriate to your drive motor budget.
If you are using two omniwheels, make sure they are on the lighter end of your chassis
Make sure you aren’t losing power to friction in your drive train – either drive components (wheels, gears, lock collars) rubbing on the chassis or chain that is too tight
That is a good point, but yes we did test the robot with heavy driving for at least 10 min and then cheacked the motors and found that they were just finally starting to get hot. In the high speed config though we never had overheating issues even after long run times (and we drove hard).
