Hi there. Referring to this thread: https://vexforum.com/t/answered-mixing-motors/21794/1, JVN mentioned that it should be okay mixing the motors. But, I am assuming that that relates to linear gearing. My question is… What happens if you were mix these motors in a compound gearing. Would that be okay? Or will it back drive the motors?
As long as the gearing between the two motors is 1:1, a mix of motors can drive any load you want, with any gearing you want.
As long as you keep the 393 on high torque they are the same speed so there wont be an issue but they have to be geared together and then geared to the arm you cant gear one motor 3:1 then geared to another motor.
As long as the 393 is kept on high torque internal gearing, both motors will have the same free speed (100rpm). So as long as they are geared the same it is ok, e.g.
(36t gear with 269) meshing with (36t gear with 393) meshing with 60t gear is ok
(36t gear with 269) meshing with (60t gear with 393) meshing with 60t gear is not.
From what i have learned from last year is mixing the different motors is not a good idea for a couple of reasons. First, in my experiences it seems that the 269 motor overheats much faster then a 393 motor, so if they are paired up the 393 motor drags the 269 motor once it has overheated causing the 393 motor to overheat. Also there is more lag in the start up of the 269 motor then in the 393 motor so the 393 motor, when paired with a 269 motor, will drag the 269 motor when the robot first starts moving
Have not heard this one before, was this based on your own testing or just something you were told? Do you have any data to back up this claim?
I’m not saying you are wrong but I have not experienced that before. Our teams used a standard configuration of 2x269s and 2x393s on the drive last year and did not have any problems all season due to mixed motors. I’m about to embark on another round of motor testing as the recent numbers released by VEX were a little worrying (high current for the 393s, not as efficient as we all thought). I will add this to my list of tests if this is something you have experienced. In practice, any two motors, mixed type or not, will have slightly different characteristics due to the manufacturing tolerances which are given as +/- 20% on the product page for the 269.
My team experienced both of the problems that i talked about in my last post, when starting the two motors at the same time we were able to see a visible difference in start up time between the 269 motors and the 393 motors. The 393 motors would begin to spin much quicker then the 269 motors. At lower power it also appeared that the 393 motors where doing all of the work and just pulling the 269 motors. We also used 2 393 motors on our base and 2 269 motors but changed them out to all be 393 motors after the first competition due to overheating issues.
Ok, do you program in ROBOTC or EasyC? Do you remember if they were on 2 wire (1 or 10) or 3 wire ports on the cortex? Or are you using a PIC? There are some subtle differences between the motor control from a 2 wire port and a 3 wire via a motor controller 29. Overheating is very much robot dependent but many have claimed that the 269 overheats sooner.
We were using a cortex with robotC,they were both running off of motor controllers. The wiring of the 393 motor and the 269 motor were identical.
Thanks, I will see if I can reproduce that.
We have also experienced 269s overheat sooner than 393s. Our 25-ish lb Round Up robot used 4 269s on its drive, and before we added motor clutches, they overheated within the first minute of every match. Our 25lb Gateway bot, however, used 4 393s on its drive and once we had it built and wired well, it rarely overheated.
Using motor clutches on 269s (on a drivetrain) has a profound effect to stop them from overheating. At Round Up Worlds, we lost our first 5 matches due to overheating problems, and then we added motor clutches. The drive motors didn’t overheat again for the rest of the championship, and we won our last 5 matches.
Thanks guys. Actually my team has tested out the mixture of 269 and 393 before with a 1:7 simple gearing. It went well and things went smoothly for us. But when we thought of changing the gearing to a 1:9 ratio and it is a compound gearing. We were afraid that the more force of such a ratio would spoil our motors. We have finally implemented it and it works just as we expected. Thanks again.
Does anyone here wish they still sold 3-wire motors?
Yep. Our kids had 4 3-wire motors and 2 393’s (6 total motors) on the drive train. The hard part is knowing when one motor is out of whack. Once geared together it’s tough to tell if you have a problem. We had a 3-wire with stripped gears and it took a while to figure out what the problem was.
Just running the 393 without the 3-wire powered caused even more strips. So pulling out the center gear in the train was the only way to really test. Anyone have any ideas on testing with everything still plugged in/configured?
Yes, you get some grind on the other weaker motors, so the different start rates might be causing that. Thanks for the helpful info. But overall the extra torque of the othe rmotors is definitely worth it in a pushing battle.
Now with up to 10 393 motors, I think proper power management across just those big motors is more the way to go. Will 2 of the 393 motors per side with proper power limits help in the pushing battle more so than a 393 + 2 old three wire motors (or 269’s)?
YES!! Or at least the Replacment Gear Kits… I Only Have the 3 Wire motors, and have bought a few on ebay, some with replacement gears, but they will wear our eventually and need to be replaced with the 2 Wire variant…
I’m still not convinced on the different startup times. Under no load they are the same, I will try and find a way to test under load but its not so easy.
This composite trace shows startup time for the two motors, both reach full speed in approximately 100mS. The 269 may be slightly slower but I doubt you would notice the difference.
Under load this may not be true, TBD.
Chaining/gearing a powered motor to an unpowered motor might be a way of providing a standard load. A string drum with a weighted string, with string starting taut might be another; its more clunky to manage, but has a specific torque value.
Gear 3 motors together, and power 2 of them from a Y cable (to ensure the same power applied), and check your same type of current profile might show if they are dragging each other.
Gear 3 motors together, and power 2 of them from independent motor ports;
the same types of current profiles may vary depending on the programming gap.
Several iterations might hit once on the maximum program gap (5 vs 40ms?) and show that a 40ms gap vs a 100ms ramp is significant (or not).
Predictions: what would drag look like?
- P1: A motor with a load will have a slower curve to minimum current.
- P2: A motor being dragged ahead will have a faster curve.
- P3: A motor dragging another motor in addition the the load will have a slower curve.
YES!!! They are so reliable, we still use them today. In fact, our Worlds robot had 4 and I generally prefer them to the 269’s. We have come across a lot of 269’s that lock up when they die, which kind of puts me off using them, since if you have numerous motors working together and one locks up, the thought just scares me. I guess that’s where clutches are still useful.
I would guess that you are running the 269’s without Clutches, but since the Clutches are still available, I wonder if that would increase their Life Expectancy…
I only have the 3wire motors, I have not yet invested in the 2wire motors…
My team last year found that there was a batch of 269 motors that had a defect that caused them to lock up when going in one direction and when they stopped they would momentarily completely lock up. We found that we could fix this problem if we switched out the back cover of the new motor with the back cover of an older 269 motor.