Window motors in parallel

[JellyMan]

We are considering using two window motors in parallel to power a lifting arm. Since worm gear transmissions cannot be back-driven, and since the motors would be working together on the same axis, we are concerned that they may bind up.
Does anyone have experience with this?
If so, how did you control both motors?

Thanks.

[Tytus Gerrish]

each motor must be on its own spike victor or jaguar. you can provide them with the same signal using a PWM "y" cable

[artdutra04]

I would strongly suggest using the FP, BaneBot 550, or Banebot 775 motors instead of the Denso window motors to power an arm, as the Denso window motors are actually among the least powerful motors in the KOP. They are also prone to overheating and tripping their internal thermal circuit breaker if you try squeezing every last Watt out of them.

[JellyMan]

Thanks for the fast replies!
The FP motor (#0673) and gearbox was our first choice for the lifting arm, but only one FP came in the 2011 KOP, and we already allocated that FP motor to an elevator function. We have two FP motors (#9015) and gearboxes from our rookie 2010 KOP, but the Andy Mark website lists the 9015 motors as illegal for 2011. Any idea why?
We are still essentially rookies in experience and resources of all kinds (especially funding), so we are stuck trying to make do with the scraps we have. We'd like very much to make use of the 2010 FP motors.

[wilsonmw04]

Originally Posted by JellyMan

Thanks for the fast replies!
The FP motor (#0673) and gearbox was our first choice for the lifting arm, but only one FP came in the 2011 KOP, and we already allocated that FP motor to an elevator function. We have two FP motors (#9015) and gearboxes from our rookie 2010 KOP, but the Andy Mark website lists the 9015 motors as illegal for 2011. Any idea why?
We are still essentially rookies in experience and resources of all kinds (especially funding), so we are stuck trying to make do with the scraps we have. We'd like very much to make use of the 2010 FP motors.

I would look at the 4 Banebots motors that were in your kit this year. one (or two) of those should be able to do any job on your bot.

We used the window motors during our rookie year (2007) to lift our tube manipulator. We used them in "parallel" on the same axis. They work fine but we ended up having to assist them when a bit of surgical tubing to get past the tipping point of the arch.

[Teched3]

With enough moment and weight, those motors can backdrive. I would recommend you test them and design an anti-backdrive mechanism if it proves out that you will need one.

[JellyMan]

Thanks. We'll take a look at the Banebot motors. Can the pinion gears be pulled off the FP 9015 or 0673 motors and pressed onto the Banebots? Will the Banebot motors mount to the FP gearboxes without modification?

Regarding the rules, I've reviewed the 2011 FRC Manual, and Section 4.3.9 Motors & Actuators <R45> states: "Motors specifically permitted on 2011 FRC ROBOTS include: A. all motors, actuators, and servos listed in the 2011 KOP Checklist". The checklist actually lists "FisherPrice Gearbox, 12VDC w/ 16 tooth pinion, -9015 motor". If the 9015 motor is illegal, then that seems to be contradicted by the 2011 checklist. If not for the statement on the AndyMark website, I would not have given it another thought.

[maddoctor90]

We used two of the window motors in parallel last year on an winch that lifted up an arm to attach a hook to the tower. We then used a CIM to to lift the robot. The two windows motors would probably work fine, but like others have said, the Banebots motors would probably work better for your application if you can make them work.

[AndyH]

Our team 1098 used a left and right wimdow motor connected with a shaft between the couplers to run our cam kicker last year. Worked GREAT. One motor would just stall but the 2 motors did the job. The programming team got them to run together perfectly, seperate outputs to seperate Jaguars.

[Tristan Lall]

Originally Posted by JellyMan

Since worm gear transmissions cannot be back-driven, and since the motors would be working together on the same axis, we are concerned that they may bind up.

The idea that worm gears can't be backdriven is a bit of a misconception. It actually depends on the design of the system—some high-efficiency worm gears can definitely be backdriven. (See page G-57 here for more details.)

As Tytus explained, they can't be electrically in parallel, only mechanically. But in that configuration one failure in a motor or electrical component will probably lock up your arm, or worse.