Running motors together to get more torque

[vivek16]

i was wondering but would it be possible to run both the nippon-denso window motors together to get twice the torque?

i am designing an arm for fun and have figured out what motors to use uptil now but i think about twice the torque of the nippon denso motors would be enough for what i want.

thanks.

[FourPenguins]

There's no reason you can't do this. It can be done programmatically or by splitting the PWM signal using a Y-cable.

The only criticism I have of this plan is that two motors can get a bit heavy. If you can get the right balance of speed and torque through gearing or with a different motor, it might be lighter. This also frees up your other ND motor for another part.

Keep in mind, of course, that next year's kit might not even have these motors.

[Alex.Norton]

No, it would be unwise to run two nippon-denso motors together because these motors use a worm gear. The worms would fight each other and eventually bind because they can't back drive each other. Even though they are the same type of motor does not mean that they will turn at exactly the same RPM.

However, If you wished to run the globe motor together with the dippon-denso motor, or any other non worm gear motor with the nippon-denso motor, this would be a good solution.

Alex

[FourPenguins]

Originally Posted by Alex.Norton

No, it would be unwise to run two nippon-denso motors together because these motors use a worm gear.

A good point, but isn't always an issue. We ran two Keyangs (also worm-driven) to power our winch this year and didn't have any binding issues. I personally don't recommend this method, and I had no part in the decision to use it, but it did work.

[haroony341]

in 04 we used 2 window motors (also with worm gears) to power our winch to hang on the bar and we never had any binding problems. they worked perfectly together.

[lynca]

We use two (keyang) window motors on our current robot arm and we have not had any problems except for the plastic adapter cracked, but this was not due to running the motors on the same shaft.

[Greg Needel]

Originally Posted by Alex.Norton

No, it would be unwise to run two nippon-denso motors together because these motors use a worm gear. The worms would fight each other and eventually bind because they can't back drive each other.Even though they are the same type of motor does not mean that they will turn at exactly the same RPM.

I think you are mixing up a few concepts here. First of all, it is a common misconception that you can not back drive a worm gear, this is false. With enough torque most well designed gearboxes (ones manufactured) can be back driven. The ability to hold position or lock of a thread (worm gear, or lead screw) is a factor of their pitch. It is possible to calculate the point in which the screw thread will lock and what it takes to overcome this. Now in worm drives within the FIRST community the drives typically have a very high gear ratio witch makes them almost impossible to back drive but none the less making broad statements isn't a good idea.

Now back to the question at hand. you are correct about motors moving different speeds in each direction. This has to do with the motor windings and the way that the internal brushes are designed. There are easy ways around this. you can tune your software to the motors by finding the difference in speed while changing the maximum signal given in each direction. You can use a feed back device on each motor with a closed loop system which will keep them going the same rate. Or mechanically you can make it so they are both moving in the same direction, utilizing an offset shaft and a coupling of some sort. The possibilities are really endless.

As for the application I Would recommend using both motors of the same sort if you have to over 2 different motors geared together. Even if the speeds are different the offset is bound to be less then the closest ratio you can get through adapting another motor. Ideally if you could get away with using 1 motor you will save your self some issues in the long run but if you need to use 2, coupling the 2 motors together is a fine way of doing things.

[dtengineering]

It most definitely works, and works well. The worm gears do make things a little tricky, for instance you really do want to make sure that you have both motors turning in the correct direction before you connect them together, and it can be a bit awkward to get them both precisely aligned onto a keyway at the same time.

It can be done... it is just a bit trickier than using, say, two globe motors that you can backdrive relatively easily.... and you really, REALLY should make sure that both motors are turning and in the correct direction before you tie them together. Yeah, I know I mentioned that twice. It kind of matters.

Once you've got them set up, though... it should work like a charm.

Jason

[Daniel_LaFleur]

If you are going to drive 2 worm gear (or other hard to backdrive) motors I suggest not direct driving them, instead us a belt or o-ring type drive where the tension can be set and a slip torque (slip clutch) can be put in. That way, should your ratio's be off enough that you need 1 motor to drive the other the whole system wont stall, it'll just slip a little.

[vivek16]

Originally Posted by dtengineering

It most definitely works, and works well. The worm gears do make things a little tricky, for instance you really do want to make sure that you have both motors turning in the correct direction before you connect them together, and it can be a bit awkward to get them both precisely aligned onto a keyway at the same time.

It can be done... it is just a bit trickier than using, say, two globe motors that you can backdrive relatively easily.... and you really, REALLY should make sure that both motors are turning and in the correct direction before you tie them together. Yeah, I know I mentioned that twice. It kind of matters.

Once you've got them set up, though... it should work like a charm.

Jason

are you allowed to use two globe motors on your robot? if i was able to i think it would make it a lot easier

thanks, vivek

p.s. this is for an after season project and not by any means for next season.

[Gamer930]

Originally Posted by vivek16

are you allowed to use two globe motors on your robot? if i was able to i think it would make it a lot easier

Yes we did this year. . . We direct drove them to the same shaft/sprocket. . . We had to do a little scaling factor because the motor in forward was slightly faster then the other in reverse. . .

[Justin M.]

We used two window motors to drive our arm, no problems at all (knock on wood). Bare bones simple and works like a charm.

[Alex.Norton]

True, in the case of a FIRST robot, there is little problem with tying the worm drive motors together. A FIRST robot is not going to see even hundreds of hours work and the problems with this set up will not be evident.

Another reason that this may not be as much of a problem is that the motors aren't working at their max speed and so aren't back driving each other. If your not going to run this for a very long time then I would suggest this, its simple easy and probably not going to fail. If you intend to use this for years to come as a recruitment tool or demonstration tool, I would suggest using a worm gear motor with, say, a globe.

Also, as a side not the keyang motor is easily backdriveable. We had to provide the motor with a holding power to keep it from falling. I haven't used the nippon-denso motor yet and do not know if it is like the keyang motor.

Thanks for the correction.

[Hadi379]

Why not a fisher price motor and gearbox? Thats what we used on our winch system and have had no back drive problems to date. Just curious?

[FourPenguins]

Originally Posted by Hadi379

Why not a fisher price motor and gearbox? Thats what we used on our winch system and have had no back drive problems to date. Just curious?

We used two fisher price motors to power a winch two years ago, and we had minor back-drive problems. (Keep in mind that this was a very heavy arm and that the winch drum was fairly large, which affected the ratio.)