Using dual motors in Chain-Drivesystem

[thoughtful]

I am very new to dual motor chain systems. There are some informaton on how to join to motors in a transmission on chief delphi. But i wanted to get your guys advice on how effective is having a Bosh and CIM motor on a single chain DriveSystem. Having them geared down to the right ratios of sprockets. And if anyone has done this before please tell us how they did it and how effective it was.

[Matt Adams]

We are doing it this year, and the way you do it isn't as complicated as people think. The short story is that you want to have the motors drawing the same current. Fortunately, the atwoods and the drills draw roughly the same current when you happen to mesh them at free speed.

I'd suggest that you mesh the drill and chip together when the drill is in high, and then control a single output shaft to that. It'll take less of a reduction.

If you'd like some more details, please ask.

Good luck!

Matt

[thoughtful]

Thanks i get an idea of what your are saying, but if you could explain it more or tell me what ratio the rpm's are it will be very helpful.Thanks a lot.

[tkwetzel]

Team 116 has developed a transmission combining the Atwood and the Drill motors. It is also a two-speed transmission. The document containing everything about it is here: http://www.team116.org/2004/Transmis...riptionV6a.zip

Good luck.

[Cory]

he wanted info on combining motors using chains and sprockets, not a geared system.

To answer the original question, check out one of the many whitepaper's based on drivetrains (Another plug for John's great whitepaper )

Cory

[thoughtful]

Thnx for everyone who posted, though yes we are looking for something easy and want to keep as far as possible away form custom machine cuts e.t.c or hightech Driveterrains..at least for this year. And yes some of your posts helped me a lot. I amlooking at the white papers now..and that is some good stuff.

[Solace]

if you want a simple way to make a 4 motor drive train, gear each motor down to the correct range, and then connect each one to a seperate wheel. That way any inconsistencies will be taken care of by way of the slipping of the wheels instead of putting an excess amount of strain on a gearbox.

it is relatively easy to make an all chain gearbox - we did it last year on our bot. the front two wheels were driven by drills and the back two by the chips.

[thoughtful]

Yes we were thinking about that, though the only question i would like to ask is that under different loads how much the RPMs of the motors will go out of sync. And what can be done to reduce it (any thing on the programming side maybe)

[Solace]

yes, the motors will go out of sync a little when under load. however, because they aren't directly connected, the slop in synchronizing them is just taken out in wheel slippage instead of having the motors directly fighting each other. The effect is somewhat reduced. You can try to create a voltage map to have the motors always be running at the same RPM, but that can get a little complicated and requires a lot of testing and experimentation

[sanddrag]

We did last year exactly what your original question was. You can see some pics on the various pages here: http://www.team696.org/forum/category.php?cid=5 It was very simple and worked fairly well. We used the kit pillow blocks and mounts on the drill motor and kept it in high gear. That drove a 10/48 reduction to the wheels. The chia was geared down directly to the drill shaft 10/35. There were a lot of issues with misalignment and overly tight chains and binding. It was a very high drag high current draw design (partially due to having 4 separate pillow blocks as you can see in our pics). However, it worked and it worked better than many out there. We seeded third in Phoenix making it to the semifinals and made it to the finals in LA. We also participated in an off season event and an exhibition event and a few demonstrations and the robot still is driving today (although it has gotten a little louder). If you have any questions about it, feel free to ask.

This year, we are gearing the Chias through a two stage GEAR reduction to match the low speed of the drill in our all new "QuadraMax G2" It is basically a slight redesign of the team 716 2003 single speed tranny.

[Matt Adams]

Okay, this is a post worth replying to, because this is a very common situation. As a matter of fact, we're combining chips and drills to a single shaft in our drive system this year, so I'll share a bit of info.

As it turns out, you don't want the shafts of the individual motors to spin at the same speed- that will be very inefficient if you combine two different motors with different specs. You want to choose a gear ratio (done with either sprockets or gears) such that when these motors are spinning pull their max torque, that a single output shaft will have an equal current contribution.

To simplify...

Let's say you throw a shaft on the end of the drill motor and let it spin with little to no load. It'll spin at around 1521 RPM. Now let's say you put a Chip attached right on to that shaft on the other end, directly connected.

The Chip has a free speed around 5300 RPM... but the motor won't spin at that... the motors will actually convege to a speed somewhere in between 5300 and 1521 RPM... the reason for this is unique for DC motors, and is known as back-emf. Where exactly this converges depends on some coefficients of the motors. The short story is that this is not optimal.

Please take the following as truth: Free speed, with the drills and chips, HAPPENS to yield approximately equal current draw. It's a coincidence.

So, to match the current draw, you'd want to put a 35 tooth sprocket on that shaft from the end of the drill motor, and a 10 tooth on the end of the Chip. Then they'll both spin around 1520 RPM, and HAPPPEN to be pulling about the same amount of current. This is a good situation.

From here, you're going to have to gear it down a bit more to get more torque. Reducing these to somewhere around 340 RPM (for a 6" wheel) is a safe speed / torque trade off for high(er) quality wheels with good traction (1.2 coefficient of friction).

If you have any questions or comments, just let me know.

Seach for recent threads that talk about dual drive motors, combining motors, and shifting... many great contributions.

I even made some graphs in one.

Good luck,
Matt

[Matt Adams]

Originally Posted by thoughtful

And what can be done to reduce it (any thing on the programming side maybe)

In general... the way you "adjust" in software is that you reduce voltage output to one motor. This is NOT optimal, so don't go there unless you have a really good reason to. In general with a drive system, do things mechanically wherever you can.

Matt

[sanddrag]

Originally Posted by Matt Adams

In general... the way you "adjust" in software is that you reduce voltage output to one motor.

Sorry to get technical but you aren't really adjusting the voltage output. Perhaps you meant the average voltage. What you are really adjusting is the pulse width.

[Mike Norton]

We use to put the motors like this

http://www.valleytech.k12.ma.us/robo...2%20Gears1.jpg

But we found out it has been better to put both chips together and both drills together. With a track system the robot goes pretty straight. But the power is at it's best becuase you do want the drill motors to be going in the different directions. there is a different between forward and backward in the drill motors.

[thoughtful]

Thnx a lot guys, now i know a lot more about how to connect these motors, yea i heard about that forward and backward difference(forward being more powerfull or something) how important is it to flip them?.

Mike Norton, that link was helpful, though that chain and sprockets looked pretty lighter than what we used last year, is it 25 mm chain..and if yes did you had any problems with it. Because we went with 35 mm last year, had no problems but was very heavy.

Also Mr.John Vielkind-Neun helped me a lot,and even went as far as drawing a sample sketch for the ratios that we need. So a a special thanks to him on behalf of my team. I am posting the link just for any other teams who want to learn about the same topic as us. Also in white papers John has an excel sheet that can do all the math for gearboxed or drivetrains for you guys.

You can see what John did, by viewing the attached thumbnail.

Thanks to all again.