Direct drive or Chain?

[Suneet]

Our team, tem 599 is debating whether or not to use chain drive or direct drive with four motors. We have heard that chain drive is more forgiving (in terms of strain on the motors) than direct on the motors, but direct drive may be faster. We had some principal concerns with both:
For chain drive:
1. Clearance
2. Are chains really worth all the trouble?
For direct drive:
1. Can we make sure that the motors run at the same speed?
2. If not, how close can we make it?
3. Does it really matter?

[Frank(Aflak)]

with 80/20 frame, chains is so much easier than gears its not even funny. We use 80/20, gonna use chain drive exclusivly (cept for the gearbox on the bosch, that gives us a good reduction we don't need to pay extra for)

edit: Its not hard to get different motors to be withing 10 or less RPM's of each other, we got like 5 or 6, which is about 1 or 2% difference, which will be fine over a period of 2 minutes. Over ten hours, you would probably burn the motors up, but 2 minutes is fine.

[Ken Leung]

The most important thing to consider about using gear is your skills in making a gear box. Usually, when you are using gears meshing with each other, you can only have a 0.001 error, maybe even less than that in order to make the gear box work.

With only drill press, or even a mill without digital read out, I fear you may not have the necessary skills and tools to fabricate a good enough gear box. That's why a lot of teams use chains, so they can tention the chain without making the whole drive system as accurate as a gear box.

If you have the resource and knowledge to make gears work, then by all means do it. Else, chain will work fine too.

As for the speed of motors... They are really about setting up a correct ratio, and both chain and gears will work for that.

[dlavery]

Originally posted by Ken L
With only drill press, or even a mill without digital read out, I fear you may not have the necessary skills and tools to fabricate a good enough gear box.

Hmmm. Guess me and my drill press with an X-Y table are going to have to go back and redesign our gearbox from scratch.

Just as a point of reference, in the hands of a skilled machinist (almost an artisan), amazing things can happen. A century ago, toolmakers regularly made precision pieces to within 0.1 mil on a regular basis, by hand. By using the right techniques, it is possible to hand grind a surface plate to one MILLIONTH of an inch accuracy. For 300 years, watchmakers have cut and filed gears by hand, with great precision.

Don't underestimate the ability of a highly skilled technician with simple tools (and don't overestimate the ability of an unskilled fool with exotic tools!).

-dave

[Rickertsen2]

we r using a combination of gears and chains

[Jeff Waegelin]

We use gears in our gearbox, but we run chain off of the output. It gives us some flexibility in adjusting speed and power, because it's a lot easier to swap out a sprocket than it is to switch out a gear.

[Jim]

>>Don't underestimate the ability of a highly skilled technician with simple tools (and don't overestimate the ability of an unskilled fool with exotic tools!).

-Amen Brother!

[DanL]

Just remember, if you use chain, make a tensioning devices. Switching rapidly between going forwards and going backwards creates a bit of slack (don't know the technical term for it), and if you're not paying attention, this slack is going to make the chain fall off.

From expierience, I know that had we made a tension device that would have stopped our chain from falling off right at the start of a key match during nats, we would have done a lot better. So don't disapoint yourselves later on - make a tensioner.

[FotoPlasma]

Originally posted by SuperDanman
Just remember, if you use chain, make a tensioning devices.

In 2001, we (258) used pieces of delrin as tentioning devices on our drivetrain.

By cutting roughly (Thursday morning, at the Los Angeles Regional), and drilling holes wide enough to feed chain through, with another set of holes to suspend the blocks with pullties. Two per wheel, two wheels per side, eight blocks total.

Yes, it was a very makeshift system, but it worked like a dream.

I wish I had a good picture of the system, right now, but you can almost see it at the bottom of this picture. The white cubes are delrin, the white strands are pullties, and the black strands are the tentioned chain.

[ChrisH]

There's an even easier way to tesion chain. Take a piece of 1/2" dia delrin rod about 1.5" long or enough longer to bridge whatever gap your chain is runing through. Drill a hole through the center of the rod perpindicular to the axis of the rod about 3/8" from each end. The two holes should be parallel to each other. Slide the rod under the chain but up against some supporting structure until it is just a little too tight. Bolt the rod down. The chain will wear into the rod until it is the right tension. It will then stop wearing into the rod as a sort of equilibrium is reached.

It takes 10 or 15 minutes to fabricate and install.

[mtaman02]

Chain Drive is what will be used by T522

[maxgebhardt]

We're going with chain giving 4X4 drive, but we've shied away from casters added to direct drive systems from some unsavory problems our rookie year. if anyone was at the Columbia regional two years ago, they remember a big gold triangle that couldn't go up the teeter totter, and was beaten by a robot that couldn't move. the reason, aside from bad gearing, was the casters caused the robot to spin wildly, as it changed from turning to going strait. the casters would spin into position moving the robot in the process. also in the same fashion as a shopping cart, if one wheel came off the ground and spun, then hits the ground again, the robot will swerve in that direction, and if a caster gets stuck, the robot will spin in large circles!
My advice: stay AWAY from casters! they are evil!

[XMATT237X]

237 uses a sproket chain setup (has for many years now) for our systems. Using 35 chain and sprockets does wonders, we've found it to be a great reliable system. It easyer to change a blown chain than to have to pull a gear bow and do damage cointrol. if the system is over stressed, the chain is usually the first to go rather than the gears being chewed. its more of a user friendly/pit friendly setup, most teams have chain, but it might be hard to find a team with a spare (insert gear specs here)..

[chellyzee93]

Your just asking to burn out your motors with direct drive.. go with the chain.Trust me

[comet22]

We last year used primarly chain drive and experienced a lot of problems with it, for one there is a little slack in all chains so this leads to increased strain on the gearbox, which last year caused us lots of problems. This year we are using belt material that has worked wonders for us...