Direct vs Chained Drive for ITZ

So my team has recently been able to take off two extra motors from other systems so that they can be used on our drivetrain so that our bot can both travel faster and burn out less.
Currently our bot runs on a 4-motor direct drive hi-speed base, and only burns when we ram into the 20-pt bar for more than 5 seconds, but is relatively slow because our robot is way too heavy atm.
Now that we have two extra motors to allocate to the drive, I’d like to know what our best options are. My teammates want to chain everything 1:2 on torque motors (so 200 rpm), but I think the weight and friction of chaining isn’t worth it, and I instead proposed a 6-wheel direct drive hi-speed or turbo base.
We’re modifying our mogo lift so that the robot weighs a lot less at the end of this, so I don’t think turbo will be an issue, as the change in motors (6/4) is the same as our change in rpm (240/160), so the torque of the new vs old system should stay the same, and our overall weight will decrease anyway.

Thoughts on the two suggestions?

you would be correct, as adding the chain drive would only serve to add friction or weight. (2:1 is a speed ratio but that’s not what this thread is) Essentially, you would be going about the same thing in two different ways. One thing to point out is that a 6 motor turbo and 4 motor high speed have the same amount of power, as in pushing power. The math works out (assuming all motors have the same amount of power) 4 motors at a 1.6:1 power. This results in a torque of 4/1.6= 2.5 motors of pushing power. Again, at 6 motors at a 2:1 ratio (or turbo which is the same) it means you end up with 3 motors of power. However slight that difference is becomes negated with the increased stalling associated with going faster. This principle essentially states that when you move faster, your motors have to do more work to slow down, due to the increase in momentum, leading to stalling at about the same time.

My recommendation is that you use a 6 motor high-speed drive, or an 8 motor turbo drive, as has been standard in most of the reveals this season. We experimented with A 6 motor turbo and found it stalled too often and was too inconsistent with stalling and lack of torque. So that’s my recommendation, I’ve seen robots pull off a 6 motor turbo, however, this year with the cones I don’t recommend it.

Thanks for the helpful advice, I was slightly worried about turbo anyway. However, that still leaves the question of a 6-wheel direct drive base vs a 4-wheel chained base. I’m assuming that since you agreed about chain adding extra weight and friction that you’d recommend the 6-wheel base, but I just want to make sure.

(Note: I believe a 6-wheel base would also make us accelerate slightly faster as there is less weight per contact point with the ground).

Just a note of advice, VEX sprockets and chains are a total pain if you have any more than 2 sprockets in the chain. What you’re are gonna want to do is have one axle with 2 motors and a wheel on it, chained to the other wheel with the other motor on that axle

Yeah that’s probably my biggest problem with chain in VEX.

I had thought about this, but I can’t have two motors on one axle because one motor would then be outside my drivetrain and therefore outside of 18"…

I am using gears to link the 2 motors together for, in my case, the back wheel. Then chain the front and back axles together. I don’t have a picture handy, but if you end up gearing two motors together I recommend screwing the sprocket and gear that are on the drive axle together. The double torque on the axle will either twist it, or strip something if the chain gets stuck. One step further would be to put screws/standoffs through all three parts, (gear, sprocket, and wheel) so the axle has no torsion on it at all. That is how I have my drive set up right now.

Just found this pic of the front, so there is no other gear in the pic… but it shows the three parts bolted together at least.

We have 3 teams. Two of them are using high speed motors and the other is using turbo motors. One of the teams that uses high speed motors is only using 4 motors direct drive and they have experience the most problems with stalling. They will be rebuilding to add more motors to the drive.

The team with turbo motors started the year with an 8 motor drive with 4 direct drive and the other 4 geared 1:1 using 60 tooth gears. Since then, they have removed 2 of the motors from the drive and have two wheels direct drive and the other two direct drive and the second motor chained using the smallest sprockets.

After spending some time practicing driving this incredibly fast robot, they competed last week and ended up tournament champions with another of our teams and a team from an area school. They experienced no issues with burn out.

They noticed very little, if any, difference in speed. The went to 6 motors on the drive as they plan to add more to their robot in the way of function, but not in weight. They actually added weight to the robot so it would not tip when picking up mogos. That weight will be shifted to something that actually functions in the coming weeks.

Unless your robot is way over weight for this game, you should be fine with 6 turbo speed motors using chain or gears.

We have a 6m turbo too, and we balanced the center of gravity of our robot with two batteries. They do a pretty good job of setting the weight of the mogo unless the driver decides to accelerate full speed forward in which case the root does a wheelie before returning to all wheels.
Personally our team prefers to have all wheel drive on our robots. Especially since you need to cross over the starting bar very often, this season.

@Colossus Our team with the turbos just changed the battery placement before the last tournament. Unfortunately, they do not have a power expander so there is only one battery. The wheely sounds fun.

For their robot, the front to wheels are powered with one motor each and the rear two wheels each have 2 motors. This helps getting over and back into the 10 point zone when they are scoring in the 20. When they were using gears, the gears would actually touch the starting bar and sort of act like a low friction wheel. It was sort of funny but there were some obvious long term issues to consider. Using chain for that seems to have helped.

Thanks for the personal accounts. Just curious, how heavy is the robot that runs on 6 motor turbo? My robot is a full dr4b with a chainbar and claw on the top, as well as a mogo lift on the bottom. Do you think 6 motor turbo could support that? I doubt it, but if it worked for a robot of that same weight then maybe I’ll try it after all.

My suggestion: If you have time, dink off. Drivetrains are relatively easy to alter, so just mess around with different ratios while sticking some weight on your bot to see how it responds until you find your sweet spot. If you don’t have time, I would go 6 motor high speed direct, it’s your best shot at getting something functional quick.

One of our teams had a 6 wheel drive and it was very helpful in stopping the robot from being pushed side to side (4 Omni wheels in the outside and 2 high traction wheels in the center). This worked good but presented a problem when trying to place mobile goals in the 20 pt zone because the middle wheel would cause the robot to get stuck on the small pole.

I would suggest you make your robot as light as you can without losing function and give turbo motors a try. We use quick swap so changing the internal gearing is quick and easy. Without seeing your robot it is hard to say if it would work. I know that our robot that has been using turbos from the beginning is the heaviest of our three robots. We have a 4 week break between our last comp and the next one since we do not participate in our own tournament so by our next tournament, I would suspect all our teams will be running on turbo.

This game more than most will be won with speed.

speed means nothing if you can’t stack cones.

I’ve always viewed turbos on a drive train as a unacceptable risk. Look what happened to 2719B at PT. They couldn’t get themselves out of a pin, and even a couple seconds of fighting took them out of the match.

we won a couple of our tournaments last year because teams drives were tripping out trying to push us from a across a fence. This year will yes require some speed, but if you aren’t capable of torque, the team is running a massive risk.

I can see where you’re coming from. To be fair though they shouldn’t have been pinned for that long. The refs just didn’t know the rules for pinning I guess. Honestly though I do see what your saying about torque being a good thing some times. Maybe you may want to push someone out of the way to score a mobile goal, etc. There are definitely good things that can come from more torque this year.

As for a direct vs. chained drive: adding just a couple sprockets to your wheels to tie them together actually doesn’t add that much friction if you build it right. My last bot that I had built had chained together wheels and it helped tremendously with being able to power both sets of wheels. My current bot doesn’t have chained together wheels and what I’ve noticed is that there’s some power loss when trying to get other the starting bar(not very much). It’s mainly due to the fact that I have an 8 motor turbo drive(sorry @TheColdedge :P) but 2 of those motors on each side are on each wheel and so they aren’t working in tandem with each other but rather it’s forcing the 4 front wheels to take on more of the load rather than having all 8 motors work together like they would if the drive was chained together.

So that’s just my two cents, I hope if nothing else it at least encourages you to try a chained drive because I think it may let you run some more aggressive gear ratios but that’s your call :slight_smile:

You’re right, but it still happened. They took the risk and it didn’t pan out well. I’m not saying you don’t need speed, but that it needs to be balanced with the ability to push things. Right now, our B team is more heavily skewed to ward pushing and not speed, and that’s been an issue. However tipping the scale too far into speed won’t help in the long haul, its about finding the proper balance.

I don’t have the math to back this statement up, but I imagine 8 motors all chained together compensate nicely for turbo gearing’s lower torque.

Both of our teams are working with 4 motor drives it’s a different design situation.

I agree with this. My co-coach (husband) has told our team that sometimes you have to go slower to go faster.

We feel that taking risks is the one of the best ways to be successful. We are now running a four motor drive but with the ratio it has just as much torque as our six motor turbo. As the season progresses and teams become more competent at stacking, I’m sure that torque will become less of a problem because teams should be focusing on scoring cones to win matches, not simply playing defense. If a robot can drive faster than it can score than it is too fast. That is my current philosophy.

That’s reasonable.

edit to add:

We just have found turbo drives can be fickle, and that risk is too much.

I am not saying that is everyone’s situation, and I have seen excellent turbo drives that work fine.

Our recently shared experience from PT was the best example I have. Another example would be 323Y’s drive failing at PT last year against us pushing at the fence.

Yes, I see where you are coming from. Their stall was a result of design. That robot was too heavy for a four motor drive.

Edit to add:
Turbo drives are in fact fickle. They take a lot of driver practice and weight cutting to make work.