Differential Extra Motor

how so even if your opponent can stack a little it’l be fine and even if they can get by it is still a big obstacle

I’d personally use the motor for strafing.
but having a tilter drive diff could be a huge advantage for dr4b trays, because they’ll be able to have 4m drive and 2m lift.

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if u already have 4 motor drive just do meckanum wheels so u can strafe

mecanum wheels have their downsides tbh. bulky, and low traction. I’d rather have a strafing wheel than 4 mecanum wheels.


Technically speaking, you should be able to use a differential to your advantage to score the highest tower as you have a spare motor to utilize.

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1m db4 hybrids can do that without a diff, but yea having a 2m db4 is a really nice advantage.

How I see it, a wall that fits on the back of a diffed tray bot isn’t gonna be heavy enough to hold opposing robots in place. Plus you’ve gotta manage the piece of string attached to the wall the whole match, which slows driving. Opposing robots pushing back from within the scoring zone will not be stopped, so they can sit around the area before deploy and make sure to be on the right side of the wall when it drops.

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I know a noob question, but what is a Goofy?

Please try to search for things before asking for them. A goofy design is really easy to find information on.


not really i built a 48 foot spool for my wall and i didn’t have to manage it

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I stand corrected. Just a guess, haven’t experimented with it personally. Wow 48 feet. So you never had entanglement issues with other robots?

walls will become less effective as autons get better. your opponents already might be able to stack 15-16 cubes in auton. sure you can put your wall down, but all your opponent has to do is play defense on you and stop you from stacking any more cubes.


I know that this is a thread mostly about speculation, but I’ve seen a few of the teams on 2381 try to build a differential and I think there’s a few things that haven’t been mentioned yet, and which should be addressed.

  1. differentials are not easy.
    Seriously. They take so so long to tune. And even then, they’re a massive pain to maintain.
  1. differentials take a lot of space.
    Differentials do take a lot of space, and they require a lot of work to become compact enough to fit onto your drive. How you decide to link your wheels together, and split power becomes a huge issue, and it actually turns into quite a massive constraint.
  2. They’re fragile
    Your drive is the most important part of your robot. Depending on how confident you are in VEX parts, a differential may or may not be too risky for you to attempt. A differential usually requires systems on both sides to be synced, and has multiple systems connected to it. One of those systems might be your drive. ‘if anything goes wrong, screw it and pushbot’ no longer works with a differential drive because if that differential breaks (and it can happen quite a lot), then you’re really in a bad position.
  3. inherent extra friction
    A lot of it. A differential has a lot more gears and friction than you would otherwise have direct, so it’s only really worth it if you can get an apparent benefit out of it. Which leads to my last point
  4. There is no real benefit
    Just about anything you can do on your robot, you can achieve passively, or by ratcheting some other mechanism.

I agree with all of this except for the maintenance. Using almost all screw joints, lithium grease, and hs gears, we have yet to run into any maintenance after about a month with ours.

Also a great point. We fit ours 25 wide 30 long but it is definitely a squeeze. I think the minimum length of a standard 7:1 is 1(pinion) + 2 * 7 (84 tooth gears) + 1(pinion idler) +1(pinion) so 17 holes. Pinion idlers are also always a bad idea so 19 holes with a 36 tooth idler.

3/4 are build quality components so I’ll leave those alone. This is probably not something new builders should attempt.

Here’s where I disagree. The 1m saving isn’t insane, but a v5 motor shouldn’t be underestimated. That’s a lot of power to do something… probably one of the things above, all of which are extra features to help differentiate from standard goofys. Any advantage you can get is worth it imo. The other difference is tilter speed is much faster. Our current one runs at 3:7, three times faster than normal, with a torque equivalent from 4 100rpm motors of about 1.9333.


This is true, however, as all vex parts require maintenance (think: all bearings, screw-joints, inserts, gears) at around the 1.5 month mark; having to maintain all of that on a differential is much more difficult. Identifying these issues and performing preventative maintenance also becomes more difficult.


I like that all important points regarding using differentials had been covered already:

  • every additional axle introduces extra friction losses - no way around it
  • it is possible, but hard, to maintain high build quality to manage friction losses
  • since systems are linked, it requires constant preventive maintenance to be reliable

Four bar could be made to work, but you pay the price with additional friction losses. My team had 4-bar differential in ITZ with 4 motors on 12T-84T-84T-12T geartrain connected to other 4 motors direct driving the wheels. It was ok, but it was, probably, losing at least one 393 motor worth of power to extra friction. With lower V5 motor limit that would be too expensive, so it made sense to switch from 4-bar to coaxial type differential to reduce friction. Similarly, this year coaxial 4 motor drive to tilter differential had been performing very well. It is the rest of the robot that needs more work and attention, because getting differential to work well and programmed correctly takes time.

There are only two scenarios where it makes sense to use differential. First one is where you have no other way to power all functions on the robot without reducing drivetrain power. However, you have to make very strong case why that design could be higher performing robot than well built and tuned Goofy with driving team having few months of practice.

And the second scenario is when you want to take the harder route to learn about system reliability, advanced mechanics and programming PID for complex systems with multiple degrees of freedom.

You may find yourself spending most of the time improving your build methods and doing in-depth research on how PID works at the expense of more driving practice. It all depends on the team which of those could have greater educational impact.


How could it do that if tilter is on top of the DR4B lift?


I believe he’s talking about a db4 tray hybrid, where you don’t lift the tray itself.

you can also have a tilter mounted to the chassis with the tray on the lift. the tilter pushes the tray forward by rubbing against a flat surface, like some polycarb. it allows you to lift a lot faster because the tilter weighs quite a lot. 6627x does this kind of dr4b tray, it works quite well.


Ngl, I don’t understand how 6627x thing is supposed to work. So, are they pushing tilter vertical while the lift is down and then lift dr4b up? Aren’t they risking the tilter falling back if the robot starts moving or am I missing something?

Then for a goofy, why would anyone want to go to all the extra effort to build a differential if they could use just one motor to lift the arm if it goes one way, and move the tilter, if it turns another?


So basically the tray isn’t connected to the tilter. The tilter is just a paddle thing that rubs the tray. When they lift the tray just falls back to resting position.