Design advice requested

I am a parent/coach to a middle school VEX team that is homeschooled. I have very little experience with robotics, and would appreciate some advice/input.

Right now our team has a robot that scores. However, our kids want to change the design before their next competition which is just over a month away.

Right now the robot has a simple pivot arm that lifts the scoring mechanish up and down. The scoring mechanism is two rotating treads that lift the balls and barrels and put them down into the 11.5 inch goal.

One idea is to have a four bar linkage where each bar has a linear slide inside. Two of the linear slides will have motors which can extend and retract to reach the 30 inch goal and also be able to fit inside the 18 inch goal. The motors lifting the bars would have a 1 stage gear reduction so that the torque is increased.

The other idea is to have a six bar linkage with a claw at the end. According to the student who wants to do this: the extension wouldn’t require any extra motors, it would retract when you go down and extend when you go up, it is very fast, and is very simple.

My questions are as follows:

Which design would be simpler to build?

Which design would be easier to learn to drive?

Do you think they have enough time to make such big changes?

Which design would have the most scoring potential?

Thanks for any advice you could give to our kids.


Which design would be simpler to build?

The 6-bar linkage would probably be easier to build. Instead of having to design two systems of movement (linear slide extension and 4-bar linkage), only one lift mechanism needs to be built. It’s quite easy to figure out the 6-bar linkage, especially with the numerous threads across the forum that have discussed lift mechanisms and 6-bar linkages in particular.

**Which design would be easier to learn to drive?
The 6-bar linkage would probably be easier to drive as well. It would be similar to your original pivot arm in that it is simply up to score, down to pick up. With the first design you outlined, it would require management of two lift mechanisms simultaneously which would be harder to adapt to, since you probably already have experience with your pivot arm.

**Do you think they have enough time to make such big changes?
1 month is a tight time frame, but if the drive train is retained, I would say it would be manageable to make a 6-bar linkage and claw in 1 month, though this is completely dependent on your team’s circumstances regarding meeting times, parts, etc.

**Which design would have the most scoring potential?
Depending on your strategy, I feel like your tread mechanism has more potential, but that the claw is easy to master. Again, depending on your circumstances, you will have to look at your general game strategy. If quick 1 object scoring is your game, then the claw is the way to go. If you prefer picking up multiple objects before beginning to score in multiple goals, then the tank tread has more potential then the claw.

Hope this was helpful and good luck with your changes!

Adding on to Mochi’s post,

Consider using some elastic, like rubber bands, to balance out your arm, especially considering it looks like you’re using steel. Direct the kids to find two points that are far apart when the arm is down, but come together as the arm goes up, so the elastic pulls the arm upward against its weight.

My team tried doing the four bar linkage with the linear slides and it didn’t go so well:( the linearity slides are really quite heavy so id go with a 6 bar also what is steering you away from the tank treads just get a better the on AURA’s Java Bot

haha not for us :wink:
we cont our timeframe by “work hours”
and i guess you guys count mins when you do a major change 4:00am in the morning! :wink:

it doesnt matter if your team is full of novices
if they spend enough time working on the robot, it will be finished guarenteed
btw how much time /week do they spend currently working on the bots?
my team currently does avg of 3hrs/day 5 days a week :slight_smile:
(and thats not counting last min competition panic!)

i would like to add that the generic “NZ” bot preforms better than the dual tank tread. it may be new to you, but with the numerous threads and videos, im sure it wouldnt be too difficult for you to figure out

Haha to each team their own :slight_smile: it’s only tradition to stay up past midnight the day of competition! Still going strong after 2 years. Oh. My team has also yet to pass inspection the first time. Our record is 7 goes so far…

Haha our team’s motto is to just finish in time for elimination matches. The most times we have been denied at inspection is 5 I believe.

Anyway, my suggestion for your kids is to let them watch some videos of other robots on youtube and make them brainstorm the most efficient robot. I have watch plenty of videos on youtube which has helped our team build our current design. I suggest that a 6 bar linkage will be easier to build and it will save you motors as every motor counts.

A 4-bar with slides on its horizontal links was tried in the College division last year by at least one team as a solution to the 30" problem. AURA didn’t take a video of it, but I remember seeing it on the live stream so it is possible that there is video somewhere.

The driver seemed to be having some trouble controlling it - they had to control 3 degrees of freedom at once (top and botom slides could be controlled separately). Getting the slides out of alignment also changes the behaviour of the 4-bar - unless the two horizontal links are precisely the same length the intake will change angle as you lift. With some programming or extra mechanics (such as chaining together the pinions for the slides) you could reduce it from 3 degrees of freedom to 2 and with some practice that might work well, but getting to that stage will involve an extra layer of difficulty.

Having linear slides and motors as the second stage on a lift system, especially if it has to be long to reach a high goal, also has inherent difficulties in that both linear slides and motors are heavy. Depending on your implementation it might not be a problem for you, it’s just a potential thing you might have to come up with a solution to.

For what it’s worth, those were the main reasons AURA chose not to use a 2-stage system for Round Up last year, and used a 6-bar instead (the other College teams last year probably mostly used two-stage systems because they didn’t see an alternative - back then 6-bars and 30" chain lifts hadn’t been used in Vex before whereas this year they have).

Of course, there’s something to be said for doing things your own way. The team members could potentially learn more by following an unconventional idea they came up with - even if it’s unconventional for a reason, so to speak. But the solution which is tried and tested to the point of being boring, and the one for which the most support will be available from other teams, is the 6-bar.

I don’t say this to try to swing your team either way, just to try to answer your questions :).

The robot snuss is referring to is here. There’s also a little bit of discussion about it in a thread here.

Thank you so much for all your advice! We have a meeting today and I’ll encourage the kids to watch videos and look at pictures of robots to help them decide what to do next. They wanted to change their design because while they did score consistently, they didn’t score enough to give them a good chance of winning a competition, especially since their next competition is against high school teams. Our kids meet twice a week for 2-3 hours, and sometimes more.

Again, thank you!


If your team is truly “2 guys and a robot” you probably have a decent chance of completing in time, especially if the members can work for long stretches (5 - 10 hours) on their own. If you have more members, especially if they’re sociable/distractable, the work tends to go more slowly. With only a month, I would estimate about 10-15 hours of work on the robot/week would be needed, but not every member would need to be present all the time.

We have 5 members and meet for 3 hours at a regular weekly meeting. Though a lot of planning and some building/programming progress is made in that time frame, it seems that most of the best building is done when one member takes the robot home. Often, s/he will take the team’s designs and work for 5-10 hours alone, troubleshooting and refining. For a mechanism that takes 1 hour to get the “basic design”, it takes 5-10 hours to make sure the parts move properly without interfering with other parts of the robot, get the game objects to fit “just right”, and deal with unexpected problems that come up. Sometimes the builder will spend 5-10 hours putting together the “basic design” (for a single mechanism, like the intake), then the rest of the team will spend 2 hours troubleshooting/refining it.

If you go with a 6-bar lift, be sure that your chassis and mounting of the lift give a good center of gravity, so the robot doesn’t tip. How many objects would your claw hold? If only one at a time, your scoring potential might increase some (over your previous design), but perhaps not as significantly as expected. You would have access to a greater variety of goals, but the time required to raise and lower the arm limits the number of deliveries you can make in the allotted time.

Finally, do you have all the parts on hand? If not, you’ll need to factor in the ordering/delivery time and how that will affect your build time.

Hope it goes well for your team!

1 month is plenty of time. Last year we changed Sheila’s drive-train, lift arms, intake and and overall chassis, in just under one month. I have no doubt you should have plenty of time if you keep working on it.


Haha I remember watching the videos that you guys posted on youtube for REX and NOVA Camp I think.

We are also going to have to build a new robot in around 3 weeks for a small competition so we can test out our concept before we take our new robot to worlds. Let’s hope we both finish our robot on time although I’m guessing that I’ll have to stay up on the friday before the tournament to finish everything. Good thing we have a three day weekend that weekend :stuck_out_tongue: BTW nice number :smiley:

Here is a thread with a plethora of useful information, including a well-written guide by team AURA, on six-bars:

Thank you again to everyone who replied. All your advice was helpful, especially the link to the guidebook on building a 6 bar lift!


While six bars are very common this year, four bars are simpler to build, and if the parallelogram is formed as high as possible, extra linkages become unnecessary.

Team 677 has successfully been using four bars powered by rack and pinions for about three years now. It is a simple design and gets a large reach. To change the speed of the lift, just change how close the rack and pinion attaches to the pivot.

677 is the robot that starts in the red isolation zone in this video.

I would highly suggest having a simple intake mechanism (verticle box or such) instead of a claw. It will take time to develope seeing as it must fit into your lift effectively, but robots with a scoring object capacity greater than one have a clear advantage for this year’s competition.

im just making sure i got this right with the four bar linear slide
you were talking about something like this right

our robot had a 6 bar and we were able to get to max height in under a second yet they took like 4 seconds

I agree with Ethan117. We tried to use a claw when we first started building our robot, and it was extremely ineffective for Gateway. Then we replaced it with an intake box and it has worked (and still does work) beautifully.

Using Only Motors, or do you have Pneumatics too?? Which Motors and How Many??

didnt see post sorry
4 high strength motors on the arm no pneumatics