double reverse four bar motor placement

I currently have a quite successful double reverse four bar (we’re going to state in two days). However, I have placed all four of my lift motors on the middle vertical section. (motor placement in 1st attached picture) I have noticed that alot of double reverse four bar lifts that are able to lift 3 cubes have 2 motors on the middle section and 2 motors on the towers in the front of the robot. (motor placement in no longer attached picture) Is there anything to this theory? I can’t think of any reason why this would affect lifting capability, however it does seem to do so…

I think you got your description of the pictures and motor placement swapped around.

I see nothing wrong with what you’re doing. I’ve seen plenty of robots like yours. Hey, if it works, it works! :slight_smile:

If those other robots are lifting 3 cubes, it might have more to do with their gear ratio than with the placement of motors.

we’ve got 1:7 gear ratio. The other picture I showed has 1:7 as well, but can lift 3.
(Additionally, the other one’s gear ratio is further lowered, by the fact that the lift goes farther in distance with the same angles due to the fact that it is sortof a 6-bar.)
We also sometimes have problems with tripping the PTC in the motors, due to overloading. (Our rubber band tension is definitely optimized, in fact it’s a constant force throughout the travel of the arm)

My question is: would be any reason, mechanically, that the other configuration could work better? (And I’m not planning on changing it in the next two days btw)

Thanks for the help!!

Well from my testing having only motors in the middle section causes more slop and in terms of lifting ability remember that you are lifting 2 motors other robots don’t.

Also most robots optimize their center tower to allow reaching to the same height as yours is able to without having as long arms.

You also lift twice as much weight in gearing because every gear is doubled up the metal gears add up fast.

I can’t tell dimensions from these photos, but perhaps arm length has something to do with the torque available. Maybe where the center of gravity of the cubes is maintained might affect what you can do with them???

The arms are 17.5" on upper and lower sides. (This pictures are a little bit outdated but the lift has not changed very much.) The cubes are held on a needle on the end/top of the lift.

Hard for me to see how your needle thing works. I presume the needle cube intake is at the end of an arm that swings out to the front of the robot during play??? If that’s the case, then I suppose your cube weight would be acting over a distance of not only the arm of your double reverse four bar but also the length of the needle’s arm. That extra needle arm length would induce a substantial torque on your motors in the middle/back of your double reverse four bar.

Torque = Force x (distance at which the force is acting)

In this case, the force would be the weight of the cubes acting at the total distance from the motors, plus the weight of the robot arms, motors, all the screws, etc. acting at whatever their respective individual distances are.

Contrast that to the other robot you pictured, which appears to keep its cubes closer to the center of the robot, so perhaps the torque for them isn’t so much.

The second picture shows team 2587z’s robot and was posted without their consent. Please remove that picture from your post. In the future, please don’t post pictures of other teams without their permission.


Ut-oh. Now everyone will want to have a peek at that robot!

right clicks saves image “he he”

I removed it. My bad.

Punkduckable, I total agree with you on this point!:mad: But, you probably should have sent him a PM next time. The views totals were almost twice of the second image than the first image once you brought attention to it.:wink:


I was wondering how you do that …Thanks LOL! There are teams reading this thread now saying, what did I miss…(skittles lover has a saved pic I’m sure!):wink:

It’s all over the internet now. For those of you who missed it…

FMM, I hope you got consent before you posted that picture! BTW, I’m not sure any of those parts are Vex legal.

I’m sure Skittles lover has studied that earlier posted pic and has a clone of that robot by now. :eek:

Perfect! This is just the design we need to win State Championship tomorrow!

Hurriedly copies robot

60 point auton confirmed.

i do :stuck_out_tongue: ahaha

a) The picture was of their robot in October.

b) If you are posting on this thread please be sure to actually make what you say relevant to the question I asked at the beginning. Thank you (:

Distributing the motors to both towers does seem to help however there are many other factors that will affect your lift much more. Having all 4 motors on the second tower will definitely work (118s original robot as an example). If you have any specific questions you can email me: