Problem with six bar linkage lift

Our team is having a problem with our robot design and would love some input. Here are pictures.

Heres a picture of one that is about to go on our D robot -

Things to remember:

  1. BEARING BLOCKS. Put these at all the joints, this is very important for structure and to make it all work smoother.

  2. All bars must be parallel

  3. Use spacers (we use the small black ones) in all the joints, again to make it lift smoother

  4. Tighten the screws tight, but not too tight, so that it can be turned with an allen key, but not too lose (lock nuts)

There is also this guide here-

Thanks, but I can’t see the image, it looks like the link to upload a picture. Do you have a working URL to the image? Thanks a lot for taking the time to help! We were thinking of putting the gears in the middle and putting an axle through both sides. Do you think this would help?

A description of what problem you’re having would be helpful… :wink: Is it not lifting, are the motors burning out, or what symptom are you having?



Oh whoops…

What do you mean by gears in the middle? I would suggest having one set of gears for each 6 bar (from what i can see you have 2?)

They way it is constructed currently, you will definitely twist that axle. You do NOT want to attach the bar only by the axle. I recommend moving the gears to the other side, and attaching the bar to the gear using multiple screws. This works better when you use High Strength gears, because they have more holes to attach to.

Yes, you should always support gears on both sides, especially those that are doing a lot of work. What problems are you actually experiencing with your 6 bar? If it is gear slip, I recommend you use bearing blocks on all the holes that the shafts are going through, and support all of the gears on two sides. This should hopefully fix your issue.

Also, the support for the shaft that the gear is on should be as close to the gear itself as possible: ie.


  is better than


(the vertical lines are the support structures, the horizontal lines are the shaft, and the equals sign is the gear)).

Yes, i understand what he means now… We attach all of ours like this (sorry for the bad lighting) (yay for having the robot at home)

Also, try not to use bar locks, we tend to screw the gears into the metal (barlocks round the axles somethimes)

The gear is skipping and the lock bar is coming apart. Also, the arm just isn’t lifting. The motors have a lot of stress on them.

I’d attempt using elastic to offset some of the weight of the robot arm, and using high strength gears…

I’d also support the gears on both sides of the axle, close to the gear.


In addition to what’s been said above, I recommend changing from a 5:1 to a 7:1 ratio on the arm (using 84-tooth gear). Not only will this mean you can lift more, it should make it easier to control as well.

Thank you to everyone who responded. You have been incredibly helpful. I’ll post pictures when we make our changes and it is actually working. :slight_smile:

We have our robot working and one of our members has made a video of the robot scoring on the 20" goal. Thank you all for your guys help! Change list:

*]Made the arm axles go all the way across the robot.
*]Purchased High Strength Gears and put those in the middle of the arm lifter.
*]Added a couple bearings between the gears to prevent the axle from bending.
*]Attached the axles to the bars using High Strength Gears, not Lock Bars.

Here is the video:! Once again, thanks everyone for making this happen!

Good job on the success! What software did you use to make the video? I am trying to find a good movie making software for XP that works great. I would also like to do the logo on the corner in some of my videos.

Thanks :smiley:

Sorry about the late reply! I used Adobe Premiere Pro CS5.5 and used the Multi Camera editor to do the multi camera effects. However, if you want simple picture in picture, Adobe Premiere Elements should be fine. I have a friend that uses Premiere Elements and he loves it.