How is our wrist looking?

Starting to put ideas together for our wrist system. It needs to be canted down in order to be able to pick up balls. I am concerned with the narrow portion that drops it, but since this years game will not involve intake-down defense I think it won’t be an issue.

Plates are .25 6061 T6 (I plan on lightening them). It’s geared to 104:1with a 36:1 57 Sport, and a 64:22 external reduction.
This is our first attempt at an articulating wrist so be brutal with the criticism!

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What sensor are you using the measure the end angle? How much backlash do you expect in the system?

I mean it looks solid. If you want, you can add a bar to hold the other end of the gear shafts together. That plate looks plenty thick, but you can hold both ends of the bars together to prevent the small gear from flexing away from the big gear. That should help if you ever get in that position.


Great point. Ill put a .125 plate on the other end. Thanks!


There is an Andymark Redline encoder on the end of the redline, its just hidden. Do we also need a limit switch to zero it?

Also, please do enlighten as to what you mean by backlash. We did not expect backlash, mainly because we do not know what it is :slight_smile:

Also look to see where your motor (775 Pro?) electrical wires are going. You might be too close to your other plate, but it might just be the angle.

backlash is the play in a gear system…it is caused by clearance between the gears, but also in stuff like this, by the elasticity of the parts that hold the gears in place.

Yup, just the angle. My fault… should have posted two views. The motor leads are outside of the other plate

I strongly strongly strongly recommend not transferring power through the hex shaft. It creates so much backlash and I’ve seen teams twist steel hex shafts with heavy arms. If possible attach your gear or sprocket directly to the wrist.

Edit: versa gears make this super easy


Ah ok. The plate is .25, and ill be adding a .125 plate on the other side of the gears too. I am not too worried about any flexing there. For gear spacing I used the pitch diameters. Is that wrong when designing something that will have a lot of force on it?

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Ok, so now imagine if you need to replace that motor or gearbox for whatever reason in competition. How easy would it be to get to it if you had to completely replace it?

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How heavy of an arm are we talking? I know some teams had issues bending shafts with 4 bars last year but our intake wont be nearly as long as that. However, I would rather aire on the side of caution so any suggestions to get a versakeyed gear directly on both tubes of the wrist?

3309 twisted a steel 3/8 hex shaft often, they had a very small little wrist with a very generous reduction. Any failure in code resulted in it twisting.

In regards to getting the versa gear on a tube you can simply drill 4/6 of the versa gear holes into the tube and bolt it on.

I am probably going to explain our method horribly, but the idea is that we would unscrew the motor plate from the 57 Sport, slide the redline back in the hole on the other plate, which would then let us take the 57 Sport out and put in a new one (or new motor)

If our gears are outside the plate, we would secure a versagear to the wrist tube, wouldn’t there will be the same amount of hex shaft as with a versahub?

The problem is not that you are pivoting on hex shaft it’s that the actual power is transferring through the hex shaft. By bolting the gear to the tube (you would have to move the wrist to the outside of the plate or the gear to the inside of the plate) you are essentially running a dead axel setup and can make your arm pivot on whatever you see fit, we prefer bushings.

Here is a great picture of 2471 2018 showing what I mean my power the arm not the shaft.

So I made some changes. I am not sure that I have a full grasp on how the forces will transfer here, but I think this fixes it. The tube is attached to a versakeyed gear, and there is still a shaft running to the other side but its only to support the other side of the intake (I think)

I’m really curious to see what you are doing with all of those elevator stages.


27’ Wallbot!


This looks a lot better, the reason most people don’t use hex shaft is because they prefer to use a larger tube thus making the setup more rigid. The choice of supplying power to the other side is not nessicary but definitely will help. For a small light arm this will work great