DR4B Offsetting

I’ve read a few things on the Fourm about offsetting the bars of a DR4B so in order to gain more height. However, I’ve tried figuring out how it works without much luck and am now here looking for advice. I get the basic principle is to not have everything as perfect as one might imagine it should be, but I’m at loss when it comes to understanding what changes are beneficial.

If you’re trying to understand how it’s beneficial, you already said it. It allows the lift to go higher. However, I haven’t actually seen any teams do this on their main lift, only on their secondary lift. I don’t recommend doing this though, because it doesn’t seem necessary.

Don’t do anything drastic to your bot for a little bit of height, it won’t be worth it.

People don’t use nearly as drastic offsetting for the main lift. However I would recommend using the front and back holes of c channel in hopes of adding an extra cone or two.

Dont offset the DR4B. Just set it. Easy money. Win all matches. 154-3

First off, I agree with most of the posters. Keeping a gearbox simple is the best way to build an efficient robot.

However, in regards to your question,

I’m not exactly sure what you’re referring to, but I’m assuming you’re referring to adding more gears in the gearbox to increase the height by a few inches? I’ve attached some designs I sketched up for Skyrise a few years ago. The pictures are of a rd4b that is driven from two locations. This is more complicated than the classic rd4b where all four motors are attached to the gearbox. I would not recommend using two driving points if this is your first build.

Offsetting the arms can be done fairly easily by inserting a few idler gears in between the two driven gears.
This is fairly easy to do, although you will want to make sure the direction of movement is correct for both driving gears. Additionally you will want to make sure your idler gear axles are well reinforced.

If you look at the pictures I’ve attached, there is a 36 tooth gear in between the driving 12 tooth and the driven 84 tooth. In this case it was used to both change the direction of the movement of the driven gear as well as adding more height to the lift.

Hope this helps, if you have more questions feel free to ask.


Just a note: the gearbox you posted pictures of isn’t going to work. The driven 12 tooth gears are direct driving the bottom 84 tooth gear but they are driving a 36 tooth and then an 84 tooth on top, causing a different gear ratio for both arms. This is going to make the bottom and top halves of the rd4b move at different speeds which (1) isn’t going to work and (2) will get rid of the linear aspect of the rd4b.
Just to make you aware :slight_smile:

If I’m not mistaken, the 36 tooth is acting as an idler gear and doesn’t affect the final gear ratio, other than it’s direction. In effect, it’s a 1:3 to a 3:7 cancelling and becoming a 1:7. Compound gear ratios only occur when two gears are on the same axle.

Not to be rude in the least, but you are completely wrong.
I built this robot 3 weeks ago with this exact gearbox.

The 36 tooth gear is an idler gear. Idler gears do not affect the gear ratio. When considering gearboxes, only the driving and driven gear matter unless the gearbox is compound. Now if there was a 36 tooth gear on the axle with two twelve tooth gears, then that would be a compound gearbox and it would not work. However, the two gears on the same axle are the same size. The driven axle (the one with the two pinions) is driving two gear trains. The first drives the bottom and is a simple pinion driving an 84 tooth gear (on the left of the gearbox). The second is the one that @Joseph | 182C was referring to. This is a pinion driving a 36 tooth gear which is further driving an 84 tooth gear. The idler gear does not affect this gear ratio, and thus the gear ratio is 7:1, just like the train driving the bottom half of the lift.

The calculation is simple.
The gear ratio would be calculated as:
Driven/Driving–>
First the 12 tooth gear drives the 36 tooth gear this is notated as 3/1
Second, the 36 tooth gear then drives the 84 tooth gear, notated as 7/3
Finally, these ratios are multiplied together, 3/1*7/3= 21/3

This simplifies to 7/1 or 7:1. The driving gear rotates 7 times for each rotation of the larger gear.

Hope this helps

Ok yeah you’re right. I probably shouldn’t be doing this late at night lol. Sorry for the confusion :slight_smile:

Joseph get some sleep

We had a team who offset their RD4B lifts. They were able to do it without an complications, but to be fair, they had a lot of play in their joints.

If you were going to offset the bars, make sure they are not offset to the point of stopping the mechanism.

(Brilliant grammar right)