Motors And Gearing For DR4B

Well thinking to build a DR4B and I was wondering where to place the motors. Also think mainly to use aluminum but I don’t think our team has all the pieces to construct a lift with just aluminium. Also gear ratio what a good ratio 1:7 or to weak. Thanks in advance :slight_smile:

I think 1:7 is the maximum ratio you can get in vex so that’s not to weak if you use rubber bands. I put the motors on the bottom of the lift, but i’ve seen many teams put it in the middle part.

I know from experience that 2 motor HS 1:5 on a dr4b works, it’s just a bit finicky. I don’t know how many motors you have, but I’d suggest anywhere between LS 1:7 to HS 1:7, LS 1:5 being tight between those.

1:7 is definitely the best external ratio for a DR4B. The ideal internal motor ratio, though, depends on how much strain you’re planning on putting on your bot.

Most bots that just use their lift to pick up cones could afford to run their motors on hi-speed gearing, but those special interesting robots that pick up the mobile goals with their lift could probably not afford to run hi-speed, or even a two motor lift at that.

Be careful though, this is all assuming that the lift is built with at least decent quality. Avoid meaningless friction (meaning no idler gears or any of that nonsense) to make it work as fast as possible. Even a 1:7 on torque motors could outspeed a 1:7 hi-speed lift if it’s built better.

So ok I say 2-4 motors for that kind of lift. What if you put motors in the tower instead of the lift. Does it change the top part at all?

Generally we use 4 motors for a dr4b geared 7:1 with internally geared for high speed. We have found torque is too slow for this year, turbo was unreliable and occasionally browned out at the end of match. I would not recommend using 2 motors on this type of lift if you are planning on making a tall dr4b… had issues with that in the past. Oh yeah, and use a ton of rubber bands in a triangle!

While technically it doesn’t change the top part of the lift, it

a) forces you to run another set of gears in the towers, which adds more weight and friction

b) now bears the stress of everything above it, which would make it less able to handle a speedier gearing

The most preferable gearing is inside the gearbox itself, usually directly above or below the set of 84-tooth gears.

Wondering if someone can provide a good DR4B picture

This is a picture of 134D’s lift from Starstruck last year. Depending on whether or not your robot is an internal stacker, your lift may need to be a bit wider. However, the concept of the gearing being done directly above and below the 84-tooth gears is what you should follow.

Ok it’s making sense my question how heavy is the lift. Would it not stress the motors?

Because of the pure amount of metal required for the lift, it can get pretty heavy. However, the stress of the motors can essentially be relieved from rubber bands. If you properly place rubber bands on the lift so that as the lift goes up, the rubber bands get closer together, it will make it a lot easier on the motors because the rubber bands help it move the arm up.

A general rule of thumb to follow is to put enough rubber bands on the lift so that it stays up by itself (without anyone holding it). That’ll have cancelled out the force of gravity pulling it down, so the motors will be doing almost no work.

However, this is all assuming that you’re not planning on picking up mobile goals with this arm, because that puts wayyyy too much strain on two motors, even with rubber bands. Especially with a speed-oriented gearing.

Ok thanks make sense little like a when I built my first six bar put as many rubber bands to hold it self

Exactly like that. Just make sure that you don’t put too many, or the lift will have trouble moving down haha. It’s all about finding that right amount.

Good luck!

Thank you will start designing this week