Baltimore City Drive Trains

Teachers from Baltimore City have formed a peer learning community in order to learn more about robotics. This month we built drive drive trains.

This thread is for Baltimore City Teachers to post links to videos of their robots. Please do not post links if you are not a Baltimore City teacher.

Constructive comments are welcomed from anyone.

I built a robot with six wheel drive. Here is a link to my video.

My conclusion is that the drive train worked great as a demo, but that it didn’t have enough power to be successful in a competition match.

5:1 on 2.75" wheels
wayyyyy too fast
if you add anything else on the robot, it will not have enough power to drive itself
i would recommend 1:1.5 ratio on the drive of a first robot with 4" wheels
if you are sticking with 2.75" small wheels, then 2:1 will still be fairly fast

My team is using 2.75" wheels geared 3:1 (for speed) with 4 393s, and it is working quite well. It’s a little faster (~3%) than 2:1 on 4" wheels, so it’s rather quick. If you are only driving around a drive base, 5:1 should be fine, but if you put any kind of weight on it (as you said) and want to be in a competition where you will need pushing ability and control, you will want to gear it down (for torque).
Generally 2:1 on 4" wheels (or equivalent) is a nice drivebase setup, if a little on the fast side (3:2 would be more balanced).

This is a gorgeous drive-train, you did an amazing job. I would have geared it 3:5 though, with the 2.75 inch wheels, you get just around the right amount of speed while still having a fair amount of pushing power. Also just want to mention the drop center is perfect, not to much so it’s wobbly, but jus the right amount for the robot to turn properly, very nice job.


Here is a link to the video of the robot I built!

I chose to build one with six wheel drive. I included treads to connect 2 wheels on each side of the robot. I used the small wheels because I had never built with them before and I wanted to try it, thinking it would make it go faster. When I tested the robot, the treads made it seem much more fragile (they could have been tighter, and now I realize I should have used thicker ones). Also, it did not go as fast as I thought it would as you can see from the video. Knowing this, I can improve on it for next time. Thanks for watching.

Here’s a link to the robot the MATHS robotics instructors built:

We built a vector drive system using omni-wheels. As you can see in the video, the robot was able to move very quickly in any direction. Between the lack of power and how easily the robot could be pushed around, it doesn’t seem like the best drive option for Gateway.

Both of those links require a login for those of us who aren’t teachers. If this was the intention, then don’t mind me. Otherwise, could you host them publicly? Thanks :slight_smile:

I built a drive train with six wheels. I wanted to try using high-strength chain. At the moment, it only has two motors but I am going to add two more. I am also going to exchange the wheels so that the omni wheels are in the back.

Drive train 2-wheel drive, using chain 1:5 ratio, slow, the wheels and axles aren’t secured for the time being but that will change next week.

What is the thought on a drive with 6 motors ( 3 on each side), 2 normal strength (269) and 1 (393) with a gearing of 5:3 on 4" wheels? too fast? Waste of motors?
Any ideas?

-M Nelson

That would not be a waste of power at all! That is actually perfect in my opinion. A lot of teams use this. It is a great drive because you could have the 2 other 393’s motors on your lift, and then other 2 269’s on your intake.

However, be cautious! That is because under a load, the 393’s and 269’s will move at different speeds. The 269’s only go 100 RPM when not under a load.

I am in the process of getting my accounts in order. I hope to post my drive train in the next few days. Camille

Hi Everyone,

Until I have access to the other thread, I will post my lift video here so at least others will be able to see it. I built a lift that consists of gears and chains connected to the base. However, if I were to build one to use in a competition it would have to have an extension piece added on to it so that it would be able to lift higher to reach the goal. It didn’t quite come out the way I wanted it to this first time around.

Any brushed DC motor will only go at its rated free speed (in the case of stock 269 and 393 motors, 100rpm) when under no load. As the torque output increases (approaching the rated stall torque), the speed proportionally decreases (approaching 0 rpm). So, at any given torque, we can calculate the output speed of the motor, and for the same torque, that speed will be higher for a 393 than it will for a 269.

However, when multiple motors are combined to do a job, they must run at the same speed, so the torque each one experiences must then change…

As multiple motors are geared together, they must all contribute power as long as all of them are running at lower than their free speed. Thus, if there is load on the system and all of the motors have the same free speed, the load will be distributed between the motors, each handling its portion of the load (not equally - larger motors will handle more, as they output more torque at the same speed - this is a good thing).

Multiple motors geared together or otherwise required to run at the same speed will all contribute power as long as the free speeds are matched, with no or very few ill effects