393 High speed - How do I?

I keep seeing mentions of 393 high speed, but cannot find where or how to do it. The application would be used on our Mecanum Wheels. We had trouble getting over the hump and it seemed like the high speed might have helped.
Can somebody point me in the right direction
Bill R.
Team 6101

If you have trouble going over the bump, the high speed option of the 393 should not help.

But if for some reason it does, this is how you change a 393 to high speed, go to page two of this document: http://www.education.rec.ri.cmu.edu/products/teaching_robotc_cortex/reference/2_wire_393_motor_ig.pdf

The high speed gears come in a little plastic bag inside every new 393 motor package. You can distinguish them from the torque gears because the high speed shaft output gear (one with the square hole) is smaller than the torque ones.

Thanks for the help. I just had a thought that it might help, but probably won’t. When we go over it, we must go backwards over it since there is more weight in the rear. It seemed like if it just had a little more it would make it. Any ideas? The bottom of the frame is 4" off the ground and is maxed out on the dimensions at 17.5 in each direction. Clearance is not an issue… traction is.

High speed wouldn’t help, as the output speed is increased by 60% (100rpm to 160rpm), but as a result the output torque or power is reduced.

When changing them, just make sure that all of the gears mesh and are in all the way. Also, make sure that the axles line up with the little holes in the cover when replacing it.

Are you using four wheels or six wheels?

We are using 4 wheels. We saw one bot that had 4 Mecanums and 2 regular wheels in the middle of each side, but I have no idea how I would do that in Easy C.

You shouldn’t. It’s completely unnecessary. There are MUCH better ways to cross the bump.

But if you want to, just add another “Arcade 2-Motor” block to your code.

If you have traction wheels in the middle, you won’t be able to strafe with the mecanums.

When you go over the bump, can the robot sit with the front wheels on the ground on one side, the back on the other, and not rest on the bump?

Our bot is completely above the hump with a 4 inch clearance from the ground to the frame. When it goes over forward the front goes over fine, but the rear goes about half way up and can’t seem to just get over. The driver whips it around and goes over backwards fine. We just loose lots of time. I will try to compress some pics and post them here or at least a link.

Here is the video of our first match at the TSA state championships.

Note: Programming skills improved throughout the day.



Okay, a couple of suggestions.

One, don’t cantilever your base. Brace your wheels on both sides.

Two, switch to Omni Wheels. You don’t seem to strafe, anyway.

Clearance shouldn’t be a problem then, so it seems that you don’t have enough power. How much does your robot weigh?

Also, make sure that you don’t have any excess friction. Check that you have bearings on all the holes and that everything lines up. One large issue I can see is that your wheels are cantilevered, or hanging off the side. Make sure that the axle for the wheel is sturdily supported on both sides of the wheel.

If you still need more power, consider putting more motors on your drive. Do you need the motorized conveyor for balls, or would a normal flat tray work fine? Unless I missed something, by removing that you can get 6 motors on your drive.

Yeah the wheels being cantilevered has been on my mind. I might could use a plate with some stand off. They do flex a little. My drivers (8th graders) did not think about the strafing for some reason. This was their first match with the Mecanum wheels. Also… 6 wheels… can you explain your idea?

He is saying take the motors off the tray and put them on the drive
6 motors instead of 4 moving the robot around so 1.5 times the torque to help with bump

It looks like to me from the video that the motors powering the back wheel are oriented sideways and are touching the bump before the wheels are.

The front two wheels are fine going over the bump, but the back two wheels get stuck while crossing the bump forwards, right? Don’t give up on the 4-wheel mecanums yet…

As someone who competed with mechanums this year, I think I can explain why you drive over the bump better backwards than forwards.

The problem lies in the center of gravity.

When you drive backwards, the momentum caries the much heaver back of the robot over just fine and the front follows rather easily.
But when you drive over forwards, the momentum carries the front over but the back stays behind because you ran out of speed.
There are two easy ways around this.

  1. bring the center of gravity to the middle.
  2. if you get stuck half-way, back track until the pair of wheels that successfully crossed over the are touching the bump and then floor it and hope that you get up enough speed to get over.

but to answer your question, I would recommend re-gearing to high speed because it would be a good idea anyway. I had my motors on high speed and I can assure you that it was definitely heaver than yours.

I went and looked at what you mentioned, but the servo and plate that it is attached to are inside the diameter of the Mecanum wheel. I looked the front as well and it is the same mount and all. The weight in the rear is significantly more than the front due to the lift and lift towers in the rear. I am not sure if the weight is the problem, but I will investigate more into what you mentioned.

Bill R.

Before you make too many changes, consider how big of a problem it is.

If you can go over well backwards and it works fine, I would consider just leaving it. Practice driving in a way that you go over the bump backwards anyways and don’t need to turn around, so that it won’t be an inconvenience in terms of time it takes.

We tried the same thing earlier in the season with a six wheel drive. we found our problem was that we weighted to much or your center of gravity but I think some one might have already said that.

Ok guys and gals… I have taken some pics of the frame and drive system after we stripped off the lift system.
The close ups are of the rear wheels which are the problem. I think it is simply the weight. Recap: The front goes over fine but not the rear. We must turn around and go over backwards.