Platforms with 393 Motors?


#1

My team currently does not have access to V5 motors. As a result, we use 2 wire 393 motors, geared for high speed. However, we are having difficulties reaching the platforms. We have done extensive modifications to the drive-train. It is an all wheel drive, using chains, the wheels (when not connected to motors) spin easily and freely, and we have used grease on all moving parts. The total length is ~15". We use 2 motors per side (4 motor drive-train). We currently have the drive-train geared for high speed, using sprockets.

We are having difficulty getting up the platforms (motor sometimes can’t push forwards, and stop the cortex). We are still looking, but it seems that the only teams that are having lots of success in platforms are the V5 teams. We can add up to 4 motors (total) to the drive-train.

Please give any and all advice, especially if you have created a 393 drive-train yourself.


#2

Is the bottom of the robot bottoming out? That seems like the most common issue. The easiest way is to make your drive a 6 wheel drive.

It could also just be how your drive train is built. Do you have any pics?


#3

@Got a Screw Loose
Our drive-train’s first wheel is able to mount the platform, but as soon as the second wheel is reached, the robot cannot go any further. We can make an 8 wheel drive, so we might just do that.
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#4

Do then wheels spin in place or not at all? It does seem like that ratio is a bit aggressive, but it shouldn’t stall out. I’ve made worse that still ran.

If the wheels spin, but you don’t move, it’s probably that you’re bottoming out. Do those plates you have on the drive have to be that large? Reducing the size of those could help.


#5

are your wheels level?


#6

They do not appear to be, but TVAConnor’s robot with the tilted chassis demonstrates a similar design working quite well.


#7

Seems like the real problem is using only 2 motors on your drive. You need 4 minimum even without climbing.


#8

He is using a total of four with two on each side of the drive.
When we still used the 393 motors we had a 4 motor (HS) drive on a 1:1 gear ratio using chain and we did not have problems getting up the platforms. I think the problem you have is that the ration in your sprockets really high causing you to not have enough torque to life yourself onto the platform.


#9

I don’t think that you have enough torque, so I would lower the ratio. We have a 4 motor 393 drive that uses torque motors and is just geared 1:1, it gets up easily with only 4 wheels.


#10

I agree with this. You’re not just running 4x 393 (HS). You’ve got them going from a 30-tooth sprocket to a 24-tooth sprocket, right? (Am I seeing that right, or are they 18-tooth sprockets at the wheels? I’ll assume 24-tooth sprockets.) You’ve geared them so that your drive has (neglecting friction) only 80% of the torque 4x 393(HS) would normally provide. Yes, you’ve got it driving 25% faster, the same 200 rpm as the normal V5 motors. But you only effectively have roughly the strength of 3x 393(HS) moving the thing. Can you get two more 393(HS) in there? It looks like you could swap out that top, middle sprocket for a bigger one and stick another motor on right there. You’d have to make a little more space for it, but it looks like you have room within the structure you’ve got.

Separately, I’m questioning some of what you’ve screwed together. Several of your bearing flats don’t have two screws in them. This leaves them more likely to wiggle and let the axles hit the metal. Also, of your six nylock nuts, I only see one where the screw is clearly into the nylon. Are the other five screws into the nylon? If not, the nylock nut isn’t functioning as a lock nut. If you can’t get a screw into the nylon, you’re better off going with a keps nut. I prefer the nylocks and the keps nuts where you have used them, but I use slightly longer screws with the nylocks.


#11

@callen
Thank you for your detailed answer.
We are operating from home currently, so parts are kind of short at the moment. However, I checked, and the bearing flats are secure. Additionally, the nylon touches the screws in the nylocks (picture is deceiving)

You are right, it is an issue with torque. A 1:1 ratio with 2 motors did not work well, but when we geared the drive-train for high torque, the drive-train was able to mount the platform. Ultimately, I think we will do a 1:1 ratio, with 4 motors per side. This is easily the most flexible design I have done, and changes generally do not exceed 5 minutes.

Thanks for the help.


#12

You’re right. The uneven wheels are extremely helpful when mounting the platform. Issues only arise upon getting to the second wheel.

Btw, we have found out that torque is the issue (as you previously mentioned), and will now use 4 motors per side, with a 1:1 ratio. Thanks for your help.


#13

a 2 motor 393 drive isn’t gonna cut it. try using 4 motors, with 6 wheels, and locked onmis in the middle, works quite well for both driving, turning, and parking.


#14

You missed a bit above. They were using 4 393 motors with 6 wheels.


#15

If you need the motors elsewhere, you don’t have to go this far. Three motors on each side at 1:1 would provide nearly twice the torque you’ve now got.


#16

oh lol thought it was still 2. looks like your good then.


#17

Never was 2. It was “2 motors per side.”


#18

@callen

We’ve done everything else. We might as well have an 8 motor drive. We were just feeling the pressure with the drive-train, because it is fairly important for the competition.


#19

oh lol. my bad then misread.


#20

Yes, it is important. With 8 motors, you might consider which is more important again: speed v. strength. 8 motors at your current gear ratio would be a little stronger than 6 motors at 1:1. That would allow you to match the speed of 200 rpm V5s while still having plenty of strength to climb. But if you want to push against V5s, then you might well have to stick with 1:1, and even then it might not be enough in many cases.