unexpected complication ...

so our robot has been working well, then we put our intake on and our arm makes such a noise … like strain/stress. So basically we are reconstructing our intake for a lightweight version … any suggestions on how we could save weight … we are using a 1:25 gear ratio

Do you have any pictures or video we could look at?

A 1:25 gear ratio is extremely strong, so I’m surprised that you’re having problems. To make sure, how many motors do you have on your arm and approximately how long is your arm?

What is the weight of your intake when it is completely empty?

You can also check friction in other parts of your arm, making sure to correctly use bearings and that your axles aren’t twisting or torqueing.

1:25 is a strong gear ratio, that is why i chose it because i wanted to over compensate. we are using 2 x 393 motors (high strength) … with a 1:25 gear ratio using high strength gears. also the arm is an 8 bar, which is approx 70cm … ish

weight of intake, well it is heavy … like 3kg … with sacks i would say like 5 (capacity is 8) … so when we tried to lift it, it was probs 5kg ish …

with axels, i did a check and they seemed fine, and all gears seem to be fine … i cant see any problems, with photos, i am going to bring it home at the weekend, so i will do some work and photos then … i will post them here … but it is pretty standard, only thing i can think is that the axel bars are nearly 2 years old … but gears and motors are brand new … out the packet …

thanks in advance !

as previously said, we are trying to strip down the intake, but i dont think we can do much more except start removing screws …

Since you’re running a 1:25 ratio, I would look exceedingly closely at the quality of your compound gearing. Often times, an arm can be put under a lot more stress just because the force is transferred through many more sets of gears/axles. A good way to check would be to remove the motors and turn the arm by hand to check for friction.

If none of this works, I think you will just have to allocate 4 motors to your arm instead, or shorten your arm.

ok thanks for your help, i think that allocating 4 motors may have to happen if we cant make the intake lighter

thanks again, will post with what happens !

Yup, no problem. Good luck with your arm and keep us updated!

A back of an envelope calculation, the same as I was doing in one of yesterdays threads, shows that with 8 sacks on your 6.5lb (!!) arm you would need somewhere around 175 in-lb of force to lift it. Two 393 motors running at reasonable speed with the 25:1 gear ratio will give 250 in-lb of force and should be able to lift that arm. One issue is that the intermediate shaft in the compound gear setup will be carrying 50 in-lb of force and needs to be well supported or the axle will probably twist. We had a roundup robot with compound gears (12 tooth driving 60 tooth followed by 36 tooth on the same axle driving an 84 tooth) that was always twisting the intermediate axle. Try and have the distance between the 12 and 60 tooth on the intermediate axle as small as possible, perhaps 1 inch maximum, and support it in a minimum of three places with bearing flats.

On a completely unrelated note:

So yeah, we did this with our 25:1. Be careful (lol)

Edit: If you look at the twisted end of the axle, it looks like we cut it. We didn’t. It snapped quite cleanly after twisting a full rotation.

VEX art! Courtesy of overly powerful gear ratios XD

Just sharpen the end and you can use it as a drill bit :p.

hi i found the problem … under the washers, the axel bar was worped beyond recognition … i have moved the gears directly next to each other and it works great …

thanks for help everyone !