775Pro 2:1 Gearbox HELP

Hey guys, rookie here, just wondering how I would get a 775pro motor to a 2:1 gearbox. Preferred if it was swappable with a mini cim mount or a versa planetary for motor testing.

And how crazy would it be to run two 775 pros with 1:1 versa planetary gearboxes per 6" wheel on each side of a shooter? Rip up the boulder like crazy? :stuck_out_tongue:

I think 3:1 with 6" wheels shoiuld put you near the optimal range for shooting IIRC. I heard 2:1 to 3:1 on 4" wheels, so 3:1 on 6" wheels is still good.
I was going to try a 1:1 reduction with 4" wheels just to see if that worked later.

The VersaPlanetary does not have a 2:1 gear ratio kit/stage, the smallest is 3:1. I think it will be difficult for you to get a 2:1 gearbox for the 775pro. If it’s for a shooter a 3:1 should also work, depending on planned wheel size and your strategy. If you want something that you can swap with a mini-cim/ lots of motors the VersaPlanetary is the best choice. Also remember that the 775pro spins more than 3 times faster than the mini-cim, so you’ll want to factor this in when working out your required gear-ratios

I strongly suggest that you do not do this, it is a really really bad idea:rolleyes:

I would use a 1:1 Versaplanetary and get the 2:1 reduction using chains or belts.

You could use a Vex CIM-ile. The reduction is 12/29 which is pretty close to what you are looking for.

Thanks for the quick responses! So would it be better (due to our extremely tight budget) just to stick with mini-cims as they spin at the same rpm as a 775 pro geared at 3:1 (6000 rpm) even though the mini-cims are heavier?

The CIM-ile gives a reduction of 2.417:1 depending on the required mounting technique you could have the 775pro inputing into a CIM-ile connected to a VP CIM adaptor going into a 1:1 hex output versa planetary.

Or just use a CIM-ile and then a 8mm to 1/2 inch hex adaptor

http://www.vexrobotics.com/217-3255.html

http://www.vexrobotics.com/vexpro/motion/gearboxes/cim-ile.html

isn’t that 1:2 ratio? so it would be cutting torque in half yet doubling rpm? that would be awesome if it is the correct rpm (or close to it) so we can mount that to a versa planetary 1:1 and swap between motors! XD

Edit* just saw the post above that answered this question lol

The decision between Mini-CIM and 775pro really comes down to two factors weight and cost.

The tight budget that you are on might mean that it might be better to go for the Mini-CIM’s, the difference in weight is significant, but shouldn’t be a problem if you plan for the weight of your robot. Also while VersaPlanetaries are reasonably expensive, the are very customisable so they can be reused season after season( providing that they are cared for).

Assuming you drive the wheels off of the MiniCim shaft with no gearbox, then yes, that would be a much cheaper option. You are losing a good bit of power going to a Mini CIM though, so your shots may not go as far as a 775Pro geared to the same speed. The VersaPlenetary (or other Gearbox) opens up your options a lot, but at the cost of money.

How much difference would you estimate? (sorry for so many questions…)

A 775pro is a bit more powerful than a CIM, and a miniCIM is about 2/3 CIM power.
So ideally you would be going 2/3 the output piwer of a 775pro (assuming many things like inertia not existing). If you are on a budget, it is much better to go miniCIM over 775pro, as gearboxes can double or triple the cost of a system.

We just received in the 775pro today and ran some testing tonight with the Vera planetary at 1:1 ratio.
We made a simple wooden jig with 2 motors assemblies spinning two 4x2 Colson wheels (flywheel style).
It could easily launch the boulder 20+ feet. This was just a quick hookup to a FRC battery that was at 12.8v.
We had not planned on using these for our shooter as we have something else planned.
Since the thrown together jig showed such promise we are going to go ahead and building an optimized (aluminum) jig with the control system. We be incorporating the Versa encoder kit with talon and really see what it can do when optimized.
I will try to upload the video from tonight sometime this weekend.
So far I like the motors, we shall see, the encoders are next…:smiley:

Aloha!

How much power are you actually losing, the motor for either motor probably won’t be running at peak power for very long.? You’re saving some efficiency without a gearbox but if you’re spinning up a fly wheel to launch a ball the main thing you’ll be losing is the acceleration. You’re only launching one boulder at a time so the mini-cim might be sufficient.

I would urge you to not run 1:1 shooter with a 775 or 775pro. The motors don’t have enough torque for this and will be overloaded. During prototyping, we overheated a 775 that way running an 6 inch single wheel shooter. It pegged our power supply current limit at 30 amps at 10 volts for 300 watts. Launch power actually seemed less than same motor with a 3:1 versaplanetary, which took 15 amps at 12 volts for 180 watts.

A 775pro with 3:1 versaplanetary outperformed both by a wide margin. I measured 5340 RPM at the wheel, so 16020 RPM at the motor. This is near the motor’s peak efficiency, so motor heating is not an issue. The versaplanetary gets hotter than the motor due to the extremely high RPM. Current Draw was 16 amps at 12 volts for 192 watts, though the analog ammeter may not be super accurate. With the right compression but otherwise imperfect mounting, this setup launched boulders more than the required distance.

The suggestion of a CIMile for 2.41:1 would work, and I estimate you’d get maybe 6800 RPM at the wheel. External 2:1 reduction with chain or belt should work too, resulting in maybe 8000 RPM. I’d be curious to hear what actual wheel speeds you achieve. Keep an eye on temps and beware wheels and tread material coming apart at high speed.

Although we are leaning towards the 2.4:1, I am definitely looking forward to seeing that video!