Having a problem trying to find out the force required to back drive a versa 2 stage box.
Plan would be bag motor driving a 2 stage box first and second stage at 10:1 giving an overall 100:1 with 1/2" hex output.
Also anyone know what the no load speed would be?
If you’re thinking of using it to hang, the answer is “not enough”. Planetary gearboxes as a general thing take a lot less force to backdrive than you might think. 150 lb of robot will probably do the trick as far as backdriving that. It won’t be the easiest thing in the world to get going, but it will probably get going eventually.
BTW, the no-load speed is the BAG no-load speed/100 (and the output torque is the BAG torque*100), assuming a perfectly efficient gearbox.
If you’re thinking of hanging with this, I’d add some sort of braking device to the output.
If you’re not attempting to hang, the important part is that second paragraph about the no-load speed.
if by speed you mean RPM then you’d get 14 000/100 = 140 RPM (Vex’s specs says =/- 10%)
Wouldn’t be hanging. Would be using to vary the angle of an arm on the bot. Was trying to figure out how much force would take to back drive. Imagine if you will having a hub on the output shaft that had say a 20" bar attached to the hub. The bar would be raised and lowered from below horizontal and also above horizontal. What amount of weight could be placed along the length of the bar before it would back drive ?
So basically it would be unwise to use the 100:1 versa gearbox to use as a winch to climb? Is it not strong enough to lift the robot or does it just have a lot of slippage?
It’s the slippage. Remember that the robot does have to stay up at the end of the match for the Scale points.
Whether it’s strong enough or not depends a lot on what motor you’ve got going into it and what you do with the output as far as gearing/winching.
This is the exact same setup that The GreenHorns have for our winch. We used the hex output shaft to drive a 1 1/2" pulley by press fitting a versa hub inside it. It would get us 21" off the ground before really struggling and eventually stalling. The pulley was about 3 inches wide so the pulley grew in diameter as it wound up. The JVN calculator said it should take about 5.5 seconds for it to winch us up to that 24" mark.
I’d recommend a smaller diameter pulley than 1.5" because that’s pushing the limits. Another thing to note is that out robot weighed only 86 lbs with the battery and without bumpers. A single bag motor at 100:1 is pushing it I think. It would suck to have an underpowered winch.
Mixing and matching the motors/gearboxes/gear ratios to get that winch to lift the robot in under 10 seconds was fun. Like trying to solve a puzzle (however we didn’t have all the pieces i.e. gearboxes at our disposal).
Edit: Also, we didn’t experience any backdrive when our robot was in the air. Again, it was only 86 lbs.
So if we use two of the 100:1 gearboxes it should, in theory, cut the load in half for each motor? Instead of the one motor picking up the whole 120lbs, with two motors, it would only be lifting 60lbs, right?
Thus , cutting the time in half to raise the robot?
2 bag motors each in a 100:1 versa planetary would have plenty of power from the testing that we’ve done. The combined motors would in fact have double the power, but having both would allow you to winch faster if you wanted at the sacrifice of power. With that much power you’ll have the luxury of optimizing speed and power.
Thanks so much. I just wanted to make sure that it could possibly work. I think this may be the way to go for our robot.
Now that the thread has been hijacked… Anyone have an idea on the force to back drive with a 20" bar on it?
Will you get the same effect will two BAGs in an adapter to one versaplanetary 100:1 or is there something about that setup which would not be suggestible?
Sorry, questions arose that were related and I felt the need to respond since it was something I literally just got done with 
As for the amount of force to back drive a 100:1 versa with a 20" bar… there’s some math the be done. I can’t speak to that situation specifically, but we ran another 100:1 versa planetary with a cim in it to control our articulated shooter. We used a 48 tooth gear on the hex output shaft to drive another 48 tooth gear (the geometry just worked nicely). The friction in the gearbox was just barely less than what we needed to stall our shooter at a horizontal position. The arm weighed around 12-15lbs and was 15" long. If I had to estimate the ditance from CoG to the output shaft I’d say it was 12".
Hope that gives some sort of reference.
That’s a good question… adding an adapter and another motor will introduce more inefficiencies to the gearbox, but you’ll have double the power. I’ve never used a setup like this, but 1 bag motor is close to the necessary power, so adding a second should give you a nice factor of safety. This will be nice especially given that you’ll be climbing when your battery has been used for a whole match.
No problem. Did you guys direct drive the wheeled shooter with cims? They may be mini sims hard to tell on YouTube
Ok so I just watched the vid with sound… So mini cims, but was said in vid that it was with versa plan at 1:1. I am wondering how you did that? Isn’t the lowest reduction 3:1 in the versa? We have designed a very similar shooter. Have to test it and a linear puncher
You are right. The lowest gear stage you can get is 3:1. However it is possible to put a Versa Planetary togeather without a gear stage. That is when you get a 1:1.
I think backdrive is about torque, not force, so it would depend on where on the arm the load would be applied.
At that point, it would act more like a shaft adapter than a planetary gearbox.
You have to get creative during Ri3D There is no such thing as ordering that one specialty component that you need, and it’s financially impossible to plan for everything. We also wanted to put them in the versa planetaries for the adjustability in case we weren’t satisfied with 1:1.
Just to be clear, running 4 inch wheels at a 1:1 ratio from a mini cim controlled down to 50% speed will stall. It needs to have that built up speed for it to intake. The great thing is, that ridiculous speed doesn’t cause the wheels to slip on the boulder. If you touch it, you own it, and it makes a seriously cool sound when you intake.
From our tests a linear punch wasn’t a highly desirable option for us anyways because it lacks a long range. The boulders absorb a lot of that impact. For your wheeled shooter, I recommend using a servo with a lever attachment to kick the ball into you wheels. It has a small profile, and doesn’t require you to add pneumatics.