# Scaling Winch Motor Help

Hi,

I’m looking for a bit of guidance regarding the motor(s) that we will be using for our scaling mechanism.

Our plan is to have a scissor lift reach up to the pull up bar and a winch to lift the robot. I imagine the motor(s) attached to the winch will need to be quite powerful considering the robot will weigh a bit over 100 lbs. Does anyone have suggestions as far as type of motors, gear ratios, etc.?

I saw one post from a couple of years ago about attaching two CIM motors to a gearbox, but wasn’t sure if this was the best way to do it or not.

Any help would be greatly appreciated.

Thanks,

Alex

We prototyped using 1 cim through a 5:1 versaplanetary gearbox and then through a 12.75:1 toughbox nano with a ratcheting mechanism to stop backdrive on a 1.5" Dia spool.
Whole thing is ~9"x5"x2.5" works great.
Overall gear ratio (63.75:1)

I see you plan on making a similar system to ours.

we had a single 775 from vex at first. i believe geared down 75:1
we doubled that at GTCR, now 2 775s, same ratio.

Principles first:

Let’s say your task is to lift 150 pounds 36 inches in 5 seconds. The mechanical power required is 150 x 36 / 5 = 1080 inch-pounds per second.

Inch-pounds are converted to Newton-meters by dividing by 8.85, which gives the required mechanical power as 122 Newton-meters per second. This unit is also called a Watt.

122 Watts mechanical output is well within the capability of a CIM motor, so an efficient (low friction) lift mechanism could climb higher than 36 inches, or in less time than 5 seconds, or some combination of the two.

In addition to everyone else’s replies, two PG71 gearmotors will also do the job quite nicely. We’re driving the winch with those, no further reduction.
Just remember that the diameter of your reel does affect the torque and speed of the lift!

As Richard indicated, the real question is: how fast do you want to lift? Once you know your speed target, you can work backwards to figure out how much mechanical power you need from your motor. Personally, I always leave in an extra factor of about 50%, since there’s friction in the gearbox, weight estimates might not be perfect, and your battery state at the end of the match probably isn’t great.

My team has lifted our robot before using a single CIM motor one year, and two mini-CIMs another year. This year, it’s two CIM motors, based mostly on availability and not needing them elsewhere - we’ll take all the speed we can get while climbing!

I strongly recommend the JVN Mechanical Design Calculator.

We use 2 Full CIM + Toughbox…tested it to well over 100lbs

Winches up bot in 6 seconds to necessary height after hooking the bar

Go to the linear motion tab, and put in the variables that you would like such as distance of raising, speed of raising and pulley size. It will help you identify the type of motor(s) that you will require and the gear reduction you will need to ensure adequate torque.

If you need help or you want me to double check your calculations just PM me:)

See all the above first.

Next, you should consider some kind of winch system. The smaller the ‘spool’ the greater the mechanical advantage, while larger spools will wind more material per rotation.

With a winch you want to prevent back-driving, the tendency for the weight to let the spool unwind when unpowered. But remember you need to be able to get the robot down, eventually.

The ‘rope’ you use needs to be more than 2x as strong as necessary. A 300 lb breaking strength is not, in my own opinon, safe enough.

Look up the term ‘fairlead’ as it applies to winches, and consider using one.

Lastly, remember that if your robot turns sideways (wheels against the tower), your ‘hook’ will be more than 15" outside your frame perimeter, which is a problem.

Good luck!

We are using a rack and pinion with a 30t gear.
775 pro with versa-planetary 7:1 gearbox then through a 20:1 worm gear.
total ratio is 140:1 and it is very fast. Also the worm gear keeps it from back driving

3506 is using a Mini-CIM on a vex versa planetary gearbox with a ratio of 63:1 on a 2" diameter spool. We realize most teams forget this but when the power to your robot shuts off you need a brake to keep your robot from back driving so we used a small pneumatic cylinder as a brake. It deploys into a cam attached to the winch spool shaft to stop the decent of our robot when the power shuts off.

We had the fastest and most reliable climber at the event with this setup but we did have a small failure on one of the sun gears that we are not sure about. It might have been overloaded, it might have been a defect but either way we had to take the gearbox apart and put a new stage in right before finals.

we are using all 4 of our drive motors with a PTO

We use a single 775 pro with a versa-planetary geared down to 125:1 (3 stages of 5:1) and it seems to lift the bot without any problems.

If you have concerns about the power or performance of the 775 pro you can easily use the same system with a mini-cim.

What size pulley are you using on that?

However the mini-cim is not a 1:1 replacement for the 775pro, although the 775pro is about 125 watts more powerful than a mini-cim the main difference is output speed the Mini-cim rotates at around 6000rpm vs the 775pro which rotates at around 19300rpm so about 3 times as fast, this means that if you were to use a mini-cim you wouldn’t require such a large gear-reduction( but also take into account that the mini-cim outputs less torque vs 775pro geared to the same speed as the mini-cim)

When you scale with this system, does it fall back down after the robot is disabled? Also, how heavy is your robot? We have a 60lb robot (excluding our potential scaling system) and I was curious how many motors we should use.

When you scale with this system, does it fall back down after the robot is disabled? Also, how heavy is your robot? We have a 60lb robot (excluding our potential scaling system) and I was curious how many motors we should use.

Ours is two 775pros on two 49-1 versaplanetaries facing each other with a 3 inch wide 1 inch diameter spool between them. A switchable 1/2 inch rachet wrench keeps it from back driving. its pretty fast.

You should check out this data from VEXPRO on maximum loading on the VersaPlanetary gearboxes. Be sure you are within the design limits of the gearboxes for the motor / gear reduction you are using.