Metal Clutches

All our clutches get stripped out where the axle goes in, even where there is not much torque applied. Every time we make an order we have to buy more clutches.
Having metal inserts like the high strength gears, or having the casing (ie not the actual clutch which works fine) made of metal would be really great.

That was what I was thinking, make it 4 times more expensive and it will still be worth the money.

This would be good, but personally, we don’t use clutches, they always give out when the motor can still keep going.

This is exactly the reason we need better clutches. Clutches cost $1.50 but motors cost $20 when they fail.

Yes, although many times the trouble with the motors are stripped gears, which are easily replaceable.

I’ve witnessed my fair share of rounded-out clutch axle holes, so I am sympathetic with the problem described. What I haven’t seen many of is dead motors. With more than 70 students, 10 VRC teams, and something like 120 motors purchased over the last four years, I think we have retired a total of about four motors as non-repairable. We have changed quite a few gearheads out, and have probably disposed of a hundred ripped-out clutches, but dead motors are a real rarity. That’s our experience, of course, and your own experience may differ. I tell our students to treat clutches as a fuse – a disposable item that protects something expensive. It’s not unusual for our more-obsessive teams to routinely inspect their clutches before every competition, and then again between qualifying and eliminations.

In our fourth year of building robots, our more-experienced teams are now incorporating repairability as a design criteria. 575’s and 10Q’s modular power packs can be removed with two screws allowing quick access to motors and clutches (picture of 575 in the gallery).

I really don’t see the point in using clutches. Replacement gears cost much less and don’t fail as easily as clutches. Sure, they are harder to replace than clutches, but for me the low cost of the gears out way that.

Clutches currently sell for $1.65 each ($4.95 for three) and a replacement gear kit for the motor is $1.99.

I’d like to add a little something. I know that in a gear chain the weakest link will give first but of the internal gears there is one in particular that ALWAYS goes. In fact after repairing over 20 motors, I can basically assume this particular gear has shredded when a shaft free-spins on a motor. I know most teams and the Vex, Robotics Inc. engineers know which one I’m talking about. Would it be possible to just maybe reinforce that one gear? I know another gear would become the point of failure but it would make the motor overall more reliable.

I’m 100% sure if you made a reinforced internal gearing package/kit for the standard motors teams would be willing to pay at least $10 for it, per motor just to have bots that can take more of a beating.

Just a thought,

In the New Zealand Regionals, we burned out 3 or 4 motors with our lifter (1 motor per side), so when we put 2 motors on each side for the championships, they were fine. We didn’t use any clutches for the lifter.

I have never used clutches on the motors since I first touched vex and my motors are still working great in fact I haven’t even had to change the gears yet. I tried them once and it didn’t do anything but take up space.

Now in a real engine or car the clutch is a very important part but I fail to see how this tiny little device protects the motor. I messed with it by hand and it seemed like a solid chunk of plastic that simply connected the two shafts and couldn’t separate.

What is the clutch suppose to do? I would like to know how exactly it protects the motor.

If you take apart a clutch there are two round bits of plastic (one connected to each axle) with teeth on. There is a spring on one side that pushes these together. When a lot of torque is applied the teeth skip (making a clicking noise). The clutches are not designed to protect the motor from stalling - the motor will stall long before enough torque is applied to make the clutch work. They are designed to protect the gears in the motors from sudden jerks - eg try putting them on a really heavy competition robot, going backwards then suddenly going forward. You can hear them working.
The clutches we received in our first kit (2 years ago?) did not work very well (like what you described), but the the newer ones work better

The replacement gears come with a set for a servo and and a motor, so they are cheaper.

I’m not entirely sure how it goes about doing it but when enough torque is applied, the clutch will “click” and enable one side to turn a little while keeping the other side stationary. It prevents the motor from receiving any extremely large jerking forces that can strip the little gears inside the motor.

Ok that makes since but I guess my clutches just don’t work well, they are from about 3 years ago. Maybe I should get a few new ones when I order some more stuff.

just make sure you dont drive a very fast heavy robot that goes full forward, then suddenly full reverse :wink:

Hummm… PID anyone? :wink:

Probably less work to train drivers to avoid sudden changes in direction.

You accelerate fastest when the clutch doesn’t click since if it clicks, you’ve just wasted a bit of energy that could’ve gone towards speeding up your bot. On the other hand, lightening your robot is probably the easiest way to avoid clicks in the first place to a certain point.

Completely agreed however I believe a machine should have built in safety precautions. If a joint can over extend, why not put a limit switch that stops the joint from accelerating in one direction when the switch is triggered?

We had two motors strip in the semifinals of the world championship, even after going through a checklist before every match and rebuilding the motors every few matches anyway.

Ah, maybe as a college student I just feel like using basic calculus because I can.