V-belts as adjustable brake/clutch

[jdunfee5]

I am designing a piece of equipment that will be mounted onto the forks of a forklift. It will pick up a long item horizontally, and either rotate it 180 deg, or take it to a vertical position. What is unusual is that we also want the ability to lift it up, and then let it go to vertical under its own weight (assuming it is picked up off-center). So, a clutch system is one answer. But, I also want to control the amount of friction. It is also beneficial to have the clutch protect the gear motor, as the load is transported by the forklift and so applies some forces back to the motor. Space constraints tend to make a normal electric clutch a much less desirable solution.

What I am thinking about is the idea of using a band-brake type of system by simply connecting the gear motor output to the rotation assembly using a flat belt. Then an an adjustable tensioner pulley in the system can apply as much friction as desired. Band brakes are common on go-carts, which is how I am familiar with them. But I am having a hard time finding sources for flat belt pulleys.

V-belts are obviously better for many applications. but they would seem to be designed for improved grip, and may not be as controllable if I want to use a V-belt system like a band-brake. I suspect that as I adjust the tension on the V-belt, it will tend to go from little friction to not slipping at all very quickly. But, I don't really have the experience to know if this is the case.

Any thoughts on this?

-Joe

 

[gearcutter]

Pictures or drawings help your ideas become our ideas.

 

[jdunfee5]

Here is a sketch of what I had in mind. The lever on the tension pulley allows the belt to slip when it is desired. In my case, it would only be used when the drive pulley is stopped, so there would not be much slippage. The pulleys are going fairly slow even when driven, with the driven pulley going perhaps 2 RPM. See the attached image.

Where this idea came from, was from my youth, when I recall seeing a mechanism similar to this that was used on a vehicle as a clutch and transmission. It was a trike-type vehicle at a mission oriented school called the "Southern Institute for Appropriate Technology" in Alabama. The vehicle was designed to be something that could be hacked by local people in less developed countries. The motor rotated a shaft with 3 small pulleys of different sizes, and each of them had a belt that went to a pulley on the shaft that drove the front wheel. Each belt had a lever, and by pulling one of the levers, you would engage one of the "gears".

-Joe

 

[hydtools]

Sounds like the wheel drive in my lawn mower. The wheel speed depends on how far I pull the tension control lever.

Ted

 

[tbuelna]

Seems like a very questionable design for use on a piece of lifting equipment. Does not appear truly fail safe, nor would it likely provide precise control of the load.

 

[jdunfee5]

While the device does hold something off the ground, this component would only control its rotation. And while one side would go down, we don't expect to grab the load too far off from center. So, the load on the side moving down would be perhaps 15 pounds. But, my goal would be for a smooth release, rather than an abrupt release.

I know that flat belt brakes are common on go-carts, so perhaps a flat belt system would be a better choice. But, flat belts and pulleys are not that common in the catalogs I have looked at, and there are only a few choices.

-Joe

 

[jdunfee5]

Ted, am I correct in guessing that in your mower, you control the drive belt slippage well enough, that you can control the speed of the wheels?

-Joe

 

[gruntguru]

I doubt the mower would be designed for sustained operation with a slipping belt. A slipping belt could be used when starting from rest. If sustained speed control is performed, it might be a variable speed v-belt system. Link

je suis charlie

 

[Strong]

The belt drive in the sketch is the same as my snow blower's auger and blower drive. The belt tension is either tight or slack and drives with full power or disengages the drive sheave. I do not believe that a rubber belt on a steel sheave can be used as a constantly slipping clutch, but only as an on/off clutch.

Walt

 

[hydtools]

Jdunfee5, yes I can control the speed by controlling how much the belt slips. The more the slippage, the lower the speed.

Ted

 

[jdunfee5]

If it is not a good way to control speed, then perhaps I should consider the "loose belt" approach to just disengaging the motor from the drive system. Then, for more control over the process, a separate cable brake system, operated by a hand operated lever, like a car's parking brake.

But, all ideas are still on the table. If we do end up trying a belt tensioner as means of doing a controlled release for the pivot, then I will report back if it is successful.

-Joe