Drivetrain Question

[1502]

Hello all,

We have a cart in progress that we are going to make motorized. Our issue is that we want to be able to disengage the drive wheels from the motors to make it easy to push when not in use. We have yet to come up with an easy way to do this.

So, CD, do you have a solution to our problem?

Thanks,

Ryan

[Chris is me]

Consider running a shifter with a neutral gear.

[Alan Anderson]

How about this? Use motorized rubber wheels in contact with the cart's wheels to spin them. Mount the driving assembly in a way that can be pivoted or lifted to break the contact.

[1502]

We have, but the problem the problem with the neutral space is that it's had to get working since they are not really meant to stay in neutral. Besides, four new shifters are not exactly in our budget.

By the way, the drive wheels are mecanum.

[MARS_James]

Originally Posted by 1502

By the way, the drive wheels are mecanum.

If this is a serious statement I would really reconsider. When moving around a mecanum wheels on anything but carpet at a quick pace you run into one of two issues
1) If it is slicker then carpet you get sliding and some minor issues with veering off to one side
2) Something rougher then carpet will damage the wheels quickly since they constantly are hitting it at an angle

(also when you push around unpowered mecanums they make a lot of noise)

[Nate Laverdure]

Certain power wheelchairs (jpg link) have clutches built into the hubs to allow the wheels to spin freely if the chair is to be manually propelled.

[RogerR]

Drive wheels with v-belt; tension it to engage the drive, loosen to coast.

[1502]

This cart has gone through a season with non powered mecanums. They do make some noise, but they are not loud at all. If anything, they make people turn around and realize that there is a robot behind them. Keep in mind this was tested on tile floors with decent grout gaps.

And to Nate: This was our prior cart.
http://www.chiefdelphi.com/forums/at...5&d=1333563144
http://www.chiefdelphi.com/forums/at...6&d=1333563152

V-belts are a good option. We don't know if the belts would slip under the stress though.

[akoscielski3]

Originally Posted by RogerR

Drive wheels with v-belt; tension it to engage the drive, loosen to coast.

This is the same way my lawn mower work's to spin the blades. Though it doesn't have a lot of torque needed so I can not say it would work or not. Prototyping is an option though

[RogerR]

Originally Posted by akoscielski3

This is the same way my lawn mower work's to spin the blades. Though it doesn't have a lot of torque needed so I can not say it would work or not. Prototyping is an option though

The idea was shamelessly stolen from stuypulse's 2005 robot: http://www.chiefdelphi.com/media/photos/20224

Evidently worked for them.

[JamesCH95]

OP, consider disabling dynamic braking before you attempt a mechanical solution. That may be enough to comfortably push the cart around.

[1502]

Originally Posted by JamesCH95

OP, consider disabling dynamic braking before you attempt a mechanical solution. That may be enough to comfortably push the cart around.

The second goal of disconnecting the wheels for the motors is a matter of safety. Whatever way we end up doing it, there will be a deadman switch that works like one off of a treadmill. We like to keep our carts safe, and we're pretty well know for that.

[Clem1640]

Ever heard of a clutch?

[JamesCH95]

Originally Posted by 1502

The second goal of disconnecting the wheels for the motors is a matter of safety. Whatever way we end up doing it, there will be a deadman switch that works like one off of a treadmill. We like to keep our carts safe, and we're pretty well know for that.

You could use the deadman switch to disconnect power to the motors directly, or through a relay, which would be similar to disconnecting them mechanically.

You could also get or mimic an OTS item like a wheelchair safety lock to prevent wheel rotation:

[tr6scott]

A couple of thoughts, If you are driving like typical robots, try using victor speed controls instead of Jags. Jags short the motor leads when off, so the motor is a brake. Victors do not do this, and you will not have this braking action when pushing.

Safety issue, put a electrical cut off switch by the controls.

Fix it electrically, of course, I'm electrical.