Van Door Worm Gear
 

A project that im working on has an application that is perfect for the Van Door motors, however the team is a little concerned about the plastic gears inside the gearbox. Im pretty sure that teams in the past have replaced the internal gears with ones made of metal. I was wondering if anyone had any information on how they did this.

Thanks,
Jim Giacchi

Re: Van Door Worm Gear
 

Jim,

I believe you will not have a problem with the plastic gear that drives the worm gear. We used these on our robot in 2000 and 2001 under constant heavy load (including shock loads) and never encountered any problems. Keep in mind that the engineers who designed this accounted for its strength characteristics under the max stall loads. So, unless your application will require some excessive shock loads, you should be OK.

I just thought of another potential problem with some plastics. They have a glass transition temperature (GTT) not to far below freezing. This means that they become brittle and will crack under minor shock loads when used in very cold environments. Some cast metals also behave this way. I know from experience that cast zinc start to become brittle at about 20 deg F.

Hope this helps.

Raul

Re: Van Door Worm Gear
 

We too have used the van door motors in some seriously high load situations (pull ups in 2000 for instance) and never had a problem with the motors. They work in cars for years, and probably are designed with a plastic that can get pretty cold, last thing the car companies want is people not being able to get out of the car just because its cold!

Re: Van Door Worm Gear
 

Since these motors are actually used on Delphi Power Sliding Door applications and I work in the Advanced Development Group for the group that designs power sliding doors, I have some knowledge of this motor.

Raul's concern about cold is probably not an issue. We test down to -40 C with no problems.

I think your real problems will come if you are impact loading the teeth. In this case, you can bend the teeth pretty quickly.

So, if you are driving a long rigid arm and expect the arm to take a lot of hard wacks in directions that will give impact loads to drivetrain you are asking for trouble. Another way to give impact loads to the gear teeth is to run into a hard stop at high speeds (stalling the motor against a hard stop should not be a problem).

I have first hand knowledge of this failure mode. We used the power sliding door motor with great success over the years. BUT, one year we used it to lift ourselves on the puck. The mechanism was such that the drive link went over center at the bottom of travel so that we could stay up when power was removed. At the end of travel we had a hard stop. Basically every time we lifted ourselves, we ran the motor at full speed into a hard stop. We were eliminated from the competition due to failure of that gear. Tests after the Championships showed us that we could fail that gear in only a handful of lifts.

Keep this in mind and you will probably have no troubles.

Good Luck.

Joe J.

Re: Van Door Worm Gear
 

On a different subject, replacing this gear with a metal one in a competition would have been illegal for the past several years. All motors with integral gearboxes and the internals of the other motors were not modifiable.

The detachable gearboxes (drill motor, globe) were modifiable.