DART linear actuator alternatives?

We are currently investigating the use of a linear actuator to power part of our robot, so I was wondering if teams had any suggestions about ones that would be easy to use, other than the DART.

The DART is currently out of stock, and while the 12" version is expected to be available tomorrow, the 6" model (which fits much better in our design) is not going to be available for at least another week.

I know that many linear actuators exist that might be appropriate, but are there any models that teams have successfully retrofitted to use legal motors?

Similar threads have existed in the past, but the few solutions given do not meet our load requirements (probably close to 200 lbs, so as to have a good safety margin).

In this thread I mentioned the use of a linear actuator that we have successfully retrofitted with a bag motor with relative ease. Put a flat on the motor shaft and drill 2 new mounting holes for the motor and voila. The mentioned actuator can be found below. It is rated for 200 lbs of static load (could probably go a little higher) and there are stronger models available. Also it is fairly cheap. Sub $100.

That actuator does look promising (if we really need extra force, we can combine, multiple ones, since they are so cheap compared to the DARTs).

Do you know how the performance changed when you put the BAG on it? Did its speed and/or force change?. If you had a model number for the original motor, that would be really helpful for comparison, since it doesn’t seem to be listed anywhere.

Thanks.

EDIT: I just noticed that it (and all other similar models) are out of stock online. Did you order it online or (since you guys are in Canada) were you able to get it in a Princess Auto store?

I believe we were fortunate enough to just walk in and grab one. We measured the rpm of the stock motor to be 1000rpm (roughly) and I recall the subteam we have working on this saying the bag was 7 times more powerful (don’t quote me on that one). However the 1000rpm is what we measured and the bag is 14000rpm. That turns the actuator into something that went 1/3in per second, to one that goes 4.6in per second now.

Also, although we think the force is around 7 times greater from the bag, I would not plan to load it much more than what its rated for (200lbs static load) as you might start having mechanical failures in the actuator.

I was also wondering about an alternative top DARTs. Unfortunately, I called Andymark today to check up on the status of the 12" actuators, and they told me that they would not be in stock until after build season :frowning:

Do you know about these?

https://www.firgelliauto.com/products/light-duty-rod-actuator

Are they legal? I cannot find anything in the rules that prohibit them. Anyway, thanks for the help especially since we are kind of relying on linear actuators for our design.

Although I cant say for certain if it would work as easily as ours did with the bag motor, it looks very similar in construction to the one we are using. If you were to swap the motor for a legal one, I don’t see why it wouldn’t be legal.

For us, the problem is that we cannot do much precision machining, so it might not be easy for us to make an adapter if a motor doesn’t fit nicely.

I contacted the company that makes them to see if I could figure out how to mount a motor on them and the sent me this picture. It shows that the motor uses a 3mm shaft with a flat to connect to the drive gear. Since the BAG has a 4mm shaft, you would need to adapt it somehow. It is also likely that new mounting holes would be needed.





Unless the linear actuator has a LEGAL MOTOR installed, it cannot legally be used on your robot. You may install a LEGAL MOTOR on any gearbox, including linear actuators, but you can’t in general, use an off-the-shelf linear actuator complete with the factory-installed motor. I’ve never seen one come with a FIRST approved motor.

It broke my heart to have to tell a team they couldn’t use their linear actuators while I was inspecting them last year. They tried to install legal motors during the competition, but never found a motor combination that could be installed and was powerful enough to run their stacking mechanism.

I was thrilled to see AndyMark sell a linear actuator that could take a legal motor, only to see my hopes for such a product dashed by AndyMark’s inability meet the demand.

Perhaps FIRST is a bit too tightly wound about motors?

I buy the motor controller constraints on the safety argument (we are sure we can kill these in X mS). Why the obsession with the rotating thingy the controller drives?

TJ