Previously, our team has used a harbor freight hydraulic cart like this one: https://www.harborfreight.com/500-lb-capacity-hydraulic-table-cart-61405.html
It worked well for us, but had a couple of issues. Mainly, it had minor trouble with the cable protectors, was a pain to transport, and didn’t have much storage. To remedy these issues, we decided to build a new cart in the off season. The new cart features massive 5 inch casters, additional storage space and a CIM motor powered scissor lift.
That’s my big concern too. As nice as it is to adjust the cart height, I personally don’t think it’s worth the expense and weight compared to a folding cart with a removable riser.
That said, your scissor lift can probably work, but it’s hard to tell if there are any flaws from the low resolution images of the CAD. Some of the parts (the x legs) look a little thin to me. I recommend you over-build. The cart has to survive a lot of abuse, and it’s a safety concern. You can’t take the same lightweight liberties that you can with an FRC robot.
You mentioned storage - think about where these items might fit on your cart:
extra battery
ethernet tether
driver station
water bottles?
other-colour bumpers (we prefer they live on the cart than in the pit)
all the random hardware and tools that collect on the cart after in-queue repairs.
Total weight is 155 pounds, most of which is the gearbox and cart base.
The base will be welded steel, but the box structure is held on by removable bolts.
Yeah, I’d definitely consider upgrading the 1/4" aluminum bars to something like 1" x 2" aluminum tubing. The scissor bars have to resist all of the side loads, and a ~2ft long 1/4" thick aluminum bar is going to be pretty flexy in that direction.
If I can convince you to give up the scissor lift, you can buy a folding “Platform Truck” in a lot of places for cheap. Add an upturned FRC tote to support the robot, and you’ve got a really nice, easily packed robot cart.
Can it fit through a standard 36” door? Because the last thing you want is to carry your robot the rest of the way to the field cause your cart is to big.
Keep in mind that many doors in older buildings are significantly narrower than 36". Maybe as narrow as 30-32" after you account for a door jambs and a door that doesn’t open fully.
Brendan is right here. 1/4" aluminum flat bar will have a ton of sway side to side in this application. Either adding some bent flanges to that part, or switching to some form of box tube/c-channel would add a tremendous amount of stiffness/rigidity to this design.
There is a reason you don’t see many scissor lift mechanisms on robots in FRCFIRST Robotics Competition, let alone a robust and well built scissor lift; They’re surprisingly challenging to build well (and light weight enough for our needs).
I can appreciate the challenge of making something like a robot cart for the design experience. In terms of the scissor lift, is there any reason you can’t just design around transplanting the harbor freight one onto a frame with better wheels and storage for your needs? Scissors lifts are easy to draw-up, seem like an intuitive solution, but hard to implement well. There is a reason teams with them on robots often find themselves on dnp lists, they are super rarely executed well and even more poorly executed when a load over 5lbs is involved.
It’s a cart, over build it and decide what is permanent weight and what is removable weight (i.e. toolbox)
I would be very concerned over a CiM powered scissor lifts. Seems a recipe for removing a finger or 2. We actually have the Harbor Freight cart We removed the original casters, welded a beefier plate and put on some good 5" casters. We also welded on a shelf to the handle for DS.
