I’m looking to build my first beetle, which will be a grab-lifter-suplexer, with a mechanism working like the Gif below.
I’ve already got some drive motors, and some escs, and all of the other parts, but I was just wondering could anyone recommend me some high-torque motors (perhaps similar to the legendary “strangbox” that Joe used in crab grab v4 - that thing has some crazy power!) And also, would a fat servo with BIG power be useful in the modern style of combat robots for this application?
If anyone knows how to get or build a “strangbox” or anything similar with over-sufficient torque, then please let me know!
The standard high torque motor is the 37D gearmotor, with 100:1 or more reduction. These are fairly cheap and reliable, and run happily off a standard brushed drive ESC. Joe used them for Grab Crabs v1-3, and Martin Christopher currently uses one to great effect in Toucan, his grab and lift (No link for this, sorry).
Your other options are, like you said, a big servo or a Strangbox.
A big servo is going to cost you a fair chunk of money, as you would probably want 100kgcm or so torque. It’d give you similar performance to a 37D, but with a couple of advantages in that it is significantly lighter, and it has positional control so you can tell it to stop at an exact angle. Jack Franklin won(!) last BBB Champs using one in Luchador (The chronicles of Luchador 1 through 3 - #3 by Jack).
The main advantage of a Strangbox over a 37D is power - you get a grab and throw rather than grab and lift. You can’t get them off the shelf, so you’d have to build one. The process is roughly the same as doing a Rotalink conversion (BRUSHLESS22MM.md · master · Alex Mordue / Saw Loser · GitLab), but you have to do more hunting around for suitable gearboxes and motors, you have to make your own shaft and press the pinion onto it, and theres more of a chance of it self destructing. It’s not an easy task.
For your first bot I’d recommend sticking with a 37D, as it’s the safest bet in case anything goes wrong. Good luck, and have fun building!
Suplexers are fun! Looking forward to seeing what the design looks like. Echoing what Jed said, 37D motors are probably the easiest option.
One downside of the 37D is its weight compared to the other options. I’ve experimented with similar setups to Grab Crab for my own grab-and-lift, running a 2830 1300kv brushless motor with a 189:1 gearbox from Aliexpress. Plenty of power, but hard to control (I have sheared the motor shaft of one during testing by stalling it at full speed, so I currently liit the power to 60%).
If you’re able to make a suitable 3mm thick spacer you can add an extra reduction stage to a 22mm brushed gearmotor for 64:1 reduction, or you can steal the ring gear from another 22mm gearmotor and thin it down to 6mm to stuff in two extra reduction stages for 256:1 (probably a bit slow).
I’m still experimenting with this in my beetle, and the advice above is probably better, but it seems promising so far - I’m running two motors modified like this in parallel and they come in at about 140g combined.
I’ve got some of the 37D motors, but I’ve been avoiding using them because it’s my drive pods rather than the lifter that are actuated, so I want to keep the ability to control them separately if possible to get them back in sync if (when) the belts slip.
Hey Ollie, posting in here to avoid my build log filling up with too much advice posts:
Honestly while I’ve had good results using my servo - its probably not something I’d really recommend for grab and lift without some major caveats.
The range of motion is limited and has to actuate both the grabbing and lifting motion, which prevents you from gearing down for more torque so it needs to be a very strong servo with an extremely high torque output.
Servos of this power tend to be either absurdly expensive or almost as heavy as a 37mm motor anyway - or in some instances both.
37mm motors are generally what I’d recommend starting with they’re much simpler to get working well. Something around 70-100rpm would be idea. They’re simple and practically indestructible.
Then using external gears to operate your weapon you can adjust the gearing to suit your needs.
A small output gear on the motor and then a large one on the lifter will provide additional reduction to increase torque further for lifting power. Then a smaller gear on the grabber will speed up that portion of the motion to make catching opponents easier - the torque on this part is irrelevant anyway because as soon as the grab starts to lift it’ll bite down with all the torque used in the lift anyway.
For gears you can either print them - big chunky gears with large module to take the strain or technobots do a good range of steel gears
