Hacker News Reader

Comment by nielsole | Hacker News Reader

Wow awesome. This is one of the most impressive arms I've seen. How much did it cost you to build? About how many newtons can you excert when fully extended? / What weight can you lift? What is your experience with backlash?

Definitely considering forking

View on HN

Thank you! I had all the parts lying around and I’ve not put together a full BOM to calculate costs. But it’s two odrives and four brushless motors plus maybe $100-150 in bearings from AliExpress, then some screws and a couple kilos of PETG. So maybe $850 if you built it from scratch?

I haven’t done testing of its capabilities yet as I just got it working today. Also I am running at 24v but I want to try 48v when I can upgrade my odrive controllers to the 56v version.

Not sure about backlash either except joint 3 has bad backlash not due to gearing but from a fixable issue with the way the output connects to the frame.

But I am very happy with this design! I think it’s pretty promising.

Also it should be noted that with my $850 estimate that is $400 worth of Odrives. For years I have longed for good brushless drives for under $100 per channel and there are some newer ones out there. But basically brushless drivers are a major chunk of the price which I think could be reduced with cheaper custom drivers.

For my previous work years ago, we did custom brushless motor drivers including basic control theory implementations. I was under the impression that the driver designs were fairly standardized/commoditized.

Could you explain more on your search of suitable drivers and on why you didn't build your own drivers? Why are these drivers so high in price?

I have designed brushless motor drivers in the past. But at the time I was fairly busy and I discovered the VESC 4.12 which is pretty good, but the creator moved to a new design that costs way more and the user community fragmented. The 4.12 designs are still for sale and pretty affordable, but I switched to Odrive due to the very active development community. It seems the price of Odrive has gone up though. I mostly use them at work so I don’t care, but this arm is a personal project and I used a couple odrives I had previously purchased.

There’s other new drivers out there that I haven’t tried. And I could take a crack at a new driver again. But really I want someone in China to produce a good design and sell them on AliExpress. Something with open source design files and code, able to handle 2kw power, able to use one or two encoders, etc. You can get a VESC on AliExpress for $75 or an Odrive clone for $95 with two channels. But I guess I feel bad buying an Odrive clone because the newer hardware isn’t open source so they are unauthorized clones, and I know the Odrive team works really hard. I would feel bad showing off my work with Odrive clones.

There’s other options out there though and I may want to try them. It’s been a while since I’ve needed new drivers at home but with this project I sure do!

In the beginning of the pandemic I've attempted to build a 6 axis arm from this project https://www.anninrobotics.com/

Overall great documentation, and the author also sells hardware kits so you don't need to source all gears by yourself.

Fun! In my case all the gears are 3D printed so there’s no sourcing issues. Tho those designs are more finished than mine!

Reply on news.ycombinator.com