I like the idea of the Wild Thumper wheels – 120 mm diameter, and 60 mm width, with knobbly rubber for traction.
The center holes are a bit small (4 mm axle, perhaps an 8 mm hex nut?) and I also would like the torque and speed of the 37D motors compared to the 25D. I’m carrying a fair bit of load and would like a 10 mph speed.
Are there similar wheels somewhere (RC hobby world, perhaps?) and some robust way to attach them to the 6 mm D axle of the 37D motors? I know nothing about how the RC hobby world works; most wheels just list the “hex size” which I imagine means the size of the hex nut that locks into the hub of the wheel – but what about axle size? Is it always half the hex? And what’s a good way to get a hex nut onto the 6 mm axle? Where can those kinds of parts/adapters be found? (Also, ideally, in 316 stainless or similar high-strength material, although I imagine the gear motors are not of that grade…)
For example, these wheels seem similar – a few millimeters smaller: www3.towerhobbies.com/cgi-bin/wt … LXXCC8&P=0
Sadly, most RC hobby sites don’t list dimensions at all, just specific car models
The second question is about suspensions – the RC hobby pages I’ve found mostly sell completed axles with transfer knots and all, which is not exactly what I want. First, the linkage to the 37D motors would have to be solved, and second, I really need the integrated encoders for each wheel (so, a motor per wheel.) Also, most of them seem a little on the flimsy side, as all they need to carry are some drawn polycarbonate chassis…
If a moderator sees this, please move it as per below.
Surfing around, I’ve gotten as far as this:
I need some kind of adapter that can go on a 6 mm D-shape shaft (with a set screw) and has a “hex” (hexagonal head bolt with screw hole in it) on the end. The sizes of hexes commonly available for the 120mm-190mm RC wheels are 12mm, 17mm and 23mm.
Fasten adapter to D-shaft, fit wheel onto adapter, screw center screw onto wheel (with threadlock, I guess?) and it’s done.
Four wheels is about $50 plus shipping and up: integy.com/st_prod.html?p_pr … JNJjcWHJ8E
Apparently, the real hobbyists either get “beadlock” wheels where you screw the rubber to separate hubs yourself, or use rubber glue to glue them to the hubs. I’d prefer less work
Suitable adapters are not something I’ve yet found sources for, I’m probably looking in the wrong places. Suggestions welcome!
Suspensions that allow individual 4-motor drives are not commonly available, so I have to either use stiff axle suspensions with 2 motors, or make my own. Getting steering linkage and everything right with that is not something I’m looking forward to.
Also, this question, while about the 37D motors, probably should be moved to another topic, like the “mechanical design” sub-forum.
I have moved your thread as you’ve requested. Unfortunately, I do not know of a good solution for mounting those particular wheels on 6mm shafts. If you come up with something, I’d love to hear about it (and in general I’m very interested to hear how your project goes).
It seems most RC drive shafts have key nubs at the end of their shafts, and thus their adapters assume this to fasten adapters rotationally. Robotmarketplace has some adapters that would actually work, although only a single set screw – I don’t know if that will take the torque, but I’m going to find out
So, those hubs will allow me to mount any RC wheels with 12mm hex hubs, which actually includes the Wild Thumper wheels, too, if I understand things correctly. So that part’s worked out
I might also just make my own (I have access to and a just enough skill to be dangerous on a CNC vertical mill.)
Next question, related to this: The drawings for the 37D motor is missing a few measurements. Inventor would say it’s “under-constrained”
How much is the inset of the motor part compared to the gearbox? ← this one is important for mounting!
What is the diameter and extent of the round nub underneath the encoder in the back?
The encoder is said to extend 12.5mm from the “back of the motor” – is this the back of the illustrated connectors, or the back face of the main motor body?
Also, the Wild Thumper wheels are under-specified, too! It doesn’t say what the hex size is. The “4mm adapters” are also under-specified for the same reason. All in all, though, Pololu is better than the RC places I’ve found at putting out dimensions and specifications. Though not as good as McMaster-Carr, so you’ve still got something to strive for
So, more information, for those who are interested in using these kinds of wheels:
RC axles all have a cross-pin through the axle, that their hex converters latch on to for traction. That doesn’t work with the D-shaft of the 37D motors, so you’re going to have to find or make something on your own that’s hexagonal on one end (with a hole for a tightening screw) and a 6 mm shaft hole with set screws on the other end. I found something that might work for 12mm hexes, but most nice-size wheels (140-170mm diameter) uses 14mm hexes, and sometimes 23mm hexes. (The dimension is measured across the flats, btw, so the diameter is bigger than the specified number.)
Luckily, a CNC mill and a 1/8" or 3/16" end mill, plus a drill press and a M6 tap, will easily turn some round (or square) aluminum or nylon stock into proper adapters
I’ll be ordering parts this week, and I have my work cut out for me…
Thank you so much for your detailed measurements! With luck, they’ll help someone other than me, too, in the future
I placed my order for the motors and mounts now, so hopefully I’ll know this week-end how it all goes. Because I’m going with the 37D motor with encoder, I ended up getting some 160 mm monster truck wheels from a local hobby store, where I could measure the hexes on those wheels as 14mm. This means I have to mill some 14mm-flats hex adapters out of 3/4 inch round stock, and drill 6mm shaft holes, M4 mount holes (with thread) and some set screw holes in them. Had you had something like this in stock, I would have included them with my order (hint, hint )
This project is moving forward, too, albeit slowly, because the mill I usually use has been out of commission for over a month :-/
Today I made the 45 minute drive down to San Jose to use a similar mill, and made couplings for Pololu style 6 mm set screw shafts to 14 mm RC style hex wheels.
They would look better if I also turned the non-hex part, but they’re quite functional as-is, which is what matters
I’m also glad that the motor plus mount fits inside the wheels – these are quite large! (HPI monster truck wheels.)
Next up: double A-frame suspension for steering front wheels.
Thanks for your post jwatte. I’m looking into the same thing as you.
The RC world is so established, I’m shocked that the robotics platforms that are being developed do not build on the RC products that already exist.
Can I ask what you are doing if anything to make sure the RC wheels can support the weight? I don’t know how much weight they can take with foam inserts.
I think I will limit my RC wheel search to 12 or 17mm hex sizes so the I can use the hubs the Michael posted since I can’t mill my own.
If anyone finds any other alternatives for hubs, please share.
I’ve been making the various parts of the suspension for this 'bot over the past several months.
Today, I screwed it all together.
Here are some pictures of:
How I put the 37D motors into knuckles (they then connect to the suspension via ball joints)
The actual suspension construction. This is from the underside. On top, there’s a RC servo for steering, for each wheel.
A picture of the actual 'bot so far – no sensors or other electronics hooked up yet. The box on top is a mini-itx M350 computer case.
It has been over two years since this thread opened, but we have finally made some progress on expanding our selection of wheel adapter solutions!
One option is to use our scooter wheel adapters, which allow you to drive most scooter, skateboard, inline skate, and other common wheels that are compatible with popular 608 ball bearings. Versions of those adapters are available for 4mm, 5mm, 6mm, and 1/4" motor shafts.
Another option, which we just released yesterday, is to use these 12mm hex wheel adapters, which allow you to drive common 12mm hobby RC wheels. We currently have versions of those adapters for 3mm, 4mm, and 6mm motor shafts, and we plan to carry short and long adapter versions for each shaft diameter in the beginning of the new year.
