Zumo Idler Sprockets

I recently purchase a Zumo 32U4 from my local (AU) supplier Little Bird Electronics
Unfortunately I was sent the previous version not the mid year updated version
No big deal this stuff happens but as my Zumo sees time in a classroom I needed the Forward LED holder.
They were great with rectifying this and sending out all the updated chassis components (from you guys) other than new screws for the idler sprockets.
However one problem still exists, the rear idler sprockets are loose (side to side)
Referring to this picture https://www.pololu.com/picture/view/0J3538 does the 8.8mm shank vary between the older white sprockets and the newer black sprockets?
I estimate this shank needs to be 3mm shorter.

Also I have just ordered an A Star 32U4 Prime for expansion. I want to add additional features to my Zumo but do not wish to remove any of its current functionality so I plan on making the two communicate via I2C. Which standoffs do you suggest for mounting the Prime atop the zumo?


Hello, Wayne.

Yes, the shoulder bolts are different between the spoked and non-spoked idler wheels (the shoulder is shorter on the bolts for the spoked sprockets). If you cannot get a pair of appropriate shoulder bolts from Little Bird Electronics, email us, mention this forum post, and we might be able to help. By the way. the picture you linked to is for the shoulder bolt that is included in the Pololu 30T and 22T Track Set, which has a longer threaded section than the shoulder bolts used in the Zumos.

As for mounting an A-Star Prime to the Zumo chassis, we do not have a straightforward recommendation for how to do that. However, you might consider using some of our aluminum standoffs to mount to a piece of laser-cut acrylic. The acrylic would have holes that simultaneously allow the standoffs to mount the acrylic to the Zumo PCB and chassis, and the A-Star Prime to mount to the acrylic. You would probably have to decide how much, if any, of the LCD screen you want to be visible. As for height, you likely just need standoff heights that allows all parts to be mounted with little clearance and without interference. The holes on the Zumo chassis and Zumo32U4 PCB will fit #2 threads.


Thank you for your reply Jon
I will email Little Bird and I am sure they will be able source the correct bolts from you guys for me.

I like your idea for an acrylic ‘intermediate’ platform to accommodate the different mounting holes in the two boards :bulb:
With the Zumo LCD I was thinking of relocating it using a ribbon cable maybe on to a second acrylic platform on top of everything with a pan/tilt mechanism I have (for ultrasonic sensor and maybe a WLToys V959-19 Missile Launcher :smiling_imp: )