Mechanical & Electrical Parts
- I've been spending time learning about BLDC motor drives to use for
Chopper's foot drive. This narrative is going to ramble a little as
I've got a lot of ground to cover.
started out planning to use a modified version of my Scooter Motor
Outer Foot Drive that was designed for R2. To allow that drive to fit
into Chopper's foot shells I proposed two modifications to the
shells. However, even
with those changes, from my perspective, Chopper's feet are still too
small to comfortably fit a 2 wheel scooter motor drive where both
wheels are driven. For Chopper I wanted
simpler, and more compact. I started looking at Brushless DC motors
(BLDC) for use in a drive. Fortunately, others in the R2BC have already
done lots of work in this area.
I stumbled around the R2 Forums until I came across the
posting Brushless motor alternative for Jaycars by
Basically the drive consists of a 268Kv BLDC motor and a
P60 16:1 gearbox. The motor has an unusually low 268Kv rating, most
motors are much higher. This means the motor turns more slowly so a
lower gear ratio gear box is adequate. The P60 gearbox is 1.9in deep,
1.5in long .5in dia. drive shaft. The two together make up a 2in dia.
package 4.2in long. By comparison the Scooter Motors are 2.68in dia and
5 to 5.25 in long. This makes component placement within the foot shell
I designed my R2's foot drive I used 5in dia Colson Wheels with .5in
dia dead shafts. The wheels turned on their own internal bushings,
driven by plate sprockets that were bolted to the
wheel. Drilling the wheels & sprockets and enlarging
center hole were all tasks left to the builders.
foot drive I have configured a design that works with off
the shelf components. What follows is the list of parts I used.
already knew that we needed a 4in wheel.
Banebots offers Colson
4in wheels http://www.banebots.com/product/WC2-4.html
fit 3/8 bore clamp hub -
The 3/8 in shaft is more than
adequate for Chopper's load. [I only used a 1/2in shaft on R2 because
that was the size of the bushing in the 5in Colson Wheel!].
They also offer to grind down the wheel's crowned surface so
flat, That provides more traction and, coincidently, saves space!
choose the grinding option and hub after you select the wheel,
chose to have my wheels cut down to 4in and the 3/8 shaft clamp type
hub press fit.
On the Banebots order page you should see:
4in x 1-1/4in
Gearbox - P60
For RS-500 Motor - http://www.banebots.com/product/P60S-44-5.html
that 16:1 gear ratio is about as high as you can go and still be able
to push your droid by hand (if you have to :-( )
(When you order your Banebots parts remember you need 4 wheels
and 2 gearboxes - yea, I got that wrong!)
- I used a 22
tooth (type B) sprocket on each wheel. Now the OD of the sprocket is
only 1.89in so
space isn't going to be a problem. Fortunately,
the 22 tooth sprocket is also available in both a 3/8in bore and
bore which pairs with the standard shaft on the P60 gearbox. However,
if you want to use sprockets that are all the same bore, you can get a
3/8in drive shaft for the P60 from Banebots (at extra cost!). Sprockets
are available from a number of suppliers. I used
B&B Manufacturing, 712 N. Fail Road, La Porte, IN - https://www.bbman.com/roller-chain-sprockets/
I ordered qty 4: 25BF22x3/8 and qty 2: 25BF22x1/2
The rest of the parts list is derived from the forum posting
note above. I have added additional
parts suppliers and comments:
Brushless motor - https://hobbyking.com/en_us/multistar-elite-3508-268kv-high-voltage-endurance-motor.html
Find more detailed info is
Brushless motor controller
If you use a different motor controller
make sure it can drive the motor in both directions.
for above - https://hobbyking.com/en_us/hobbykingr-tm-programming-card-for-car-esc.html
- Multistar High Capacity 4S 5200mAh Multi-Rotor Lipo Pack (my choice based on what I used with R2 - your mileage may vary!)
You might also want to buy mating connectors for the ESC to
Motor and Battery connection (The ESC does not come with connectors!).
I used a Pololu ESC when I built R2 partly because it did the
conversion from Left/Right and Front/Back R/C controller Joystick
signals to the Tank Drive signal needed for R2 & Chopper. The ESC
noted above does not do that. Fortunately, PaulG pointed me at DasMikro
RC Signal Mixer For Tank Dual Bidirectional Motor Control from www.banggood.com
standard P60 comes without
grease. Banebots recommends Mobil XHP 222 Special grease,
available from a number of suppliers - Grainger has Mobilgrease XHP 222
Special, 13.7 oz - https://www.grainger.com/product/4ZF44
purchased from Grainger only because I was also ordering other parts
from them at the same time - there are lots of suppliers]
Replacement Motor Shaft
- The gearbox pinion is sized for a 3.2mm shaft, the motor has a 4mm
hardened shaft. It's easier to replace the motor shaft with:
HK-2221 Motor Shaft Kit (3.17mm) -
Since the wheel shafts are now live in this
design you are
going to need bearings and shaft collars for them.
I used FR6ZZ 3/8" x 7/8" x 9/32" Metal Shielded Flanged Ball Bearings
- I got them them on Ebay, a package of 10 for less than $10.
I got a package of 10 of 3/8 in bore Shaft Collars on
Ebay for $10. I suspect I could have
done better if I kept looking!
3/8 steel shaft cut to 4.2in long
You'll need need 2pcs of #25 chain each 22.5 in
long measured inside link to inside link (see
pix). Lots of Suppliers.
Master Link: Master links are used to splice chain, Get
extras as the
small clip parts are prone to flying off into corners of your workbench
never to be seen again! I got a package of 10 from an eBay
supplier there are many!
Chain Tensioner: I used a W75-8372
Chain Tensioner for the Razor E100, E150, E175, & E90 Scooters
from Monster Scooter Parts
Parts Used to Hang Battery Box from Foot Shell
Battery Boxes are hung at the top from a pair of studs that extend out
from the top of the Foot Shell and are held in place at the bottom by a
pair of magnets.
Studs consist of a 4-40 x 1/2 in bolt held in place
by a 4-40 nylon insert lock nut. Over the Bolt is an Aluminum Spacer
and a Fender Washer.
Fender Washer: 3mm x 9mm Metric Fender Washer (Bolt Depot #17828)
Spacer: Aluminum Spacer 6.35mm OD x 3.1mm ID x 6mm Long (http://www.aluminumspacers.com/catalogsearch/result/?q=mas6.35-3-6)
The length of the space is chosen to be slightly longer than the
thickness of the plastic (.1875) the Fender Washer provides an edge.
This design is
copyright Media-Conversions LLC and is made available for non-commercial