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When last we left our intrepid droid builder, he was printing lenses and still waffling over what sort of drive system to use for Treadwell. For a variety of reasons, absolutely no other progress has been made in the interim.
![[Image: Kc2rvhF.jpg]](https://i.imgur.com/Kc2rvhF.jpg)
However, another Dragon Con has come and gone (two if you count the virtual con in 2020), and once again the urge to build has seized hold of his soul. To be specific, the urge to build a droid that people might actually recognize.
So, yeah. At Dragon Con this year, I decided that I would make every effort to get Treadwell built in time for next year, or at least a lot closer than he is now. It may be a severely optimistic goal, considering the nearly 0 percent progress I've made on actually building him since I started back in 2016, but that's how I roll.
As mentioned, I was waffling on the drive system ... err ... three years ago. I still don't really have much more of an idea on what the track drive might need than I did back then, so at some point, I'm going to have to just commit to something and hope it'll work.
I'm going with a brushless system using Oliver Steeples' brushless Jaycar replacement for R2 as a guide, as previously discussed. However, some things have changed since Oliver wrote the Astromech thread (and even since the part links were updated in 2019). Here is my logic and the parts I am leaning toward:
Unlike Paul's wooden base, I suspect that a styrene base Treadwell is likely to be lighter than a styrene R2, as there's less material to its body. Given that Oliver's R2 drive was capable of propelling Oliver himself, I think (hope) the stronger brushless motors and the weight difference will be more than sufficient to counter the friction difference between the wheeled R2 and Tracked Treadwell drives.
* 2 ESCs @ $31.75 each:
These are the HK-60A speed controllers that Oliver listed for those who wanted to run higher voltages. More importantly for my purposes, they are 60A, which may be necessary for Treadwell. Unfortunately for me, the programming card for the ESC is currently backordered, with no ETA.
* 2 Motors @ $19.99 each (and 50% off the second motor):
The Multistar 268kv motors that Oliver recommended have been discontinued. I found a variety of motors that might work on Amazon and Hobbyking (like the Turnigy Aerodrive 4250 350kv), but there were open questions with all of them. Another option is the Rev Robotics Neo motor that Maxstang uses in his Maxdrive R2 drive system:
However, for now I found these iFlyRC 3508 380kv motors on ebay. They are similar enough to the original multistar motor and at a low enough price that I'm willing to roll the dice to see if they are sufficient. If not, I can likely use them elsewhere (such as my D-O concept droid). And if they are junk, I won't be out all that much. I just need to make sure the rest of my parts can support upgraded motors if I need something stronger. Especially the most expensive components, the...
* 2 Gearboxes @ $67.25 each:
Because I chose a higher kv motor than Oliver recommended, I want to gear it down more than he did, in order to trade some of that excess speed for power. However, as Oliver cautions, higher gear ratios also make the geartrain harder to backdrive and therefore the droid is more difficult to push around when unpowered. I'm electing to go with a 20:1 ratio gearbox instead of Oliver's 16:1 or my original plan of 26:1. I'm also choosing the "RS-5nn or 7nn" variant of the gearboxes, in case I need to upgrade to a motor with a 5mm shaft later (like the Aerodrive motor above).
If that's a good compromise between power and pushability, fantastic. If not, I'm not too concerned with pushing him, since I could remove the treads and slightly tilt Treadwell to simply roll him around on his non-driven wheels. I could also build in removable casters. But Vagabond Elf on the Astromech forum pointed out that real life track drives have the drive sprocket off the ground. If I built in a liftable drive wheel or a removable spacer, that'd leave the droid with his other 8 sets of wheels to be pushed on, once the belts were removed.
Then there are the sundries, like the shaft kits to go down from the motor's 4mm to the 3.17mm of the pinion, the programming card, etc.
I'm planning to do either a full RC or a dual RC/Bluetooth system. To that end, I've ordered a Taranis Q X7 16 channel ACCST radio and a 2100mah LiFePo battery to power it (~$150 total). Still deciding on what receiver to get. (By the way, FrSky is currently controversial because of their new ACCESS and ACCST v2 protocols breaking compatibility with legacy and -- by no coincidence -- third party receivers. I went with this radio primarily because it was affordable and I knew it was compatible with the Kyber system. But I have no qualms about ditching companies that are too anti-consumer for my tastes, so if it becomes a problem I'll be happy to jump ship to their competitors. The RadioMaster TX16 was what I was originally looking at and seemed to be a great option, esp. if it also proves to be Kyber-compatible.
On the bluetooth side, I'm leaning toward Skelmir's Penumbra system, which uses ESC32 boards and their built-in Bluetooth. These are a bit easier and cheaper to source than a Mega ADK + BT dongle setup.
If you are curious, Oliver's original 268kv motor/16:1 gearbox combo running at 3S LIPO nominal voltage of 11.1 would give an output of 185.925 RPM. With Treadwell's 4 inch drive wheels, that equates to a speed of 3.56 kph or 2.21 mph. The iFlyRC motors are 380kv and at 20:1 would have an output of 210.9 RPM, for a speed of 4.04 kph or 2.51 mph. The Neo motors are 473 kv and at 20:1 would have an output of 262.5 RPM, for a speed of 5.03 kph or 3.12 mph.
Edit: OK, I've written this edit at least twice and haven't managed to post it either time.
The above parts list were in fact my intent. As of right now, though, the only drive parts I've bought are the iFlyRC motors, and as mentioned before, I was willing to accept it if I ended up not using them. Everything else is still in flux until the dollars fly out of my wallet and off to their new homes.
Around the time of writing it was suggested to consider the Neo motors used by the Maxdrive, and while doing that, I remembered that brushless speed controllers need to know where the motor is in its rotation to time things correctly. At high RPM, even a sensorless ESC can determine that info from the energy fed back from the motor. But that doesn't help when the motor first starts up, because nothing can be coming back. I'd totally forgotten that the result for a sensorless motor/ESC is poor startup behavior and acceleration at low rpm, esp. in high torque situations.
As a sensored motor with a sensorless ESC doesn't help that situation, if I switch to the Neo, I'd also have to go with some other speed controller (the Spark Max that is designed for it is Out of Stock, however), and it's an 8mm shaft motor so I'd need to rethink the gearbox too (or find a shaft kit). Fortunately, BaneBots and AndyMark both sell compatible gearboxes.
However, another Dragon Con has come and gone (two if you count the virtual con in 2020), and once again the urge to build has seized hold of his soul. To be specific, the urge to build a droid that people might actually recognize.
So, yeah. At Dragon Con this year, I decided that I would make every effort to get Treadwell built in time for next year, or at least a lot closer than he is now. It may be a severely optimistic goal, considering the nearly 0 percent progress I've made on actually building him since I started back in 2016, but that's how I roll.
As mentioned, I was waffling on the drive system ... err ... three years ago. I still don't really have much more of an idea on what the track drive might need than I did back then, so at some point, I'm going to have to just commit to something and hope it'll work.
I'm going with a brushless system using Oliver Steeples' brushless Jaycar replacement for R2 as a guide, as previously discussed. However, some things have changed since Oliver wrote the Astromech thread (and even since the part links were updated in 2019). Here is my logic and the parts I am leaning toward:
Unlike Paul's wooden base, I suspect that a styrene base Treadwell is likely to be lighter than a styrene R2, as there's less material to its body. Given that Oliver's R2 drive was capable of propelling Oliver himself, I think (hope) the stronger brushless motors and the weight difference will be more than sufficient to counter the friction difference between the wheeled R2 and Tracked Treadwell drives.
* 2 ESCs @ $31.75 each:
These are the HK-60A speed controllers that Oliver listed for those who wanted to run higher voltages. More importantly for my purposes, they are 60A, which may be necessary for Treadwell. Unfortunately for me, the programming card for the ESC is currently backordered, with no ETA.
* 2 Motors @ $19.99 each (and 50% off the second motor):
The Multistar 268kv motors that Oliver recommended have been discontinued. I found a variety of motors that might work on Amazon and Hobbyking (like the Turnigy Aerodrive 4250 350kv), but there were open questions with all of them. Another option is the Rev Robotics Neo motor that Maxstang uses in his Maxdrive R2 drive system:
However, for now I found these iFlyRC 3508 380kv motors on ebay. They are similar enough to the original multistar motor and at a low enough price that I'm willing to roll the dice to see if they are sufficient. If not, I can likely use them elsewhere (such as my D-O concept droid). And if they are junk, I won't be out all that much. I just need to make sure the rest of my parts can support upgraded motors if I need something stronger. Especially the most expensive components, the...
* 2 Gearboxes @ $67.25 each:
Because I chose a higher kv motor than Oliver recommended, I want to gear it down more than he did, in order to trade some of that excess speed for power. However, as Oliver cautions, higher gear ratios also make the geartrain harder to backdrive and therefore the droid is more difficult to push around when unpowered. I'm electing to go with a 20:1 ratio gearbox instead of Oliver's 16:1 or my original plan of 26:1. I'm also choosing the "RS-5nn or 7nn" variant of the gearboxes, in case I need to upgrade to a motor with a 5mm shaft later (like the Aerodrive motor above).
If that's a good compromise between power and pushability, fantastic. If not, I'm not too concerned with pushing him, since I could remove the treads and slightly tilt Treadwell to simply roll him around on his non-driven wheels. I could also build in removable casters. But Vagabond Elf on the Astromech forum pointed out that real life track drives have the drive sprocket off the ground. If I built in a liftable drive wheel or a removable spacer, that'd leave the droid with his other 8 sets of wheels to be pushed on, once the belts were removed.
Then there are the sundries, like the shaft kits to go down from the motor's 4mm to the 3.17mm of the pinion, the programming card, etc.
I'm planning to do either a full RC or a dual RC/Bluetooth system. To that end, I've ordered a Taranis Q X7 16 channel ACCST radio and a 2100mah LiFePo battery to power it (~$150 total). Still deciding on what receiver to get. (By the way, FrSky is currently controversial because of their new ACCESS and ACCST v2 protocols breaking compatibility with legacy and -- by no coincidence -- third party receivers. I went with this radio primarily because it was affordable and I knew it was compatible with the Kyber system. But I have no qualms about ditching companies that are too anti-consumer for my tastes, so if it becomes a problem I'll be happy to jump ship to their competitors. The RadioMaster TX16 was what I was originally looking at and seemed to be a great option, esp. if it also proves to be Kyber-compatible.
On the bluetooth side, I'm leaning toward Skelmir's Penumbra system, which uses ESC32 boards and their built-in Bluetooth. These are a bit easier and cheaper to source than a Mega ADK + BT dongle setup.
If you are curious, Oliver's original 268kv motor/16:1 gearbox combo running at 3S LIPO nominal voltage of 11.1 would give an output of 185.925 RPM. With Treadwell's 4 inch drive wheels, that equates to a speed of 3.56 kph or 2.21 mph. The iFlyRC motors are 380kv and at 20:1 would have an output of 210.9 RPM, for a speed of 4.04 kph or 2.51 mph. The Neo motors are 473 kv and at 20:1 would have an output of 262.5 RPM, for a speed of 5.03 kph or 3.12 mph.
Edit: OK, I've written this edit at least twice and haven't managed to post it either time.
The above parts list were in fact my intent. As of right now, though, the only drive parts I've bought are the iFlyRC motors, and as mentioned before, I was willing to accept it if I ended up not using them. Everything else is still in flux until the dollars fly out of my wallet and off to their new homes.
Around the time of writing it was suggested to consider the Neo motors used by the Maxdrive, and while doing that, I remembered that brushless speed controllers need to know where the motor is in its rotation to time things correctly. At high RPM, even a sensorless ESC can determine that info from the energy fed back from the motor. But that doesn't help when the motor first starts up, because nothing can be coming back. I'd totally forgotten that the result for a sensorless motor/ESC is poor startup behavior and acceleration at low rpm, esp. in high torque situations.
As a sensored motor with a sensorless ESC doesn't help that situation, if I switch to the Neo, I'd also have to go with some other speed controller (the Spark Max that is designed for it is Out of Stock, however), and it's an 8mm shaft motor so I'd need to rethink the gearbox too (or find a shaft kit). Fortunately, BaneBots and AndyMark both sell compatible gearboxes.